24 results on '"Koo, Abraham J. K."'
Search Results
2. Regulation and Function of Arabidopsis JASMONATE ZIM-Domain Genes in Response to Wounding and Herbivory
- Author
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Chung, Hoo Sun, Koo, Abraham J. K., Gao, Xiaoli, Jayanty, Sastry, Thines, Bryan, Jones, A. Daniel, and Howe, Gregg A.
- Published
- 2008
- Full Text
- View/download PDF
3. Identification of Acyltransferases Required for Cutin Biosynthesis and Production of Cutin with Suberin-Like Monomers
- Author
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Li, Yonghua, Beisson, Fred, Koo, Abraham J. K., Molina, Isabel, Pollard, Mike, and Ohlrogge, John
- Published
- 2007
- Full Text
- View/download PDF
4. Functional Diversification of Acyl-Coenzyme A Oxidases in Jasmonic Acid Biosynthesis and Action
- Author
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Schilmiller, Anthony L., Koo, Abraham J. K., and Howe, Gregg A.
- Published
- 2007
- Full Text
- View/download PDF
5. Elicitation of Jasmonate-Mediated Defense Responses by Mechanical Wounding and Insect Herbivory
- Author
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Herde, Marco, primary, Koo, Abraham J. K., additional, and Howe, Gregg A., additional
- Published
- 2013
- Full Text
- View/download PDF
6. A chemical complementation approach reveals genes and interactions of flavonoids with other pathways
- Author
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Pourcel, Lucille, Irani, Niloufer G., Koo, Abraham J. K., Bohorquez-Restrepo, Andres, Howe, Gregg A., and Grotewold, Erich
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- 2013
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- View/download PDF
7. Identification of a plastid acyl-acyl carrier protein synthetase in Arabidopsis and its role in the activation and elongation of exogenous fatty acids
- Author
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Koo, Abraham J. K., Fulda, Martin, Browse, John, and Ohlrogge, John B.
- Published
- 2005
8. A bHLH-type transcription factor, JA-ASSOCIATED MYC2-LIKE1, acts as repressor to negatively regulate jasmonate signaling in Arabidopsis
- Author
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Nakata, Masaru, Mitsuda, Nobutaka, Herde, Marco, Koo, Abraham J. K., Moreno, Javier Edgardo, Suzuki, Kaoru, Howe, Gregg A., and Ohme Takagi, Masaru
- Subjects
JAM1 ,Ciencias Biológicas ,repressor ,bHLH ,Bioquímica y Biología Molecular ,jasmonate ,CIENCIAS NATURALES Y EXACTAS - Abstract
Jasmonates (JAs) are plant hormones that regulate the balance between plant growth and responses to biotic and abiotic stresses. Although recent studies have uncovered the mechanisms for JA-induced responses in Arabidopsis thaliana, the mechanisms by which plants attenuate the JA-induced responses remain elusive. Here, we report that a basic helix-loop-helix-type transcription factor, ABA-INDUCIBLE BHLH-TYPE TRANSCRIPTION FACTOR/JA-ASSOCIATED MYC2-LIKE1 (JAM1), acts as a transcriptional repressor and negatively regulates JA signaling. Gain-of-function transgenic plants expressing the chimeric repressor for JAM1 exhibited substantial reduction of JA responses, including JA-induced inhibition of root growth, accumulation of anthocyanin, and male fertility. These plants were also compromised in resistance to attack by the insect herbivore Spodoptera exigua. Conversely, jam1 loss-of-function mutants showed enhanced JA responsiveness, including increased resistance to insect attack. JAM1 and MYC2 competitively bind to the target sequence of MYC2, which likely provides the mechanism for negative regulation of JA signaling and suppression of MYC2 functions by JAM1. These results indicate that JAM1 negatively regulates JA signaling, thereby playing a pivotal role in fine-tuning of JA-mediated stress responses and plant growth. Fil: Nakata, Masaru. National Institute of Advanced Industrial Science and Technology. Bioproduction Research Institute; Japón Fil: Mitsuda, Nobutaka. National