Metabolic fate of jasmonates in tobacco bright yellow-2 cells

Jasmonates, gibberellins, and powdery mildew modify cell cycle progression and evoke differential spatiotemporal responses along the barley leaf

Barley (Hordeum vulgare) is an important cereal crop, and its development, defence, and stress responses are modulated by different hormones including jasmonates (JAs) and the antagonistic gibberellins (GAs). Barley productivity is severely affected by the foliar biotrophic fungal pathogen Blumeria hordei. In this study, primary leaves were used to examine the molecular processes regulating responses to methyl-jasmonate (MeJA) and GA to B. hordei infection along the leaf axis. Flow cytometry, microscopy, and spatiotemporal expression patterns of genes associated with JA, GA, defence, and the cell cycle provided insights on cell cycle progression and on the gradient of susceptibility to B. hordei observed along the leaf. Notably, the combination of B. hordei with MeJA or GA pre-treatment had a different effect on the expression patterns of the analysed genes compared to individual treatments. MeJA reduced susceptibility to B. hordei in the proximal part of the leaf blade. Overall, distinctive spatiotemporal gene expression patterns correlated with different degrees of cell proliferation, growth capacity, responses to hormones, and B. hordei infection along the leaf. Our results highlight the need to further investigate differential spatial and temporal responses to pathogens at the organ, tissue, and cell levels in order to devise effective disease control strategies in crops.

MsNRAMP2 Enhances Tolerance to Iron Excess Stress in Nicotiana tabacum and MsMYB Binds to Its Promoter

Iron(Fe) is a trace metal element necessary for plant growth, but excess iron is harmful to plants. Natural resistance-associated macrophage proteins (NRAMPs) are important for divalent metal transport in plants. In this study, we isolated the MsNRAMP2 (MN_547960) gene from alfalfa, the perennial legume forage. The expression of MsNRAMP2 is specifically induced by iron excess. Overexpression of MsNRAMP2 conferred transgenic tobacco tolerance to iron excess, while it conferred yeast sensitivity to excess iron. Together with the MsNRAMP2 gene, MsMYB (MN_547959) expression is induced by excess iron. Y1H indicated that the MsMYB protein could bind to the "CTGTTG" cis element of the MsNRAMP2 promoter. The results indicated that MsNRAMP2 has a function in iron transport and its expression might be regulated by MsMYB. The excess iron tolerance ability enhancement of MsNRAMP2 may be involved in iron transport, sequestration, or redistribution.

Molecular insights into the jasmonate signaling and associated defense responses against wilt caused by Fusarium oxysporum

Biotic and abiotic stress factors drastically limit plant growth and development as well as alter the physiological, biochemical and cellular processes. This negatively impacts plant productivity, ultimately leading to agricultural and economical loss. Plant defense mechanisms elicited in response to these stressors are crucially regulated by the intricate crosstalk between defense hormones such as jasmonic acid (JA), salicylic acid and ethylene. These hormones orchestrate adaptive responses by modulating the gene regulatory networks leading to sequential changes in the root architecture, cell wall composition, secondary metabolite production and expression of defense-related genes. Fusarium wilt is a widespread vascular disease in plants caused by the soil-borne ascomycete Fusarium oxysporum and is known to attack several economically important plant cultivars. JA along with its conjugated forms methyl jasmonate and jasmonic acid isoleucine critically tunes plant defense mechanisms by regulating the expression of JA-associated genes imparting resistance phenotype. However, it should be noted that some members of F. oxysporum utilize the JA signaling pathway for disease development leading to susceptibility in plants. Therefore, JA signaling pathway becomes one of the important targets amenable for modulation to develop resistance response against Fusarium wilt in plants. In this review, we have emphasized on the physiological and molecular aspects of JA and its significant role in mounting an early defense response against Fusarium wilt disease. Further, utilization of the inherent JA signaling pathway and/or exogenous application of JA in generating Fusarium wilt resistant plants is discussed.

Jasmonate and Melatonin Act Synergistically to Potentiate Cold Tolerance in Tomato Plants

Both jasmonic acid (JA) and melatonin (MT) have been demonstrated to play positive roles in cold tolerance, however, whether and how they crosstalk in the cold responses in plants remain elusive. Here, we report that JA and MT act synergistically in the cold tolerance in tomato plants (Solanum lycopersicum). It was found that JA and MT were both substantially accumulated in response to cold stress and foliar applications of methyl jasmonate (MeJA) and MT promoted cold tolerance as evidenced by increased Fv/Fm, decreased relative electrolyte leakage (EL) and declined H₂O₂ accumulation in tomato plants. Inhibition of MT biosynthesis attenuated MeJA-induced cold tolerance, while inhibition of JA biosynthesis reduced MT accumulation in tomato plants under cold conditions. Furthermore, qRT-PCR analysis showed that the expressions of two MT biosynthetic genes, SlSNAT and SlAMST, were strongly induced by MeJA, whereas suppression of SlMYC2, a master JA signaling regulator, abated the expressions of SlSNAT and SlAMST under cold stress. Additionally, suppression of SlMYC2 reduced MT accumulation, decreased Fv/Fm and increased EL in cold-stressed tomato plants. Interestingly, exogenous MT promoted JA accumulation, while inhibition of MT biosynthesis significantly reduced JA accumulation in tomato plants under the cold condition. Taken together, these results suggest that JA and MT act cooperatively in cold tolerance and form a positive feedback loop, amplifying the cold responses of tomato plants. Our findings might be translated into the development of cold-resistant tomato cultivars by genetically manipulating JA and MT pathways.

Kaolin and Jasmonic acid improved cotton productivity under water stress conditions

Drought is one of the most emerging threat that causes a severe reduction in cotton plant growth and development. Being cotton is a major cash crop has great threat to prevailing drought events in Pakistan. A field experiment was conducted in Kharif season 2018 at Research Area of MNS-University of Agriculture, Multan, Pakistan to assess the role of foliar applied kaolin and jasmonic acid on vegetative growth, gas exchange and reproductive traits of cotton under normal irrigated and artificial water deficit conditions. The experiment was laid -out in a factorial randomized complete block design with split - split plot arrangement. Main plots were allocated for irrigation levels, sub-plots for two -cotton genotypes viz. NIAB - 878 and SLH - 19 while sub - sub plots for treatments of kaolin and Jasmonic acid. Water deficit stress was created by skipping irrigation at flowering for 21 days. Foliar sprays of Kaolin (5%, w/v) and Jasmonic acid (100 μM) were applied alone or in combination at 60 days after planntinon both to normal irrigated and water-stresse skip irrigation while irrigation water alone was sprayed in control plots. Both cotton genotypes responded variably to normal irrigated and skip conditions. Skipping irrigation for up to 21 days at flowering caused a significant decrease in leaf relative water content, SPAD values, net photosynthetic rate and seed cotton yield in both the genotypes. Seed cotton yield showed an overall decline of 24.7% in skip over Normal irrigated crop. The genotype NIAB - 878 produced maximum seed cotton yield of 3.304 Mg ha-1 in normal that dropped to 2.579 Mg ha-1 in skip, thus showing an average decline of 21.9 %. Similarly, SLH - 19 produced 2.537 Mg ha-1 seed cotton under normal that dropped to 1.822 Mg ha-1 in skip, showing an average decline of 28.2%. The Application of Kaolin and JA Jasmonic acid, either applied individually or in combination, improved vegetative and reproductive development of both cotton varieties in normal and skip regimes. However, combined kaolin and Jasmonic Acid application proved to be more beneficial in terms of seed cotton production and other parameters studied.

