(3R,7S)-12-Hydroxy-jasmonoyl-l-isoleucine is the genuine bioactive stereoisomer of a jasmonate metabolite in Arabidopsis thaliana.

The oxylipin plant hormone (3R,7S)-jasmonoyl-l-isoleucine [or (+)-7-iso-jasmonoyl-l-isoleucine, JA-Ile] is widely recognized as a plant defense hormone against pathogens and chewing insects. The metabolism of JA-Ile into 12-OH-JA-Ile and 12-COOH-JA-Ile is the central mechanism for the inactivation of JA signaling. Recently, 12-OH-JA-Ile was reported to function as a ligand for the JA-Ile co-receptor COI1-JAZ. However, in previous studies, '12-OH-JA-Ile' used was a mixture of four stereoisomers, the naturally occurring cis-isomer (3R,7S)-12-OH-JA-Ile and the trans-isomer (3R,7R)-12-OH-JA-Ile, and the unnatural cis-isomer (3S,7R)-12-OH-JA-Ile and the trans-isomer (3S,7S)-12-OH-JA-Ile. Thus, the genuine bioactive form of 12-OH-JA-Ile has not yet been identified. In the present study, we prepared pure stereoisomers of 12-OH-JA-Ile and identified (3R,7S)-12-OH-JA-Ile as the naturally occurring bioactive form of 12-OH-JA-Ile and found that it binds to COI1-JAZ9 as effectively as (3R,7S)-JA-Ile. In addition, we revealed that the unnatural trans-isomer (3S,7S)-12-OH-JA-l-Ile functions as another bioactive isomer. The pure (3R,7S)-12-OH-JA-Ile causes partial JA-responsive gene expression without affecting the expression of JAZ8/10, which is involved in the negative feedback regulation of JA-signaling. Thus, (3R,7S)-12-OH-JA-Ile could cause weak and sustainable expression of certain JA-responsive genes until the catabolism of (3R,7S)-12-OH-JA-Ile into (3R,7S)-12-COOH-JA-Ile occurs. The use of chemically pure (3R,7S)-12-OH-JA-Ile confirmed the genuine biological activities of '12-OH-JA-Ile' by excluding the possible effects of other stereoisomers. A chemical supply of pure (3R,7S)-12-OH-JA-Ile with an exact bioactivity profile will enable further detailed studies of the unique role of 12-OH-JA-Ile in planta.

Design, synthesis and systemic acquired resistance of 2-benzothiadiazolylquinoline-4-carboxamides by COI1 based virtual screening.

Coronatine-insensitive 1 (COI1) has been identified as a target receptor of plant elicitor coronatine (COR). To discover novel plant elicitor leads, most of the potential molecules among 129 compounds discovered from the ZINC database by docking based virtual screening targeting COI1 were quinoline amides. On this lead basis, 2-benzothiadiazolylquinoline-4-carboxamides were rationally designed and synthesized for bioassay. All target compounds did not show significantly in vitro antifungal activity, compounds 4d, 4e and 4o displayed good in vivo systemic acquired resistance activity for Arabidopsis thaliana against Hyaloperonospora arabidopsidis isolate Noco2 with over 80% of inhibitory rate at the concentration of 50 µM. These results indicate that 2-benzothiadiazolylquinoline-4-carboxamides are promising plant elicitor leads for further study.

Lyso-phosphatidylethanolamine triggers immunity against necrotrophs by promoting JA-signaling and ROS-homeostasis.

