Roles of jasmonate signalling in plant inflorescence and flower development

Integrated Proteomics and Metabolomics Analysis Provides Insights into Ganoderic Acid Biosynthesis in Response to Methyl Jasmonate in Ganoderma Lucidum

Ganoderma lucidum is widely recognized as a medicinal basidiomycete. It was previously reported that the plant hormone methyl jasmonate (MeJA) could induce the biosynthesis of ganoderic acids (GAs), which are the main active ingredients of G. lucidum. However, the regulatory mechanism is still unclear. In this study, integrated proteomics and metabolomics were employed on G. lucidum to globally identify differences in proteins and metabolites under MeJA treatment for 15 min (M15) and 24 h (M24). Our study successfully identified 209 differential abundance proteins (DAPs) in M15 and 202 DAPs in M24. We also identified 154 metabolites by GC-MS and 70 metabolites by LC-MS in M24 that are involved in several metabolic pathways. With an in-depth analysis, we found some DAPs and metabolites that are involved in the oxidoreduction process, secondary metabolism, energy metabolism, transcriptional and translational regulation, and protein synthesis. In particular, our results reveal that MeJA treatment leads to metabolic rearrangement that inhibited the normal glucose metabolism, energy supply, and protein synthesis of cells but promoted secondary metabolites, including GAs. In conclusion, our proteomics and metabolomics data further confirm the promoting effect of MeJA on the biosynthesis of GAs in G. lucidum and will provide a valuable resource for further investigation of the molecular mechanisms of MeJA signal response and GA biosynthesis in G. lucidum and other related species.

Metabolic Control within the Jasmonate Biochemical Pathway

Regulation of defense and developmental responses by jasmonates (JAs) has been intensively investigated at genetic and transcriptional levels. Plasticity in the jasmonic acid (JA) metabolic pathway as a means to control signal output has received less attention. Although the amplitude of JA responses generally follows the accumulation dynamics of the active hormone jasmonoyl-isoleucine (JA-Ile), emerging evidence has identified cases where this relationship is distorted and that we discuss in this review. JA-Ile is turned over in Arabidopsis by two inducible, intertwined catabolic pathways; one is oxidative and mediated by cytochrome P450 enzymes of the subfamily 94 (CYP94), and the other proceeds via deconjugation by amidohydrolases. Their genetic inactivation has profound effects on JAs homeostasis, including strong JA-Ile overaccumulation, but this correlates with enhanced defense and tolerance to microbial or insect attacks only in the absence of overinduction of negative signaling regulators. By contrast, the impairment of JA oxidation in the jasmonic acid oxidase 2 (jao2) mutant turns on constitutive defense responses without elevating JA-Ile levels in naive leaves and enhances resistance to subsequent biotic stress. This latter and other recent cases of JA signaling are associated with JA-Ile catabolites accumulation rather than more abundant hormone, reflecting increased metabolic flux through the pathway. Therefore, manipulating upstream and downstream JA-Ile homeostatic steps reveals distinct metabolic nodes controlling defense signaling output.

PYL9 is involved in the regulation of ABA signaling during tomato fruit ripening

Abscisic acid (ABA) regulates fruit ripening, yet little is known about the exact roles of ABA receptors in fruit. In this study, we reveal the role of SlPYL9, a tomato pyrabactin resistance (PYR)/pyrobactin resistance-like (PYL)/regulatory component of ABA receptors (RCAR) protein, as a positive regulator of ABA signaling and fruit ripening. SlPYL9 inhibits protein phosphatase-type 2C (PP2C2/6) in an ABA dose-dependent way, and it interacts physically with SlPP2C2/3/4/5 in an ABA-dependent manner. Expression of SlPYL9 was observed in the seeds, flowers, and fruits. Overexpression and suppression of SlPYL9 induced a variety of phenotypes via altered expression of ABA signaling genes (SlPP2C1/2/9, SlSnRK2.8, SlABF2), thereby affecting expression of ripening-related genes involved in ethylene release and cell wall modification. SlPYL9-OE/RNAi plants showed a typical ABA hyper-/hypo-sensitive phenotype in terms of seed germination, primary root growth, and response to drought. Fruit ripening was significantly accelerated in SlPYL9-OE by 5-7 d as a result of increased endogenous ABA accumulation and advanced release of ethylene compared with the wild-type. In the SlPYL9-RNAi lines, fruit ripening was delayed, mesocarp thickness was enhanced, and petal abscission was delayed compared with the wild-type, resulting in conical/oblong and gourd-shaped fruits. These results suggest that SlPYL9 is involved in ABA signaling, thereby playing a role in the regulation of flower abscission and fruit ripening in tomato.