Jasmonate Compounds and Their Derivatives in the Regulation of the Neoplastic Processes

Cancer is a serious problem in modern medicine, mainly due to the insufficient effectiveness of currently available therapies. There is a particular interest in compounds of natural origin, which can be used in the prophylaxis, as well as in the treatment and support of cancer treatment. One such compound is jasmonic acid (3-oxo-2-(pent-2'-enyl)cyclopentane acetic acid; isolated active form: trans-(-)-(3R,7R)- and cis-(+)-(3R,7S)-jasmonic acid) and its derivatives, which, due to their wide range of biological activities, are also proposed as potential therapeutic agents. Therefore, a review of literature data on the biological activity of jasmonates was prepared, with particular emphasis on the mechanisms of jasmonate action in neoplastic diseases. The anti-tumor activity of jasmonate compounds is based on altered cellular ATP levels; induction of re-differentiation through the action of Mitogen Activated Protein Kinases (MAPKs); the induction of the apoptosis by reactive oxygen species. Jasmonates can be used in anti-cancer therapy in combination with other known drugs, such as cisplatin, paclitaxel or doxorubicin, showing a synergistic effect. The structure-activity relationship of novel jasmonate derivatives with anti-tumor, anti-inflammatory and anti-aging effects is also shown.

Multiple Roles of Jasmonates in Shaping Rhizotaxis: Emerging Integrators

The root system and its architecture enormously contribute to plant survival and adaptation to the environment. Depending on the intrinsic genetic information and the surrounding rhizosphere, plants develop a highly plastic root system, which is a critical determinant for survival. Plant root system, which includes primary root (PR), lateral roots (LR) and adventitious roots (AR), is shaped by tightly controlled developmental programs. Phytohormones are the main signaling components that orchestrate and coordinate the genetic information and the external stimuli to shape the root system patterning or rhizotaxis. Besides their role in plant stress responses and defense against herbivory and pathogen attacks, jasmonic acid and its derivatives, including the receptor-active conjugate jasmonoyl-L-isoleucine (JA-Ile), emerge as potential regulators of rhizotaxis. In this chapter, we summarize and discuss the recent progress achieved during the recent years to understand the JA-mediated genetic and molecular networks guiding PR, LR, and AR initiation. We highlight the role of JAs as critical integrators in shaping rhizotaxis.

The glycosyltransferase UGT76E1 significantly contributes to 12-O-glucopyranosyl-jasmonic acid formation in wounded Arabidopsis thaliana leaves

Jasmonoyl-isoleucine (JA-Ile) is a phytohormone that orchestrates plant defenses in response to wounding, feeding insects, or necrotrophic pathogens. JA-Ile metabolism has been studied intensively, but its catabolism as a potentially important mechanism for the regulation of JA-Ile-mediated signaling is not well-understood. Especially the enzyme(s) responsible for specifically glycosylating 12-hydroxy-jasmonic acid (12-OH-JA) and thereby producing 12-O-glucopyranosyl-jasmonic acid (12-O-Glc-JA) is still elusive. Here, we used co-expression analyses of available Arabidopsis thaliana transcriptomic data, identifying four UDP-dependent glycosyltransferase (UGT) genes as wound-induced and 12-OH-JA-related, namely, UGT76E1, UGT76E2, UGT76E11, and UGT76E12 We heterologously expressed and purified the corresponding proteins to determine their individual substrate specificities and kinetic parameters. We then used an ex vivo metabolite-fingerprinting approach to investigate these proteins in conditions as close as possible to their natural environment, with an emphasis on greatly extending the range of potential substrates. As expected, we found that UGT76E1 and UGT76E2 are 12-OH-JA-UGTs, with UGT76E1 contributing a major in vivo UGT activity, as deduced from Arabidopsis mutants with abolished or increased UGT gene expression. In contrast, recombinant UGT76E11 acted on an unidentified compound and also glycosylated two other oxylipins, 11-hydroxy-7,9,13-hexadecatrienoic acid (11-HHT) and 13-hydroxy-9,11,15-octadecatrienoic acid (13-HOT), which were also accepted by recombinant UGT76E1, UGT76E2, and UGT76E12 enzymes. UGT76E12 glycosylated 12-OH-JA only to a low extent, but also accepted an artificial hydroxylated fatty acid and low amounts of kaempferol. In conclusion, our findings have elucidated the missing step in the wound-induced synthesis of 12-O-glucopyranosyl-jasmonic acid in A. thaliana.

The roles of methyl jasmonate to stress in plants

Plants are constantly exposed to various stresses, which can degrade their health. The stresses can be alleviated by the application of methyl jasmonate (MeJA), which is a hormone involved in plant signalling. MeJA induces synthesis of defensive compounds and initiates the expression of pathogenesis-related genes involved in systemic acquired resistance and local resistance. Thus, MeJA may be used against pathogens, salt stress, drought stress, low temperature, heavy metal stress and toxicities of other elements. The application of MeJA improves growth, induces the accumulation of active compounds, and affects endogenous hormones levels, and other physiological and biochemical characteristics in stressed plants. Furthermore, MeJA antagonises the adverse effects of osmotic stress by regulating inorganic penetrating ions or organic penetrants to suppress the absorption of toxic ions. MeJA also mitigates oxidative stress by activating antioxidant systems to scavenge reactive oxygen species (ROS) in stressed plants. For these reasons, we reviewed the use of exogenous MeJA in alleviating biotic (pathogens and insects) and abiotic stresses in plants.

Unraveling the Initial Plant Hormone Signaling, Metabolic Mechanisms and Plant Defense Triggering the Endomycorrhizal Symbiosis Behavior

Arbuscular mycorrhizal (AM) fungi establish probably one of the oldest mutualistic relationships with the roots of most plants on earth. The wide distribution of these fungi in almost all soil ecotypes and the broad range of host plant species demonstrate their strong plasticity to cope with various environmental conditions. AM fungi elaborate fine-tuned molecular interactions with plants that determine their spread within root cortical tissues. Interactions with endomycorrhizal fungi can bring various benefits to plants, such as improved nutritional status, higher photosynthesis, protection against biotic and abiotic stresses based on regulation of many physiological processes which participate in promoting plant performances. In turn, host plants provide a specific habitat as physical support and a favorable metabolic frame, allowing uptake and assimilation of compounds required for the life cycle completion of these obligate biotrophic fungi. The search for formal and direct evidences of fungal energetic needs raised strong motivated projects since decades, but the impossibility to produce AM fungi under axenic conditions remains a deep enigma and still feeds numerous debates. Here, we review and discuss the initial favorable and non-favorable metabolic plant context that may fate the mycorrhizal behavior, with a focus on hormone interplays and their links with mitochondrial respiration, carbon partitioning and plant defense system, structured according to the action of phosphorus as a main limiting factor for mycorrhizal symbiosis. Then, we provide with models and discuss their significances to propose metabolic targets that could allow to develop innovations for the production and application of AM fungal inocula.