Modulation of the plant defense response by bioactive molecules is of increasing interest. However, despite plant cell lipids being one of the major cellular components, their role in plant immunity remains elusive. We found that the exogenous application of the cell-membrane localized phospholipid lyso-phosphatidylethanolamine (LPE) reprograms the plant transcript profile in favor of defense-associated genes thereby priming the plant immune system. Exogenous LPE application to different Arabidopsis accessions increases resistance against the necrotrophic pathogens, Botrytis cinerea and Cochliobolus heterostrophus. We found that the immunity-promoting effect of LPE is repealed in the jasmonic acid (JA) receptor mutant coi1, but multiplied in the JA-hypersensitive mutant feronia (fer-4). The JA-signaling repressor JAZ1 is degraded following LPE administration, suggesting that JA-signaling is promoted by LPE. Following LPE-treatment, reactive oxygen species (ROS) accumulation is affected in coi1 and fer-4. Moreover, FER signaling inhibitors of the RALF family are strongly expressed after LPE application, and RALF23 is internalized in stress granules, suggesting the LPE-mediated repression of FER-signaling by promoting RALF function. The in-situ increase of LPE-abundance in the LPE-catabolic mutants lpeat1 and lpeat2 elevates plant resistance to B. cinerea, in contrast to the endogenous LPE-deficient mutant pla2-alpha. We show that LPE increases plant resistance against necrotrophs by promoting JA-signaling and ROS-homeostasis, thereby paving the way for the LPE-targeted genomic engineering of crops to raise their ability to resist biotic threats.

The intragenic suppressor mutation Leu59Phe compensates for the effect of detrimental mutations in the jasmonate receptor COI1.

The phytohormones jasmonates (JAs) control plant development, growth, and defense against insects and pathogens. The Arabidopsis JA receptor Coronatine Insensitive 1 (COI1) interacts with ARABIDOPSIS SKP-LIKE1 (ASK1)/ASK2 to form the SCFCOI1 E3 ligase and mediate JA responses. Here, we performed a genetic suppressor screen using the leaky coi1-2 (COI1Leu245Phe ) mutant for restored sensitivity to JA, and identified the intragenic suppressor mutation Leu59Phe, which was in the region connecting the F-box and leucine-rich repeats domains of COI1. The L59F substitution not only restores the COI1L245F function, but also the COI1Gly434Glu (coi1-22rsp ) function in JA responses, through recovering their interactions with ASK1 or ASK2 and their protein levels. The L59F change itself could not enhance the interactions between COI1 and ASK1/2, nor affect JA responses. The present study reveals that the Leu59Phe substitution compensates for the effect of some deleterious mutations in the JA receptor COI1.

Genome-wide identification and expression analysis of the coronatine-insensitive 1 (COI1) gene family in response to biotic and abiotic stresses in Saccharum.

BACKGROUND: The coronatine insensitive 1 (COI1) gene is the core member of jasmonate signaling pathway, which is closely related to plant biotic and abiotic resistance. However, there have been no reports on COI1 in sugarcane (Sacharum spp.). Hence, systematically investigating the characteristics of the COI1 multigene family in sugarcane can provide a means to study and manipulate the jasmonic acid signaling pathway. RESULTS: A total of 156 COI1 proteins were obtained from the genomes of 19 land plants, while none were obtained from five algae species. A phylogenetic tree demonstrated that these COI1 proteins were classified into four groups, while 31 proteins of SsCOI1 from Saccharum spontaneum, SbCOI1 from Sorghum bicolor, and ShCOI1 from Saccharum spp. hybrid cultivar R570 clustered into three groups. Synteny analysis and duplication patterns revealed that COI1 genes expanded through various genome replication events and could have experienced strong purifying selective pressure during evolution in S. spontaneum, S. bicolor, and R570. An investigation of cis-acting elements suggests that COI1 genes may be involved in plant growth and development and response to various stresses. Expression analysis implied that 21 SsCOI1 genes were constitutively expressed, and had positive responses to drought, cold, and Sporisorium scitamineum stresses with different expression patterns. Among them, seven SsCOI1 haplotype genes may play different roles in response to methyl jasmonate. Furthermore, the ShCOI1-4, ShCOI1-5, and ShCOI1-6 genes were cloned from Saccharum spp. hybrid cultivar ROC22. Real-time quantitative PCR (RT-qPCR) analysis demonstrated that these three ShCOI1 genes had divergent expression profiles in response to salicylic acid, abscisic acid, polyethylene glycol, cold, and S. scitamineum. CONCLUSIONS: These results suggest that COI1 genes may act in sugarcane growth, development, and response to various stresses via different regulatory mechanisms, which laying a foundation for the functional identification of the sugarcane COI1 gene.

JA signal-mediated immunity of Dendrobium catenatum to necrotrophic Southern Blight pathogen.

