59 results on '"Christensen SA"'
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2. The p/q-active uncapacitated facility location problem: Investigation of the solution space and an LP-fitting heuristic
- Author
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Dohn, Anders, Christensen, SA[cedilla]Ren Gram, and RousA[cedilla]e, David Magid
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Company legal issue ,Business ,Business, general ,Business, international - Abstract
To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2006.05.007 Byline: Anders Dohn, SA[cedilla]ren Gram Christensen, David Magid RousA[cedilla]e Keywords: p/q-active; p-active; Uncapacitated facility location; Heuristic solution methods; LP-relaxation; LP-fit; MIP-heuristics; FBA-search; First better admissible search Abstract: The p/q-active uncapacitated facility location problem is the problem of locating p facilities on n possible sites each serving at least q of the m clients at the minimum cost. The problem is an extension of the uncapacitated facility location problem (UFL) where constraints on the number of facilities and their minimum activity have been added. A use of this formulation could be the opening of p new schools where each must have at least q pupils. p/q-active is NP-hard like the UFL. In this paper we present a thorough investigation of the p/q-active UFL and propose a heuristic solution method. Different geometric and random cost problem instances are considered. Experiments show that 60% of the problems can be solved to optimality just by solving the corresponding LP-relaxation. Using a simple local search heuristic, the remaining geometric problems are solved with an average gap of 0.1% to a lower bound found by LP-relaxation. An effort is put into isolating problem types that are hard to solve. Problems with low p, p * q close to m combined with clustered clients or a low variation in the facility opening cost are most likely to give results worse than average. Gaps up to 8% are observed in the worst cases. Author Affiliation: Informatics and Mathematical Modelling, Technical University of Denmark, Kgs. Lyngby, Denmark Article History: Received 21 July 2005; Accepted 3 May 2006 more...
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- 2007
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3. Areas of desired change among married midlife individuals.
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Christensen SA and Miller RB
- Subjects
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ATTITUDE (Psychology) , *CHANGE , *COMMUNICATIVE competence , *FRIENDSHIP , *MARRIAGE , *QUESTIONNAIRES , *RESEARCH , *STATISTICAL sampling , *SATISFACTION , *SURVEYS , *TIME , *QUALITATIVE research , *FINANCIAL management , *THEMATIC analysis , *SOCIAL role change - Abstract
While much research has been conducted on marital satisfaction, few studies have examined areas of desired change in marriage. This issue was examined by using data from a national random sample of 542 married persons aged 40-50. Using qualitative methods to analyze the responses to an open-ended question, six major and nine minor categories emerged from the data. The overwhelmingly most common area of desired change was not being able to spend enough time together. Disappointment about their sexual relationship, problems with communication and conflict resolution, and displeasure with the affection and closeness in the relationship were also common themes. These findings suggest the importance of clinicians working with midlife couples to recognize the time demands faced in midlife and to help couples prioritize and structure time to spend together. [ABSTRACT FROM AUTHOR] more...
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- 2006
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4. One Health collaboration is more effective than single-sector actions at mitigating SARS-CoV-2 in deer.
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Cook JD, Rosenblatt E, Direnzo GV, Campbell Grant EH, Mosher BA, Arce F, Christensen SA, Ghai RR, and Runge MC
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- Animals, Humans, Public Health, Deer virology, COVID-19 transmission, COVID-19 prevention & control, COVID-19 virology, COVID-19 epidemiology, SARS-CoV-2, One Health, Animals, Wild virology
- Abstract
One Health aims to achieve optimal health outcomes for people, animals, plants, and shared environments. We describe a multisector effort to understand and mitigate SARS-CoV-2 transmission risk to humans via the spread among and between captive and wild white-tailed deer. We first framed a One Health problem with three governance sectors that manage captive deer, wild deer populations, and public health. The problem framing included identifying fundamental objectives, causal chains for transmission, and management actions. We then developed a dynamic model that linked deer herds and simulated SARS-CoV-2. Next, we evaluated management alternatives for their ability to reduce SARS-CoV-2 spread in white-tailed deer. We found that single-sector alternatives reduced transmission, but that the best-performing alternative required collaborative actions among wildlife management, agricultural management, and public health agencies. Here, we show quantitative support that One Health actions outperform single-sector responses, but may depend on coordination to track changes in this evolving system., (© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.) more...
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- 2024
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5. Thermal characterization and separation of whey proteins by differential scanning calorimetry.
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Jennings CC, Freidenberger M, Christensen SA, Conlin J, Freidenberger O, and Kenealey JD
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- Whey Proteins, Calorimetry, Differential Scanning, Temperature, Thermodynamics, Protein Denaturation, Proteins
- Abstract
Most commercially available whey products contain a mixture of 6-7 whey proteins; however, there is an increased focus on using the individual whey proteins for their unique biological activities. Before extracting individual whey proteins for use, it is important to quantify how much of a particular protein is present in whey mixtures as well as if the protein is still structurally folded. We first characterized the denaturation temperature and enthalpy values for the six purified whey proteins at six pHs (3-9) and under ion chelation using a nano-differential scanning calorimeter (DSC). From the individual protein scans, we determined the optimal condition for detecting all 6 proteins on a single DSC scan was whey in an EDTA MOPs pH 6.7 buffer., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.) more...
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- 2024
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6. Enhancing Health Literacy.
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Cutilli C and Christensen SA
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- Health Literacy
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- 2024
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7. Quality of life in congenital diaphragmatic hernia survivors treated at a non-ECMO centre from 1998 to 2015: a cross-sectional study.
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Larsen UL, Christensen SA, Herskind AM, Strøm T, Toft P, and Halken S
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- Child, Female, Humans, Infant, Male, Cross-Sectional Studies, Quality of Life, Surveys and Questionnaires, Survivors, Hernias, Diaphragmatic, Congenital psychology, Hernias, Diaphragmatic, Congenital therapy
- Abstract
Background: Survival of infants with congenital diaphragmatic hernia (CDH) has increased and more insight is warranted on the long-term issues of this condition., Methods: We conducted a cross-sectional study on consecutively born infants with CDH treated at a non-extracorporeal membrane oxygenation centre (ECMO) from 1998 to 2015. Quality of life was evaluated using the Pediatric Quality of Life Inventory Generic Core Scale 4.0 (PedsQL(4.0)) Questionnaire and an interview was conducted to assess for CDH-related morbidity., Results: 71 eligible CDH survivors were identified and 51 consented to participate: aged 5-21 years, 28 (54.9%) male, 42 (82.4%) with left-sided hernias, 10 (19.6%) needed patch repair, median length of stay in hospital was 27.96 days (IQR 18.54-61.56). Forty-nine completed the questionnaire with a median PedsQL total score for participants of 82.6 vs 83.7 of the total proxy parent score (p=0.04). Total score was significantly lower for participants aged 5-12 years compared with participants aged 13-21 years (p=0.04); however, when reported by domains, only the physical score remained significantly lower (p=0.048). Two (4.1%) participants' and 8 (16.7%) proxy parents' scores were below 70 and considered at risk of impaired quality of life. We identified the presence of CDH-related morbidity in our population, and confirmed an association between respiratory morbidity and lower PedsQL scores (p=0.04)., Conclusion: We report an overall good quality of life in our population with CDH. However, a lower physical score was noted when compared with a national Danish cohort and individuals at risk of reduced quality of life were recognised. Structured follow-up programmes to identify and ensure early management of CDH-related issues may prevent a negative impact on quality of life., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.) more...
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- 2024
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8. 9,10-KODA, an α-ketol produced by the tonoplast-localized 9-lipoxygenase ZmLOX5, plays a signaling role in maize defense against insect herbivory.
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Yuan P, Borrego E, Park YS, Gorman Z, Huang PC, Tolley J, Christensen SA, Blanford J, Kilaru A, Meeley R, Koiwa H, Vidal S, Huffaker A, Schmelz E, and Kolomiets MV
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- Animals, Insecta, Abscisic Acid, Cyclopentanes metabolism, Hormones, Lipoxygenases genetics, Oxylipins metabolism, Zea mays genetics, Zea mays metabolism
- Abstract
13-Lipoxygenases (LOXs) initiate the synthesis of jasmonic acid (JA), the best-understood oxylipin hormone in herbivory defense. However, the roles of 9-LOX-derived oxylipins in insect resistance remain unclear. Here, we report a novel anti-herbivory mechanism mediated by a tonoplast-localized 9-LOX, ZmLOX5, and its linolenic acid-derived product, 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (9,10-KODA). Transposon-insertional disruption of ZmLOX5 resulted in the loss of resistance to insect herbivory. lox5 knockout mutants displayed greatly reduced wound-induced accumulation of multiple oxylipins and defense metabolites, including benzoxazinoids, abscisic acid (ABA), and JA-isoleucine (JA-Ile). However, exogenous JA-Ile failed to rescue insect defense in lox5 mutants, while applications of 1 μM 9,10-KODA or the JA precursor, 12-oxo-phytodienoic acid (12-OPDA), restored wild-type resistance levels. Metabolite profiling revealed that exogenous 9,10-KODA primed the plants for increased production of ABA and 12-OPDA, but not JA-Ile. While none of the 9-oxylipins were able to rescue JA-Ile induction, the lox5 mutant accumulated lower wound-induced levels of Ca
2+ , suggesting this as a potential explanation for lower wound-induced JA. Seedlings pretreated with 9,10-KODA exhibited rapid or more robust wound-induced defense gene expression. In addition, an artificial diet supplemented with 9,10-KODA arrested fall armyworm larvae growth. Finally, analysis of single and double lox5 and lox10 mutants showed that ZmLOX5 also contributed to insect defense by modulating ZmLOX10-mediated green leaf volatile signaling. Collectively, our study uncovered a previously unknown anti-herbivore defense and hormone-like signaling activity for a major 9-oxylipin α-ketol., (Copyright © 2023 The Author. Published by Elsevier Inc. All rights reserved.) more...- Published
- 2023
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9. A non-JA producing oxophytodienoate reductase functions in salicylic acid-mediated antagonism with jasmonic acid during pathogen attack.
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Huang PC, Tate M, Berg-Falloure KM, Christensen SA, Zhang J, Schirawski J, Meeley R, and Kolomiets MV
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- Oxylipins, Cyclopentanes, Gene Expression Regulation, Plant, Oxidoreductases, Salicylic Acid
- Abstract
Peroxisome-localized oxo-phytodienoic acid (OPDA) reductases (OPR) are enzymes converting 12-OPDA into jasmonic acid (JA). However, the biochemical and physiological functions of the cytoplasmic non-JA producing OPRs remain largely unknown. Here, we generated Mutator-insertional mutants of the maize OPR2 gene and tested its role in resistance to pathogens with distinct lifestyles. Functional analyses showed that the opr2 mutants were more susceptible to the (hemi)biotrophic pathogens Colletotrichum graminicola and Ustilago maydis, but were more resistant to the necrotrophic fungus Cochliobolus heterostrophus. Hormone profiling revealed that increased susceptibility to C. graminicola was associated with decreased salicylic acid (SA) but increased JA levels. Mutation of the JA-producing lipoxygenase 10 (LOX10) reversed this phenotype in the opr2 mutant background, corroborating the notion that JA promotes susceptibility to this pathogen. Exogenous SA did not rescue normal resistance levels in opr2 mutants, suggesting that this SA-inducible gene is the key downstream component of the SA-mediated defences against C. graminicola. Disease assays of the single and double opr2 and lox10 mutants and the JA-deficient opr7opr8 mutants showed that OPR2 negatively regulates JA biosynthesis, and that JA is required for resistance against C. heterostrophus. Overall, this study uncovers a novel function of a non-JA producing OPR as a major negative regulator of JA biosynthesis during pathogen infection, a function that leads to its contrasting contribution to either resistance or susceptibility depending on pathogen lifestyle., (© 2023 The Authors. Molecular Plant Pathology published by British Society for Plant Pathology and John Wiley & Sons Ltd.) more...