Enhanced Production of Phenolic Compounds in Compact Callus Aggregate Suspension Cultures of Rhodiola imbricata Edgew

Rhodiola imbricata is a rare medicinal plant of the trans-Himalayan region of Ladakh. It is used for the treatment of numerous health ailments. Compact callus aggregate (CCA) suspension cultures of Rhodiola imbricata were established to counter extinction threats and for production of therapeutically valuable phenolic compounds to meet their increasing industrial demands. The present study also investigated the effect of jasmonic acid (JA) on production of phenolic compounds and bioactivities in CCA suspension cultures. CCA suspension cultures established in an optimized Murashige and Skoog medium supplemented with 30 g/l sucrose, 3 mg/l NAA, and 3 mg/l BAP showed maximum biomass accumulation (8.43 g/l DW) and highest salidroside production (3.37 mg/g DW). Upon 100 μM JA treatment, salidroside production (5.25 mg/g DW), total phenolic content (14.69 mg CHA/g DW), total flavonoid content (4.95 mg RE/g DW), and ascorbic acid content (17.93 mg/g DW) were significantly increased in cultures. In addition, DPPH-scavenging activity (56.32%) and total antioxidant capacity (60.45 mg QE/g DW) were significantly enhanced upon JA treatment, and this was positively correlated with increased accumulation of phenolic compounds. JA-elicited cultures exhibited highest antimicrobial activity against Escherichia coli. This is the first report describing the enhanced production of phenolic compounds and bioactivities from JA-elicited CCA suspension cultures of Rhodiola imbricata.

The Active Jasmonate JA-Ile Regulates a Specific Subset of Plant Jasmonate-Mediated Resistance to Herbivores in Nature

The jasmonate hormones are essential regulators of plant defense against herbivores and include several dozen derivatives of the oxylipin jasmonic acid (JA). Among these, the conjugate jasmonoyl isoleucine (JA-Ile) has been shown to interact directly with the jasmonate co-receptor complex to regulate responses to jasmonate signaling. However, functional studies indicate that some aspects of jasmonate-mediated defense are not regulated by JA-Ile. Thus, it is not clear whether JA-Ile is best characterized as the master jasmonate regulator of defense, or if it regulates more specific aspects. We investigated possible functions of JA-Ile in anti-herbivore resistance of the wild tobacco Nicotiana attenuata, a model system for plant-herbivore interactions. We first analyzed the soluble and volatile secondary metabolomes of irJAR4xirJAR6, asLOX3, and WT plants, as well as an RNAi line targeting the jasmonate co-receptor CORONATINE INSENSITIVE 1 (irCOI1), following a standardized herbivory treatment. irJAR4xirJAR6 were the most similar to WT plants, having a ca. 60% overlap in differentially regulated metabolites with either asLOX3 or irCOI1. In contrast, while at least 25 volatiles differed between irCOI1 or asLOX3 and WT plants, there were few or no differences in herbivore-induced volatile emission between irJAR4xirJAR6 and WT plants, in glasshouse- or field-collected samples. We then measured the susceptibility of jasmonate-deficient vs. JA-Ile-deficient plants in nature, in comparison to wild-type (WT) controls, and found that JA-Ile-deficient plants (irJAR4xirJAR6) are much better defended even than a mildly jasmonate-deficient line (asLOX3). The differences among lines could be attributed to differences in damage from specific herbivores, which appeared to prefer either one or the other jasmonate-deficient phenotype. We further investigated the elicitation of one herbivore-induced volatile known to be jasmonate-regulated and to mediate resistance to herbivores: (E)-α-bergamotene. We found that JA was a more potent elicitor of (E)-α-bergamotene emission than was JA-Ile, and when treated with JA, irJAR4xirJAR6 plants emitted 20- to 40-fold as much (E)-α-bergamotene than WT. We conclude that JA-Ile regulates specific aspects of herbivore resistance in N. attenuata. This specificity may allow plants flexibility in their responses to herbivores and in managing trade-offs between resistance, vs. growth and reproduction, over the course of ontogeny.

Does methyl jasmonate modify the oxidative stress response in Phaseolus coccineus treated with Cu?

The contribution of methyl jasmonate (MJ) as a signal molecule able to take part in the defense mechanism against copper (Cu)-imposed oxidative stress was studied in the leaves and roots of runner bean (Phaseolus coccineus) plants. Roots of plants cultivated hydroponically were preincubated in MJ (10µM) for 1h or 24h and subsequently exposed to Cu (50µM) for 5h (short-term experiment) or 5 days (long-term experiment). Enzymatic (activity of superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; guaiacol peroxidase, POX) and non-enzymatic (accumulation of malondialdehyde, MDA; homoglutathione, hGSH; proline; anthocyanins; low molecular weight organic acids, LMWOAs) responses were determined in the leaves and roots. The antioxidative defense mechanism was significantly activated after Cu supplementation. In most cases, activities of ROS (reactive oxygen species) scavenging enzymes like SOD, CAT, APX, POX, as well as MDA, hGSH and proline concentrations increased following Cu exposure. MJ showed a time-dependent effect on antioxidative enzymes activity. In the short-term experiment, MJ elevated CAT, APX and POX activities in the roots, and POX activity in the leaves of non-Cu-treated plants. In the long-term experiment, MJ not only decreased POX and partially CAT activity in the roots, but also increased the MDA level and partially CAT activity in the leaves of the control plants. In Cu-treated plants, MJ reduced APX, but elevated POX activity in the leaves after 5-h exposure. After 5-day-Cu treatment, MJ inhibited POX activity in the leaves and mainly reduced SOD and CAT activities in the roots. Moreover, in the long-term experiment, MJ reduced tartrate and pyruvate in the leaves of Cu-stressed plants, but mostly elevated tartrate and malate in the roots comparing with Cu alone treatment. MJ alone and under Cu excess did not alter accumulation of MDA, hGSH and proline comparing with Cu alone, but partially elevated anthocyanin concentration. The results indicated that MJ was both partially potent in modifying the antioxidative enzymes activity and metabolites accumulation in non-stress and Cu-stress conditions.