BACKGROUND: Dendrobium catenatum belongs to the Orchidaceae, and is a precious Chinese herbal medicine. In the past 20 years, D. catenatum industry has developed from an endangered medicinal plant to multi-billion dollar grade industry. The necrotrophic pathogen Sclerotium delphinii has a devastating effection on over 500 plant species, especially resulting in widespread infection and severe yield loss in the process of large-scale cultivation of D. catenatum. It has been widely reported that Jasmonate (JA) is involved in plant immunity to pathogens, but the mechanisms of JA-induced plant resistance to S. delphinii are unclear. RESULTS: In the present study, the role of JA in enhancing D. catenatum resistance to S. delphinii was investigated. We identified 2 COI1, 13 JAZ, and 12 MYC proteins in D. catenatum genome. Subsequently, systematic analyses containing phylogenetic relationship, gene structure, protein domain, and motif architecture of core JA pathway proteins were conducted in D. catenatum and the newly characterized homologs from its closely related orchid species Phalaenopsis equestris and Apostasia shenzhenica, along with the well-investigated homologs from Arabidopsis thaliana and Oryza sativa. Public RNA-seq data were investigated to analyze the expression patterns of D. catenatum core JA pathway genes in various tissues and organs. Transcriptome analysis of MeJA and S. delphinii treatment showed exogenous MeJA changed most of the expression of the above genes, and several key members, including DcJAZ1/2/5 and DcMYC2b, are involved in enhancing defense ability to S. delphinii in D. catenatum. CONCLUSIONS: The findings indicate exogenous MeJA treatment affects the expression level of DcJAZ1/2/5 and DcMYC2b, thereby enhancing D. catenatum resistance to S. delphinii. This research would be helpful for future functional identification of core JA pathway genes involved in breeding for disease resistance in D. catenatum.

Functional specificity, diversity, and redundancy of Arabidopsis JAZ family repressors in jasmonate and COI1-regulated growth, development, and defense.

In response to jasmonates (JAs), the JA receptor Coronatine Insensitive 1 (COI1) recruits JA-zinc-finger inflorescence meristem (ZIM)-domain (JAZ) family repressors for destruction to regulate plant growth, development, and defense. As Arabidopsis encodes 13 JAZ repressors, their functional specificity, diversity, and redundancy in JA/COI1-mediated responses remain unclear. We generated a broad range of jaz mutants based on their phylogenetic relationship to investigate their roles in JA responses. The group I JAZ6 may play an inhibitory role in resistance to Botrytis cinerea, group II (JAZ10)/III (JAZ11/12) in JA-regulated root growth inhibition and susceptibility to Pseudomonas syringae pv tomato DC3000, and group IV JAZ3/4/9 in flowering time delay and defense against insects. JAZs exhibit high redundancy in apical hook curvature. The undecuple jaz1/2/3/4/5/6/7/9/10/11/12 (jaz1-7,9-12) mutations enhance JA responses and suppress the phenotypes of coi1-1 in flowering time, rosette growth, and defense. The JA hypersensitivity of jaz1-7,9-12 in root growth, hook curvature, and leaf yellowing is blocked by coi1-1. jaz1-7,9-12 does not influence the stamen phenotypes of wild-type and coi1-1. jaz1-7,9-12 affects JA-regulated transcriptional profile and recovers a fraction of that in coi1-1. This study contributes to elucidating the specificity, diversity, and redundancy of JAZ members in JA/COI1-regulated growth, development, and defense responses.

A comprehensive in vitro fluorescence anisotropy assay system for screening ligands of the jasmonate COI1-JAZ co-receptor in plants.

The phytohormone (+)-7-iso-jasmonoyl-l-isoleucine regulates many developmental and stress responses in plants and induces protein-protein interactions between COI1, the F-box component of E3 ubiquitin ligase, and jasmonate ZIM domain (JAZ) repressors. These interactions cause JAZ degradation and activate jasmonate (JA), leading to plant defense responses, growth inhibition, and senescence. Thirteen JAZ subtypes are encoded in the Arabidopsis thaliana genome, but a detailed understanding of the physiological functions of these JAZ subtypes remains unclear, partially because of the genetic redundancy of JAZ genes. One strategy to elucidate the complex JA signaling pathways is to develop a reliable and comprehensive binding assay system of the ligands with all combinations of the co-receptors. Herein, we report the development of a fluorescence anisotropy-based in vitro binding assay system to screen for the ligands of the COI1-JAZ co-receptors. Our assay enabled the first quantitative analysis of the affinity values and JAZ-subtype selectivity of various endogenous JA derivatives, such as coronatine, jasmonic acid, and 12-hydroxyjasmonoyl-l-isoleucine. Because of its high signal-to-noise ratio and convenient mix-and-read assay system, our screening approach can be used in plate reader-based assays of both agonists and antagonists of COI1-JAZ co-receptors.

