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SUMMARY: Chewing herbivores activate plant defense responses through a combination of mechanical wounding and elicitation by herbivore‐associated molecular patterns (HAMPs). HAMPs are wound response amplifiers; however, specific defense outputs may also exist that strictly require HAMP‐mediated defense signaling. To investigate HAMP‐mediated signaling and defense responses, we characterized cowpea (Vigna unguiculata) transcriptome changes following elicitation by inceptin, a peptide HAMP common in Lepidoptera larvae oral secretions. Following inceptin treatment, we observed large‐scale reprogramming of the transcriptome consistent with three different response categories: (i) amplification of mechanical wound responses, (ii) temporal extension through accelerated or prolonged responses, and (iii) examples of inceptin‐specific elicitation and suppression. At both early and late timepoints, namely 1 and 6 h, large sets of transcripts specifically accumulated following inceptin elicitation. Further early inceptin‐regulated transcripts were classified as reversing changes induced by wounding alone. Within key signaling‐ and defense‐related gene families, inceptin‐elicited responses included target subsets of wound‐induced transcripts. Transcripts displaying the largest inceptin‐elicited fold changes included transcripts encoding terpene synthases (TPSs) and peroxidases (POXs) that correspond with induced volatile production and increased POX activity in cowpea. Characterization of inceptin‐elicited cowpea defenses via heterologous expression in Nicotiana benthamiana demonstrated that specific cowpea TPSs and POXs were able to confer terpene emission and the reduced growth of beet armyworm (Spodoptera exigua) herbivores, respectively. Collectively, our present findings in cowpea support a model where HAMP elicitation both amplifies concurrent wound responses and specifically contributes to the activation of selective outputs associated with direct and indirect antiherbivore defenses. Significance Statement: Plants recognize herbivore‐associated molecular patterns (HAMPs) and increase defense production, but interactions with the more general wound response are not well understood. We examined an established HAMP–receptor interaction to characterize the transcriptomic modulation of wound responses by the HAMP peptide inceptin. Inceptin not only amplifies wound responses, but can also specifically induce or suppress transcripts with demonstrated functions in direct and indirect defense against herbivores. The plant immune system thus recognizes HAMPs to fine‐tune wound responses against insect herbivores. [ABSTRACT FROM AUTHOR]

SUMMARY: Crop damage by herbivorous insects remains a significant contributor to annual yield reductions. Following attack, maize (Zea mays) responds to herbivore‐associated molecular patterns (HAMPs) and damage‐associated molecular patterns (DAMPs), activating dynamic direct and indirect antiherbivore defense responses. To define underlying signaling processes, comparative analyses between plant elicitor peptide (Pep) DAMPs and fatty acid–amino acid conjugate (FAC) HAMPs were conducted. RNA sequencing analysis of early transcriptional changes following Pep and FAC treatments revealed quantitative differences in the strength of response yet a high degree of qualitative similarity, providing evidence for shared signaling pathways. In further comparisons of FAC and Pep responses across diverse maize inbred lines, we identified Mo17 as part of a small subset of lines displaying selective FAC insensitivity. Genetic mapping for FAC sensitivity using the intermated B73 × Mo17 population identified a single locus on chromosome 4 associated with FAC sensitivity. Pursuit of multiple fine‐mapping approaches further narrowed the locus to 19 candidate genes. The top candidate gene identified, termed FAC SENSITIVITY ASSOCIATED (ZmFACS), encodes a leucine‐rich repeat receptor‐like kinase (LRR‐RLK) that belongs to the same family as a rice (Oryza sativa) receptor gene previously associated with the activation of induced responses to diverse Lepidoptera. Consistent with reduced sensitivity, ZmFACS expression was significantly lower in Mo17 as compared to B73. Transient heterologous expression of ZmFACS in Nicotiana benthamiana resulted in a significantly increased FAC‐elicited response. Together, our results provide useful resources for studying early elicitor‐induced antiherbivore responses in maize and approaches to discover gene candidates underlying HAMP sensitivity in grain crops. Significance Statement: Expression analyses and forward genetics approaches were used to identify a maize locus and receptor kinase gene candidate associated with response sensitivity to fatty acid–amino acid conjugate (FAC) elicitors widely present in insect oral secretions. Despite broad overlap, herbivore‐associated molecular pattern (HAMP) responses can be decoupled from damage‐associated molecular pattern (DAMP) responses, providing defined resources to investigate early signaling events underlying plant responses to diverse lepidoptera herbivores. [ABSTRACT FROM AUTHOR]