Jasmonates: Emerging Players in Controlling Temperature Stress Tolerance

The sedentary life of plants has forced them to live in an environment that is characterized by the presence of numerous challenges in terms of biotic and abiotic stresses. Phytohormones play essential roles in mediating plant physiology and alleviating various environmental perturbations. Jasmonates are a group of oxylipin compounds occurring ubiquitously in the plant kingdom that play pivotal roles in response to developmental and environmental cues. Jasmonates (JAs) have been shown to participate in unison with key factors of other signal transduction pathway, including those involved in response to abiotic stress. Recent findings have furnished large body of information suggesting the role of jasmonates in cold and heat stress. JAs have been shown to regulate C-repeat binding factor (CBF) pathway during cold stress. The interaction between the integrants of JA signaling and components of CBF pathway demonstrates a complex relationship between the two. JAs have also been shown to counteract chilling stress by inducing ROS avoidance enzymes. In addition, several lines of evidence suggest the positive regulation of thermotolerance by JA. The present review provides insights into biosynthesis, signal transduction pathway of jasmonic acid and their role in response to temperature stress.

Metabolic fingerprinting of Arabidopsis thaliana accessions

In the post-genomic era much effort has been put on the discovery of gene function using functional genomics. Despite the advances achieved by these technologies in the understanding of gene function at the genomic and proteomic level, there is still a big genotype-phenotype gap. Metabolic profiling has been used to analyze organisms that have already been characterized genetically. However, there is a small number of studies comparing the metabolic profile of different tissues of distinct accessions. Here, we report the detection of over 14,000 and 17,000 features in inflorescences and leaves, respectively, in two widely used Arabidopsis thaliana accessions. A predictive Random Forest Model was developed, which was able to reliably classify tissue type and accession of samples based on LC-MS profile. Thereby we demonstrate that the morphological differences among A. thaliana accessions are reflected also as distinct metabolic phenotypes within leaves and inflorescences.

Methyl jasmonate represses growth and affects cell cycle progression in cultured Taxus cells

Methyl jasmonate elicitation of Taxus cultures enhances paclitaxel accumulation, but represses growth by inhibition of cell cycle progression. Growth repression is evident both at the culture level and transcriptional level. Methyl jasmonate (MeJA) elicitation is an effective strategy to induce and enhance synthesis of the anticancer agent paclitaxel (Taxol(®)) in Taxus cell suspension cultures; however, concurrent decreases in growth are often observed, which is problematic for large-scale bioprocessing. Here, increased accumulation of paclitaxel in Taxus cuspidata suspension cultures with MeJA elicitation was accompanied by a concomitant decrease in cell growth, evident within the first 3 days post-elicitation. Both MeJA-elicited and mock-elicited cultures exhibited similar viability with no apoptosis up to day 16 and day 24 of the cell culture period, respectively, suggesting that growth repression is not attributable to cell death. Flow cytometric analyses demonstrated that MeJA perturbed cell cycle progression of asynchronously dividing Taxus cells. MeJA slowed down cell cycle progression, impaired the G1/S transition as observed by an increase in G0/G1 phase cells, and decreased the number of actively dividing cells. Through a combination of deep sequencing and gene expression analyses, the expression status of Taxus cell cycle-associated genes correlated with observations at the culture level. Results from this study provide valuable insight into the mechanisms governing MeJA perception and subsequent events leading to repression of Taxus cell growth.

bHLH003, bHLH013 and bHLH017 are new targets of JAZ repressors negatively regulating JA responses

Cell reprogramming in response to jasmonates requires a tight control of transcription that is achieved by the activity of JA-related transcription factors (TFs). Among them, MYC2, MYC3 and MYC4 have been described as activators of JA responses. Here we characterized the function of bHLH003, bHLH013 and bHLH017 that conform a phylogenetic clade closely related to MYC2, MYC3 and MYC4. We found that these bHLHs form homo- and heterodimers and also interact with JAZ repressors in vitro and in vivo. Phenotypic analysis of JA-regulated processes, including root and rosette growth, anthocyanin accumulation, chlorophyll loss and resistance to Pseudomonas syringae, on mutants and overexpression lines, suggested that these bHLHs are repressors of JA responses. bHLH003, bHLH013 and bHLH017 are mainly nuclear proteins and bind DNA with similar specificity to that of MYC2, MYC3 and MYC4, but lack a conserved activation domain, suggesting that repression is achieved by competition for the same cis-regulatory elements. Moreover, expression of bHLH017 is induced by JA and depends on MYC2, suggesting a negative feed-back regulation of the activity of positive JA-related TFs. Our results suggest that the competition between positive and negative TFs determines the output of JA-dependent transcriptional activation.

Jasmonates: biosynthesis, perception, signal transduction and action in plant stress response, growth and development. An update to the 2007 review in Annals of Botany

BACKGROUND

Jasmonates are important regulators in plant responses to biotic and abiotic stresses as well as in development. Synthesized from lipid-constituents, the initially formed jasmonic acid is converted to different metabolites including the conjugate with isoleucine. Important new components of jasmonate signalling including its receptor were identified, providing deeper insight into the role of jasmonate signalling pathways in stress responses and development.

SCOPE

The present review is an update of the review on jasmonates published in this journal in 2007. New data of the last five years are described with emphasis on metabolites of jasmonates, on jasmonate perception and signalling, on cross-talk to other plant hormones and on jasmonate signalling in response to herbivores and pathogens, in symbiotic interactions, in flower development, in root growth and in light perception.

CONCLUSIONS

The last few years have seen breakthroughs in the identification of JASMONATE ZIM DOMAIN (JAZ) proteins and their interactors such as transcription factors and co-repressors, and the crystallization of the jasmonate receptor as well as of the enzyme conjugating jasmonate to amino acids. Now, the complex nature of networks of jasmonate signalling in stress responses and development including hormone cross-talk can be addressed.

Jasmonates: biosynthesis, perception, signal transduction and action in plant stress response, growth and development. An update to the 2007 review in Annals of Botany

BACKGROUND

Jasmonates are important regulators in plant responses to biotic and abiotic stresses as well as in development. Synthesized from lipid-constituents, the initially formed jasmonic acid is converted to different metabolites including the conjugate with isoleucine. Important new components of jasmonate signalling including its receptor were identified, providing deeper insight into the role of jasmonate signalling pathways in stress responses and development.

SCOPE

The present review is an update of the review on jasmonates published in this journal in 2007. New data of the last five years are described with emphasis on metabolites of jasmonates, on jasmonate perception and signalling, on cross-talk to other plant hormones and on jasmonate signalling in response to herbivores and pathogens, in symbiotic interactions, in flower development, in root growth and in light perception.

CONCLUSIONS

The last few years have seen breakthroughs in the identification of JASMONATE ZIM DOMAIN (JAZ) proteins and their interactors such as transcription factors and co-repressors, and the crystallization of the jasmonate receptor as well as of the enzyme conjugating jasmonate to amino acids. Now, the complex nature of networks of jasmonate signalling in stress responses and development including hormone cross-talk can be addressed.