Institute of Advanced Industrial Science and Technology. Bioproduction Research Institute; Japón Fil: Herde, Marco. Michigan State University; Estados Unidos Fil: Koo, Abraham J. K.. Michigan State University; Estados Unidos Fil: Moreno, Javier Edgardo. Michigan State University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentina Fil: Suzuki, Kaoru. National Institute of Advanced Industrial Science and Technology. Bioproduction Research Institute; Japón Fil: Howe, Gregg A.. Michigan State University; Estados Unidos Fil: Ohme Takagi, Masaru. National Institute of Advanced Industrial Science and Technology. Bioproduction Research Institute; Japón. Saitama University. Institute for Environmental Science and Technology ; Japón
- Published
- 2013
9. Catabolism and Deactivation of the Lipid-Derived Hormone Jasmonoyl-Isoleucine
- Author
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Koo, Abraham J. K., primary and Howe, Gregg A., additional
- Published
- 2012
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10. ChemInform Abstract: The Wound Hormone Jasmonate
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Koo, Abraham J. K., primary and Howe, Gregg A., additional
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- 2010
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11. Temporal Dynamics of Growth and Photosynthesis Suppression in Response to Jasmonate Signaling.
- Author
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Attaran, Elham, Major, Ian T., Cruz, Jeffrey A., Rosa, Bruce A., Koo, Abraham J. K., Jin Chen, Kramer, David M., Sheng Yang He, and Howe, Gregg A.
- Subjects
REGULATION of photosynthesis ,JASMONATE ,GENE expression in plants ,ARABIDOPSIS thaliana genetics ,CHLOROPHYLL spectra ,RNA sequencing - Abstract
Biotic stress constrains plant productivity in natural and agricultural ecosystems. Repression of photosynthetic genes is a conserved plant response to biotic attack, but how this transcriptional reprogramming is linked to changes in photosynthesis and the transition from growth- to defense-oriented metabolism is poorly understood. Here, we used a combination of noninvasive chlorophyll fluorescence imaging technology and RNA sequencing to determine the effect of the defense hormone jasmonate (JA) on the growth, photosynthetic efficiency, and gene expression of Arabidopsis (Arabidopsis thaliana) rosette leaves. High temporal resolution was achieved through treatment with coronatine (COR), a high-affinity agonist of the JA receptor. We show that leaf growth is rapidly arrested after COR treatment and that this effect is tightly correlated with changes in the expression of genes involved in growth, photosynthesis, and defense. Rapid COR-induced expression of defense genes occurred concomitantly with the repression of photosynthetic genes but was not associated with a reduced quantum efficiency of photosystem II. These findings support the view that photosynthetic capacity is maintained during the period in which stress-induced JA signaling redirects metabolism from growth to defense. Chlorophyll fluorescence images captured in a multiscale time series, however, revealed a transient COR-induced decrease in quantum efficiency of photosystem II at dawn of the day after treatment. Physiological studies suggest that this response results from delayed stomatal opening at the night-day transition. These collective results establish a high-resolution temporal view of how a major stress response pathway modulates plant growth and photosynthesis and highlight the utility of chlorophyll fluorescence imaging for revealing transient stress-induced perturbations in photosynthetic performance. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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12. A rapid wound signal activates the systemic synthesis of bioactive jasmonates in Arabidopsis.
- Author
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Koo, Abraham J. K., Xiaoli Gao, Jones, A. Daniel, and Howe, Gregg A.
