F-box Protein COI1 Research Articles

Ectopic Expression of OsJAZs Alters Plant Defense and Development.

A key step in jasmonic acid (JA) signaling is the ligand-dependent assembly of a coreceptor complex comprising the F-box protein COI1 and JAZ transcriptional repressors. The assembly of this receptor complex results in proteasome-mediated degradation of JAZ repressors, which in turn bind and repress MYC transcription factors. Many studies on JAZs have been performed in Arabidopsis thaliana, but the function of JAZs in rice is largely unknown. To systematically reveal the function of OsJAZs, in this study, we compared the various phenotypes resulting from 13 OsJAZs via ectopic expression in Arabidopsis thaliana and the phenotypes of 12 AtJAZs overexpression (OE) lines. Phylogenetic analysis showed that the 25 proteins could be divided into three major groups. Yeast two-hybrid (Y2H) assays revealed that most OsJAZ proteins could form homodimers or heterodimers. The statistical results showed that the phenotypes of the OsJAZ OE plants were quite different from those of AtJAZ OE plants in terms of plant growth, development, and immunity. As an example, compared with other JAZ OE plants, OsJAZ11 OE plants exhibited a JA-insensitive phenotype and enhanced resistance to Pst DC3000. The protein stability after JA treatment of OsJAZ11 emphasized the specific function of the protein. This study aimed to explore the commonalities and characteristics of different JAZ proteins functions from a genetic perspective, and to screen genes with disease resistance value. Overall, the results of this study provide insights for further functional analysis of rice JAZ family proteins.

Protein–protein interactions between jasmonate-related master regulator MYC and transcriptional mediator MED25 depend on a short binding domain

A network of protein–protein interactions (PPI) is involved in the activation of (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile), a plant hormone that regulates plant defense responses as well as plant growth and development. In the absence of JA-Ile, inhibitory protein jasmonate-ZIM-domain (JAZ) represses JA-related transcription factors, including a master regulator, MYC. In contrast, when JA-Ile accumulates in response to environmental stresses, PPI occurs between JAZ and the F-box protein COI1, which triggers JAZ degradation, resulting in derepressed MYC that can interact with the transcriptional mediator MED25 and upregulate JA-Ile-related gene expression. Activated JA signaling is eventually suppressed through the catabolism of JA-Ile and feedback suppression by JAZ splice variants containing a cryptic MYC-interacting domain (CMID). However, the detailed structural basis of some PPIs involved in JA-Ile signaling remains unclear. Herein, we analyzed PPI between MYC3 and MED25, focusing on the key interactions that activate the JA-Ile signaling pathway. Biochemical assays revealed that a short binding domain of MED25 (CMIDM) is responsible for the interaction with MYC, and that a bipartite interaction is critical for the formation of a stable complex. We also show the mode of interaction between MED25 and MYC is closely related to that of CMID and MYC. In addition, quantitative analyses on the binding of MYC3-JAZs and MYC3-MED25 revealed the order of binding affinity as JAZJas < MED25CMIDM < JAZCMID, suggesting a mechanism for how the transcriptional machinery causes activation and negative feedback regulation during jasmonate signaling. These results further illuminate the transcriptional machinery responsible for JA-Ile signaling.

A new functional JAZ degron sequence in strawberry JAZ1 revealed by structural and interaction studies on the COI1\u2013JA-Ile/COR\u2013JAZs complexes