Mediator subunit MED25 links the jasmonate receptor to transcriptionally active chromatin.

Jasmonoyl-isoleucine (JA-Ile), the active form of the plant hormone jasmonate (JA), is sensed by the F-box protein CORONATINE INSENSITIVE 1 (COI1), a component of a functional Skp-Cullin-F-box E3 ubiquitin ligase complex. Sensing of JA-Ile by COI1 rapidly triggers genome-wide transcriptional changes that are largely regulated by the basic helix-loop-helix transcription factor MYC2. However, it remains unclear how the JA-Ile receptor protein COI1 relays hormone-specific regulatory signals to the RNA polymerase II general transcriptional machinery. Here, we report that the plant transcriptional coactivator complex Mediator directly links COI1 to the promoters of MYC2 target genes. MED25, a subunit of the Mediator complex, brings COI1 to MYC2 target promoters and facilitates COI1-dependent degradation of jasmonate-ZIM domain (JAZ) transcriptional repressors. MED25 and COI1 influence each other's enrichment on MYC2 target promoters. Furthermore, MED25 physically and functionally interacts with HISTONE ACETYLTRANSFERASE1 (HAC1), which plays an important role in JA signaling by selectively regulating histone (H) 3 lysine (K) 9 (H3K9) acetylation of MYC2 target promoters. Moreover, the enrichment and function of HAC1 on MYC2 target promoters depend on COI1 and MED25. Therefore, the MED25 interface of Mediator links COI1 with HAC1-dependent H3K9 acetylation to activate MYC2-regulated transcription of JA-responsive genes. This study exemplifies how a single Mediator subunit integrates the actions of both genetic and epigenetic regulators into a concerted transcriptional program.

Recent Advances in Plant Chemical Biology of Jasmonates.

Lipid-derived plant hormone jasmonates are implicated in plant growth, reproductive performance, senescence, secondary metabolite productions, and defense against both necrotrophic pathogens and feeding insects. A major jasmonate is (+)-7-iso-jasmonoyl-l-isoleucine (JA-Ile), which is perceived by the unique COI1-JAZ coreceptor system. Recent advances in plant chemical biology have greatly informed the bioscience of jasmonate, including the development of chemical tools such as the antagonist COR-MO; the agonist NOPh; and newly developed jasmonates, including JA-Ile-macrolactone and 12-OH-JA-Ile. This review article summarizes the current status of plant chemical biology as it pertains to jasmonates, and offers some perspectives for the future.

12-Hydroxy-Jasmonoyl-l-Isoleucine Is an Active Jasmonate That Signals through CORONATINE INSENSITIVE 1 and Contributes to the Wound Response in Arabidopsis.

12-hydroxy-jasmonoyl-isoleucine (12OH-JA-Ile) is a metabolite in the catabolic pathway of the plant hormone jasmonate, and is synthesized by the cytochrome P450 subclade 94 enzymes. Contrary to the well-established function of jasmonoyl-isoleucine (JA-Ile) as the endogenous bioactive form of jasmonate, the function of 12OH-JA-Ile is unclear. Here, the potential role of 12OH-JA-Ile in jasmonate signaling and wound response was investigated. Exogenous application of 12OH-JA-Ile mimicked several JA-Ile effects including marker gene expression, anthocyanin accumulation and trichome induction in Arabidopsis thaliana. Genome-wide transcriptomics and untargeted metabolite analyses showed large overlaps between those affected by 12OH-JA-Ile and JA-Ile. 12OH-JA-Ile signaling was blocked by mutation in CORONATINE INSENSITIVE 1. Increased anthocyanin accumulation by 12OH-JA-Ile was additionally observed in tomato and sorghum, and was disrupted by the COI1 defect in tomato jai1 mutant. In silico ligand docking predicted that 12OH-JA-Ile can maintain many of the key interactions with COI1-JAZ1 residues identified earlier by crystal structure studies using JA-Ile as ligand. Genetic alternation of jasmonate metabolic pathways in Arabidopsis to deplete both JA-Ile and 12OH-JA-Ile displayed enhanced jasmonate deficient wound phenotypes and was more susceptible to insect herbivory than that depleted in only JA-Ile. Conversely, mutants overaccumulating 12OH-JA-Ile showed intensified wound responses compared with wild type with similar JA-Ile content. These data are indicative of 12OH-JA-Ile functioning as an active jasmonate signal and contributing to wound and defense response in higher plants.