- Subjects
- *
PLANT diseases , *ARABIDOPSIS , *HEREDITY , *GENES , *ARABIDOPSIS thaliana - Abstract
Jasmonic acid (JA) and its biologically active derivatives (bioactive JAs) perform a critical role in regulating plant responses to wound stress. The perception of bioactive JAs by the F-box protein COI1 triggers the SCFCOI1/ubiquitin-dependent degradation of JASMONATE ZIM-DOMAIN (JAZ) proteins that repress the expression of JA-response genes. JA is required for many wound-inducible systemic defense responses, but little is known about the role of the hormone in long-distance signal relay between damaged and undamaged leaves. Here, we show that the wounding of Arabidopsis thaliana leaves results in the rapid (<5 min) accumulation of jasmonoyl-l-isoleucine (JA-Ile), the bioactive form of JA, in leaves distal to the wound site. The rapid systemic increase in JA-Ile preceded the onset of early transcriptional responses, and was associated with JAZ degradation. Wound-induced systemic production of JA-Ile required the JA biosynthetic enzyme 12-oxo-phytodienoic acid (OPDA) reductase 3 (OPR3) in undamaged responding leaves, but not in wounded leaves, and was largely dependent on the JA-conjugating enzyme JAR1. Interestingly, the wound-induced synthesis of JA/JA-Ile in systemic leaves was correlated with a rapid decline in OPDA levels. These results are consistent with a model in which a rapidly transmitted wound signal triggers the systemic synthesis of JA, which, upon conversion to JA-Ile, activates the expression of early response genes by the SCFCOI1/JAZ pathway. [ABSTRACT FROM AUTHOR]
- Published
- 2009
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13. Regulation and Function of Arabidopsis JASMONATE ZIM-Domain Genes in Response to Wounding and Herbivory.
- Author
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Hoo Sun Chung, Koo, Abraham J. K., Xiaoli Gao, Jayanty, Sastry, Thines, Bryan, Jones, A. Daniel, and Howe, Gregg A.
- Subjects
- *
ARABIDOPSIS thaliana , *JASMONIC acid , *PLANT hormones , *PLANT defenses , *ANIMAL-plant relationships , *PLANT ecophysiology - Abstract
Jasmonate (JA) and its amino acid conjugate, jasmonoyl-isoleucine (JA-Ile), play important roles in regulating plant defense responses to insect herbivores. Recent studies indicate that JA-Ile promotes the degradation of JASMONATE ZIM-domain (JAZ) transcriptional repressors through the activity of the E3 ubiquitin-ligase SCFCOI1. Here, we investigated the regulation and function of JAZ genes during the interaction of Arabidopsis (Arabidopsis thaliana) with the generalist herbivore Spodoptera exigua. Most members of the JAZ gene family were highly expressed in response to S. exigua feeding and mechanical wounding. JAZ transcript levels increased within 5 min of mechanical tissue damage, coincident with a large (approximately 25-fold) rise in JA and JA-Ile levels. Wound-induced expression of JAZ and other CORONATINE-INSENSITIVE1 (COI1)-dependent genes was not impaired in the jar1-1 mutant that is partially deficient in the conversion of JA to JA-Ile. Experiments performed with the protein synthesis inhibitor cycloheximide provided evidence that JAZs, MYC2, and genes encoding several JA biosynthetic enzymes are primary response genes whose expression is derepressed upon COI1-dependent turnover of a labile repressor protein(s). We also show that overexpression of a modified form of JAZ1 (JAZ1Δ3A) that is stable in the presence of JA compromises host resistance to feeding by S. exigua larvae. These findings establish a role for JAZ proteins in the regulation of plant anti-insect defense, and support the hypothesis that JA-Ile and perhaps other JA derivatives activate COI1-dependent wound responses in Arabidopsis. Our results also indicate that the timing of JA-induced transcription in response to wounding is more rapid than previously realized. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
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14. Identification of acyltransferases required for cutin biosynthesis and production of cutin with suberin-like monomers.