The phytohormone jasmonoyl-isoleucine (JA-Ile) regulates fundamental plant processes as developmental and defense responses. JA-Ile mediates the interaction between the F-box protein COI1 (part of the SCFCOI1 E3 ubiquitin ligase) and a JAZ repressor leading to early jasmonate responses. The Arabidopsis JAZ1 protein contains the canonical LPIARR degron sequence, which is responsible for the stabilization of the AtCOI1-JA-Ile-AtJAZ1 complex. In strawberry (Fragaria × ananassa) JAZ family was described at the transcriptional level during fruit development but the information about the interaction mode of this complex is still scarce at the molecular level. To gain insight into the strawberry JA-Ile receptor complex, we evaluated the interaction at the structural level, and protein models were built and analyzed for FaCOI1 and FaJAZ1, FaJAZ8.1, and FaJAZ10. The interaction between FaCOI1 and FaJAZ1, FaJAZ8.1 and FaJAZ10 were explored using several ligands, through molecular docking and molecular dynamics (MD) simulations, finding the strongest interaction with (+)-7-iso-JA-Ile than other ligands. Additionally, we tested interactions between FaCOI1 and FaJAZs by yeast two-hybrid assays in the presence of coronatine (COR, a JA-Ile mimic). We detected strong COR-dependent interactions between FaCOI1 and FaJAZ1. Interestingly, FaJAZ1 contains a new non-canonical (IPMQRK) functional degron sequence, in which Arg and Lys are the key residues for maintaining the interaction of the FaCOI1–COR–FaJAZ1 complex as we observed in mutated versions of the FaJAZ1 degron. Phylogenetic analysis showed that the IPMQRK degron is only present in orthologs belonging to the Rosoideae but not in other Rosaceae subfamilies. Together, this study uncovers a new degron sequence in plants, which could be required to make an alternative and functional JA-Ile perception complex in strawberry.

Molecular Rewiring of the Jasmonate Signaling Pathway to Control Auxin-Responsive Gene Expression.

The plant hormone jasmonic acid (JA) has an important role in many aspects of plant defense response and developmental process. JA triggers interaction between the F-box protein COI1 and the transcriptional repressors of the JAZ family that leads the later to proteasomal degradation. The Jas-motif of JAZs is critical for mediating the COI1 and JAZs interaction in the presence of JA. Here, by using the protoplast transient gene expression system we reported that the Jas-motif of JAZ1 was necessary and sufficient to target a foreign reporter protein for COI1-facilitated degradation. We fused the Jas-motif to the SHY2 transcriptional repressor of auxin signaling pathway to create a chimeric protein JaSHY. Interestingly, JaSHY retained the transcriptional repressor function while become degradable by the JA coreceptor COI1 in a JA-dependent fashion. Moreover, the JA-induced and COI1-facilitated degradation of JaSHY led to activation of a synthetic auxin-responsive promoter activity. These results showed that the modular components of JA signal transduction pathway can be artificially redirected to regulate auxin signaling pathway and control auxin-responsive gene expression. Our work provides a general strategy for using synthetic biology approaches to explore and design cell signaling networks to generate new cellular functions in plant systems.

AaCOI1, Encoding a CORONATINE INSENSITIVE 1-Like Protein of Artemisia annua L., Is Involved in Development, Defense, and Anthocyanin Synthesis.

Artemisia annua is an important medicinal plant producing the majority of the antimalarial compound artemisinin. Jasmonates are potent inducers of artemisinin accumulation in Artemisisa annua plants. As the receptor of jasmonates, the F-box protein COI1 is critical to the JA signaling required for plant development, defense, and metabolic homeostasis. AaCOI1 from Artemisia annua, homologous to Arabidopsis AtCOI1, encodes a F-box protein located in the nuclei. Expressional profiles of the AaCOI1 in the root, stem, leaves, and inflorescence was investigated. The mRNA abundance of AaCOI1 was the highest in inflorescence, followed by in the leaves. Upon mechanical wounding or MeJA treatment, expression of AaCOI1 was upregulated after 6 h. When ectopically expressed, driven by the native promoter from Arabidopsis thaliana, AaCOI1 could partially complement the JA sensitivity and defense responses, but fully complemented the fertility, and the JA-induced anthocyanin accumulation in a coi1-16 loss-of-function mutant. Our study identifies the paralog of AtCOI1 in Artemisia annua, and revealed its implications in development, hormone signaling, defense, and metabolism. The results provide insight into JA perception in Artemisia annua, and pave the way for novel molecular breeding strategies in the canonical herbs to manipulate the anabolism of pharmaceutic compounds on the phytohormonal level.

Reconstitution of the Jasmonate Signaling Pathway in Plant Protoplasts.