A non-targeted approach for extended liquid chromatography-mass spectrometry profiling of free and esterified jasmonates after wounding

Upon wounding or herbivory, plants quickly react by activating various defense mechanisms. A major part of these defenses is thought to be regulated by the jasmonate pathway through the induction of jasmonic acid and its biologically active jasmonoyl-isoleucine conjugate. Yet, these well-known phytohormones are only two among the numerous compounds that compose the jasmonate family. Here, we describe a method based on ultrahigh-pressure liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry that can potentially profile the full range of known free and esterified jasmonates in a non-targeted manner. The developed approach is illustrated by the analysis of Arabidopsis thaliana leaves after mechanical wounding.

Catabolism and deactivation of the lipid-derived hormone jasmonoyl-isoleucine

The oxylipin hormone jasmonate controls myriad processes involved in plant growth, development, and immune function. The discovery of jasmonoyl-l-isoleucine (JA-Ile) as the major bioactive form of the hormone highlights the need to understand biochemical and cell biological processes underlying JA-Ile homeostasis. Among the major metabolic control points governing the accumulation of JA-Ile in plant tissues are the availability of jasmonic acid, the immediate precursor of JA-Ile, and oxidative enzymes involved in catabolism and deactivation of the hormone. Recent studies indicate that JA-Ile turnover is mediated by a ω-oxidation pathway involving members of the CYP94 family of cytochromes P450. This discovery opens new opportunities to genetically manipulate JA-Ile levels for enhanced resistance to environmental stress, and further highlights ω-oxidation as a conserved pathway for catabolism of lipid-derived signals in plants and animals. Functional characterization of the full complement of CYP94 P450s promises to reveal new pathways for jasmonate metabolism and provide insight into the evolution of oxylipin signaling in land plants.

Conjugates of abscisic acid, brassinosteroids, ethylene, gibberellins, and jasmonates

Phytohormones, including auxins, abscisic acid, brassinosteroids, cytokinins, ethylene, gibberellins, and jasmonates, are involved in all aspects of plant growth, and developmental processes as well as environmental responses. However, our understanding of hormonal homeostasis is far from complete. Phytohormone conjugation is considered as a part of the mechanism to control cellular levels of these compounds. Active phytohormones are changed into multiple forms by acylation, esterification or glycosylation, for example. It seems that conjugated compounds could serve as pool of inactive phytohormones that can be converted to active forms by de-conjugation reactions. Some conjugates are thought to be temporary storage forms, from which free active hormones can be released after hydrolysis. It is also believed that conjugation serves functions, such as irreversible inactivation, transport, compartmentalization, and protection against degradation. The nature of abscisic acid, brassinosteroid, ethylene, gibberellin, and jasmonate conjugates is discussed.

12-hydroxyjasmonic acid glucoside is a COI1-JAZ-independent activator of leaf-closing movement in Samanea saman

Jasmonates are ubiquitously occurring plant growth regulators with high structural diversity that mediate numerous developmental processes and stress responses. We have recently identified 12-O-β-D-glucopyranosyljasmonic acid as the bioactive metabolite, leaf-closing factor (LCF), which induced nyctinastic leaf closure of Samanea saman. We demonstrate that leaf closure of isolated Samanea pinnae is induced upon stereospecific recognition of (-)-LCF, but not by its enantiomer, (+)-ent-LCF, and that the nonglucosylated derivative, (-)-12-hydroxyjasmonic acid also displays weak activity. Similarly, rapid and cell type-specific shrinkage of extensor motor cell protoplasts was selectively initiated upon treatment with (-)-LCF, whereas flexor motor cell protoplasts did not respond. In these bioassays related to leaf movement, all other jasmonates tested were inactive, including jasmonic acid (JA) and the potent derivates JA-isoleucine and coronatine. By contrast, (-)-LCF and (-)-12-hydroxyjasmonic acid were completely inactive with respect to activation of typical JA responses, such as induction of JA-responsive genes LOX2 and OPCL1 in Arabidopsis (Arabidopsis thaliana) or accumulation of plant volatile organic compounds in S. saman and lima bean (Phaseolus lunatus), generally considered to be mediated by JA-isoleucine in a COI1-dependent fashion. Furthermore, application of selective inhibitors indicated that leaf movement in S. saman is mediated by rapid potassium fluxes initiated by opening of potassium-permeable channels. Collectively, our data point to the existence of at least two separate JA signaling pathways in S. saman and that 12-O-β-D-glucopyranosyljasmonic acid exerts its leaf-closing activity through a mechanism independent of the COI1-JAZ module.

Identification of a beta-glucosidase hydrolyzing tuberonic acid glucoside in rice (Oryza sativa L.)

Tuberonic acid (TA) and its glucoside (TAG) have been isolated from potato (Solanum tuberosum L.) leaflets and shown to exhibit tuber-inducing properties. These compounds were reported to be biosynthesized from jasmonic acid (JA) by hydroxylation and subsequent glycosylation, and to be contained in various plant species. Here we describe the in vivo hydrolytic activity of TAG in rice. In this study, the TA resulting from TAG was not converted into JA. Tuberonic acid glucoside (TAG)-hydrolyzing beta-glucosidase, designated OsTAGG1, was purified from rice by six purification steps with an approximately 4300-fold purification. The purified enzyme migrated as a single band on native PAGE, but as two bands with molecular masses of 42 and 26 kDa on SDS-PAGE. Results from N-terminal sequencing and peptide mass fingerprinting of both polypeptides suggested that both bands were derived from a single polypeptide, which is a member of the glycosyl hydrolase family 1. In the native enzyme, the K(m) and V(max) values of TAG were 31.7 microM and 0.25 microkatal/mg protein, OsTAGG1 preferentially hydrolyzed TAG and methyl TAG. Here we report that OsTAGG1 is a specific beta-glucosidase hydrolyzing TAG, which releases the physiologically active TA.

Mass spectrometry-based metabolomics oriented by correlation analysis for wound-induced molecule discovery: identification of a novel jasmonate glucoside

INTRODUCTION

Jasmonates are members of the oxylipin family involved in various plant regulatory processes, particularly in the response to biotic and abiotic stresses. They are present in very low amounts in wounded plants, which complicates their detection within complex plant extracts. Therefore, advanced analytical methods are needed for the profiling and characterisation of novel jasmonate derivatives.

OBJECTIVE

To use metabolomics to search for original wound-induced metabolites belonging to the jasmonate family.

METHODOLOGY

Numerous Arabidopsis specimens harvested at various time points after wounding were analysed by ultra-high pressure liquid chromatography coupled to time-of-flight mass spectrometry (UHPLC/TOFMS). A correlation analysis based on kinetic profile similarities with known jasmonates was applied to find wound-induced molecules having a potential role in defence signalling. Their characterisation was performed by tandem mass spectrometry and capillary nuclear magnetic resonance spectroscopy.