The enantioselective synthesis of zealexin A1, a sesquiterpene phytoalexin isolated from maize Zea mays is described for the first time. Our methodology for the total synthesis of zealexin A1 involved the stereoselective construction of the stereogenic center via enzymatic resolution followed by Johnson–Claisen rearrangement. The absolute configuration of the natural product was determined through gas chromatography analyses for the methyl esters for both synthetic and natural zealexin A1. [ABSTRACT FROM AUTHOR]

Summary: The production and regulation of defensive specialized metabolites play a central role in pathogen resistance in maize (Zea mays) and other plants. Therefore, identification of genes involved in plant specialized metabolism can contribute to improved disease resistance.We used comparative metabolomics to identify previously unknown antifungal metabolites in maize seedling roots, and investigated the genetic and physiological mechanisms underlying their natural variation using quantitative trait locus mapping and comparative transcriptomics approaches.Two maize metabolites, smilaside A (3,6‐diferuloyl‐3′,6′‐diacetylsucrose) and smiglaside C (3,6‐diferuloyl‐2′,3′,6′‐triacetylsucrose), were identified that could contribute to maize resistance against Fusarium graminearum and other fungal pathogens. Elevated expression of an ethylene signaling gene, ETHYLENE INSENSITIVE 2 (ZmEIN2), co‐segregated with a decreased smilaside A : smiglaside C ratio. Pharmacological and genetic manipulation of ethylene availability and sensitivity in vivo indicated that, whereas ethylene was required for the production of both metabolites, the smilaside A : smiglaside C ratio was negatively regulated by ethylene sensitivity. This ratio, rather than the absolute abundance of these two metabolites, was important for maize seedling root defense against F. graminearum.Ethylene signaling regulates the relative abundance of the two F. graminearum‐resistance‐related metabolites and affects resistance against F. graminearum in maize seedling roots. [ABSTRACT FROM AUTHOR]

Maize ( Z ea mays) production, which is of global agro-economic importance, is largely limited by herbivore pests, pathogens and environmental conditions, such as drought. Zealexins and kauralexins belong to two recently identified families of acidic terpenoid phytoalexins in maize that mediate defence against both pathogen and insect attacks in aboveground tissues. However, little is known about their function in belowground organs and their potential to counter abiotic stress. In this study, we show that zealexins and kauralexins accumulate in roots in response to both biotic and abiotic stress including, D iabrotica balteata herbivory, F usarium verticillioides infection, drought and high salinity. We find that the quantity of drought-induced phytoalexins is positively correlated with the root-to-shoot ratio of different maize varieties, and further demonstrate that mutant an2 plants deficient in kauralexin production are more sensitive to drought. The induction of phytoalexins in response to drought is root specific and does not influence phytoalexin levels aboveground; however, the accumulation of phytoalexins in one tissue may influence the induction capacity of other tissues. [ABSTRACT FROM AUTHOR]

Maize is by quantity the most important C4 cereal crop; however, future climate changes are expected to increase maize susceptibility to mycotoxigenic fungal pathogens and reduce productivity. While rising atmospheric [ CO2] is a driving force behind the warmer temperatures and drought, which aggravate fungal disease and mycotoxin accumulation, our understanding of how elevated [ CO2] will effect maize defences against such pathogens is limited. Here we report that elevated [ CO2] increases maize susceptibility to Fusarium verticillioides proliferation, while mycotoxin levels are unaltered. Fumonisin production is not proportional to the increase in F. verticillioides biomass, and the amount of fumonisin produced per unit pathogen is reduced at elevated [ CO2]. Following F. verticillioides stalk inoculation, the accumulation of sugars, free fatty acids, lipoxygenase ( LOX) transcripts, phytohormones and downstream phytoalexins is dampened in maize grown at elevated [ CO2]. The attenuation of maize 13- LOXs and jasmonic acid production correlates with reduced terpenoid phytoalexins and increased susceptibility. Furthermore, the attenuated induction of 9- LOXs, which have been suggested to stimulate mycotoxin biosynthesis, is consistent with reduced fumonisin per unit fungal biomass at elevated [ CO2]. Our findings suggest that elevated [ CO2] will compromise maize LOX-dependent signalling, which will influence the interactions between maize and mycotoxigenic fungi. [ABSTRACT FROM AUTHOR]