The phytohormone jasmonic acid (JA) plays an important role in various plant developmental processes and environmental adaptations. The JA signaling pathway has been well-elucidated in the reference plant Arabidopsis thaliana. It starts with the perception of the active JA derivative, jasmonoyl-isoleucine (JA-Ile), by the F-box protein COI1 which is part of the E3-ligase SCFCOI1. Binding of JA-Ile enables the interaction between COI1 and JAZ repressor proteins. Subsequent degradation of JAZ proteins leads to the activation of transcription factors like e.g., MYC2. Here we demonstrate that the pathway can be reconstituted in transiently transformed protoplasts. Analysis of the stability of a JAZ1-fLuc fusion protein as a function of COI1 transiently expressed in coi1 protoplasts allows structure function analysis of both JAZs and COI1. Using this system, we found that conserved cysteines in COI1 influence steady state COI1 protein levels. Using a luciferase reporter gene under the control of the JAZ1 promoter enable to address those features of JAZ1 that are required for MYC2 repression. Interestingly, the conserved TIFY-motif previously described to interact with NINJA to recruit the corepressor TOPLESS is not necessary for repression. This result is in favor of the alternative repression mode that proposes a direct competition between repressive JAZs and promotive MEDIATOR25 at MYC2. Finally, using protoplasts from the aos coi1 double mutant, which is deficient in JA synthesis and perception, we provide a system that has the potential to study the activity of different COI1 variants in the presence of different ligands.

Jasmonate action in plant defense against insects.

Herbivorous insects represent one of the major threats to sessile plants. To cope with herbivore challenges, plants have evolved sophisticated defense systems, in which the lipid-derived phytohormone jasmonate plays a crucial role. Perception of insect attack locally and systemically elicits rapid synthesis of jasmonate, which is perceived by the F-box protein COI1 to further recruit JAZ repressors for ubiquitination and degradation, thereby releasing transcription factors that subsequently activate plant defense against insect attack. Here, we review recent progress in understanding the molecular basis of jasmonate action in plant defense against insects.

Jasmonate Signal Receptor Gene Family ZmCOIs Restore Male Fertility and Defense Response of Arabidopsis mutant coi1-1

Jasmonates (JAs) play an important role in many developmental processes, such as root growth, leaf senescence, male fertility, and defense responses against insects and pathogens. The F-box protein COI1, which plays a central role in JA signal transduction, perceives the JA signal and is required for all the JA-mediated defense responses against biotic and abiotic stresses. JA signaling elements including COI1 have been extensively investigated in Arabidopsise. However, the elements of the JA signaling pathway in maize are largely unknown. In this study, we identified four F-box protein genes from the maize genome, which share high homology with AtCOI1, designated as ZmCOI1a, ZmCOI1b, ZmCOI1c, and ZmCOI2, collectively ZmCOIs. To test whether or not the homologous genes of maize are functionally conservative in JA signaling, we over-expressed ZmCOIs in the Arabidopsis coi1-1 mutant. The results showed that over-expression of ZmCOI1a, ZmCOI1b or ZmCOI1c in the coi1-1 mutant resulted in the restoration of male fertility, indicating successful complementation of coi1-1 sterility by ZmCOI1a, ZmCOI1b, and ZmCOI1c. However, ZmCOI2 was not able to restore male fertility of the mutant, indicating that ZmCOI2 has a function diverged from JA signaling. Furthermore, over-expression of the ZmCOI1a, ZmCOI1b, and ZmCOI1c genes, except ZmCOI2, which, in the coi1-1 mutant, caused restoration of resistance to the leaf pathogen Botrytis cinerea and the soil-borne pathogen Pythium aristosporum. In addition, a set of JA-dependent genes are highly induced by wounding in the transformants of ZmCOIa, ZmCOI1b, and ZmCOI1c, but not inducible in transformants of ZmCOI2 or in the coi1-1 mutant, indicating that ZmCOIa, ZmCOI1b, and ZmCOI1c, except ZmCOI2, which can compensate coi1-1 mutation of Arabidopsis for the stress defense response. Putting all the data together, our results suggested that ZmCOIa, ZmCOI1b, and ZmCOI1c, but not ZmCOI2, act as AtCOI1 orthologues in maize for JA signal transduction.

Dynamic Perception of Jasmonates by the F-Box Protein COI1

Jasmonates (JAs) are cyclic fatty acid-derived phytohormones that regulate diverse aspects of plant defense and development. The endogenous active JA molecule (+)-7-iso-JA-L-Ile (JA-Ile) and its analog coronatine trigger formation of a complex with the F-box protein COI1 and JAZ repressors to induce degradation of the JAZs through the 26S proteasome pathway in a COI1-dependent manner. To reveal the formation process of COI1–JA–JAZ ternary complex, we employed several biochemical approaches to examine how JA is dynamically perceived. These analyses showed that the COI1 proteins of Arabidopsis and rice bind JA with appreciable binding affinity and revealed the kinetics and thermodynamics of the COI1–JA–JAZ ternary complex. Our results suggest that COI1 is the primary receptor perceiving the active JA molecule to initially form a COI1–JA complex that subsequently recruits JAZs for further signal transduction.