RESULTS

The statistical data treatment highlighted several previously reported jasmonates as well as a new glucoside derivative of the jasmonate 3-oxo-2-(2Z-pentenyl) cyclopentane-1-butyric acid (OPC-4). The monitoring of its kinetics in response to wounding revealed a delayed accumulation compared to the profile of OPC-4. This suggests an inactivation or elimination of OPC-4 through the formation of a polar glucosylated metabolite.

CONCLUSION

The metabolomic approach developed has proved useful in the discovery of original jasmonates synthesised in response to plant wounding.

Jasmonates

ARABIDOPSIS IS A SUPERB MODEL FOR THE STUDY OF AN IMPORTANT SUBGROUP OF OXYLIPINS: the jasmonates. Jasmonates control many responses to cell damage and invasion and are essential for reproduction. Jasmonic acid (JA) is a prohormone and is conjugated to hydrophobic amino acids to produce regulatory ligands. The major receptor for active jasmonate ligands is closely related to auxin receptors and, as in auxin signaling, jasmonate signaling requires the destruction of repressor proteins. This chapter uses a frequently asked question (FAQ) approach and concludes with a practical section.

Adventitious rooting is enhanced by methyl jasmonate in tobacco thin cell layers

Adventitious roots (ARs) are induced by auxins. Jasmonic acid (JA) and methyl jasmonate (MeJA) are also plant growth regulators with many effects on development, but their role on ARs needs investigation. To this aim, we analyzed AR formation in tobacco thin cell layers (TCLs) cultured with 0.01-10 microM MeJA, either under root-inductive conditions, i.e., on medium containing 10 microM indole-3-butyric acid (IBA) and 0.1 microM kinetin, or without hormones. The explants were excised from the cultivars Samsun, Xanthii and Petite Havana, and from genotypes with altered AR-forming ability in response to auxin, namely the non-rooting rac mutant and the over-rooting Agrobacterium rhizogenes rolB transgenic line. Results show that NtRNR1 (G1/S) and Ntcyc29 (G2/M) gene activity, cell proliferation and meristemoid formation were stimulated in hormone-cultured TCLs by submicromolar MeJA concentrations. The meristemoids developed either into ARs and xylogenic nodules, or into xylogenic nodules only (rac TCLs). MeJA-induced meristemoid over-production characterized rolB TCLs. No rooting or xylogenesis occurred under hormone-free conditions, independently of MeJA and genotype. Endogenous JA progressively (days 1-4) increased in hormone-cultured TCLs in the absence of MeJA. JA levels were enhanced by 0.1 microM MeJA, on both days 1 and 4. Endogenous IBA was the only auxin detected, both in the free form and as IBA-glucose. Free IBA increased up to day 2, remaining constant thereafter (day 4). Its level was enhanced by 0.1 microM MeJA only on day 1, while IBA conjugation was not affected by MeJA. Taken together, these results show that an interplay between jasmonates and auxins regulates AR formation and xylogenesis in tobacco TCLs.

Kinetics of the accumulation of jasmonic acid and its derivatives in systemic leaves of tobacco (Nicotiana tabacum cv. Xanthi nc) and translocation of deuterium-labeled jasmonic acid from the wounding site to the systemic site

In plants, the mobile signal needed for wound-induced systemic acquired resistance (WSR) has been elusive. The signal compound involved in WSR is supposed to be JA or its derivatives. On the basis of kinetic study of the accumulation of JA or its derivatives, it was discovered that JA, JA-Ile, tuberonic acid (TA, 12-OH epi-JA), and tuberonic acid glucoside (TAG) accumulated in systemic tissues in response to mechanical wounding stress in the tobacco plant (Nicotiana tabacum). Attempts to recover deuterium-labeled JA in systemic leaves after feeding the wounded leaves with deuterium-labeled JA were successfully done. It was also found that the translocated deuterium-labeled JA was metabolized to TA in systemic leaves under feeding of deuterium-labeled JA to the wounding leaves.

Methods for the analysis of oxylipins in plants

Plant oxylipins comprise a highly diverse and complex class of molecules that are derived from lipid oxidation. The initial oxidation of unsaturated fatty acids may either occur by enzymatic or chemical reactions. A large variety of oxylipin classes are generated by an array of alternative reactions further converting hydroperoxy fatty acids. The structural diversity of oxylipins is further increased by their occurrence either as free fatty acid derivatives or as esters in complex lipids. Lipid peroxidation is common to all biological systems, appearing in developmentally regulated processes and as a response to environmental changes. The oxylipins formed may perform various biological roles; some of them have signaling functions. In order to elucidate the roles of oxylipins in a given biological context, comprehensive analytical assays are available for determining the oxylipin profiles of plant tissues. This review summarizes indirect methods to estimate the general peroxidation state of a sample and more sophisticated techniques for the identification, structure determination and quantification of oxylipins.

The tryptophan conjugates of jasmonic and indole-3-acetic acids are endogenous auxin inhibitors

Most conjugates of plant hormones are inactive, and some function to reduce the active hormone pool. This study characterized the activity of the tryptophan (Trp) conjugate of jasmonic acid (JA-Trp) in Arabidopsis (Arabidopsis thaliana). Unexpectedly, JA-Trp caused agravitropic root growth in seedlings, unlike JA or nine other JA-amino acid conjugates. The response was dose dependent from 1 to 100 microm, was independent of the COI1 jasmonate signaling locus, and unlike the jasmonate signal JA-isoleucine, JA-Trp minimally inhibited root growth. The Trp conjugate with indole-3-acetic acid (IAA-Trp) produced a similar response, while Trp alone and conjugates with benzoic and cinnamic acids did not. JA-Trp and IAA-Trp at 25 microm nearly eliminated seedling root inhibition caused by 2 microm IAA. The TIR1 auxin receptor is required for activity because roots of tir1-1 grew only approximately 60% of wild-type length on IAA plus JA-Trp, even though tir1-1 is auxin resistant. However, neither JA-Trp nor IAA-Trp interfered with IAA-dependent interaction between TIR1 and Aux/IAA7 in cell-free assays. Trp conjugates inhibited IAA-stimulated lateral root production and DR5-beta-glucuronidase gene expression. JA-deficient mutants were hypersensitive to IAA and a Trp-overaccumulating mutant was less sensitive, suggesting endogenous conjugates affect auxin sensitivity. Conjugates were present at 5.8 pmol g(-1) fresh weight or less in roots, seedlings, leaves, and flowers, and the values increased approximately 10-fold in roots incubated in 25 microm Trp and IAA or JA at 2 microm. These results show that JA-Trp and IAA-Trp constitute a previously unrecognized mechanism to regulate auxin action.