Spatial and temporal patterns of insect damage in relation to aflatoxin contamination in a corn field with plants of uniform genetic background are not well understood. After previous examination of spatial patterns of insect damage and aflatoxin in pre-harvest corn fields, we further examined both spatial and temporal patterns of cob- and kernel-feeding insect damage, and aflatoxin level with two samplings at pre-harvest in 2008 and 2009. The feeding damage by each of the ear/kernel-feeding insects (i.e., corn earworm/fall armyworm damage on the silk/cob, and discoloration of corn kernels by stink bugs) and maize weevil population were assessed at each grid point with five ears. Sampling data showed a field edge effect in both insect damage and aflatoxin contamination in both years. Maize weevils tended toward an aggregated distribution more frequently than either corn earworm or stink bug damage in both years. The frequency of detecting aggregated distribution for aflatoxin level was less than any of the insect damage assessments. Stink bug damage and maize weevil number were more closely associated with aflatoxin level than was corn earworm damage. In addition, the indices of spatial-temporal association (χ) demonstrated that the number of maize weevils was associated between the first (4 weeks pre-harvest) and second (1 week pre-harvest) samplings in both years on all fields. In contrast, corn earworm damage between the first and second samplings from the field on the Belflower Farm, and aflatoxin level and corn earworm damage from the field on the Lang Farm were dissociated in 2009. [ABSTRACT FROM AUTHOR]

Phytopathogen infections are frequently influenced by both biotic and abiotic factors in a crop field. The effect of brown stink bug, Euschistus servus (Hemiptera: Pentatomidae), feeding and planting date and sampling time on common smut ( Ustilago maydis) infection percentage of maize plants was examined in 2005 and 2006, and 2010 and 2011, respectively. Brown stink bug adult feeding on maize hybrid 'DKC6971' at flowering in 2005 and 2006 did not influence smut infection percentage when examined using 3 treatments (i.e., 0 adult, 5 adults, and 5 adults mixed with the smut spores). The smut infection percentages were <3% ( n = 12) in the 3 treatments. The smut infection percentage among the 4 weekly samplings was the same, so was natural aflatoxin contamination at harvest among the treatments. The 2nd experiment showed that planting date did not affect the smut infection percentage in either 2010 or 2011. But, the smut infection percentage from the postflowering sampling was greater than preflowering sampling in both years. The smut infection percentage varied among the germplasm lines in 2010, but not in 2011. This study demonstrated that brown stink bug feeding at flowering had no effect on smut infection in maize, and the best time for smut evaluation would be after flowering. The temperature and precipitation might have also influenced the percentage of smut-infected maize plants during the 4 years when the experiments were conducted. The similarity between kernel-colonizing U. maydis and Aspergillus flavus infections and genotype × environment interaction were also discussed. [ABSTRACT FROM AUTHOR]