Inositol Polyphosphate Binding Specificity of the Jasmonate Receptor Complex.

Inositol polyphosphate binding specificity of the jasmonate receptor is largely determined by the F-box protein COI1.

Enhancing heterogenous expression and purification of bioactive Arabidopsis COI1 protein in tobacco

Jasmonate (JA) and its derivatives play an important role in plant development and defense. The JA signal receptor is an F-box protein COI1. COI1 combines with SKP1 and Cullin1 to form a SCFCOI1 complex that interacts with JAZ repressors after combining with JA leading to ubiquitination and degradation of JAZ1 by 26S proteasome. JA-related transcriptional factors are released to control the downstream gene expression. Identification of COI1 is essential to understand the JA signaling pathway. However, expression and purification of bioactive COI1 protein is extremely difficult, limiting the study of further biological function. In this study, COI1 protein was fused with specific sequence tag and transferred into tobacco. After optimizing transformation time, and extraction procedure, the fusion protein was successfully isolated by affinity purification. Pull-down assay indicated that the purified protein interacted with JAZ1 present in JA-Ile, suggesting that the fusion protein was bioactive. The methodology developed in this study provides an efficient strategy to express and purify eukaryotic protein with bioactivity.

Transcription factor-dependent nuclear localization of a transcriptional repressor in jasmonate hormone signaling

The plant hormone jasmonate (JA) plays an important role in regulating growth, development and immunity. A key step in JA signaling is ligand-dependent assembly of a coreceptor complex consisting of the F-box protein COI1 and JAZ transcriptional repressors. Assembly of this receptor complex results in proteasome-mediated degradation of JAZ repressors, which at resting state bind to and repress the MYC transcription factors. Although the JA receptor complex is believed to function within the nucleus, how this receptor complex enters the nucleus and, more generally, the cell biology of jasmonate signaling are not well understood. In this study, we conducted mutational analysis of the C termini (containing the conserved Jas motif) of two JAZ repressors, JAZ1 and JAZ9. These analyses unexpectedly revealed different subcellular localization patterns of JAZ1ΔJas and JAZ9ΔJas, which were associated with differential interaction of JAZ1ΔJas and JAZ9ΔJas with MYC2 and differential repressor activity in vivo. Importantly, physical interaction with MYC2 appears to play an active role in the nuclear targeting of JAZ1 and JAZ9, and the nuclear localization of JAZ9 was compromised in myc2 mutant plants. We identified a highly conserved arginine residue in the Jas motif that is critical for coupling MYC2 interaction with nuclear localization of JAZ9 and JAZ9 repressor function in vivo. Our results suggest a model for explaining why some JAZΔJas proteins, but not others, confer constitutive JA-insensitivity when overexpressed in plants. Results also provide evidence for a transcription factor-dependent mechanism for nuclear import of a cognate transcriptional repressor JAZ9 in plants.

Another JA/COI1-independent role of OPDA detected in tomato embryo development

Jasmonates (JAs) are ubiquitously occurring signaling compounds in plants formed in response to biotic and abiotic stress as well as in development. (+)-7-iso-jasmonoyl isoleucine, the bioactive JA, is involved in most JA-dependent processes mediated by the F-box protein COI1 in a proteasome-dependent manner. However, there is an increasing number of examples, where the precursor of JA biosynthesis, cis-(+)-12-oxophytodienoic acid (OPDA) is active in a JA/COI1-independent manner. Here, we discuss those OPDA-dependent processes, thereby giving emphasis on tomato embryo development. Recent data on seed coat-generated OPDA and its role in embryo development is discussed based on biochemical and genetic evidences.