Molecular mechanisms underlying plant memory in JA-mediated defence responses

Plants must respond to biotic and abiotic challenges to optimize their Darwinian fitness in nature. Many of these challenges occur repeatedly during a plant's lifetime, and their sequence and timing can profoundly influence the fitness outcome of a plant's response. The ability to perceive, store and recall previous stressful events is likely useful for efficient, rapid and cost-effective responses, but we know very little about the mechanisms involved. Using jasmonate-elicited anti-herbivore defence responses as an example, we consider how 'memories' of previous attacks could be created in (1) the biosynthetic processes involved in the generation of the oxylipin bursts elicited by herbivore attacks; (2) the perception of oxylipins and their transduction into cellular events by transcription factors and transcriptional activators; and (3) the role of small RNAs in the formation of long-term stress imprints in plants.

Spatial and temporal dynamics of jasmonate synthesis and accumulation in Arabidopsis in response to wounding

A new metabolite profiling approach combined with an ultrarapid sample preparation procedure was used to study the temporal and spatial dynamics of the wound-induced accumulation of jasmonic acid (JA) and its oxygenated derivatives in Arabidopsis thaliana. In addition to well known jasmonates, including hydroxyjasmonates (HOJAs), jasmonoyl-isoleucine (JA-Ile), and its 12-hydroxy derivative (12-HOJA-Ile), a new wound-induced dicarboxyjasmonate, 12-carboxyjasmonoyl-l-isoleucine (12-HOOCJA-Ile) was discovered. HOJAs and 12-HOOCJA-Ile were enriched in the midveins of wounded leaves, strongly differentiating them from the other jasmonate metabolites studied. The polarity of these oxylipins at physiological pH correlated with their appearance in midveins. When the time points of accumulation of different jasmonates were determined, JA levels were found to increase within 2-5 min of wounding. Remarkably, these changes occurred throughout the plant and were not restricted to wounded leaves. The speed of the stimulus leading to JA accumulation in leaves distal to a wound is at least 3 cm/min. The data give new insights into the spatial and temporal accumulation of jasmonates and have implications in the understanding of long-distance wound signaling in plants.

Methyl jasmonate-elicited herbivore resistance: does MeJA function as a signal without being hydrolyzed to JA?

Treatment with methyl jasmonate (MeJA) elicits herbivore resistance in many plant species and over-expression of JA carboxyl methyltransferase (JMT) constitutively increases JA-induced responses in Arabidopsis. When wild-type (WT) Nicotiana attenuata plants are treated with MeJA, a rapid transient endogenous JA burst is elicited, which in turn increases levels of nicotine and trypsin proteinase inhibitors (TPIs) and resistance to larvae of the specialist herbivore, Manduca sexta. All of these responses are impaired in plants silenced in lipoxygenase 3 expression (asLOX3) but are restored to WT levels by MeJA treatment. Whether these MeJA-induced responses are directly elicited by MeJA or by its cleavage product, JA, is unknown. Using virus-induced gene silencing (VIGS), we silenced MeJA-esterase (NaMJE) expression and found this gene responsible for most of the MeJA-cleaving activity in N. attenuata protein extracts. Silencing NaMJE in asLOX3, but not in WT plants, significantly reduced MeJA-induced nicotine levels and resistance to M. sexta, but not TPI levels. MeJA-induced transcript levels of threonine deaminase (NaTD) and phenylalanine ammonia lyase (NaPAL1) were also decreased in VIGS MJE (asLOX3) plants. Finally the performance of M. sexta larvae that fed on plants treated with JA or MeJA demonstrated that silencing NaMJE inhibited MeJA-induced but not JA-induced resistance in asLOX3 plants. From these results, we conclude that the resistance elicited by MeJA treatment is directly elicited not by MeJA but by its de-methylated product, JA.

Hydroxylated jasmonates are commonly occurring metabolites of jasmonic acid and contribute to a partial switch-off in jasmonate signaling

In potato 12-hydroxyjasmonic acid (12-OH-JA) is a tuber-inducing compound. Here, it is demonstrated that 12-OH-JA, as well as its sulfated and glucosylated derivatives, are constituents of various organs of many plant species. All accumulate differentially and usually to much higher concentrations than jasmonic acid (JA). In wounded tomato leaves, 12-OH-JA and its sulfated, as well as glucosylated, derivative accumulate after JA, and their diminished accumulation in wounded leaves of the JA-deficient mutants spr2 and acx1 and also a JA-deficient 35S::AOCantisense line suggest their JA-dependent formation. To elucidate how signaling properties of JA/JAME (jasmonic acid methyl ester) are affected by hydroxylation and sulfation, germination and root growth were recorded in the presence of the different jasmonates, indicating that 12-OH-JA and 12-hydroxyjasmonic acid sulfate (12-HSO(4)-JA) were not bioactive. Expression analyses for 29 genes showed that expression of wound-inducible genes such as those coding for PROTEINASE INHIBITOR2, POLYPHENOL OXIDASE, THREONINE DEAMINASE or ARGINASE was induced by JAME and less induced or even down-regulated by 12-OH-JA and 12-HSO(4)-JA. Almost all genes coding for enzymes in JA biosynthesis were up-regulated by JAME but down-regulated by 12-OH-JA and 12-HSO(4)-JA. The data suggest that wound-induced metabolic conversion of JA/JAME into 12-OH-JA alters expression pattern of genes including a switch off in JA signaling for a subset of genes.

Jasmonates: an update on biosynthesis, signal transduction and action in plant stress response, growth and development

BACKGROUND

Jasmonates are ubiquitously occurring lipid-derived compounds with signal functions in plant responses to abiotic and biotic stresses, as well as in plant growth and development. Jasmonic acid and its various metabolites are members of the oxylipin family. Many of them alter gene expression positively or negatively in a regulatory network with synergistic and antagonistic effects in relation to other plant hormones such as salicylate, auxin, ethylene and abscisic acid.

SCOPE

This review summarizes biosynthesis and signal transduction of jasmonates with emphasis on new findings in relation to enzymes, their crystal structure, new compounds detected in the oxylipin and jasmonate families, and newly found functions.

CONCLUSIONS

Crystal structure of enzymes in jasmonate biosynthesis, increasing number of jasmonate metabolites and newly identified components of the jasmonate signal-transduction pathway, including specifically acting transcription factors, have led to new insights into jasmonate action, but its receptor(s) is/are still missing, in contrast to all other plant hormones.

Plant peroxisomes as a source of signalling molecules

Peroxisomes are pleiomorphic, metabolically plastic organelles. Their essentially oxidative function led to the adoption of the name 'peroxisome'. The dynamic and diverse nature of peroxisome metabolism has led to the realisation that peroxisomes are an important source of signalling molecules that can function to integrate cellular activity and multicellular development. In plants defence against predators and a hostile environment is of necessity a metabolic and developmental response--a plant has no place to hide. Mutant screens are implicating peroxisomes in disease resistance and signalling in response to light. Characterisation of mutants disrupted in peroxisomal beta-oxidation has led to a growing appreciation of the importance of this pathway in the production of jasmonic acid, conversion of indole butyric acid to indole acetic acid and possibly in the production of other signalling molecules. Likewise the role of peroxisomes in the production and detoxification of reactive oxygen, and possibly reactive nitrogen species and changes in redox status, suggests considerable scope for peroxisomes to contribute to perception and response to a wide range of biotic and abiotic stresses. Whereas the peroxisome is the sole site of beta-oxidation in plants, the production and detoxification of ROS in many cell compartments makes the specific contribution of the peroxisome much more difficult to establish. However progress in identifying peroxisome specific isoforms of enzymes associated with ROS metabolism should allow a more definitive assessment of these contributions in the future.