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- 2023
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10. Liguleless narrow and narrow odd dwarf act in overlapping pathways to regulate maize development and metabolism.
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Abraham-Juárez MJ, Busche M, Anderson AA, Lunde C, Winders J, Christensen SA, Hunter CT, Hake S, and Brunkard JO
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- Plant Leaves metabolism, Phenotype, Mutation, Gene Expression Regulation, Plant, Zea mays metabolism, Plant Proteins genetics, Plant Proteins metabolism
- Abstract
Narrow odd dwarf (nod) and Liguleless narrow (Lgn) are pleiotropic maize mutants that both encode plasma membrane proteins, cause similar developmental patterning defects, and constitutively induce stress signaling pathways. To investigate how these mutants coordinate maize development and physiology, we screened for protein interactors of NOD by affinity purification. LGN was identified by this screen as a strong candidate interactor, and we confirmed the NOD-LGN molecular interaction through orthogonal experiments. We further demonstrated that LGN, a receptor-like kinase, can phosphorylate NOD in vitro, hinting that they could act in intersecting signal transduction pathways. To test this hypothesis, we generated Lgn-R;nod mutants in two backgrounds (B73 and A619), and found that these mutations enhance each other, causing more severe developmental defects than either single mutation on its own, with phenotypes including very narrow leaves, increased tillering, and failure of the main shoot. Transcriptomic and metabolomic analyses of the single and double mutants in the two genetic backgrounds revealed widespread induction of pathogen defense genes and a shift in resource allocation away from primary metabolism in favor of specialized metabolism. These effects were similar in each single mutant and heightened in the double mutant, leading us to conclude that NOD and LGN act cumulatively in overlapping signaling pathways to coordinate growth-defense tradeoffs in maize., (© 2022 The Authors. The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.) more...
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- 2022
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11. Online suicidal thoughts and/or behaviours talk: A scoping review protocol.
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Lamont-Mills A, Bayliss LT, and Christensen SA
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- Humans, Suicidal Ideation, Review Literature as Topic, Social Media, Suicide Prevention
- Abstract
The anonymity that the internet and social media affords users means that suicidal thoughts and/or behaviours can be talked about with a sense of freedom and disinhibition that is often not possible in face-to-face contexts. Better understanding online suicidal thoughts and/or behaviour talk is critical as more people turn to online spaces for support. Without this the potentiality of such spaces as sites for suicide prevention and intervention is likely to remain unrealised. Currently there are no scoping or systematic review syntheses focusing on internet and/or on social media suicidal thoughts and/or behaviour talk. This lack of synthesis is problematic as it makes it more difficult for online suicide prevention and intervention practices, policies, and our understanding of suicide to advance in a coherent and evidence-based manner. A scoping review protocol following Arksey and O'Malley's six-step modified framework has been developed to address this synthesis gap. It aims to systematically map the empirical literature that has investigated online suicidal thoughts and/or behaviours talk. It is anticipated that review outcomes could inform the training of health practitioners and peer/professional online moderators in how to best talk with people experiencing suicidal thoughts and/or behaviours. Outcomes could also form an evidence-base for developing policies and practices that focus on online places as safe spaces to talk about suicidal thoughts and/or behaviours. Developers of safe language guidelines could also use the outcomes to audit how well current guidelines reflect empirical evidence. Outcomes could enable researchers to design future online suicidal thoughts and/behaviours talk studies that extend our understandings of suicide leading to potential refinements of contemporary suicide theories/models., Competing Interests: The authors have declared that no competing interests exist. more...
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- 2022
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12. Dedicated farnesyl diphosphate synthases circumvent isoprenoid-derived growth-defense tradeoffs in Zea mays.
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Tang HV, Berryman DL, Mendoza J, Yactayo-Chang JP, Li QB, Christensen SA, Hunter CT, Best N, Soubeyrand E, Akhtar TA, Basset GJ, and Block AK
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- Polyisoprenyl Phosphates, Terpenes metabolism, Ubiquinone metabolism, Zea mays genetics, Zea mays metabolism, Phytoalexins, Geranyltranstransferase genetics, Geranyltranstransferase metabolism, Sesquiterpenes metabolism
- Abstract
Zea mays (maize) makes phytoalexins such as sesquiterpenoid zealexins, to combat invading pathogens. Zealexins are produced from farnesyl diphosphate in microgram per gram fresh weight quantities. As farnesyl diphosphate is also a precursor for many compounds essential for plant growth, the question arises as to how Z. mays produces high levels of zealexins without negatively affecting vital plant systems. To examine if specific pools of farnesyl diphosphate are made for zealexin synthesis we made CRISPR/Cas9 knockouts of each of the three farnesyl diphosphate synthases (FPS) in Z. mays and examined the resultant impacts on different farnesyl diphosphate-derived metabolites. We found that FPS3 (GRMZM2G098569) produced most of the farnesyl diphosphate for zealexins, while FPS1 (GRMZM2G168681) made most of the farnesyl diphosphate for the vital respiratory co-factor ubiquinone. Indeed, fps1 mutants had strong developmental phenotypes such as reduced stature and development of chlorosis. The replication and evolution of the fps gene family in Z. mays enabled it to produce dedicated FPSs for developmentally related ubiquinone production (FPS1) or defense-related zealexin production (FPS3). This partitioning of farnesyl diphosphate production between growth and defense could contribute to the ability of Z. mays to produce high levels of phytoalexins without negatively impacting its growth., (© 2022 Society for Experimental Biology and John Wiley & Sons Ltd. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.) more...
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- 2022
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13. Production of the Green Leaf Volatile ( Z )-3-Hexenal by a Zea mays Hydroperoxide Lyase.
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Yactayo-Chang JP, Hunter CT, Alborn HT, Christensen SA, and Block AK
- Abstract
Plant-produced volatile compounds play important roles in plant signaling and in the communication of plants with other organisms. Many plants emit green leaf volatiles (GLVs) in response to damage or attack, which serve to warn neighboring plants or attract predatory or parasitic insects to help defend against insect pests. GLVs include aldehydes, esters, and alcohols of 6-carbon compounds that are released rapidly following wounding. One GLV produced by maize ( Zea mays ) is the volatile ( Z )-3-hexenal; this volatile is produced from the cleavage of (9Z,11E,15Z)-octadecatrienoic acid by hydroperoxide lyases (HPLs) of the cytochrome P450 CYP74B family. The specific HPL in maize involved in ( Z )-3-hexenal production had not been determined. In this study, we used phylogenetics with known HPLs from other species to identify a candidate HPL from maize ( ZmHPL ). To test the ability of the putative HPL to produce ( Z )-3-hexenal, we constitutively expressed the gene in Arabidopsis thaliana ecotype Columbia-0 that contains a natural loss-of-function mutant in AtHPL and examined the transgenic plants for restored ( Z )-3-hexenal production. Volatile analysis of leaves from these transgenic plants showed that they did produce ( Z )-3-hexenal, confirming that ZmHPL can produce ( Z )-3-hexenal in vivo. Furthermore, we used gene expression analysis to show that expression of ZmHPL is induced in maize in response to both wounding and the insect pests Spodoptera frugiperda and Spodoptera exigua . Our study demonstrates that ZmHPL can produce GLVs and highlights its likely role in ( Z )-3-hexenal production in response to mechanical damage and herbivory in maize. more...
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- 2022
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14. RNAi-induced knockdown of white gene in the southern green stink bug (Nezara viridula L.).
- Author
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Souza D, Christensen SA, Wu K, Buss L, Kleckner K, Darrisaw C, Shirk PD, and Siegfried BD
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- Animals, Crops, Agricultural, RNA Interference, Heteroptera genetics, Heteroptera metabolism
- Abstract
The southern green stink bug (SGSB) Nezara viridula L. is one of the most common stink bug species in the United States and can cause significant yield loss in a variety of crops. A suitable marker for the assessment of gene-editing tools in SGSB has yet to be characterized. The white gene, first documented in Drosophila, has been a useful target to assess the efficiency of introduced mutations in many species as it controls pigmentation processes and mutants display readily identifiable phenotypes. In this study we used the RNAi technique to investigate functions and phenotypes associated with the white ortholog in the SGSB and to validate white as a marker for genetic transformation in this species. This study revealed that white may be a suitable marker for germline transformation in the SGSB as white transcript knockdown was not lethal, did not impair embryo development and provided a distinguishable phenotype. Our results demonstrated that the white ortholog in SGSB is involved in the pathway for ommochrome synthesis and suggested additional functions of this gene such as in the integument composition, management of hemolymph compounds and riboflavin mobilization., (© 2022. The Author(s).) more...
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- 2022
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15. Fusarium verticillioides Induces Maize-Derived Ethylene to Promote Virulence by Engaging Fungal G-Protein Signaling.
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Park YS, Borrego EJ, Gao X, Christensen SA, Schmelz E, Lanubile A, Drab DA, Cody W, Yan H, Shim WB, and Kolomiets MV
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- Ethylenes, GTP-Binding Proteins, Virulence, Zea mays, Fumonisins, Fusarium
- Abstract
Seed maceration and contamination with mycotoxin fumonisin inflicted by Fusarium verticillioides is a major disease concern for maize producers worldwide. Meta-analyses of quantitative trait loci for Fusarium ear rot resistance uncovered several ethylene (ET) biosynthesis and signaling genes within them, implicating ET in maize interactions with F. verticillioides . We tested this hypothesis using maize knockout mutants of the 1-aminocyclopropane-1-carboxylate (ACC) synthases ZmACS2 and ZmACS6 . Infected wild-type seed emitted five-fold higher ET levels compared with controls, whereas ET was abolished in the acs2 and acs6 single and double mutants. The mutants supported reduced fungal biomass, conidia, and fumonisin content. Normal susceptibility was restored in the acs6 mutant with exogenous treatment of ET precursor ACC. Subsequently, we showed that fungal G-protein signaling is required for virulence via induction of maize-produced ET. F. verticillioides G
β subunit and two regulators of G-protein signaling mutants displayed reduced seed colonization and decreased ET levels. These defects were rescued by exogenous application of ACC. We concluded that pathogen-induced ET facilitates F. verticillioides colonization of seed, and, in turn, host ET production is manipulated via G-protein signaling of F. verticillioides to facilitate pathogenesis.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license. more...- Published
- 2021
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16. A maize leucine-rich repeat receptor-like protein kinase mediates responses to fungal attack.
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Block AK, Tang HV, Hopkins D, Mendoza J, Solemslie RK, du Toit LJ, and Christensen SA
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- Bipolaris, Fusarium, Leucine, Plant Diseases, Protein Kinases, Ascomycota, Zea mays genetics
- Abstract
Main Conclusion: A maize receptor kinase controls defense response to fungal pathogens by regulating jasmonic acid and antimicrobial phytoalexin production. Plants use a range of pattern recognition receptors to detect and respond to biotic threats. Some of these receptors contain leucine-rich repeat (LRR) domains that recognize microbial proteins or peptides. Maize (Zea mays) has 226 LRR-receptor like kinases, making it challenging to identify those important for pathogen recognition. In this study, co-expression analysis with genes for jasmonic acid and phytoalexin biosynthesis was used to identify a fungal induced-receptor like protein kinase (FI-RLPK) likely involved in the response to fungal pathogens. Loss-of-function mutants in fi-rlpk displayed enhanced susceptibility to the necrotrophic fungal pathogen Cochliobolus heterostrophus and reduced accumulation of jasmonic acid and the anti-microbial phytoalexins -kauralexins and zealexins- in infected tissues. In contrast, fi-rlpk mutants displayed increased resistance to stem inoculation with the hemibiotrophic fungal pathogen Fusarium graminearum. These data indicate that FI-RLPK is important for fungal recognition and activation of defenses, and that F. graminearum may be able to exploit FI-RLPK function to increase its virulence., (© 2021. This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.) more...