- Author
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Yonghua Li, Beisson, Fred, Koo, Abraham J. K., Molina, Isabel, Pollard, Mike, and Ohlrogge, John
- Subjects
ACYLTRANSFERASES ,CUTIN ,ARABIDOPSIS ,MONOMERS ,BIOSYNTHESIS - Abstract
Cutin and suberin are the two major lipid-based polymers of plants. Cutin is the structural polymer of the epidermal cuticle, the waterproof layer covering primary aerial organs and which is often the structure first encountered by phytopathogens. Suberin contributes to the control of diffusion of water and solutes across internal root tissues and in periderms. The enzymes responsible for assembly of the cutin polymer are largely unknown. We have identified two Arabidopsis acyltransferases essential for cutin biosynthesis. glycerol-3-phosphate acyltransferase (GPAT) 4 and GPAT8. Double knockouts gpat4/gpat8 were strongly reduced in cutin and were less resistant to desiccation and to infection by the fungus Alternaria brassicicola. They also showed striking defects in stomata structure including a lack of cuticular ledges between guard cells, highlighting the importance of cutin in stomatal biology. Overexpression of GPAT4 or GPAT8 in Arabidopsis increased the content of C16 and C18 cutin monomers in leaves and stems by 80%. In order to modify cutin composition, the acyltransferase GPAT5 and the cytochrome P450-dependent fatty acyl oxidase CYP86A1, two enzymes associated with suberin biosyn- thesis, were overexpressed. When both enzymes were overexpressed together the epidermal polyesters accumulated new C20 and C22 ω-hydroxyacids and α,ω-diacids typical of suberin, and the fine structure and water-barrier function of the cuticle were altered. These results identify GPATs as partners of fatty acyl oxidases in lipid polyester synthesis and indicate that their cooverexpression provides a strategy to probe the role of cutin composition and quantity in the function of plant cuticles. [ABSTRACT FROM AUTHOR]
- Published
- 2007
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15. Identification of a Peroxisomal Acyl-activating Enzyme Involved in the Biosynthesis of Jasmonic Acid in Arabidopsis*.
- Author
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Koo, Abraham J. K., Hoo Sun Chung, Kobayashit, Yuichi, and Howe, Gregg A.
- Subjects
- *
JASMONIC acid , *LINOLENIC acids , *ARABIDOPSIS , *BIOSYNTHESIS , *PEROXISOMES - Abstract
Jasmonic acid (JA) is a lipid-derived signal that regulates a wide variety of developmental and defense-related processes in higher plants. JA is synthesized from linolenic acid via an enzymatic pathway that initiates in the plastid and terminates in peroxisomes. The C18 JA precursor 12-oxo-phytodienoic acid (OPDA) is converted in the peroxisome to 3-oxo-2-(2′-[Z] -pentenyl)cyclopentane-1-octanoic acid (OPC-8:0), which subsequently undergoes three rounds of β-oxidation to yield JA. Although most JA biosynthetic enzymes have been identified, several key steps in the pathway remain to be elucidated. To address this knowledge gap, we employed co-expression analysis to identify genes that are coordinately regulated with known JA biosynthetic components in Arabidopsis. Among the candidate genes uncovered by this approach was a 4-coumarate-CoA ligase-like member of the acyl-activating enzyme (AAE) gene family, which we have named C-8:0 CoA Ligase1 (OPCL1). In response to wounding, opcl1 null mutants exhibited reduced levels of JA and hyperaccumulation of OPC-8:0. Recombinant OPCL1 was active against both OPDA and OPC-8:0, as well as medium-to-long straight-chain fatty acids. Subcellular localization studies with green fluorescent protein-tagged OPCL1 showed that the protein is targeted to peroxisomes. These findings establish a physiological role for OPCL1 in the activation of JA biosynthetic precursors in leaf peroxisomes, and further indicate that OPC-8:0 is a physiological substrate for the activation step. The results also demonstrate the utility of co-expression analysis for identification of factors that contribute to jasmonate homeostasis. [ABSTRACT FROM AUTHOR]
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- 2006
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16. The predicted candidates of Arabidopsis plastid inner envelope membrane proteins and their expression profiles.