A long-standing goal in plant research is to optimize the protective function of biochemical agents that impede pest and pathogen attack. Nearly 40 years ago, pathogen-inducible diterpenoid production was described in rice, and these compounds were shown to function as antimicrobial phytoalexins. Using rice and maize as examples, we discuss recent advances in the discovery, biosynthesis, elicitation and functional characterization of monocot terpenoid phytoalexins. The recent expansion of known terpenoid phytoalexins now includes not only the labdane-related diterpenoid superfamily but also casbane-type diterpenoids and β-macrocarpene-derived sequiterpenoids. Biochemical approaches have been used to pair pathway precursors and end products with cognate biosynthetic genes. The number of predicted terpenoid phytoalexins is expanding through advances in cereal genome annotation and terpene synthase characterization that likewise enable discoveries outside the Poaceae. At the cellular level, conclusive evidence now exists for multiple plant receptors of fungal-derived chitin elicitors, phosphorylation of membrane-associated signaling complexes, activation of mitogen-activated protein kinase, involvement of phytohormone signals, and the existence of transcription factors that mediate the expression of phytoalexin biosynthetic genes and subsequent accumulation of pathway end products. Elicited production of terpenoid phytoalexins exhibit additional biological functions, including root exudate-mediated allelopathy and insect antifeedant activity. Such findings have encouraged consideration of additional interactions that blur traditionally discrete phytoalexin classifications. The establishment of mutant collections and increasing ease of genetic transformation assists critical examination of further biological roles. Future research directions include examination of terpenoid phytoalexin precursors and end products as potential signals mediating plant physiological processes. [ABSTRACT FROM AUTHOR]

Formation of galactose-acylated monogalactosyldiacylglycerols has been shown to be induced by leaf homogenization, mechanical wounding, avirulent bacterial infection and thawing after snap-freezing. Here, lipidomic analysis using mass spectrometry showed that galactose-acylated mono-galactosyldiacylglycerols, formed in wheat ( Triticum aestivum) and tomato ( Solanum lycopersicum) leaves upon wounding, have acyl-galactose profiles that differ from those of wounded Arabidopsis thaliana, indicating that different plant species accumulate different acyl-galactose components in response to the same stress. Additionally, the composition of the acyl-galactose component of Arabidopsis acMGDG (galactose-acylated monogalactosyl-diacylglycerol) depends on the stress treatment. After sub-lethal freezing treatment, acMGDG contained mainly non-oxidized fatty acids esterified to galactose, whereas mostly oxidized fatty acids accumulated on galactose after wounding or bacterial infection. Compositional data are consistent with acMGDG being formed in vivo by transacylation with fatty acids from digalactosyldiacylglycerols. Oxophytodienoic acid, an oxidized fatty acid, was more concentrated on the galactosyl ring of acylated monogalactosyldiacylglycerols than in galactolipids in general. Also, oxidized fatty acid-containing acylated monogalactosyldiacylglycerols increased cumulatively when wounded Arabidopsis leaves were wounded again. These findings suggest that, in Arabidopsis, the pool of galactose-acylated monogalactosyldiacylglycerols may serve to sequester oxidized fatty acids during stress responses. [ABSTRACT FROM AUTHOR]

Fusarium verticillioides is a widely distributed fungus that can associate with maize as a deleterious pathogen and an advantageous endophyte. Here, we show that seed treatment with live F. verticillioides enhances maize resistance to secondary stalk rot infection and further demonstrate that dead F. verticillioides is sufficient to equivalently reduce F. verticillioides biomass. Seed treatment with live or dead F. verticillioides primes maize plants, and upon subsequent stalk infection, terpenoid phytoalexins accumulate faster than control-treated plants. Seed treatment did not constitutively activate plant defences nor did it impact plant growth. These results suggest that seed treatment with dead F. verticillioides can be used as a 'vaccination' method to decrease the severity of stalk rot and potentially pathogen infection throughout the plant. [ABSTRACT FROM AUTHOR]

Diverse pathogens secrete effector proteins into plant cells to manipulate host cellular processes. Oomycete pathogens contain large complements of predicted effector genes defined by an RXLR host cell entry motif. The genome of Hyaloperonospora arabidopsidis (Hpa, downy mildew of Arabidopsis) contains at least 134 candidate RXLR effector genes. Only a small subset of these genes is conserved in related oomycetes from the Phytophthora genus. Here, we describe a comparative functional characterization of the Hpa RXLR effector gene HaRxL96 and a homologous gene, PsAvh163, from the Glycine max (soybean) pathogen Phytophthora sojae. HaRxL96 and PsAvh163 are induced during the early stages of infection and carry a functional RXLR motif that is sufficient for protein uptake into plant cells. Both effectors can suppress immune responses in soybean. HaRxL96 suppresses immunity in Nicotiana benthamiana, whereas PsAvh163 induces an HR-like cell death response in Nicotiana that is dependent on RARI and Hsp90.1. Transgenic Arabidopsis plants expressing HaRxL96or PsAvh 163 exhibit elevated susceptibility to virulent and avirulent Hpa, as well as decreased callose deposition in response to non-pathogenic Pseudomonas syringae. Both effectors interfere with defense marker gene induction, but do not affect salicylic acid biosynthesis. Together, these experiments demonstrate that evolutionarily conserved effectors from different oomycete species can suppress immunity in plant species that are divergent from the source pathogen's host. [ABSTRACT FROM AUTHOR]