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- 2021
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17. Detecting the Conspecific: Herbivory-Induced Olfactory Cues in the Fall Armyworm (Lepidoptera: Noctuidae).
- Author
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Ingber DA, Christensen SA, Alborn HT, and Hiltpold I
- Abstract
The fall armyworm (FAW), Spodoptera frugiperda (Smith), is a polyphagous pest whose larval feeding threatens several economically important crops worldwide with especially severe damage to corn ( Zea mays L.). Field-derived resistance to several conventional pesticides and Bt toxins have threatened the efficacy of current management strategies, necessitating the development of alternative pest management methods and technologies. One possible avenue is the use of volatile organic compounds (VOCs) and other secondary metabolites that are produced and sequestered by plants as a response to larval feeding. The effects of conspecific larval feeding on fall armyworm oviposition preferences and larval fitness were examined using two-choice oviposition experiments, larval feeding trials, targeted metabolomics, and VOC analyses. There was a significant preference for oviposition on corn plants that lacked larval feeding damage, and larvae fed tissue from damaged plants exhibited reduced weights and head capsule widths. All larval feeding promoted significantly increased metabolite and VOC concentrations compared to corn plants without any feeding. Metabolite differences were driven primarily by linoleic acid (which is directly toxic to fall armyworm) and tricarboxylic acids. Several VOCs with significantly increased concentrations in damaged corn plants were known oviposition deterrents that warrant further investigation in an integrated pest management context. more...
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- 2021
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18. Using Robinson-Foulds supertrees in divide-and-conquer phylogeny estimation.
- Author
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Yu X, Le T, Christensen SA, Molloy EK, and Warnow T
- Abstract
One of the Grand Challenges in Science is the construction of the Tree of Life, an evolutionary tree containing several million species, spanning all life on earth. However, the construction of the Tree of Life is enormously computationally challenging, as all the current most accurate methods are either heuristics for NP-hard optimization problems or Bayesian MCMC methods that sample from tree space. One of the most promising approaches for improving scalability and accuracy for phylogeny estimation uses divide-and-conquer: a set of species is divided into overlapping subsets, trees are constructed on the subsets, and then merged together using a "supertree method". Here, we present Exact-RFS-2, the first polynomial-time algorithm to find an optimal supertree of two trees, using the Robinson-Foulds Supertree (RFS) criterion (a major approach in supertree estimation that is related to maximum likelihood supertrees), and we prove that finding the RFS of three input trees is NP-hard. Exact-RFS-2 is available in open source form on Github at https://github.com/yuxilin51/GreedyRFS . more...
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- 2021
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19. Analysis of the transcriptomic, metabolomic, and gene regulatory responses to Puccinia sorghi in maize.
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Kim SB, Van den Broeck L, Karre S, Choi H, Christensen SA, Wang GF, Jo Y, Cho WK, and Balint-Kurti P
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- Gene Expression Profiling, Metabolomics, Plant Proteins genetics, Plant Proteins metabolism, Zea mays microbiology, Host-Pathogen Interactions, Metabolome, Plant Diseases microbiology, Puccinia physiology, Transcriptome, Zea mays genetics
- Abstract
Common rust, caused by Puccinia sorghi, is a widespread and destructive disease of maize. The Rp1-D gene confers resistance to the P. sorghi IN2 isolate, mediating a hypersensitive cell death response (HR). To identify differentially expressed genes (DEGs) and metabolites associated with the compatible (susceptible) interaction and with Rp1-D-mediated resistance in maize, we performed transcriptomics and targeted metabolome analyses of P. sorghi IN2-infected leaves from the near-isogenic lines H95 and H95:Rp1-D, which differed for the presence of Rp1-D. We observed up-regulation of genes involved in the defence response and secondary metabolism, including the phenylpropanoid, flavonoid, and terpenoid pathways. Metabolome analyses confirmed that intermediates from several transcriptionally up-regulated pathways accumulated during the defence response. We identified a common response in H95:Rp1-D and H95 with an additional H95:Rp1-D-specific resistance response observed at early time points at both transcriptional and metabolic levels. To better understand the mechanisms underlying Rp1-D-mediated resistance, we inferred gene regulatory networks occurring in response to P. sorghi infection. A number of transcription factors including WRKY53, BHLH124, NKD1, BZIP84, and MYB100 were identified as potentially important signalling hubs in the resistance-specific response. Overall, this study provides a novel and multifaceted understanding of the maize susceptible and resistance-specific responses to P. sorghi., (© 2021 The Authors. Molecular Plant Pathology published by British Society for Plant Pathology and John Wiley & Sons Ltd.) more...
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- 2021
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20. Brachypodium Phenylalanine Ammonia Lyase (PAL) Promotes Antiviral Defenses against Panicum mosaic virus and Its Satellites.
- Author
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Pant SR, Irigoyen S, Liu J, Bedre R, Christensen SA, Schmelz EA, Sedbrook JC, Scholthof KBG, and Mandadi KK
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- Brachypodium enzymology, Gene Expression Regulation, Plant, Metabolomics, RNA Interference, Salicylic Acid metabolism, Satellite Viruses, Transcriptome, Brachypodium genetics, Brachypodium metabolism, Host Microbial Interactions, Phenylalanine Ammonia-Lyase genetics, Phenylalanine Ammonia-Lyase metabolism, Tombusviridae immunology
- Abstract
Brachypodium distachyon has recently emerged as a premier model plant for monocot biology, akin to Arabidopsis thaliana We previously reported genome-wide transcriptomic and alternative splicing changes occurring in Brachypodium during compatible infections with Panicum mosaic virus (PMV) and its satellite virus (SPMV). Here, we dissected the role of Brachypodium phenylalanine ammonia lyase 1 (PAL1), a key enzyme for phenylpropanoid and salicylic acid (SA) biosynthesis and the induction of plant defenses. Targeted metabolomics profiling of PMV-infected and PMV- plus SPMV-infected (PMV/SPMV) Brachypodium plants revealed enhanced levels of multiple defense-related hormones and metabolites such as cinnamic acid, SA, and fatty acids and lignin precursors during disease progression. The virus-induced accumulation of SA and lignin was significantly suppressed upon knockdown of B. distachyon PAL1 ) using RNA interference (RNAi). The compromised SA accumulation in PMV/SPMV-infected BdPAL1 RNAi plants correlated with weaker induction of multiple SA-related defense gene markers (pathogenesis related 1 [ BdPAL1 RNAi plants correlated with weaker induction of multiple SA-related defense gene markers (pathogenesis related 1 [ PR-1 ], PR-3 , PR-5 ) and enhanced susceptibility to PMV/SPMV compared to that of wild-type (WT) plants. Furthermore, exogenous application of SA alleviated the PMV/SPMV necrotic disease phenotypes and delayed plant death caused by single and mixed infections. Together, our results support an antiviral role for WRKY75 ) and enhanced susceptibility to PMV/SPMV compared to that of wild-type (WT) plants. Furthermore, exogenous application of SA alleviated the PMV/SPMV necrotic disease phenotypes and delayed plant death caused by single and mixed infections. Together, our results support an antiviral role for BdPAL1 during compatible host-virus interaction, perhaps as a last resort attempt to rescue the infected plant. IMPORTANCE Although the role of plant defense mechanisms against viruses are relatively well studied in dicots and in incompatible plant-microbe interactions, studies of their roles in compatible interactions and in grasses are lagging behind. In this study, we leveraged the emerging grass model Brachypodium (PMV)- and its satellite virus (SPMV)-compatible grass-virus interactions. We found a significant role for PAL1 in the production of salicylic acid (SA) in response to PMV/SPMV infections and that SA is an essential component of the defense response preventing the plant from succumbing to viral infection. Our results suggest a convergent role for the SA defense pathway in both compatible and incompatible plant-virus interactions and underscore the utility of Panicum mosaic virus (PMV)- and its satellite virus (SPMV)-compatible grass-virus interactions. We found a significant role for PAL1 in the production of salicylic acid (SA) in response to PMV/SPMV infections and that SA is an essential component of the defense response preventing the plant from succumbing to viral infection. Our results suggest a convergent role for the SA defense pathway in both compatible and incompatible plant-virus interactions and underscore the utility of Brachypodium for grass-virus biology. more...
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- 2021
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21. SPATIAL VARIATION OF WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS) POPULATION IMPACTS AND RECOVERY FROM EPIZOOTIC HEMORRHAGIC DISEASE.
- Author
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Christensen SA, Williams DM, Rudolph BA, and Porter WF
- Subjects
- Animals, Michigan epidemiology, Reoviridae Infections epidemiology, Reoviridae Infections virology, Deer virology, Hemorrhagic Disease Virus, Epizootic, Reoviridae Infections veterinary
- Abstract
Epizootic hemorrhagic disease (EHD) is the most significant source of viral disease-related mortality in white-tailed deer (Odocoileus virginianus) in the US. Deer mortality from EHD has increased in the state of Michigan, US, since 2006, with the largest outbreak occurring in 2012. The 2012 outbreak provided an opportunity to evaluate how this disease affected EHD-related mortality in deer populations at a spatial scale typical of that expected for the greatest disease risk. Our objectives were to quantify the population impacts and spatial extent of EHD associated with areas of disease risk for deer populations and to determine how populations recovered over time following localized EHD impacts. We estimated the annual local abundance of deer for 5 yr immediately following a recent EHD outbreak. Because proximity to wetlands may affect EHD occurrence, we surveyed deer at varying distances (about 1 km and 5 km) from a riparian corridor to determine spatial variation in population impacts. Further, we assessed differences in deer abundance for sites affected and unaffected by EHD. Abundance estimates were lower along transects near the riparian corridor only in the affected area, reflecting EHD mortality associated with wetlands. The only change in abundance over time was a significant increase in the riparian strata in the EHD-affected site., (© Wildlife Disease Association 2021.) more...
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- 2021
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22. Metabolomics by UHPLC-HRMS reveals the impact of heat stress on pathogen-elicited immunity in maize.
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Christensen SA, Santana EA, Alborn HT, Block AK, and Chamberlain CA
- Subjects
- Chromatography, High Pressure Liquid, Host-Pathogen Interactions, Mass Spectrometry, Plant Diseases microbiology, Zea mays microbiology, Heat-Shock Response, Metabolome, Metabolomics methods, Plant Diseases immunology, Zea mays immunology, Zea mays metabolism
- Abstract
Introduction: Studies investigating crop resistance to abiotic and biotic stress have largely focused on plant responses to singular forms of stress and individual biochemical pathways that only partially represent stress responses. Thus, combined abiotic and biotic stress treatments and the global assessment of their elicited metabolic expression remains largely unexplored. In this study, we employed targeted and untargeted metabolomics to investigate the molecular responses of maize (Zea mays) to abiotic, biotic, and combinatorial stress., Objective: We compared the inducible metabolomes of heat-stressed (abiotic) and C. heterostrophus-infected (biotic) maize and examined the effects of heat stress on the ability of maize to defend itself against C. heterostrophus., Methods: Ultra-high-performance liquid chromatography-high-resolution mass spectrometry was performed on plants grown under control conditions (28 °C), heat stress (38 °C), Cochliobolus heterostrophus infection, or combinatorial stress [heat (38 °C) + C. heterostrophus infection]., Results: Multivariate analyses revealed differential metabolite expression between heat stress, C. heterostrophus infection, and their respective controls. In combinatorial experiments, treatment with heat stress prior to fungal inoculation negatively impacted maize disease resistance against C. heterostrophus, and distinct metabolome separation between combinatorial stressed plants and the non-heat-stressed infected controls was observed. Targeted analysis revealed inducible primary and secondary metabolite responses to abiotic/biotic stress, and combinatorial experiments indicated that deficiency in the hydroxycinnamic acid, p-coumaric acid, may contribute to the heat-induced susceptibility of maize to C. heterostrophus., Conclusion: These findings demonstrate that abiotic stress can predispose crops to more severe disease symptoms, underlining the increasing need to investigate defense chemistry in plants under combinatorial stress. more...