- Author
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Koo, Abraham J K and Ohlrogge, John B
- Abstract
Plastid envelope proteins from the Arabidopsis nuclear genome were predicted using computational methods. Selection criteria were: first, to find proteins with NH(2)-terminal plastid-targeting peptides from all annotated open reading frames from Arabidopsis; second, to search for proteins with membrane-spanning domains among the predicted plastidial-targeted proteins; and third, to subtract known thylakoid membrane proteins. Five hundred forty-one proteins were selected as potential candidates of the Arabidopsis plastid inner envelope membrane proteins (AtPEM candidates). Only 34% (183) of the AtPEM candidates could be assigned to putative functions based on sequence similarity to proteins of known function (compared with the 69% function assignment of the total predicted proteins in the genome). Of the 183 candidates with assigned functions, 40% were classified in the category of "transport facilitation," indicating that this collection is highly enriched in membrane transporters. Information on the predicted proteins, tissue expression data from expressed sequence tags and microarrays, and publicly available T-DNA insertion lines were collected. The data set complements proteomic-based efforts in the increased detection of integral membrane proteins, low-abundance proteins, or those not expressed in tissues selected for proteomic analysis. Digital northern analysis of expressed sequence tags suggested that the transcript levels of most AtPEM candidates were relatively constant among different tissues in contrast to stroma and the thylakoid proteins. However, both digital northern and microarray analyses identified a number of AtPEM candidates with tissue-specific expression patterns.
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- 2002
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17. Predicting gene function from uncontrolled expression variation among individual wild-type Arabidopsis plants.
- Author
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Bhosale R, Jewell JB, Hollunder J, Koo AJ, Vuylsteke M, Michoel T, Hilson P, Goossens A, Howe GA, Browse J, and Maere S
- Subjects
- Arabidopsis drug effects, Cyclopentanes pharmacology, Gene Regulatory Networks genetics, Molecular Sequence Annotation, Oxylipins pharmacology, Signal Transduction drug effects, Signal Transduction genetics, Software, Arabidopsis genetics, Gene Expression Regulation, Plant drug effects, Genes, Plant genetics
- Abstract
Gene expression profiling studies are usually performed on pooled samples grown under tightly controlled experimental conditions to suppress variability among individuals and increase experimental reproducibility. In addition, to mask unwanted residual effects, the samples are often subjected to relatively harsh treatments that are unrealistic in a natural context. Here, we show that expression variations among individual wild-type Arabidopsis thaliana plants grown under the same macroscopic growth conditions contain as much information on the underlying gene network structure as expression profiles of pooled plant samples under controlled experimental perturbations. We advocate the use of subtle uncontrolled variations in gene expression between individuals to uncover functional links between genes and unravel regulatory influences. As a case study, we use this approach to identify ILL6 as a new regulatory component of the jasmonate response pathway.
- Published
- 2013
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18. A bHLH-type transcription factor, ABA-INDUCIBLE BHLH-TYPE TRANSCRIPTION FACTOR/JA-ASSOCIATED MYC2-LIKE1, acts as a repressor to negatively regulate jasmonate signaling in arabidopsis.
- Author
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Nakata M, Mitsuda N, Herde M, Koo AJ, Moreno JE, Suzuki K, Howe GA, and Ohme-Takagi M
- Subjects