SUMMARY The moss Physcomitrella patens is an evolutionarily basal model system suitable for the analysis of plant defence responses activated after pathogen assault. Upon infection with the necrotroph Botrytis cinerea, several defence mechanisms are induced in P. patens, including the fortification of the plant cell wall by the incorporation of phenolic compounds and the induced expression of related genes. Botrytis cinerea infection also activates the accumulation of reactive oxygen species and cell death with hallmarks of programmed cell death in moss tissues. Salicylic acid (SA) levels also increase after fungal infection, and treatment with SA enhances transcript accumulation of the defence gene phenylalanine ammonia-lyase ( PAL) in P. patens colonies. The expression levels of the genes involved in 12-oxo-phytodienoic acid (OPDA) synthesis, including lipoxygenase ( LOX) and allene oxide synthase ( AOS), increase in P. patens gametophytes after pathogen assault, together with a rise in free linolenic acid and OPDA concentrations. However, jasmonic acid (JA) could not be detected in healthy or infected tissues of this plant. Our results suggest that, although conserved defence signals, such as SA and OPDA, are synthesized and are probably involved in the defence response of P. patens against B. cinerea infection, JA production appears to be missing. Interestingly, P. patens responds to OPDA and methyl jasmonate by reducing moss colony growth and rhizoid length, suggesting that jasmonate perception is present in mosses. Thus, P. patens can provide clues with regard to the evolution of different defence pathways in plants, including signalling and perception of OPDA and jasmonates in nonflowering and flowering plants. [ABSTRACT FROM AUTHOR]

Methyl salicylate (MeSA) is a volatile plant secondary metabolite that is an important contributor to taste and scent of many fruits and flowers. It is synthesized from salicylic acid (SA), a phytohormone that contributes to plant pathogen defense. MeSA is synthesized by members of a family of O-methyltransferases. In order to elaborate the mechanism of MeSA synthesis in tomato, we screened a set of O-methyltransferases for activity against multiple substrates. An enzyme that specifically catalyzes methylation of SA, SlSAMT, as well as enzymes that act upon jasmonic acid and indole-3-acetic acid were identified. Analyses of transgenic over- and under-producing lines validated the function of SlSAMT in vivo. The SlSAMT gene was mapped to a position near the bottom of chromosome 9. Analysis of MeSA emissions from an introgression population derived from a cross with Solanum pennellii revealed a quantitative trait locus (QTL) linked to higher fruit methyl salicylate emissions. The higher MeSA emissions associate with significantly higher SpSAMT expression, consistent with SAMT gene expression being rate limiting for ripening-associated MeSA emissions. Transgenic plants that constitutively over-produce MeSA exhibited only slightly delayed symptom development following infection with the disease-causing bacterial pathogen, Xanthomonas campestris pv. vesicatoria (Xcv). Unexpectedly, pathogen-challenged leaves accumulated significantly higher levels of SA as well as glycosylated forms of SA and MeSA, indicating a disruption in control of the SA-related metabolite pool. Taken together, the results indicate that SlSAMT is critical for methyl salicylate synthesis and methyl salicylate, in turn, likely has an important role in controlling SA synthesis. [ABSTRACT FROM AUTHOR]