Jasmonate biosynthesis in Arabidopsis thaliana--enzymes, products, regulation

Among the plant hormones jasmonic acid and related derivatives are known to mediate stress responses and several developmental processes. Biosynthesis, regulation, and metabolism of jasmonic acid in Arabidopsis thaliana are reviewed, including properties of mutants of jasmonate biosynthesis. The individual signalling properties of several jasmonates are described.

Efficient induction of ginsenoside biosynthesis and alteration of ginsenoside heterogeneity in cell cultures of Panax notoginseng by using chemically synthesized 2-hydroxyethyl jasmonate

Chemically synthesized 2-hydroxyethyl jasmonate (HEJA) was for the first time employed to induce the ginsenoside biosynthesis and to manipulate the product heterogeneity in plant cell cultures. The dose response and timing of HEJA elicitation were investigated in cell suspension cultures of Panax notoginseng. The optimal concentration and timing of HEJA addition for both cell growth and ginsenoside accumulation was identified to be 200 microM added on day 4. It was interestingly found that HEJA could stimulate ginsenosides biosynthesis and change their heterogeneity more efficiently than methyl jasmonate (MJA), i.e., the total ginsenoside content and the Rb/Rg ratio increased about 60 and 30% with HEJA elicitation than that by MJA, respectively. The activity of Rb1 biosynthetic enzyme, i.e., UDPG-ginsenoside Rd glucosyltransferase (UGRdGT), was also higher in the former case. A maximal production titer of ginsenoside Rg1, Re, Rb1, and Rd was 47.4+/-4.8, 52.3+/-4.4, 190+/-18, and 12.1+/-2.5 mg/l with HEJA elicitation, which was about 1.3-, 1.3-, 1.7-, and 2.1-fold than that using MJA, respectively. Early signal events in plant defense response, including oxidative burst and jasmonic acid (JA) biosynthesis, were also examined. Levels of H2O2 and NO in medium and L-phenylalanine ammonia lyase activity in cells were not affected by addition of MJA and HEJA. On the other hand, the JA content in cells was increased with external jasmonates elicitation, and it was inhibited with the addition of JA biosynthesis inhibitors. The results suggest that oxidative burst might not be involved in the jasmonates-elicited signal transduction pathway, and MJA and HEJA may induce the ginsenoside biosynthesis via induction of endogenous JA biosynthesis and key enzymes (such as UGRdGT) in the ginsenoside biosynthetic pathway of P. notoginseng cells. The information is useful for hyperproduction of plant-specific heterogeneous products.

Role of beta-oxidation in jasmonate biosynthesis and systemic wound signaling in tomato

Jasmonic acid (JA) is a lipid-derived signal that regulates plant defense responses to biotic stress. Here, we report the characterization of a JA-deficient mutant of tomato (Lycopersicon esculentum) that lacks local and systemic expression of defensive proteinase inhibitors (PIs) in response to wounding. Map-based cloning studies demonstrated that this phenotype results from loss of function of an acyl-CoA oxidase (ACX1A) that catalyzes the first step in the peroxisomal beta-oxidation stage of JA biosynthesis. Recombinant ACX1A exhibited a preference for C12 and C14 straight-chain acyl-CoAs and also was active in the metabolism of C18 cyclopentanoid-CoA precursors of JA. The overall growth, development, and reproduction of acx1 plants were similar to wild-type plants. However, the mutant was compromised in its defense against tobacco hornworm (Manduca sexta) attack. Grafting experiments showed that loss of ACX1A function disrupts the production of the transmissible signal for wound-induced PI expression but does not affect the recognition of this signal in undamaged responding leaves. We conclude that ACX1A is essential for the beta-oxidation stage of JA biosynthesis and that JA or its derivatives is required both for antiherbivore resistance and the production of the systemic wound signal. These findings support a role for peroxisomes in the production of lipid-based signaling molecules that promote systemic defense responses.

Metabolic profiling of Medicago truncatula cell cultures reveals the effects of biotic and abiotic elicitors on metabolism

GC-MS-based metabolite profiling was used to analyse the response of Medicago truncatula cell cultures to elicitation with methyl jasmonate (MeJa), yeast elicitor (YE), or ultraviolet light (UV). Marked changes in the levels of primary metabolites, including several amino acids, organic acids, and carbohydrates, were observed following elicitation with MeJa. A similar, but attenuated response was observed following YE elicitation, whereas little response was observed following UV elicitation. MeJa induced the accumulation of the triterpene beta-amyrin, a precursor to the triterpene saponins, and LC-MS analysis confirmed the accumulation of triterpene saponins in MeJa-elicited samples. In addition, YE induced a slight, but significant accumulation of shikimic acid, an early precursor to the phenylpropanoid pathway, which was also demonstrated to be YE-inducible by LC-MS analyses. Correlation analyses of metabolite relationships revealed perturbation of the glycine, serine, and threonine biosynthetic pathway, and suggested the induction of threonine aldolase activity, an enzyme as yet uncharacterized from plants. Members of the branched chain amino acid pathway accumulated in a concerted fashion, with the strongest correlation being that between leucine and isoleucine (r2=0.941). While UV exposure itself had little effect on primary metabolites, the experimental procedure, as revealed by control treatments, induced changes in several metabolites which were similar to those following MeJa elicitation. Sucrose levels were lower in MJ- and YE-elicited samples compared with control samples, suggesting that a portion of the effects observed on the primary metabolic pool are a consequence of fundamental metabolic repartitioning of carbon resources rather than elicitor-specific induction. In addition, beta-alanine levels were elevated in all elicited samples, which, when viewed in the context of other elicitation responses, suggests the altered metabolism of coenzyme A and its esters, which are essential in secondary metabolism.

Jasmonic acid prevents the accumulation of cyclin B1;1 and CDK-B in synchronized tobacco BY-2 cells

Jasmonic acid (JA) plays a crucial role in plant fertility and defense responses. It exerts an inhibitory effect on plant growth when applied exogenously. This effect seems to be somehow related to a negative regulation of cell cycle progression in the meristematic tissues. In this report, we focus on the molecular events that occur during JA-induced G2 arrest. We demonstrate that JA prevents the accumulation of B-type cyclin-dependent kinases and the expression of cyclin B1;1, which are both essential for the initiation of mitosis. This feature suggests the existence of an early G2 checkpoint that is affected by JA.