Efficient ASK-assisted system for expression and purification of plant F-box proteins.

Ubiquitin-mediated protein degradation plays an essential role in plant growth and development as well as responses to environmental and endogenous signals. F-box protein is one of the key components of the SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase complex, which recruit specific substrate proteins for subsequent ubiquitination and 26S proteasome-mediated degradation to regulate developmental processes and signaling networks. However, it is not easy to obtain purified F-box proteins with high activity due to their unstable protein structures. Here, we found that Arabidopsis SKP-like proteins (ASKs) can significantly improve soluble expression of F-box proteins and maintain their bioactivity. We established an efficient ASK-assisted method to express and purify plant F-box proteins. The method meets a broad range of criteria required for the biochemical analysis or protein crystallization of plant F-box proteins.

Plant growth-promoting bacteria Kosakonia radicincitans mediate anti-herbivore defense in Arabidopsis thaliana.

MAIN CONCLUSION: This study demonstrates that the application of the PGPB strain, Kosakonia radicincitans enhances a plant's resistance against phloem-feeding and chewing insects in Arabidopsis thaliana. The plant growth-promoting bacterial strain K. radicincitans DSM 16656 applied to A. thaliana reduced the number of phloem-feeding insects of both the specialist Brevicoryne brassicae and the generalist Myzus persicae. While weight gain of the generalist chewing insect Spodoptera exigua was reduced by 30% on A. thaliana plants treated with K. radicincitans, growth of the specialist caterpillar Pieris brassicae was not affected when compared with caterpillars from control plants. Since generalist and specialist chewing insects responded differentially to PGPB application, the implication of signaling pathways in PGPB mediated changes in plant defense was studied using two signaling pathway mutants impaired in their salicylic acid (npr1-1 mutant) or jasmonic acid (coi1-1 mutant) pathway. We found that the jasmonic acid pathway is relevant for upregulation of aliphatic glucosinolates and suppression of the chewing generalist S. exigua larval growth. Chewing from generalist P. brassicae increased glucosinolate content in A. thaliana leaves mediated via both signaling pathways. However, only in the npr1-1 mutant, which contains the highest aliphatic glucosinolate content, the P. brassicae induced further enrichment of glucosinolates, resulting in a reduction of larval growth. Effects of K. radicincitans on plant resistance could not be explained by changes in glucosinolate contents or composition. Our results demonstrate the distinct role played by K. radicincitans in suppressing insect performance in A. thaliana.

A network of jasmonate-responsive bHLH factors modulate monoterpenoid indole alkaloid biosynthesis in Catharanthus roseus.

The pharmaceutically valuable monoterpene indole alkaloids (MIAs) in Catharanthus roseus are derived from the indole and iridoid pathways that respond to jasmonate (JA) signaling. Two classes of JA-responsive bHLH transcription factor (TF), CrMYC2 and BIS1/BIS2, are known to regulate the indole and iridoid pathways, respectively. However, upregulation of either one of the TF genes does not lead to increased MIA accumulation. Moreover, little is known about the interconnection between the CrMYC2 and BIS transcriptional cascades and the hierarchical position of BIS1/BIS2 in JA signaling. Here, we report that a newly identified bHLH factor, Repressor of MYC2 Targets 1 (RMT1), is activated by CrMYC2 and BIS1, and acts as a repressor of the CrMYC2 targets. In addition, we isolated and functionally characterized the core C. roseus JA signaling components, including CORONATINE INSENSITIVE 1 (COI1) and JASMONATE ZIM domain (JAZ) proteins. CrMYC2 and BIS1 are repressed by the JAZ proteins in the absence of JA, but de-repressed by the SCFCOI1 complex on perception of JA. Our findings suggest that the repressors, JAZs and RMT1, mediate crosstalk between the CrMYC2 and BIS regulatory cascades to balance the metabolic flux in MIA biosynthesis.