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- 2021
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23. Genetic elucidation of interconnected antibiotic pathways mediating maize innate immunity.
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Ding Y, Weckwerth PR, Poretsky E, Murphy KM, Sims J, Saldivar E, Christensen SA, Char SN, Yang B, Tong AD, Shen Z, Kremling KA, Buckler ES, Kono T, Nelson DR, Bohlmann J, Bakker MG, Vaughan MM, Khalil AS, Betsiashvili M, Dressano K, Köllner TG, Briggs SP, Zerbe P, Schmelz EA, and Huffaker A more...
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- Disease Resistance physiology, Gene Expression Profiling, Genes, Plant genetics, Genes, Plant physiology, Metabolomics, Multigene Family genetics, Multigene Family physiology, Proteomics, Zea mays immunology, Zea mays metabolism, Zea mays microbiology, Anti-Bacterial Agents biosynthesis, Disease Resistance genetics, Immunity, Innate genetics, Metabolic Networks and Pathways genetics, Zea mays genetics
- Abstract
Specialized metabolites constitute key layers of immunity that underlie disease resistance in crops; however, challenges in resolving pathways limit our understanding of the functions and applications of these metabolites. In maize (Zea mays), the inducible accumulation of acidic terpenoids is increasingly considered to be a defence mechanism that contributes to disease resistance. Here, to understand maize antibiotic biosynthesis, we integrated association mapping, pan-genome multi-omic correlations, enzyme structure-function studies and targeted mutagenesis. We define ten genes in three zealexin (Zx) gene clusters that encode four sesquiterpene synthases and six cytochrome P450 proteins that collectively drive the production of diverse antibiotic cocktails. Quadruple mutants in which the ability to produce zealexins (ZXs) is blocked exhibit a broad-spectrum loss of disease resistance. Genetic redundancies ensuring pathway resiliency to single null mutations are combined with enzyme substrate promiscuity, creating a biosynthetic hourglass pathway that uses diverse substrates and in vivo combinatorial chemistry to yield complex antibiotic blends. The elucidated genetic basis of biochemical phenotypes that underlie disease resistance demonstrates a predominant maize defence pathway and informs innovative strategies for transferring chemical immunity between crops. more...
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- 2020
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24. The 13-lipoxygenase MSD2 and the ω-3 fatty acid desaturase MSD3 impact Spodoptera frugiperda resistance in Sorghum.
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Block AK, Xin Z, and Christensen SA
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- Animals, Herbivory, Mutation, Oxylipins metabolism, Fatty Acid Desaturases metabolism, Lipoxygenase genetics, Lipoxygenase metabolism, Plant Defense Against Herbivory genetics, Sorghum enzymology, Sorghum genetics, Sorghum parasitology, Spodoptera physiology
- Abstract
Main Conclusion: Linolenic acid produced by the ω-3 fatty acid desaturase MSD3 in sorghum is used for insect-induced jasmonic acid production and is important for resistance against Spodoptera frugiperda. Jasmonic acid (JA) is a phytohormone that regulates both plant development and stress responses. In sorghum (Sorghum bicolor), the ω-3 fatty acid desaturase Multiseeded3 (MSD3) and the 13-lipoxygenase Multiseeded2 (MSD2) are important for producing JA to regulate panicle development and spikelet fertility, but their function in plant defense remains unknown. In this study, we examined whether these genes are important for the production of JA in response to herbivory by the insect pest Spodoptera frugiperda. Compared to wild-type controls, the msd3 mutant accumulated less JA in leaves of both infested and uninfested plants, revealing that MSD3 is involved in stress-induced JA production. In contrast, herbivore-induced JA production in the msd2 mutant was indistinguishable from wild type, indicating that MSD2 does not function in herbivore-induced JA production. An increase of S. frugiperda growth was observed on both the msd3 and msd2 mutants, hinting at roles for both JA and additional oxylipins in sorghum's defense responses. more...
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- 2020
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25. The role of drought as a determinant of hemorrhagic disease in the eastern United States.
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Christensen SA, Ruder MG, Williams DM, Porter WF, and Stallknecht DE
- Subjects
- Animals, Droughts, United States, Bluetongue virus, Deer, Hemorrhagic Disease Virus, Epizootic, Reoviridae Infections
- Abstract
Bluetongue virus and epizootic hemorrhagic disease (HD) virus are globally distributed, vector-borne viruses that infect and cause disease in domestic and wild ruminant species. The forces driving increases in resulting HD may be linked to weather conditions and increasing severity has been noted in northerly latitudes. We evaluated the role of drought severity in both space and time on changes in HD reports across the eastern United States for a recent 15 year period. The objectives of this study were to: (a) develop a spatiotemporal model to evaluate if drought severity explains changing patterns of HD presence; and (b) determine whether this potential risk factor varies in importance over the present range of HD in the eastern United States. Historic data (2000-2014) from an annual HD presence-absence survey conducted by the Southeastern Cooperative Wildlife Disease Study and from the United States Drought Monitor were used for this analysis. For every county in 23 states and for each of 15 years, data were based on reported drought status for August, wetland cover, the physiographic region, and the status of HD in the previous year. We used a generalized linear mixed model to explain HD presence and evaluated spatiotemporal predictors across the region. We found that drought severity was a significant predictor of HD presence and the significance of this relationship was dependent on latitude. In more northerly latitudes, where immunological naivety is most likely, we demonstrated the increasing strength of drought severity as a determinant of reported HD and established the importance of variation in drought severity as a risk factor over the present range of HD in the eastern United States. Our research provides spatially explicit evidence for the link between climate forces and emerging disease patterns across latitude for a globally distributed disease., (© 2020 John Wiley & Sons Ltd.) more...
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- 2020
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26. Green leaf volatiles and jasmonic acid enhance susceptibility to anthracnose diseases caused by Colletotrichum graminicola in maize.
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Gorman Z, Christensen SA, Yan Y, He Y, Borrego E, and Kolomiets MV
- Subjects
- Cyclopentanes metabolism, Gene Expression Regulation, Plant, Oxylipins metabolism, Salicylic Acid metabolism, Zea mays genetics, Colletotrichum pathogenicity, Lipoxygenase metabolism, Plant Diseases microbiology, Zea mays metabolism
- Abstract
Colletotrichum graminicola is a hemibiotrophic fungus that causes anthracnose leaf blight (ALB) and anthracnose stalk rot (ASR) in maize. Despite substantial economic losses caused by these diseases, the defence mechanisms against this pathogen remain poorly understood. Several hormones are suggested to aid in defence against C. graminicola, such as jasmonic acid (JA) and salicylic acid (SA), but supporting genetic evidence was not reported. Green leaf volatiles (GLVs) are a group of well-characterized volatiles that induce JA biosynthesis in maize and are known to function in defence against necrotrophic pathogens. Information regarding the role of GLVs and JA in interactions with (hemi)biotrophic pathogens remains limited. To functionally elucidate GLVs and JA in defence against a hemibiotrophic pathogen, we tested GLV- and JA-deficient mutants, lox10 and opr7 opr8, respectively, for resistance to ASR and ALB and profiled jasmonates and SA in their stalks and leaves throughout infection. Both mutants were resistant and generally displayed elevated levels of SA and low amounts of jasmonates, especially at early stages of infection. Pretreatment with GLVs restored susceptibility of lox10 mutants, but not opr7 opr8 mutants, which coincided with complete rescue of JA levels. Exogenous methyl jasmonate restored susceptibility in both mutants when applied before inoculation, whereas methyl salicylate did not induce further resistance in either of the mutants, but did induce mutant-like resistance in the wild type. Collectively, this study reveals that GLVs and JA contribute to maize susceptibility to C. graminicola due to suppression of SA-related defences., (© 2020 The Authors. Molecular Plant Pathology published by British Society for Plant Pathology and John Wiley & Sons Ltd.) more...
- Published
- 2020
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27. Setaria viridis as a model for translational genetic studies of jasmonic acid-related insect defenses in Zea mays.
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Hunter CT, Block AK, Christensen SA, Li QB, Rering C, and Alborn HT
- Subjects
- Animals, Insecta, Setaria Plant metabolism, Zea mays metabolism, Cyclopentanes metabolism, Herbivory, Oxylipins metabolism, Plant Proteins biosynthesis, Protein Biosynthesis, Setaria Plant genetics, Zea mays genetics
- Abstract
Little is known regarding insect defense pathways in Setaria viridis (setaria), a model system for panicoid grasses, including Zea mays (maize). It is thus of interest to compare insect herbivory responses of setaria and maize. Here we use metabolic, phylogenetic, and gene expression analyses to measure a subset of jasmonic acid (JA)-related defense responses to leaf-chewing caterpillars. Phylogenetic comparisons of known defense-related maize genes were used to identify putative orthologs in setaria, and candidates were tested by quantitative PCR to determine transcriptional responses to insect challenge. Our findings show that while much of the core JA-related metabolic and genetic responses appear conserved between setaria and maize, production of downstream secondary metabolites such as benzoxazinoids and herbivore-induced plant volatiles are dissimilar. This diversity of chemical defenses and gene families involved in secondary metabolism among grasses presents new opportunities for cross species engineering. The high degree of genetic similarity and ease of orthologous gene identification between setaria and maize make setaria an excellent species for translational genetic studies, but the species specificity of downstream insect defense chemistry makes some pathways unamenable to cross-species comparisons., (Published by Elsevier B.V.) more...
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- 2020
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28. Fighting on two fronts: Elevated insect resistance in flooded maize.
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Block AK, Hunter CT, Sattler SE, Rering C, McDonald S, Basset GJ, and Christensen SA
- Subjects
- Animals, Catechol Oxidase metabolism, Gene Expression Regulation, Plant, Herbivory physiology, Larva physiology, Peroxidase metabolism, Plant Diseases, Salicylic Acid metabolism, Spodoptera physiology, Disease Resistance physiology, Floods, Insecta physiology, Zea mays metabolism
- Abstract
To grow and thrive plants must be able to adapt to both adverse environmental conditions and attack by a variety of pests. Elucidating the sophisticated mechanisms plants have developed to achieve this has been the focus of many studies. What is less well understood is how plants respond when faced with multiple stressors simultaneously. In this study, we assess the response of Zea mays (maize) to the combinatorial stress of flooding and infestation with the insect pest Spodoptera frugiperda (fall armyworm). This combined stress leads to elevated production of the defence hormone salicylic acid, which does not occur in the individual stresses, and the resultant salicylic acid-dependent increase in S. frugiperda resistance. Remodelling of phenylpropanoid pathways also occurs in response to this combinatorial stress leading to increased production of the anti-insect C-glycosyl flavones (maysins) and the herbivore-induced volatile phenolics, benzyl acetate, and phenethyl acetate. Furthermore, changes in cellular redox status also occur, as indicated by reductions in peroxidase and polyphenol oxidase activity. These data suggest that metabolite changes important for flooding tolerance and anti-insect defence may act both additively and synergistically to provide extra protection to the plant., (© 2019 John Wiley & Sons Ltd.) more...