- Amino Acid Sequence, Animals, Anthocyanins metabolism, Arabidopsis metabolism, Arabidopsis parasitology, Arabidopsis Proteins metabolism, Base Sequence, Basic Helix-Loop-Helix Leucine Zipper Transcription Factors metabolism, Basic Helix-Loop-Helix Transcription Factors metabolism, Cyclopentanes metabolism, Gene Expression Profiling, Gene Expression Regulation, Plant drug effects, Host-Parasite Interactions drug effects, Microscopy, Fluorescence, Molecular Sequence Data, Oligonucleotide Array Sequence Analysis, Oxylipins metabolism, Plant Growth Regulators metabolism, Plant Growth Regulators pharmacology, Plants, Genetically Modified, Protein Binding, Reverse Transcriptase Polymerase Chain Reaction, Sequence Homology, Amino Acid, Sequence Homology, Nucleic Acid, Signal Transduction genetics, Spodoptera physiology, Arabidopsis genetics, Arabidopsis Proteins genetics, Basic Helix-Loop-Helix Leucine Zipper Transcription Factors genetics, Basic Helix-Loop-Helix Transcription Factors genetics, Cyclopentanes pharmacology, Oxylipins pharmacology
- Abstract
Jasmonates (JAs) are plant hormones that regulate the balance between plant growth and responses to biotic and abiotic stresses. Although recent studies have uncovered the mechanisms for JA-induced responses in Arabidopsis thaliana, the mechanisms by which plants attenuate the JA-induced responses remain elusive. Here, we report that a basic helix-loop-helix-type transcription factor, ABA-INDUCIBLE BHLH-TYPE TRANSCRIPTION FACTOR/JA-ASSOCIATED MYC2-LIKE1 (JAM1), acts as a transcriptional repressor and negatively regulates JA signaling. Gain-of-function transgenic plants expressing the chimeric repressor for JAM1 exhibited substantial reduction of JA responses, including JA-induced inhibition of root growth, accumulation of anthocyanin, and male fertility. These plants were also compromised in resistance to attack by the insect herbivore Spodoptera exigua. Conversely, jam1 loss-of-function mutants showed enhanced JA responsiveness, including increased resistance to insect attack. JAM1 and MYC2 competitively bind to the target sequence of MYC2, which likely provides the mechanism for negative regulation of JA signaling and suppression of MYC2 functions by JAM1. These results indicate that JAM1 negatively regulates JA signaling, thereby playing a pivotal role in fine-tuning of JA-mediated stress responses and plant growth.
- Published
- 2013
- Full Text
- View/download PDF
19. Altered lipid composition and enhanced nutritional value of Arabidopsis leaves following introduction of an algal diacylglycerol acyltransferase 2.
- Author
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Sanjaya, Miller R, Durrett TP, Kosma DK, Lydic TA, Muthan B, Koo AJ, Bukhman YV, Reid GE, Howe GA, Ohlrogge J, and Benning C
- Subjects
- Acyl Coenzyme A metabolism, Animals, Arabidopsis genetics, Chlamydomonas reinhardtii genetics, Diacylglycerol O-Acyltransferase genetics, Fatty Acids chemistry, Fatty Acids metabolism, Herbivory, Lipid Metabolism genetics, Membrane Lipids genetics, Membrane Lipids metabolism, Nutritive Value, Phylogeny, Plant Leaves chemistry, Plant Leaves genetics, Plants, Genetically Modified, Recombinant Proteins genetics, Recombinant Proteins metabolism, Seedlings genetics, Seedlings growth & development, Sphingolipids chemistry, Sphingolipids metabolism, Spodoptera physiology, Triglycerides metabolism, Waxes metabolism, Yeasts genetics, Arabidopsis metabolism, Chlamydomonas reinhardtii enzymology, Diacylglycerol O-Acyltransferase metabolism, Lipids chemistry, Plant Leaves metabolism
- Abstract
Enhancement of acyl-CoA-dependent triacylglycerol (TAG) synthesis in vegetative tissues is widely discussed as a potential avenue to increase the energy density of crops. Here, we report the identification and characterization of Chlamydomonas reinhardtii diacylglycerol acyltransferase type two (DGTT) enzymes and use DGTT2 to alter acyl carbon partitioning in plant vegetative tissues. This enzyme can accept a broad range of acyl-CoA substrates, allowing us to interrogate different acyl pools in transgenic plants. Expression of DGTT2 in Arabidopsis thaliana increased leaf TAG content, with some molecular species containing very-long-chain fatty acids. The acyl compositions of sphingolipids and surface waxes were altered, and cutin was decreased. The increased carbon partitioning into TAGs in the leaves of DGTT2-expressing lines had little effect on transcripts of the sphingolipid/wax/cutin pathway, suggesting that the supply of acyl groups for the assembly of these lipids is not transcriptionally adjusted. Caterpillars of the generalist herbivore Spodoptera exigua reared on transgenic plants gained more weight. Thus, the nutritional value and/or energy density of the transgenic lines was increased by ectopic expression of DGTT2 and acyl groups were diverted from different pools into TAGs, demonstrating the interconnectivity of acyl metabolism in leaves.