A new Zea mays viviparous seed mutant, viviparous15 ( vp15), was isolated from the UniformMu transposon-tagging population. In addition to precocious germination, v p15 has an early seedling lethal phenotype. Biochemical analysis showed reduced activities of several enzymes that require molybdenum cofactor (MoCo) in vp15 mutant seedlings. Because MoCo is required for abscisic acid (ABA) biosynthesis, the viviparous phenotype is probably caused by ABA deficiency. We cloned the vp15 mutant using a novel high-throughput strategy for analysis of high-copy Mu lines: We used MuTAIL PCR to extract genomic sequences flanking the Mu transposons in the vp15 line. The Mu insertions specific to the vp15 line were identified by in silico subtraction using a database of MuTAIL sequences from 90 UniformMu lines. Annotation of the vp15-specific sequences revealed a Mu insertion in a gene homologous to human MOCS2A, the small subunit of molybdopterin (MPT) synthase. Molecular analysis of two allelic mutations confirmed that Vp15 encodes a plant MPT synthase small subunit (ZmCNX7). Our results, and a related paper reporting the cloning of maize viviparous10, demonstrate robust cloning strategies based on MuTAIL-PCR. The Vp15/ CNX7, together with other CNX genes , is expressed in both embryo and endosperm during seed maturation. Expression of Vp15 appears to be regulated independently of MoCo biosynthesis. Comparisons of Vp15 loci in genomes of three cereals and Arabidopsis thaliana identified a conserved sequence element in the 5′ untranslated region as well as a micro-synteny among the cereals. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA), auxin and nitrate are important signaling molecules that affect plant growth responses to the environment. The synthesis or metabolism of these compounds depends on the molybdenum cofactor (MoCo). We show that maize ( Zea mays) viviparous10 ( vp10) mutants have strong precocious germination and seedling lethal phenotypes that cannot be rescued with tissue culture. We devised a novel PCR-based method to clone a transposon-tagged allele of vp10, and show that Vp10 encodes the ortholog of Cnx1, which catalyzes the final common step of MoCo synthesis. The seedling phenotype of vp10 mutants is consistent with disruptions in ABA and auxin biosynthesis, as well as a disruption in nitrate metabolism. Levels of ABA and auxin are reduced in vp10 mutants, and vp10 seedlings lack MoCo-dependent enzyme activities that are repairable with exogenous molybdenum. vp10 and an Arabidopsis cnx1 mutant, chlorate6 ( chl6), have similar defects in aldehyde oxidase (AO) enzyme activity, which is required for ABA synthesis. Surprisingly, chl6 mutants do not show defects in abiotic stress responses. These observations confirm an orthologous function for Cnx1 and Vp10, as well as defining a characteristic viviparous phenotype to identify other maize cnx mutants. Finally, the vp10 mutant phenotype suggests that cnx mutants can have auxin- as well as ABA-biosynthesis defects, while the chl6 mutant phenotype suggests that low levels of AO activity are sufficient for normal abiotic stress responses. [ABSTRACT FROM AUTHOR]

The phytotoxin coronatine is a jasmonate mimic produced byPseudomonas syringaepv.tomato(Pst). Coronatine acts as a virulence factor in Arabidopsis and mutants insensitive to coronatine are resistant toPstand have higher levels of salicylic acid (SA). In this work we used the SA-deficient lines NahG andsid2-2to determine if coronatine acts directly as a virulence factor or indirectly by SA suppression. Using coronatine-deficientPstmutants we demonstrated that the lack of coronatine compromisesPstvirulence in both wild-type and SA-deficient Arabidopsis. Thus, the action of coronatine is not due to SA suppression. Rather, SA-independent jasmonate-responses are the most likely mechanism for its action. [ABSTRACT FROM AUTHOR]