- Published
- 2020
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29. Sorghum MSD3 Encodes an ω-3 Fatty Acid Desaturase that Increases Grain Number by Reducing Jasmonic Acid Levels.
- Author
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Dampanaboina L, Jiao Y, Chen J, Gladman N, Chopra R, Burow G, Hayes C, Christensen SA, Burke J, Ware D, and Xin Z
- Subjects
- Alleles, Crops, Agricultural drug effects, Crops, Agricultural genetics, Crops, Agricultural growth & development, Cyclopentanes pharmacology, Edible Grain drug effects, Edible Grain genetics, Edible Grain growth & development, High-Throughput Nucleotide Sequencing, Linoleic Acid chemistry, Linoleic Acid metabolism, Mutation, Oxylipins pharmacology, Phenotype, Seeds drug effects, Seeds genetics, Seeds growth & development, Sorghum genetics, Sorghum metabolism, alpha-Linolenic Acid biosynthesis, alpha-Linolenic Acid chemistry, Crops, Agricultural enzymology, Cyclopentanes metabolism, Fatty Acid Desaturases genetics, Fatty Acid Desaturases metabolism, Oxylipins metabolism, Sorghum enzymology
- Abstract
Grain number per panicle is an important component of grain yield in sorghum ( Sorghum bicolor (L.)) and other cereal crops. Previously, we reported that mutations in multi-seeded 1 ( MSD1) and MSD2 genes result in a two-fold increase in grain number per panicle due to the restoration of the fertility of the pedicellate spikelets, which invariably abort in natural sorghum accessions. Here, we report the identification of another gene, MSD3, which is also involved in the regulation of grain numbers in sorghum. Four bulked F
2 populations from crosses between BTx623 and each of the independent msd mutants p6, p14, p21, and p24 were sequenced to 20× coverage of the whole genome on a HiSeq 2000 system. Bioinformatic analyses of the sequence data showed that one gene, Sorbi_3001G407600, harbored homozygous mutations in all four populations. This gene encodes a plastidial ω-3 fatty acid desaturase that catalyzes the conversion of linoleic acid (18:2) to linolenic acid (18:3), a substrate for jasmonic acid (JA) biosynthesis. The msd3 mutants had reduced levels of linolenic acid in both leaves and developing panicles that in turn decreased the levels of JA. Furthermore, the msd3 panicle phenotype was reversed by treatment with methyl-JA (MeJA). Our characterization of MSD1, MSD2, and now MSD3 demonstrates that JA-regulated processes are critical to the msd phenotype. The identification of the MSD3 gene reveals a new target that could be manipulated to increase grain number per panicle in sorghum, and potentially other cereal crops, through the genomic editing of MSD3 functional orthologs. more...- Published
- 2019
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30. Fertility of Pedicellate Spikelets in Sorghum Is Controlled by a Jasmonic Acid Regulatory Module.
- Author
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Gladman N, Jiao Y, Lee YK, Zhang L, Chopra R, Regulski M, Burow G, Hayes C, Christensen SA, Dampanaboina L, Chen J, Burke J, Ware D, and Xin Z
- Subjects
- Amino Acid Sequence, Binding Sites, Edible Grain, Gene Expression Profiling, Gene Expression Regulation, Plant, Metabolic Networks and Pathways, Phylogeny, Plant Proteins chemistry, Plant Proteins genetics, Plant Proteins metabolism, Promoter Regions, Genetic, Protein Binding, Sorghum classification, Transcription Factors metabolism, Cyclopentanes metabolism, Fertility, Oxylipins metabolism, Plant Development, Sorghum physiology
- Abstract
As in other cereal crops, the panicles of sorghum ( Sorghum bicolor (L.) Moench) comprise two types of floral spikelets (grass flowers). Only sessile spikelets (SSs) are capable of producing viable grains, whereas pedicellate spikelets (PSs) cease development after initiation and eventually abort. Consequently, grain number per panicle (GNP) is lower than the total number of flowers produced per panicle. The mechanism underlying this differential fertility is not well understood. To investigate this issue, we isolated a series of ethyl methane sulfonate (EMS)-induced multiseeded ( msd ) mutants that result in full spikelet fertility, effectively doubling GNP. Previously, we showed that MSD1 is a TCP (Teosinte branched/Cycloidea/PCF) transcription factor that regulates jasmonic acid (JA) biosynthesis, and ultimately floral sex organ development. Here, we show that MSD2 encodes a lipoxygenase (LOX) that catalyzes the first committed step of JA biosynthesis. Further, we demonstrate that MSD1 binds to the promoters of MSD2 and other JA pathway genes. Together, these results show that a JA-induced module regulates sorghum panicle development and spikelet fertility. The findings advance our understanding of inflorescence development and could lead to new strategies for increasing GNP and grain yield in sorghum and other cereal crops. more...
- Published
- 2019
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31. Multiple genes recruited from hormone pathways partition maize diterpenoid defences.
- Author
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Ding Y, Murphy KM, Poretsky E, Mafu S, Yang B, Char SN, Christensen SA, Saldivar E, Wu M, Wang Q, Ji L, Schmitz RJ, Kremling KA, Buckler ES, Shen Z, Briggs SP, Bohlmann J, Sher A, Castro-Falcon G, Hughes CC, Huffaker A, Zerbe P, and Schmelz EA more...
- Subjects
- Ascomycota, Cytochrome P-450 Enzyme System metabolism, Disease Resistance genetics, Genome-Wide Association Study, Gibberellins metabolism, Metabolic Networks and Pathways genetics, Plant Diseases immunology, Plant Diseases microbiology, Zea mays immunology, Zea mays metabolism, Zea mays microbiology, Diterpenes, Kaurane metabolism, Genes, Plant, Plant Growth Regulators genetics, Zea mays genetics
- Abstract
Duplication and divergence of primary pathway genes underlie the evolution of plant specialized metabolism; however, mechanisms partitioning parallel hormone and defence pathways are often speculative. For example, the primary pathway intermediate ent-kaurene is essential for gibberellin biosynthesis and is also a proposed precursor for maize antibiotics. By integrating transcriptional coregulation patterns, genome-wide association studies, combinatorial enzyme assays, proteomics and targeted mutant analyses, we show that maize kauralexin biosynthesis proceeds via the positional isomer ent-isokaurene formed by a diterpene synthase pair recruited from gibberellin metabolism. The oxygenation and subsequent desaturation of ent-isokaurene by three promiscuous cytochrome P450s and a new steroid 5α reductase indirectly yields predominant ent-kaurene-associated antibiotics required for Fusarium stalk rot resistance. The divergence and differential expression of pathway branches derived from multiple duplicated hormone-metabolic genes minimizes dysregulation of primary metabolism via the circuitous biosynthesis of ent-kaurene-related antibiotics without the production of growth hormone precursors during defence. more...
- Published
- 2019
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32. A maize polygalacturonase functions as a suppressor of programmed cell death in plants.
- Author
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He Y, Karre S, Johal GS, Christensen SA, and Balint-Kurti P
- Subjects
- Apoptosis genetics, Chromosome Mapping, Chromosomes, Plant, Genes, Plant, Leucine, Plant Proteins chemistry, Plant Proteins genetics, Polygalacturonase chemistry, Polygalacturonase genetics, Recombination, Genetic, Repetitive Sequences, Amino Acid, Nicotiana genetics, Zea mays enzymology, Zea mays genetics, Zea mays immunology, Apoptosis physiology, Plant Proteins physiology, Polygalacturonase physiology, Zea mays physiology
- Abstract
Background: The hypersensitive defense response (HR) in plants is a fast, localized necrotic response around the point of pathogen ingress. HR is usually triggered by a pathogen recognition event mediated by a nucleotide-binding site, leucine-rich repeat (NLR) protein. The autoactive maize NLR gene Rp1-D21 confers a spontaneous HR response in the absence of pathogen recognition. Previous work identified a set of loci associated with variation in the strength of Rp1-D21-induced HR. A polygalacturonase gene homolog, here termed ZmPGH1, was identified as a possible causal gene at one of these loci on chromosome 7., Results: Expression of ZmPGH1 inhibited the HR-inducing activity of both Rp1-D21 and that of another autoactive NLR, RPM1(D505V), in a Nicotiana benthamiana transient expression assay system. Overexpression of ZmPGH1 in a transposon insertion line of maize was associated with suppression of chemically-induced programmed cell death and with suppression of HR induced by Rp1-D21 in maize plants grown in the field., Conclusions: ZmPGH1 functions as a suppressor of programmed cell death induced by at least two autoactive NLR proteins and by two chemical inducers. These findings deepen our understanding of the control of the HR in plants. more...
- Published
- 2019
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33. Biosynthesis and function of terpenoid defense compounds in maize (Zea mays).
- Author
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Block AK, Vaughan MM, Schmelz EA, and Christensen SA
- Subjects
- Animals, Gene Expression Regulation, Plant, Insecta pathogenicity, Plant Diseases parasitology, Sesquiterpenes metabolism, Phytoalexins, Terpenes metabolism, Zea mays metabolism, Zea mays parasitology
- Abstract
Main Conclusion: Maize produces an array of herbivore-induced terpene volatiles that attract parasitoids to infested plants and a suite of pathogen-induced non-volatile terpenoids with antimicrobial activity to defend against pests. Plants rely on complex blends of constitutive and dynamically produced specialized metabolites to mediate beneficial ecological interactions and protect against biotic attack. One such class of metabolites are terpenoids, a large and structurally diverse class of molecules shown to play significant defensive and developmental roles in numerous plant species. Despite this, terpenoids have only recently been recognized as significant contributors to pest resistance in maize (Zea mays), a globally important agricultural crop. The current review details recent advances in our understanding of biochemical structures, pathways and functional roles of maize terpenoids. Dependent upon the lines examined, maize can harbor more than 30 terpene synthases, underlying the inherent diversity of maize terpene defense systems. Part of this defensive arsenal is the inducible production of volatile bouquets that include monoterpenes, homoterpenes and sesquiterpenes, which often function in indirect defense by enabling the attraction of parasitoids and predators. More recently discovered are a subset of sesquiterpene and diterpene hydrocarbon olefins modified by cytochrome P450s to produce non-volatile end-products such kauralexins, zealexins, dolabralexins and β-costic acid. These non-volatile terpenoid phytoalexins often provide effective defense against both microbial and insect pests via direct antimicrobial and anti-feedant activity. The diversity and promiscuity of maize terpene synthases, coupled with a variety of secondary modifications, results in elaborate defensive layers whose identities, regulation and precise functions are continuing to be elucidated. more...
- Published
- 2019
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34. Interactions Among Plants, Insects, and Microbes: Elucidation of Inter-Organismal Chemical Communications in Agricultural Ecology.