- Published
- 2013
- Full Text
- View/download PDF
20. Elicitation of jasmonate-mediated defense responses by mechanical wounding and insect herbivory.
- Author
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Herde M, Koo AJ, and Howe GA
- Subjects
- Animals, Arabidopsis metabolism, Disease Resistance, Herbivory, Larva physiology, Plant Leaves metabolism, Arabidopsis immunology, Butterflies physiology, Cyclopentanes metabolism, Oxylipins metabolism, Plant Growth Regulators physiology, Plant Leaves immunology
- Abstract
Many plant immune responses to biotic stress are mediated by the wound hormone jasmonate (JA). Functional and mechanistic studies of the JA signaling pathway often involve plant manipulations that elicit JA production and subsequent changes in gene expression in local and systemic tissues. Here, we describe a simple mechanical wounding procedure to effectively trigger JA responses in the Arabidopsis thaliana rosette. For comparison, we also present a plant-insect bioassay to elicit defense responses with the chewing insect Trichoplusia ni. This latter procedure can be used to determine the effect of JA-regulated defenses on growth and development of insect herbivores.
- Published
- 2013
- Full Text
- View/download PDF
21. The wound hormone jasmonate.
- Author
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Koo AJ and Howe GA
- Subjects
- Arabidopsis Proteins genetics, Arabidopsis Proteins metabolism, Cyclopentanes chemistry, Gene Expression Regulation, Plant genetics, Gene Expression Regulation, Plant physiology, Isoleucine analogs & derivatives, Isoleucine chemistry, Isoleucine metabolism, Isoleucine physiology, Models, Biological, Molecular Structure, Oxylipins chemistry, Signal Transduction genetics, Signal Transduction physiology, Cyclopentanes metabolism, Oxylipins metabolism
- Abstract
Plant tissues are highly vulnerable to injury by herbivores, pathogens, mechanical stress, and other environmental insults. Optimal plant fitness in the face of these threats relies on complex signal transduction networks that link damage-associated signals to appropriate changes in metabolism, growth, and development. Many of these wound-induced adaptive responses are triggered by de novo synthesis of the plant hormone jasmonate (JA). Recent studies provide evidence that JA mediates systemic wound responses through distinct cell autonomous and non-autonomous pathways. In both pathways, bioactive JAs are recognized by an F-box protein-based receptor system that couples hormone binding to ubiquitin-dependent degradation of transcriptional repressor proteins. These results provide a framework for understanding how plants recognize and respond to tissue injury.
- Published
- 2009
- Full Text
- View/download PDF
22. Jasmonate signaling: a conserved mechanism of hormone sensing.
- Author
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Katsir L, Chung HS, Koo AJ, and Howe GA
- Subjects
- Amino Acids chemistry, Amino Acids metabolism, Cyclopentanes chemistry, Indenes chemistry, Indenes metabolism, Oxylipins chemistry, Plant Proteins chemistry, Plant Proteins metabolism, Receptors, Cell Surface metabolism, Cyclopentanes metabolism, Oxylipins metabolism, Signal Transduction
- Abstract
The lipid-derived hormone jasmonate (JA) regulates diverse aspects of plant immunity and development. Among the central components of the JA signaling cascade are the E3 ubiquitin ligase SCFCOI1 and Jasmonate ZIM-domain (JAZ) proteins that repress transcription of JA-responsive genes. Recent studies provide evidence that amino acid-conjugated forms of JA initiate signal transduction upon formation of a coronatine-insensitive1 (COI1)-JA-JAZ ternary complex in which JAZs are ubiquitinated and subsequently degraded. Coronatine, a virulence factor produced by the plant pathogen Pseudomonas syringae, is a potent agonist of this hormone receptor system. Coronatine-induced targeting of JAZs to COI1 obstructs host immune responses to P. syrinage, providing a striking example of how pathogens exploit hormone signaling pathways in the host to promote disease. These findings, together with homology between COI1 and the auxin receptor, TIR1, extend the paradigm of F-box proteins as intracellular sensors of small molecules, and suggest a common evolutionary origin of the auxin and JA response pathways.