Formation of α- and ß-Cembratriene-Diols in Tobacco (Nicotiana tabacum L.) Is Regulated by Jasmonate-Signaling Components via Manipulating Multiple Cembranoid Synthetic Genes.

Cembranoids are a group of natural diterpenoid compounds with pharmaceutical potentials, and the cembratriene-diols produced by Nicotiana (tobacco) species display activities in anti-nicotine addiction and neuron protection. Although the enzymes catalyzing cembratriene-diols' formation in tobacco have been investigated, the regulatory mechanism underlying this physiological process remains unknown. This study has investigated the roles of phytohormone jasmonic acid (JA) in regulating cembratriene-diol formation in N. tabacum cv. TN90 and found that JA and COI1, the receptor protein of the bioactive derivative of JA (i.e., JA-Ile), display critical roles in regulating cembratriene-diols' formation and the expression of cembranoid synthetic genes CBTS, P450 and NtLTP1. Further studies showed that over-expressing either the gene encoding bHLH transcription factor MYC2a or that encoding MYB transcription factor MYB305 could upregulate the cembranoid synthetic genes and enhance the cembranoid production in plants with dysfunction of COI1. Further studies suggest that COI1 and its downstream regulators MYC2a and MYB305 also modulate the trichome secretion, which is correlated with cembranoid formation. Taken together, this study has demonstrated a critical role of JA-signaling components in governing the cembratriene-diol formation and the transcription of cembratriene-diol synthetic genes in tobacco. Findings in this study are of great importance to reveal the molecular regulatory mechanism underlying cembranoid synthesis.

Epidermal jasmonate perception is sufficient for all aspects of jasmonate-mediated male fertility in Arabidopsis.

Jasmonate (JA) signaling is essential for several environmental responses and reproductive development in many plant species. In Arabidopsis thaliana, the most obvious phenotype of JA biosynthetic and perception mutants is profound sporophytic male sterility characterized by failure of stamen filament elongation, severe delay of anther dehiscence and pollen inviability. The site of action of JA in the context of reproductive development has been discussed, but the ideas have not been tested experimentally. To this end we used targeted expression of a COI1-YFP transgene in the coi1-1 mutant background. As COI1 is an essential component of the JA co-receptor complex, the null coi1-1 mutant is male sterile due to lack of JA perception. We show that expression of COI1-YFP in the epidermis of the stamen filament and anther in coi1 mutant plants is sufficient to rescue filament elongation, anther dehiscence and pollen viability. In contrast, filament expression alone or expression in the tapetum do not restore dehiscence and pollen viability. These results demonstrate that epidermal JA perception is sufficient for anther function and pollen viability, and suggest the presence of a JA-dependent non-autonomous signal produced in the anther epidermis to synchronize both anther dehiscence and pollen maturation.

Jasmonate-induced biosynthesis of steroidal glycoalkaloids depends on COI1 proteins in tomato.

In tomato, perception of jasmonates by a receptor complex, which includes the F-box protein CORONATINE INSENSITIVE 1 (COI1), elicits biosynthesis of defensive steroidal glycoalkaloids (SGAs) via a jasmonate-responsive ERF transcription factor, JRE4/GAME9. Although JRE4 is upregulated by jasmonate and induces the expression of many metabolic genes involved in SGA biosynthesis, it is not known whether JRE4 alone is sufficient for increased SGA biosynthesis upon activation of jasmonate signaling. Here, we show that application of methyl jasmonate induces the expression of JRE4 and SGA biosynthesis genes in leaves and hairy roots of wild-type tomato, but not in jasmonic acid insensitive 1 (jai1), a loss-of-function mutant allele of the tomato COI1 gene. Induced overexpression of JRE4 increased the expression of SGA biosynthesis genes in transgenic hairy roots of both wild-type tomato and the jai1 mutant, suggesting that JRE4 is the primary transcription factor that functions downstream of the jasmonate signaling pathway.