- Author
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Beck JJ, Alborn HT, Block AK, Christensen SA, Hunter CT, Rering CC, Seidl-Adams I, Stuhl CJ, Torto B, and Tumlinson JH
- Subjects
- Agriculture, Animals, Insecta microbiology, Plant Physiological Phenomena, Plants microbiology, Plants parasitology, Volatile Organic Compounds metabolism, Ecosystem, Insecta physiology, Microbiota, Plants metabolism
- Abstract
The last 2 decades have witnessed a sustained increase in the study of plant-emitted volatiles and their role in plant-insect, plant-microbe, and plant-plant interactions. While each of these binary systems involves complex chemical and biochemical processes between two organisms, the progression of increasing complexity of a ternary system (i.e., plant-insect-microbe), and the study of a ternary system requires nontrivial planning. This planning can include an experimental design that factors in potential overarching ecological interactions regarding the binary or ternary system, correctly identifying and understanding unexpected observations that may occur during the experiment and thorough interpretation of the resultant data. This challenge of planning, performing, and interpreting a plant's defensive response to multiple biotic stressors will be even greater when abiotic stressors (i.e., temperature or water) are factored into the system. To fully understand the system, we need to not only continue to investigate and understand the volatile profiles but also include and understand the biochemistry of the plant's response to these stressors. In this review, we provide examples and discuss interaction considerations with respect to how readers and future authors of the Journal of Agricultural and Food Chemistry can contribute their expertise toward the extraction and interpretation of chemical information exchanged between agricultural commodities and their associated pests. This holistic, multidisciplinary, and thoughtful approach to interactions of plants, insects, and microbes, and the resultant response of the plants can lead to a better understanding of agricultural ecology, in turn leading to practical and viable solutions to agricultural problems. more...
- Published
- 2018
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35. Contrasting insect attraction and herbivore-induced plant volatile production in maize.
- Author
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Block AK, Hunter CT, Rering C, Christensen SA, and Meagher RL
- Subjects
- Animals, Benzoxazines metabolism, Gene Expression Profiling, Indoles metabolism, Models, Biological, Terpenes metabolism, Zea mays parasitology, Herbivory, Pheromones metabolism, Spodoptera parasitology, Volatile Organic Compounds metabolism, Wasps physiology, Zea mays metabolism
- Abstract
Main Conclusion: The maize inbred line W22 has lower herbivore-induced volatile production than B73 but both fall armyworm larvae and the wasps that parasitize them prefer W22 over B73. Maize inbred line W22 is an important resource for genetic studies due to the availability of the UniformMu mutant population and a complete genome sequence. In this study, we assessed the suitability of W22 as a model for tritrophic interactions between maize, Spodoptera frugiperda (fall armyworm) and the parasitoid wasp Cotesia marginiventris. W22 was found to be a good model for studying the interaction as S. frugiperda prefers W22 over B73 and a higher parasitism rate by C. marginiventris was observed on W22 compared to the inbred line B73. W22 also produced lower amounts of many herbivore-induced volatile terpenes and indole emission upon treatment with S. frugiperda oral secretions. We propose that some of the major herbivore-induced terpene volatiles are perhaps impeding S. frugiperda and C. marginiventris preference and that as yet unidentified compounds are produced at low abundance may be positively impacting these interactions. more...
- Published
- 2018
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36. Fungal and herbivore elicitation of the novel maize sesquiterpenoid, zealexin A4, is attenuated by elevated CO 2 .
- Author
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Christensen SA, Huffaker A, Sims J, Hunter CT, Block A, Vaughan MM, Willett D, Romero M, Mylroie JE, Williams WP, and Schmelz EA
- Subjects
- Alkyl and Aryl Transferases metabolism, Anti-Infective Agents metabolism, Aspergillus flavus metabolism, Carbon Dioxide pharmacology, Gene Expression Regulation, Plant drug effects, Plant Immunity, Rhizopus metabolism, Seedlings metabolism, Zea mays drug effects, Zea mays microbiology, Sesquiterpenes metabolism, Zea mays metabolism
- Abstract
Main Conclusion: Chemical isolation and NMR-based structure elucidation revealed a novel keto-acidic sesquiterpenoid, termed zealexin A4 (ZA4). ZA4 is elicited by pathogens and herbivory, but attenuated by heightened levels of CO
2 . The identification of the labdane-related diterpenoids, termed kauralexins and acidic sesquiterpenoids, termed zealexins, demonstrated the existence of at least ten novel stress-inducible maize metabolites with diverse antimicrobial activity. Despite these advances, the identity of co-occurring and predictably related analytes remains largely unexplored. In the current effort, we identify and characterize the first sesquiterpene keto acid derivative of β-macrocarpene, named zealexin A4 (ZA4). Evaluation of diverse maize inbreds revealed that ZA4 is commonly produced in maize scutella during the first 14 days of seedling development; however, ZA4 production in the scutella was markedly reduced in seedlings grown in sterile soil. Elevated ZA4 production was observed in response to inoculation with adventitious fungal pathogens, such as Aspergillus flavus and Rhizopus microsporus, and a positive relationship between ZA4 production and expression of the predicted zealexin biosynthetic genes, terpene synthases 6 and 11 (Tps6 and Tps11), was observed. ZA4 exhibited significant antimicrobial activity against the mycotoxigenic pathogen A. flavus; however, ZA4 activity against R. microsporus was minimal, suggesting the potential of some fungi to detoxify ZA4. Significant induction of ZA4 production was also observed in response to infestation with the stem tunneling herbivore Ostrinia nubilalis. Examination of the interactive effects of elevated CO2 (E-CO2 ) on both fungal and herbivore-elicited ZA4 production revealed significantly reduced levels of inducible ZA4 accumulation, consistent with a negative role for E-CO2 on ZA4 production. Collectively, these results describe a novel β-macrocarpene-derived antifungal defense in maize and expand the established diversity of zealexins that are differentially regulated in response to biotic/abiotic stress. more...- Published
- 2018
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37. Commercial hybrids and mutant genotypes reveal complex protective roles for inducible terpenoid defenses in maize.
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Christensen SA, Sims J, Vaughan MM, Hunter C, Block A, Willett D, Alborn HT, Huffaker A, and Schmelz EA
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- Ascomycota physiology, Colletotrichum physiology, Fusarium physiology, Genotype, Hybridization, Genetic, Mutation, Plant Breeding, Zea mays genetics, Zea mays microbiology, Antibiosis, Plant Diseases microbiology, Plant Growth Regulators metabolism, Terpenes metabolism, Zea mays physiology
- Abstract
Plant defense research is facilitated by the use of genome-sequenced inbred lines; however, a foundational knowledge of interactions in commercial hybrids remains relevant to understanding mechanisms present in crops. Using an array of commercial maize hybrids, we quantified the accumulation patterns of defense-related metabolites and phytohormones in tissues challenged with diverse fungal pathogens. Across hybrids, Southern leaf blight (Cochliobolus heterostrophus) strongly elicited specific sesqui- and diterpenoid defenses, namely zealexin A4 (ZA4) and kauralexin diacids, compared with the stalk-rotting agents Fusarium graminearum and Colletotrichum graminicola. With respect to biological activity, ZA4 and kauralexin diacids demonstrated potent antimicrobial action against F. graminearum. Unexpectedly, ZA4 displayed an opposite effect on C. graminicola by promoting growth. Overall, a negative correlation was observed between total analyzed terpenoids and fungal growth. Statistical analyses highlighted kauralexin A3 and abscisic acid as metabolites most associated with fungal suppression. As an empirical test, mutants of the ent-copalyl diphosphate synthase Anther ear 2 (An2) lacking kauralexin biosynthetic capacity displayed increased susceptibility to C. heterostrophus and Fusarium verticillioides. Our results highlight a widely occurring defensive function of acidic terpenoids in commercial hybrids and the complex nature of elicited pathway products that display selective activities on fungal pathogen species. more...
- Published
- 2018
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38. Maize w3 disrupts homogentisate solanesyl transferase (ZmHst) and reveals a plastoquinone-9 independent path for phytoene desaturation and tocopherol accumulation in kernels.
- Author
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Hunter CT, Saunders JW, Magallanes-Lundback M, Christensen SA, Willett D, Stinard PS, Li QB, Lee K, DellaPenna D, and Koch KE
- Subjects
- Abscisic Acid metabolism, Alkyl and Aryl Transferases genetics, Carotenoids genetics, Carotenoids metabolism, Mutation, Oxidoreductases genetics, Oxidoreductases metabolism, Phenotype, Photosynthesis, Phylogeny, Plant Leaves genetics, Plant Leaves metabolism, Plant Proteins genetics, Plastids genetics, Plastids metabolism, Seeds genetics, Seeds metabolism, Vitamin E genetics, Vitamin E metabolism, Zea mays genetics, Alkyl and Aryl Transferases metabolism, Plant Proteins metabolism, Plastoquinone metabolism, Tocopherols metabolism, Zea mays metabolism
- Abstract
Maize white seedling 3 (w3) has been used to study carotenoid deficiency for almost 100 years, although the molecular basis of the mutation has remained unknown. Here we show that the w3 phenotype is caused by disruption of the maize gene for homogentisate solanesyl transferase (HST), which catalyzes the first and committed step in plastoquinone-9 (PQ-9) biosynthesis in the plastid. The resulting PQ-9 deficiency prohibits photosynthetic electron transfer and eliminates PQ-9 as an oxidant in the enzymatic desaturation of phytoene during carotenoid synthesis. As a result, light-grown w3 seedlings are albino, deficient in colored carotenoids and accumulate high levels of phytoene. However, despite the absence of PQ-9 for phytoene desaturation, dark-grown w3 seedlings can produce abscisic acid (ABA) and homozygous w3 kernels accumulate sufficient carotenoids to generate ABA needed for seed maturation. The presence of ABA and low levels of carotenoids in w3 nulls indicates that phytoene desaturase is able to use an alternate oxidant cofactor, albeit less efficiently than PQ-9. The observation that tocopherols and tocotrienols are modestly affected in w3 embryos and unaffected in w3 endosperm indicates that, unlike leaves, grain tissues deficient in PQ-9 are not subject to severe photo-oxidative stress. In addition to identifying the molecular basis for the maize w3 mutant, we: (1) show that low levels of phytoene desaturation can occur in w3 seedlings in the absence of PQ-9; and (2) demonstrate that PQ-9 and carotenoids are not required for vitamin E accumulation., (© 2018 The Authors. The Plant Journal published by John Wiley & Sons Ltd and Society for Experimental Biology.) more...
- Published
- 2018
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39. MSD1 regulates pedicellate spikelet fertility in sorghum through the jasmonic acid pathway.
- Author
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Jiao Y, Lee YK, Gladman N, Chopra R, Christensen SA, Regulski M, Burow G, Hayes C, Burke J, Ware D, and Xin Z
- Subjects
- Edible Grain, Gene Ontology, High-Throughput Nucleotide Sequencing, Inflorescence genetics, Inflorescence growth & development, Inflorescence metabolism, Molecular Sequence Annotation, Plant Growth Regulators genetics, Plant Growth Regulators metabolism, Plant Proteins genetics, Plant Proteins metabolism, Seeds genetics, Seeds growth & development, Seeds metabolism, Signal Transduction, Sorghum genetics, Sorghum growth & development, Sorghum metabolism, Transcription Factors genetics, Transcription Factors metabolism, Cyclopentanes pharmacology, Gene Expression Regulation, Plant, Inflorescence drug effects, Oxylipins pharmacology, Plant Growth Regulators pharmacology, Seeds drug effects, Sorghum drug effects
- Abstract
Grain number per panicle (GNP) is a major determinant of grain yield in cereals. However, the mechanisms that regulate GNP remain unclear. To address this issue, we isolate a series of sorghum [Sorghum bicolor (L.) Moench] multiseeded (msd) mutants that can double GNP by increasing panicle size and altering floral development so that all spikelets are fertile and set grain. Through bulk segregant analysis by next-generation sequencing, we identify MSD1 as a TCP (Teosinte branched/Cycloidea/PCF) transcription factor. Whole-genome expression profiling reveals that jasmonic acid (JA) biosynthetic enzymes are transiently activated in pedicellate spikelets. Young msd1 panicles have 50% less JA than wild-type (WT) panicles, and application of exogenous JA can rescue the msd1 phenotype. Our results reveal a new mechanism for increasing GNP, with the potential to boost grain yield, and provide insight into the regulation of plant inflorescence architecture and development. more...