- Published
- 2008
- Full Text
- View/download PDF
23. On the export of fatty acids from the chloroplast.
- Author
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Koo AJ, Ohlrogge JB, and Pollard M
- Subjects
- Acyl Carrier Protein metabolism, Acyl Coenzyme A metabolism, Biological Assay, Substrate Specificity, Chloroplasts metabolism, Fatty Acids, Nonesterified metabolism
- Abstract
The model for export of fatty acids from plastids proposes that the acyl-ACP (acyl carrier protein) product of de novo fatty acid synthesis is hydrolyzed in the stroma by acyl-ACP thioesterases and the free fatty acid (FFA) released is then transferred to the outer envelope of the plastid where it is reactivated to acyl-CoA for utilization in cytosolic glycerolipid synthesis. Experiments were performed to assess whether the delivery of nascent FFA from the stroma for long chain acyl-CoA synthesis (LACS) occurs via simple diffusion or a more complex mechanism. The flux through the in vivo FFA pool was estimated using kinetic labeling experiments with spinach and pea leaves. The maximum half-life for FFA in the export pool was < or =1 s. Isolated pea chloroplasts incubated in the light with [14C]acetate gave a linear accumulation of FFA. When CoASH and ATP were present there was also a linear accumulation of acyl-CoA thioesters (plus derived polar lipids), with no measurable lag phase (<30 s), indicating that the FFA pool supplying LACS rapidly reached steady state. The LACS reaction was also measured independently in the dark after in situ generated FFA had accumulated yielding estimates of LACS substrate-velocity relationships. Based on these experiments the LACS reaction with in situ generated FFA as substrate is only about 3% of the LACS activity required in vivo at the very low concentrations of the FFA export pool calculated from the in vivo experiment. Furthermore, bovine serum albumin rapidly removed in situ generated FFA from chloroplasts, but could not compete effectively for "nascent" FFA substrates of LACS. Together the data suggest a locally channeled pool of exported FFA that is closely linked to LACS.
- Published
- 2004
- Full Text
- View/download PDF
24. Arabidopsis genes involved in acyl lipid metabolism. A 2003 census of the candidates, a study of the distribution of expressed sequence tags in organs, and a web-based database.
- Author
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Beisson F, Koo AJ, Ruuska S, Schwender J, Pollard M, Thelen JJ, Paddock T, Salas JJ, Savage L, Milcamps A, Mhaske VB, Cho Y, and Ohlrogge JB
- Subjects
- Acylation, Arabidopsis enzymology, Arabidopsis metabolism, Arabidopsis Proteins genetics, Chromosome Mapping, Gene Library, Arabidopsis genetics, Databases, Genetic, Enzymes genetics, Expressed Sequence Tags, Lipid Metabolism
- Abstract
The genome of Arabidopsis has been searched for sequences of genes involved in acyl lipid metabolism. Over 600 encoded proteins have been identified, cataloged, and classified according to predicted function, subcellular location, and alternative splicing. At least one-third of these proteins were previously annotated as "unknown function" or with functions unrelated to acyl lipid metabolism; therefore, this study has improved the annotation of over 200 genes. In particular, annotation of the lipolytic enzyme group (at least 110 members total) has been improved by the critical examination of the biochemical literature and the sequences of the numerous proteins annotated as "lipases." In addition, expressed sequence tag (EST) data have been surveyed, and more than 3,700 ESTs associated with the genes were cataloged. Statistical analysis of the number of ESTs associated with specific cDNA libraries has allowed calculation of probabilities of differential expression between different organs. More than 130 genes have been identified with a statistical probability > 0.95 of preferential expression in seed, leaf, root, or flower. All the data are available as a Web-based database, the Arabidopsis Lipid Gene database (http://www.plantbiology.msu.edu/lipids/genesurvey/index.htm). The combination of the data of the Lipid Gene Catalog and the EST analysis can be used to gain insights into differential expression of gene family members and sets of pathway-specific genes, which in turn will guide studies to understand specific functions of individual genes.
- Published
- 2003
- Full Text
- View/download PDF
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