Chemical and genetic exploration of jasmonate biosynthesis and signaling paths

Jasmonates are lipid-derived compounds that act as signals in plant stress responses and developmental processes. Enzymes participating in biosynthesis of jasmonic acid (JA) and components of JA signaling have been extensively characterized by biochemical and molecular-genetic tools. Mutants have helped to define the pathway for synthesis of jasmonoyl-L-isoleucine (JA-Ile), the bioactive form of JA, and to identify the F-box protein COI1 as central regulatory unit. Details on the molecular mechanism of JA signaling were recently unraveled by the discovery of JAZ proteins that together with the adaptor protein NINJA and the general co-repressor TOPLESS form a transcriptional repressor complex. The current model of JA perception and signaling implies the SCF(COI1) complex operating as E3 ubiquitin ligase that upon binding of JA-Ile targets JAZ proteins for degradation by the 26S proteasome pathway, thereby allowing MYC2 and other transcription factors to activate gene expression. Chemical strategies, as integral part of jasmonate research, have helped the establishment of structure-activity relationships and the discovery of (+)-7-iso-JA-L-Ile as the major bioactive form of the hormone. The transient nature of its accumulation highlights the need to understand catabolism and inactivation of JA-Ile and recent studies indicate that oxidation of JA-Ile by cytochrome P450 monooxygenase is the major mechanism for turning JA signaling off. Plants contain numerous JA metabolites, which may have pronounced and differential bioactivity. A major challenge in the field of plant lipid signaling is to identify the cognate receptors and modes of action of these bioactive jasmonates/oxylipins.

Herbivore-induced and floral homoterpene volatiles are biosynthesized by a single P450 enzyme (CYP82G1) in Arabidopsis

Terpene volatiles play important roles in plant-organism interactions as attractants of pollinators or as defense compounds against herbivores. Among the most common plant volatiles are homoterpenes, which are often emitted from night-scented flowers and from aerial tissues upon herbivore attack. Homoterpene volatiles released from herbivore-damaged tissue are thought to contribute to indirect plant defense by attracting natural enemies of pests. Moreover, homoterpenes have been demonstrated to induce defensive responses in plant-plant interaction. Although early steps in the biosynthesis of homoterpenes have been elucidated, the identity of the enzyme responsible for the direct formation of these volatiles has remained unknown. Here, we demonstrate that CYP82G1 (At3g25180), a cytochrome P450 monooxygenase of the Arabidopsis CYP82 family, is responsible for the breakdown of the C(20)-precursor (E,E)-geranyllinalool to the insect-induced C(16)-homoterpene (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT). Recombinant CYP82G1 shows narrow substrate specificity for (E,E)-geranyllinalool and its C(15)-analog (E)-nerolidol, which is converted to the respective C(11)-homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). Homology-based modeling and substrate docking support an oxidative bond cleavage of the alcohol substrate via syn-elimination of the polar head, together with an allylic C-5 hydrogen atom. CYP82G1 is constitutively expressed in Arabidopsis stems and inflorescences and shows highly coordinated herbivore-induced expression with geranyllinalool synthase in leaves depending on the F-box protein COI-1. CYP82G1 represents a unique characterized enzyme in the plant CYP82 family with a function as a DMNT/TMTT homoterpene synthase.

Alternative splicing expands the repertoire of dominant JAZ repressors of jasmonate signaling

Jasmonates (JAs) are fatty acid-derived signaling compounds that control diverse aspects of plant growth, development and immunity. The F-box protein COI1 functions both as a receptor for jasmonoyl-l-isoleucine (JA-Ile) and as the component of an E3-ubiquitin ligase complex (SCF(COI1) ) that targets JAZ transcriptional regulators for degradation. A key feature of JAZ proteins is the C-terminal Jas motif that mediates the JA-Ile-dependent interaction with COI1. Here, we show that most JAZ genes from evolutionarily diverse plants contain a conserved intron that splits the Jas motif into 20 N-terminal and seven C-terminal (X(5) PY) amino acid submotifs. In most members of the Arabidopsis JAZ family, alternative splicing events involving retention of this intron generate proteins that are truncated before the X(5) PY sequence. In vitro pull-down and yeast two-hybrid assays indicate that these splice variants have reduced capacity to form stable complexes with COI1 in the presence of the bioactive stereoisomer of the hormone (3R,7S)-JA-Ile. cDNA overexpression studies showed that some, but not all, truncated splice variants are dominant repressors of JA signaling. We also show that strong constitutive expression of an intron-containing JAZ10 genomic clone is sufficient to repress JA responses. These findings provide evidence for functional differences between JAZ isoforms, and establish a direct link between the alternative splicing of JAZ pre-mRNA and the dominant repression of JA signal output. We propose that production of dominant JAZ repressors by alternative splicing reduces the negative consequences associated with inappropriate or hyperactivation of the JA response pathway.