- Published
- 2018
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40. Herbivore-derived fatty-acid amides elicit reactive oxygen species burst in plants.
- Author
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Block A, Christensen SA, Hunter CT, and Alborn HT
- Subjects
- Animals, Arabidopsis Proteins metabolism, Fatty Acids, Food Chain, NADPH Oxidases metabolism, Spodoptera, Amides metabolism, Arabidopsis physiology, Herbivory, Solanum lycopersicum physiology, Moths, Reactive Oxygen Species metabolism
- Abstract
Reactive oxygen species (ROS) can be elicited by many forms of stress, including pathogen attack, abiotic stress, damage and insect infestation. Perception of microbe- or damage-associated elicitors triggers an ROS burst in many plant species; however, the impact of herbivore fatty-acid amides on ROS elicitation remains largely unexplored. In this study we show that the lepidopteran-derived fatty-acid amide elicitor N-linolenoyl-L-glutamine (GLN18:3) can induce a ROS burst in multiple plant species. Furthermore, in Arabidopsis this ROS burst is partially dependent on the plasma membrane localized NADPH oxidases RBOHD and RBOHF, and an Arabidopsis rbohD/F double mutant produces enhanced GLN18:3-induced jasmonic acid. Quantification of GLN18:3-induced ROS in phytohormone-deficient lines revealed that in Arabidopsis reduced levels of jasmonic acid resulted in a larger elicitor-induced ROS burst, while in tomato reduction of either jasmonic acid or salicylic acid led to higher induced ROS production. These data indicate that GLN18:3-induced ROS is antagonistic to jasmonic acid production in these species. In biological assays, rbohD/F mutant plants were more resistant to the generalist herbivores Spodoptera exigua and Trichoplusia ni but not to the specialist Plutella xylostella. Collectively, these results demonstrate that in Arabidopsis herbivore-induced ROS may negatively regulate plant defense responses to herbivory. more...
- Published
- 2018
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41. Exploring the metabolic variation between domesticated and wild tetraploid wheat genotypes in response to corn leaf aphid infestation.
- Author
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Chandrasekhar K, Shavit R, Distelfeld A, Christensen SA, and Tzin V
- Subjects
- Animals, Genotype, Plant Leaves genetics, Plant Leaves parasitology, Zea mays genetics, Zea mays parasitology, Aphids pathogenicity, Triticum genetics, Triticum parasitology
- Abstract
Infestation of Triticum (wheat) plants by their pest Rhopalosiphum maidis (corn leaf aphid) causes severe vegetative damage. Despite the agro-economic importance of wheat, the metabolic diversity of Triticum turgidum (tetraploid wheat) in response to aphid attack has not been sufficiently addressed. In this study, we compared the metabolic diversity of two tetraploid wheat genotypes, domesticated and wild emmer. The plants were grown in a control growth room and infested with aphids for 96 h. Our untargeted metabolic analysis performed on plants with and without aphids revealed massive differences between the two genotypes. The targeted metabolic analysis highlighted the differences in the biosynthesis of phytohormones. The aphid progeny was lower in the cultivated durum wheat than in the wild emmer wheat. Overall, these observations emphasize the potential of using the natural diversity of wheat species to better understand the metabolic responses to pest damage. more...
- Published
- 2018
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42. RNA-Seq analysis of resistant and susceptible sub-tropical maize lines reveals a role for kauralexins in resistance to grey leaf spot disease, caused by Cercospora zeina.
- Author
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Meyer J, Berger DK, Christensen SA, and Murray SL
- Subjects
- Gene Ontology, Plant Diseases microbiology, Plant Leaves microbiology, Sequence Analysis, RNA, Zea mays metabolism, Zea mays microbiology, Ascomycota pathogenicity, Disease Resistance genetics, Plant Diseases genetics, Terpenes metabolism, Zea mays genetics
- Abstract
Background: Cercospora zeina is a foliar pathogen responsible for maize grey leaf spot in southern Africa that negatively impacts maize production. Plants use a variety of chemical and structural mechanisms to defend themselves against invading pathogens such as C. zeina, including the production of secondary metabolites with antimicrobial properties. In maize, a variety of biotic and abiotic stressors induce the accumulation of the terpenoid phytoalexins, zealexins and kauralexins., Results: C. zeina-susceptible line displayed pervasive rectangular grey leaf spot lesions, running parallel with the leaf veins in contrast to C. zeina-resistant line that had restricted disease symptoms. Analysis of the transcriptome of both lines indicated that genes involved in primary and secondary metabolism were up-regualted, and although different pathways were prioritized in each line, production of terpenoid compounds were common to both. Targeted phytoalexin analysis revealed that C. zeina-inoculated leaves accumulated zealexins and kauralexins. The resistant line shows a propensity toward accumulation of the kauralexin B series metabolites in response to infection, which contrasts with the susceptible line that preferentially accumulates the kauralexin A series. Kauralexin accumulation was correlated to expression of the kauralexin biosynthetic gene, ZmAn2 and a candidate biosynthetic gene, ZmKSL2. We report the expression of a putative copalyl diphosphate synthase gene that is induced by C. zeina in the resistant line exclusively., Discussion: This study shows that zealexins and kauralexins, and expression of their biosynthetic genes, are induced by C. zeina in both resistant and susceptible germplasm adapted to the southern African climate. The data presented here indicates that different forms of kauralexins accumulate in the resistant and susceptible maize lines in response to C. zeina, with the accumulation of kauralexin B compounds in a resistant maize line and kauralexin A compounds accumulating in the susceptible line. more...
- Published
- 2017
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43. Elevated carbon dioxide reduces emission of herbivore-induced volatiles in Zea mays.
- Author
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Block A, Vaughan MM, Christensen SA, Alborn HT, and Tumlinson JH
- Subjects
- Alkyl and Aryl Transferases genetics, Animals, Cyclopentanes metabolism, Diet, Gene Expression Regulation, Plant drug effects, Genes, Plant, Larva growth & development, Oxylipins metabolism, Plant Leaves drug effects, Plant Leaves metabolism, Plant Stomata drug effects, Plant Stomata physiology, Salicylic Acid metabolism, Sesquiterpenes analysis, Spodoptera growth & development, Volatile Organic Compounds chemistry, Zea mays drug effects, Zea mays genetics, Zea mays growth & development, Carbon Dioxide pharmacology, Herbivory physiology, Volatile Organic Compounds analysis, Zea mays physiology
- Abstract
Terpene volatiles produced by sweet corn (Zea mays) upon infestation with pests such as beet armyworm (Spodoptera exigua) function as part of an indirect defence mechanism by attracting parasitoid wasps; yet little is known about the impact of climate change on this form of plant defence. To investigate how a central component of climate change affects indirect defence, we measured herbivore-induced volatile emissions in plants grown under elevated carbon dioxide (CO
2 ). We found that S. exigua infested or elicitor-treated Z. mays grown at elevated CO2 had decreased emission of its major sesquiterpene, (E)-β-caryophyllene and two homoterpenes, (3E)-4,8-dimethyl-1,3,7-nonatriene and (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast, inside the leaves, elicitor-induced (E)-β-caryophyllene hyper-accumulated at elevated CO2 , while levels of homoterpenes were unaffected. Furthermore, gene expression analysis revealed that the induction of terpene synthase genes following treatment was lower in plants grown at elevated CO2 . Our data indicate that elevated CO2 leads both to a repression of volatile synthesis at the transcriptional level and to limitation of volatile release through effects of CO2 on stomatal conductance. These findings suggest that elevated CO2 may alter the ability of Z. mays to utilize volatile terpenes to mediate indirect defenses., (© 2017 John Wiley & Sons Ltd.) more...- Published
- 2017
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44. Rapid defense responses in maize leaves induced by Spodoptera exigua caterpillar feeding.
- Author
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Tzin V, Hojo Y, Strickler SR, Bartsch LJ, Archer CM, Ahern KR, Zhou S, Christensen SA, Galis I, Mueller LA, and Jander G
- Subjects
- Animals, Benzoxazines metabolism, Cyclopentanes metabolism, Gene Expression Profiling, Gene Knockout Techniques, Herbivory, Mutation, Oxylipins metabolism, Plant Growth Regulators metabolism, Plant Leaves genetics, Zea mays genetics, Gene Expression Regulation, Plant, Spodoptera physiology, Zea mays physiology
- Abstract
Insects such as the beet armyworm (Spodoptera exigua) cause extensive damage to maize (Zea mays). Maize plants respond by triggering defense signaling, changes in gene expression, and biosynthesis of specialized metabolites. Leaves of maize inbred line B73, which has an available genome sequence, were infested with S. exigua for 1 to 24 h, followed by comparisons of the transcript and metabolite profiles with those of uninfested controls. The most extensive gene expression responses occurred rapidly, within 4-6 h after caterpillar infestation. However, both gene expression and metabolite profiles were altered within 1 h and continued to change during the entire 24 h experiment. The defensive functions of three caterpillar-induced genes were examined using available Dissociation transposon insertions in maize inbred line W22. Whereas mutations in the benzoxazinoid biosynthesis pathway (Bx1 and Bx2) significantly improved caterpillar growth, the knockout of a 13-lipoxygenase (Lox8) involved in jasmonic acid biosynthesis did not. Interestingly, 9-lipoxygenases, which lead to the production of maize death acids, were more strongly induced by caterpillar feeding than 13-lipoxygenases, suggesting an as yet unknown function in maize defense against herbivory. Together, these results provide a comprehensive view of the dynamic transcriptomic and metabolomic responses of maize leaves to caterpillar feeding., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology.) more...
- Published
- 2017
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45. Systems genetics reveals a transcriptional network associated with susceptibility in the maize-grey leaf spot pathosystem.
- Author
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Christie N, Myburg AA, Joubert F, Murray SL, Carstens M, Lin YC, Meyer J, Crampton BG, Christensen SA, Ntuli JF, Wighard SS, Van de Peer Y, and Berger DK
- Subjects
- Ascomycota pathogenicity, Chromosomes, Plant genetics, Gene Regulatory Networks genetics, Gene Regulatory Networks physiology, Plant Diseases genetics, Plant Diseases microbiology, Quantitative Trait Loci genetics, Plant Leaves genetics, Plant Leaves microbiology, Zea mays genetics, Zea mays microbiology
- Abstract
We used a systems genetics approach to elucidate the molecular mechanisms of the responses of maize to grey leaf spot (GLS) disease caused by Cercospora zeina, a threat to maize production globally. Expression analysis of earleaf samples in a subtropical maize recombinant inbred line population (CML444 × SC Malawi) subjected in the field to C. zeina infection allowed detection of 20 206 expression quantitative trait loci (eQTLs). Four trans-eQTL hotspots coincided with GLS disease QTLs mapped in the same field experiment. Co-expression network analysis identified three expression modules correlated with GLS disease scores. The module (GY-s) most highly correlated with susceptibility (r = 0.71; 179 genes) was enriched for the glyoxylate pathway, lipid metabolism, diterpenoid biosynthesis and responses to pathogen molecules such as chitin. The GY-s module was enriched for genes with trans-eQTLs in hotspots on chromosomes 9 and 10, which also coincided with phenotypic QTLs for susceptibility to GLS. This transcriptional network has significant overlap with the GLS susceptibility response of maize line B73, and may reflect pathogen manipulation for nutrient acquisition and/or unsuccessful defence responses, such as kauralexin production by the diterpenoid biosynthesis pathway. The co-expression module that correlated best with resistance (TQ-r; 1498 genes) was enriched for genes with trans-eQTLs in hotspots coinciding with GLS resistance QTLs on chromosome 9. Jasmonate responses were implicated in resistance to GLS through co-expression of COI1 and enrichment of genes with the Gene Ontology term 'cullin-RING ubiquitin ligase complex' in the TQ-r module. Consistent with this, JAZ repressor expression was highly correlated with the severity of GLS disease in the GY-s susceptibility network., (© 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.) more...