Through complex networks of signaling interactions, phytohormones regulate growth, development, reproduction and responses to biotic and abiotic stress. Comprehensive metabolomic approaches, seeking to quantify changes in vast numbers of plant metabolites, may ultimately clarify these complex signaling interactions and consequently explain pleiotropic effects on plant metabolism. Synergistic and antagonistic phytohormone signaling interactions, referred to as crosstalk, are often considered at the level of transduction without proper consideration of synthesis or accumulation of phytohormones because of the limitation and difficulty in quantifying numerous signals. Significant progress has recently been made in the expansion of metabolic profiling and analysis of multiple phytohormones [Birkemeyer et al. ( J. Chromatogr. A, 2003, 993, 89); Chiwocha et al. ( Plant J., 2003, 35, 405); Müller et al. ( Planta, 2002, 216, 44); Schmelz et al. ( Proc. Natl Acad. Sci. USA, 2003, 100, 10552)]. We recently presented a novel metabolic profiling approach to the analysis of acidic phytohormones and other metabolites based on a simplistic preparation scheme and analysis by chemical ionization-gas chromatography/mass spectrometry. We now provide a detailed description of this vapor phase extraction technique and use pathogen infection of Arabidopsis with Pseudomonas syringae DC3000 to illustrate metabolic changes in salicylic acid, cinnamic acid, jasmonic acid, indole-3-acetic acid, abscisic acid, unsaturated C18 fatty acids, 12-oxo-phytodienoic acid, and phytotoxin coronatine. Directions for further method expansion are provided and include issues of recovery, derivatization, range of accessible analytes, optimization, reproducibility and future directions. [ABSTRACT FROM AUTHOR]

Plants display differential responses following mechanical damage and insect herbivory. Both caterpillar attack and the application of caterpillar oral secretions (OS) to wounded leaves stimulates volatile emission above mechanical damage alone. Volicitin (N- 17-hydroxylinolenoyl-l-glutamine), present in beet armyworm (BAW, Spodoptera exigua ) OS, is a powerful elicitor of volatiles in excised maize seedlings (Zea mays cv. Delprim). We consider some of the mechanistic differences between wounding and insect herbivory in maize by examining the activity of volicitin, changes in jasmonic acid (JA) levels, and volatile emission from both intact plant and excised leaf bioassays. Compared to mechanical damage alone, volicitin stimulated increases in both JA levels and sesquiterpene volatiles when applied to intact plants. In a bioassay comparison, excised leaves were more sensitive and produced far greater volatile responses than intact plants following applications of both volicitin and JA. In the excised leaf bioassay, volicitin applications (10–500 pmol) to wounded leaves resulted in dose dependent JA increases and a direct positive relationship between JA and sesquiterpene volatile emission. Interestingly, volicitin-induced JA levels did not differ between intact and excised bioassays, suggesting a possible interaction of JA with other regulatory signals in excised plants. In addition to JA, insect herbivory is known to stimulate the production of ethylene. Significant increases in ethylene were induced only by BAW herbivory and not by either wounding or volicitin treatments. Using intact plant bioassays, ethylene (at 1 µl l-1 or less) greatly promoted volatile emission induced by volicitin and JA but not mechanical damage alone. For intact plants, wounding, elicitor-induced JA and insect-induced ethylene appear to be important interacting components in the stimulation of insect-induced volatile emission. [ABSTRACT FROM AUTHOR]

Reports on the use of methyl ester (MJ) to stimulate the induced defense in wild tobacco plant Nicotiana sylvestris. Background on the study method used; Biomass; Nicotine production; Nicotine accumulation.

Summary Ethylene and salicylic acid (SA) are key intermediates in a host's response to pathogens. Previously, we have shown using a tomato compatible interaction that ethylene and SA act sequentially and are essential for disease symptom production. Here, we have examined the relationship between the two signals in the Arabidopsis–Xanthomonas campestris pv. campestris (Xcc ) compatible interaction. Preventing SA accumulation by expression of the nahG gene reduced subsequent ethylene production and altered the development of disease symptoms, with plants showing no visible chlorosis. The ethylene insensitive lines, etr1-1 and etr2-1 , on the other hand, accumulated SA and exhibited normal but precocious symptom development. Therefore, Arabidopsis , like tomato, was found to exhibit co-operative ethylene and SA action for the production of disease symptoms. However, in Arabidopsis , SA was found to act upstream of ethylene. Jasmonic acid and indole-3-acetic acid levels were also found to increase in response to Xcc . In contrast to ethylene, accumulation of these hormones was not found to be dependent on SA action. These results indicate that the plants response to a virulent pathogen is a composite of multiple signaling pathways. [ABSTRACT FROM AUTHOR]