Proteomics Study of COI1‐regulated Proteins in Arabidopsis Flower

Jasmonates (JAs) are a new class of plant hormone that regulate expression of diverse genes to mediate various plant responses. The Arabidopsis F-box protein COI1 is required for plant defense and male fertility in JA signal pathway. To further investigate the regulatory role of COI1 in male fertility, we compared the proteomics profiles of Arabidopsis wild type (WT) flowers with coi1-1 mutant male-sterile flowers using two-dimensional difference gel electrophoresis coupled with matrix-assisted laser desoption/ionization-time-of-flight mass spectrometry. Sixteen proteins with potential function in specific biological processes such as metabolism processes and defense/stress responses were differentially expressed in WT and coi1-1 mutant flowers. Verification on a phi class glutathione transferase AtGSTF9, one out of these 16 identified proteins, revealed that the expression of AtGSTF9 was severely downregulated in flowers of coi1-1 mutant compared with that of WT. Further function analyses of these genes would provide new insights into the molecular basis of COI1-regulated male fertility.

Jasmonates: Structural Requirements for Lipid-Derived Signals Active in Plant Stress Responses and Development

Jasmonates are lipid-derived signals that mediate plant stress responses and development processes. Enzymes participating in biosynthesis of jasmonic acid (JA) (1, 2) and components of JA signaling have been extensively characterized by biochemical and molecular-genetic tools. Mutants of Arabidopsis and tomato have helped to define the pathway for synthesis of jasmonoyl-isoleucine (JA-Ile), the active form of JA, and to identify the F-box protein COI1 as central regulatory unit. However, details of the molecular mechanism of JA signaling have only recently been unraveled by the discovery of JAZ proteins that function in transcriptional repression. The emerging picture of JA perception and signaling cascade implies the SCF(COI1) complex operating as E3 ubiquitin ligase that upon binding of JA-Ile targets JAZ repressors for degradation by the 26S-proteasome pathway, thereby allowing the transcription factor MYC2 to activate gene expression. The fact that only one particular stereoisomer, (+)-7-iso-JA-l-Ile (4), shows high biological activity suggests that epimerization between active and inactive diastereomers could be a mechanism for turning JA signaling on or off. The recent demonstration that COI1 directly binds (+)-7-iso-JA-l-Ile (4) and thus functions as JA receptor revealed that formation of the ternary complex COI1-JA-Ile-JAZ is an ordered process. The pronounced differences in biological activity of JA stereoisomers also imply strict stereospecific control of product formation along the JA biosynthetic pathway. The pathway of JA biosynthesis has been unraveled, and most of the participating enzymes are well-characterized. For key enzymes of JA biosynthesis the crystal structures have been established, allowing insight into the mechanisms of catalysis and modes of substrate binding that lead to formation of stereospecific products.

A rapid wound signal activates the systemic synthesis of bioactive jasmonates in Arabidopsis

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 SCF(COI1)/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 SCF(COI1)/JAZ pathway.

Molecular mechanism for jasmonate-induction of anthocyanin accumulation in Arabidopsis

Anthocyanins are important plant pigments that fulfil many physiological and ecological functions. Anthocyanin biosynthesis is controlled by numerous regulatory factors at the transcriptional level. Jasmonates (JAs) has been shown to induce anthocyanin accumulation in several plant species, however, the molecular mechanism for JA-regulated anthocyanin accumulation remains unknown. In this study, genetic, molecular, and physiological approaches were used to reveal the molecular basis of JA-regulated pigmentation in Arabidopsis. It was found that the F-box protein COI1 was required for JA-specific induced expression of the 'late' anthocyanin biosynthetic genes DFR, LDOX, and UF3GT. It is further demonstrated that COI1 was essential for JA-induction of transcription factors PAP1, PAP2, and GL3. It is speculated that COI1 regulates the expression of the transcription factors, including PAP1, PAP2, and GL3, which mediates the 'late' anthocyanin biosynthetic genes DFR, LDOX, and UF3GT, thereby modulating JA-induced anthocyanin biosynthesis in Arabidopsis.