- Published
- 2017
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46. Interactive Effects of Elevated [CO2] and Drought on the Maize Phytochemical Defense Response against Mycotoxigenic Fusarium verticillioides.
- Author
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Vaughan MM, Huffaker A, Schmelz EA, Dafoe NJ, Christensen SA, McAuslane HJ, Alborn HT, Allen LH, and Teal PE
- Subjects
- Abscisic Acid metabolism, Biomass, Climate Change, Plant Growth Regulators metabolism, Plant Roots metabolism, Sesquiterpenes metabolism, Stress, Physiological physiology, Phytoalexins, Carbon Dioxide metabolism, Droughts, Fumonisins metabolism, Fusarium growth & development, Plant Diseases microbiology, Zea mays metabolism, Zea mays microbiology
- Abstract
Changes in climate due to rising atmospheric carbon dioxide concentration ([CO2]) are predicted to intensify episodes of drought, but our understanding of how these combined conditions will influence crop-pathogen interactions is limited. We recently demonstrated that elevated [CO2] alone enhances maize susceptibility to the mycotoxigenic pathogen, Fusarium verticillioides (Fv) but fumonisin levels remain unaffected. In this study we show that maize simultaneously exposed to elevated [CO2] and drought are even more susceptible to Fv proliferation and also prone to higher levels of fumonisin contamination. Despite the increase in fumonisin levels, the amount of fumonisin produced in relation to pathogen biomass remained lower than corresponding plants grown at ambient [CO2]. Therefore, the increase in fumonisin contamination was likely due to even greater pathogen biomass rather than an increase in host-derived stimulants. Drought did not negate the compromising effects of elevated [CO2] on the accumulation of maize phytohormones and metabolites. However, since elevated [CO2] does not influence the drought-induced accumulation of abscisic acid (ABA) or root terpenoid phytoalexins, the effects elevated [CO2] are negated belowground, but the stifled defense response aboveground may be a consequence of resource redirection to the roots. more...
- Published
- 2016
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47. A maize death acid, 10-oxo-11-phytoenoic acid, is the predominant cyclopentenone signal present during multiple stress and developmental conditions.
- Author
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Christensen SA, Huffaker A, Hunter CT, Alborn HT, and Schmelz EA
- Subjects
- Biosynthetic Pathways, Cyclopentanes chemistry, Herbivory, Lipoxygenases chemistry, Lipoxygenases metabolism, Models, Biological, Signal Transduction, Zea mays growth & development, Zea mays metabolism, Cyclopentanes metabolism, Stress, Physiological, Zea mays physiology
- Abstract
Recently we investigated the function of the 9-lipoxygenase (LOX) derived cyclopentenones 10-oxo-11-phytoenoic acid (10-OPEA) and 10-oxo-11,15-phytodienoic acid (10-OPDA) and identified their C-14 and C-12 derivatives. 10-OPEA accumulation is elicited by fungal and insect attack and acts as a strong inhibitor of microbial and herbivore growth. Although structurally similar, comparative analyses between 10-OPEA and its 13-LOX analog 12-oxo-phytodienoic acid (12-OPDA) demonstrate specificity in transcript accumulation linked to detoxification, secondary metabolism, jasmonate regulation, and protease inhibition. As a potent cell death signal, 10-OPEA activates cysteine protease activity leading to ion leakage and apoptotic-like DNA fragmentation. In this study we further elucidate the distribution, abundance, and functional roles of 10-OPEA, 10-OPDA, and 12-OPDA, in diverse organs under pathogen- and insect-related stress. more...
- Published
- 2016
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48. Genetic mapping shows intraspecific variation and transgressive segregation for caterpillar-induced aphid resistance in maize.
- Author
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Tzin V, Lindsay PL, Christensen SA, Meihls LN, Blue LB, and Jander G
- Subjects
- Alleles, Animals, Benzoxazines chemistry, Genotype, Glucosides chemistry, Inbreeding, Larva, Quantitative Trait Loci, Spodoptera, Zea mays chemistry, Aphids, Chromosome Mapping, Herbivory, Zea mays genetics
- Abstract
Plants in nature have inducible defences that sometimes lead to targeted resistance against particular herbivores, but susceptibility to others. The metabolic diversity and genetic resources available for maize (Zea mays) make this a suitable system for a mechanistic study of within-species variation in such plant-mediated interactions between herbivores. Beet armyworms (Spodoptera exigua) and corn leaf aphids (Rhopalosiphum maidis) are two naturally occurring maize herbivores with different feeding habits. Whereas chewing herbivore-induced methylation of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc) to form 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) promotes caterpillar resistance, lower DIMBOA-Glc levels favour aphid reproduction. Thus, caterpillar-induced DIMBOA-Glc methyltransferase activity in maize is predicted to promote aphid growth. To test this hypothesis, the impact of S. exigua feeding on R. maidis progeny production was assessed using seventeen genetically diverse maize inbred lines. Whereas aphid progeny production was increased by prior caterpillar feeding on lines B73, Ki11, Ki3 and Tx303, it decreased on lines Ky21, CML103, Mo18W and W22. Genetic mapping of this trait in a population of B73 × Ky21 recombinant inbred lines identified significant quantitative trait loci on maize chromosomes 1, 7 and 10. There is a transgressive segregation for aphid resistance, with the Ky21 alleles on chromosomes 1 and 7 and the B73 allele on chromosome 10 increasing aphid progeny production. The chromosome 1 QTL coincides with a cluster of three maize genes encoding benzoxazinoid O-methyltransferases that convert DIMBOA-Glc to HDMBOA-Glc. Gene expression studies and benzoxazinoid measurements indicate that S. exigua -induced responses in this pathway differentially affect R. maidis resistance in B73 and Ky21., (© 2015 John Wiley & Sons Ltd.) more...
- Published
- 2015
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49. Symptom burden and integrative medicine in cancer survivorship.
- Author
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Cutshall SM, Cha SS, Ness SM, Stan DL, Christensen SA, Bhagra A, Price KA, Thompson CA, Hashmi SK, Chon TY, McCray TJ, Sood A, Bauer BA, and Ruddy KJ
- Subjects
- Aged, Female, Humans, Integrative Medicine methods, Male, Middle Aged, Surveys and Questionnaires, Survival Rate, Integrative Medicine standards, Neoplasms mortality, Survivors statistics & numerical data
- Abstract
Purpose: The purpose of the study was to learn about the level of experience with, interest in, and desire for knowledge about integrative medicine (IM) among cancer survivors., Methods: Cancer survivors attending the 2014 National Cancer Survivors Day in Rochester, MN, were recruited to participate in a one-page survey about their ongoing health concerns and symptoms, as well as their experience with, interest in, and desire for knowledge about IM. Two-sided t test was used for univariate analyses of impact of sex, time since diagnosis, and age., Results: Among the 260 cancer survivors, 171 persons (female, 74 %; male, 26 %) completed the survey (mean age, 64.6 years). Symptoms most commonly somewhat or more bothersome were fear of recurrence (52 %), stress (43 %), fatigue (43 %), difficulty sleeping (33 %), and weight gain (31 %). The most used IM resources were exercise (75 %), improved nutrition and diet (66 %), stress management (42 %), dietary supplementation (33 %), meditation (25 %), and massage (22 %). Older patients (age, ≥65 years) were less experienced with, interested in, and desiring of knowledge about IM techniques. Sex and time since diagnosis were not strongly predictive of most survey response categories., Conclusions: Cancer survivors have adverse effects for years into survivorship. They use and express interest in various IM techniques to help manage symptoms. It is critical that oncology providers help survivors address ongoing health concerns. Education about and access to evidence-based IM techniques may have important roles in comprehensive cancer survivorship programs. more...
- Published
- 2015
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50. Maize death acids, 9-lipoxygenase-derived cyclopente(a)nones, display activity as cytotoxic phytoalexins and transcriptional mediators.
- Author
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Christensen SA, Huffaker A, Kaplan F, Sims J, Ziemann S, Doehlemann G, Ji L, Schmitz RJ, Kolomiets MV, Alborn HT, Mori N, Jander G, Ni X, Sartor RC, Byers S, Abdo Z, and Schmelz EA
- Subjects
- Ascomycota physiology, Cyclopentanes chemistry, Cyclopentanes pharmacology, Cystatins genetics, Cystatins metabolism, Gene Expression Profiling, Gene Expression Regulation, Plant drug effects, Host-Pathogen Interactions, Immunoblotting, Lipoxygenase genetics, Magnetic Resonance Spectroscopy, Molecular Structure, Oligonucleotide Array Sequence Analysis, Oxylipins chemistry, Oxylipins metabolism, Plant Diseases genetics, Plant Diseases microbiology, Plant Leaves genetics, Plant Leaves metabolism, Plant Leaves microbiology, Plant Proteins genetics, Reverse Transcriptase Polymerase Chain Reaction, Sesquiterpenes chemistry, Sesquiterpenes pharmacology, Zea mays genetics, Zea mays microbiology, Phytoalexins, Cyclopentanes metabolism, Lipoxygenase metabolism, Plant Proteins metabolism, Sesquiterpenes metabolism, Zea mays metabolism
- Abstract
Plant damage promotes the interaction of lipoxygenases (LOXs) with fatty acids yielding 9-hydroperoxides, 13-hydroperoxides, and complex arrays of oxylipins. The action of 13-LOX on linolenic acid enables production of 12-oxo-phytodienoic acid (12-OPDA) and its downstream products, termed "jasmonates." As signals, jasmonates have related yet distinct roles in the regulation of plant resistance against insect and pathogen attack. A similar pathway involving 9-LOX activity on linolenic and linoleic acid leads to the 12-OPDA positional isomer, 10-oxo-11-phytodienoic acid (10-OPDA) and 10-oxo-11-phytoenoic acid (10-OPEA), respectively; however, physiological roles for 9-LOX cyclopentenones have remained unclear. In developing maize (Zea mays) leaves, southern leaf blight (Cochliobolus heterostrophus) infection results in dying necrotic tissue and the localized accumulation of 10-OPEA, 10-OPDA, and a series of related 14- and 12-carbon metabolites, collectively termed "death acids." 10-OPEA accumulation becomes wound inducible within fungal-infected tissues and at physiologically relevant concentrations acts as a phytoalexin by suppressing the growth of fungi and herbivores including Aspergillus flavus, Fusarium verticillioides, and Helicoverpa zea. Unlike previously established maize phytoalexins, 10-OPEA and 10-OPDA display significant phytotoxicity. Both 12-OPDA and 10-OPEA promote the transcription of defense genes encoding glutathione S transferases, cytochrome P450s, and pathogenesis-related proteins. In contrast, 10-OPEA only weakly promotes the accumulation of multiple protease inhibitor transcripts. Consistent with a role in dying tissue, 10-OPEA application promotes cysteine protease activation and cell death, which is inhibited by overexpression of the cysteine protease inhibitor maize cystatin-9. Unlike jasmonates, functions for 10-OPEA and associated death acids are consistent with specialized roles in local defense reactions. more...
- Published
- 2015
- Full Text
- View/download PDF
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