Jasmonate action in plant growth and development.

Phytohormones, including jasmonates (JAs), gibberellin, ethylene, abscisic acid, and auxin, integrate endogenous developmental cues with environmental signals to regulate plant growth, development, and defense. JAs are well- recognized lipid-derived stress hormones that regulate plant adaptations to biotic stresses, including herbivore attack and pathogen infection, as well as abiotic stresses, including wounding, ozone, and ultraviolet radiation. An increasing number of studies have shown that JAs also have functions in a remarkable number of plant developmental events, including primary root growth, reproductive development, and leaf senescence. Since the 1980s, details of the JA biosynthesis pathway, signaling pathway, and crosstalk during plant growth and development have been elucidated. Here, we summarize recent advances and give an updated overview of JA action and crosstalk in plant growth and development.

Arabidopsis Elongator subunit 2 positively contributes to resistance to the necrotrophic fungal pathogens Botrytis cinerea and Alternaria brassicicola.

The evolutionarily conserved Elongator complex functions in diverse biological processes including salicylic acid-mediated immune response. However, how Elongator functions in jasmonic acid (JA)/ethylene (ET)-mediated defense is unknown. Here, we show that Elongator is required for full induction of the JA/ET defense pathway marker gene PLANT DEFENSIN1.2 (PDF1.2) and for resistance to the necrotrophic fungal pathogens Botrytis cinerea and Alternaria brassicicola. A loss-of-function mutation in the Arabidopsis Elongator subunit 2 (ELP2) alters B. cinerea-induced transcriptome reprogramming. Interestingly, in elp2, expression of WRKY33, OCTADECANOID-RESPONSIVE ARABIDOPSIS AP2/ERF59 (ORA59), and PDF1.2 is inhibited, whereas transcription of MYC2 and its target genes is enhanced. However, overexpression of WRKY33 or ORA59 and mutation of MYC2 fail to restore PDF1.2 expression and B. cinerea resistance in elp2, suggesting that ELP2 is required for induction of not only WRKY33 and ORA59 but also PDF1.2. Moreover, elp2 is as susceptible as coronatine-insensitive1 (coi1) and ethylene-insensitive2 (ein2) to B. cinerea, indicating that ELP2 is an important player in B. cinerea resistance. Further analysis of the lesion sizes on the double mutants elp2 coi1 and elp2 ein2 and the corresponding single mutants revealed that the function of ELP2 overlaps with COI1 and is additive to EIN2 for B. cinerea resistance. Finally, basal histone acetylation levels in the coding regions of WRKY33, ORA59, and PDF1.2 are reduced in elp2 and a functional ELP2-GFP fusion protein binds to the chromatin of these genes, suggesting that constitutive ELP2-mediated histone acetylation may be required for full activation of the WRKY33/ORA59/PDF1.2 transcriptional cascade.

Jasmonates: signal transduction components and their roles in environmental stress responses.

Jasmonates, oxylipin-type plant hormones, are implicated in diverse aspects of plant growth development and interaction with the environment. Following diverse developmental and environmental cues, jasmonate is produced, conjugated to the amino acid isoleucine and perceived by a co-receptor complex composed of the Jasmonate ZIM-domain (JAZ) repressor proteins and an E3 ubiquitin ligase complex containing the F-box CORONATINE INSENSITIVE 1 (COI1). This event triggers the degradation of the JAZ proteins and the release of numerous transcription factors, including MYC2 and its homologues, which are otherwise bound and inhibited by the JAZ repressors. Here, we will review the role of the COI1, JAZ and MYC2 proteins in the interaction of the plant with its environment, illustrating the significance of jasmonate signalling, and of the proteins involved, for responses to both biotic stresses caused by insects and numerous microbial pathogens and abiotic stresses caused by adverse climatic conditions. It has also become evident that crosstalk with other hormone signals, as well as light and clock signals, plays an important role in the control and fine-tuning of these stress responses. Finally, we will discuss how several pathogens exploit the jasmonate perception and early signalling machinery to decoy the plants defence systems.