Comparative gene expression profile analysis of ovules provides insights into Jatropha curcas L. ovule development

Jatropha curcas, an economically important biofuel feedstock with oil-rich seeds, has attracted considerable attention among researchers in recent years. Nevertheless, valuable information on the yield component of this plant, particularly regarding ovule development, remains scarce. In this study, transcriptome profiles of anther and ovule development were established to investigate the ovule development mechanism of J. curcas. In total, 64,325 unigenes with annotation were obtained, and 1723 differentially expressed genes (DEGs) were identified between different stages. The DEG analysis showed the participation of five transcription factor families (bHLH, WRKY, MYB, NAC and ERF), five hormone signaling pathways (auxin, gibberellic acid (GA), cytokinin, brassinosteroids (BR) and jasmonic acid (JA)), five MADS-box genes (AGAMOUS-2, AGAMOUS-1, AGL1, AGL11, and AGL14), SUP and SLK3 in ovule development. The role of GA and JA in ovule development was evident with increases in flower buds during ovule development: GA was increased approximately twofold, and JA was increased approximately sevenfold. In addition, the expression pattern analysis using qRT-PCR revealed that CRABS CLAW and AGAMOUS-2 were also involved in ovule development. The upregulation of BR signaling genes during ovule development might have been regulated by other phytohormone signaling pathways through crosstalk. This study provides a valuable framework for investigating the regulatory networks of ovule development in J. curcas.

A gamma-thionin protein from apple, MdD1, is required for defence against S-RNase-induced inhibition of pollen tube prior to self/non-self recognition

Apple exhibits S-RNase-mediated self-incompatibility. Although the cytotoxic effect of S-RNase inside the self-pollen tube has been studied extensively, the underlying defence mechanism in pollen tube in Rosaceae remains unclear. On exposure to stylar S-RNase, plant defence responses are activated in the pollen tube; however, how these are regulated is currently poorly understood. Here, we show that entry of both self and non-self S-RNase into pollen tubes of apple (Malus domestica) stimulates jasmonic acid (JA) production, in turn inducing the accumulation of MdMYC2 transcripts, a transcription factor in the JA signalling pathway widely considered to be involved in plant defence processes. MdMYC2 acts as a positive regulator in the pollen tube activating expression of MdD1, a gene encoding a defence protein. Importantly, MdD1 was shown to bind to the RNase activity sites of S-RNase leading to inhibition of enzymatic activity. This work provides intriguing insights into an ancient defence mechanism present in apple pollen tubes where MdD1 likely acts as a primary line of defence to inhibit S-RNase cytotoxicity prior to self/non-self recognition.

Fertility of Pedicellate Spikelets in Sorghum Is Controlled by a Jasmonic Acid Regulatory Module

As in other cereal crops, the panicles of sorghum (Sorghum bicolor (L.) Moench) comprise two types of floral spikelets (grass flowers). Only sessile spikelets (SSs) are capable of producing viable grains, whereas pedicellate spikelets (PSs) cease development after initiation and eventually abort. Consequently, grain number per panicle (GNP) is lower than the total number of flowers produced per panicle. The mechanism underlying this differential fertility is not well understood. To investigate this issue, we isolated a series of ethyl methane sulfonate (EMS)-induced multiseeded (msd) mutants that result in full spikelet fertility, effectively doubling GNP. Previously, we showed that MSD1 is a TCP (Teosinte branched/Cycloidea/PCF) transcription factor that regulates jasmonic acid (JA) biosynthesis, and ultimately floral sex organ development. Here, we show that MSD2 encodes a lipoxygenase (LOX) that catalyzes the first committed step of JA biosynthesis. Further, we demonstrate that MSD1 binds to the promoters of MSD2 and other JA pathway genes. Together, these results show that a JA-induced module regulates sorghum panicle development and spikelet fertility. The findings advance our understanding of inflorescence development and could lead to new strategies for increasing GNP and grain yield in sorghum and other cereal crops.

Arabidopsis Flowers Unlocked the Mechanism of Jasmonate Signaling

The Arabidopsis male-sterile phenotype has been a wonderful model for jasmonate action in plants. It has allowed us to identify transcription factors that control gene expression during stamen and pollen maturation and provided for the discovery of the JAZ repressor proteins and the mechanism of jasmonate signaling. More recently, it has revealed intriguing details of the spatial localization of jasmonate synthesis and perception in stamen tissues. The extensive and thoughtful application of protein–protein interaction assays to identify JAZ-interacting partners has led to a much richer appreciation of the mechanisms by which jasmonate integrates with the actions of other hormones to regulate plant growth and physiological responses. This integration is strikingly evident in stamen and pollen development in Arabidopsis, which requires the actions of many hormones. Just as importantly, it is now evident that jasmonate has very different actions during flower development and reproduction in other plant species. This integration and diversity of action indicates that many exciting discoveries remain to be made in this area of jasmonate hormone signaling and response.

Ecology of Plastic Flowers

Plant phenotypic plasticity in response to herbivore attack includes changes in flower traits. Such herbivore-induced changes in flower traits have consequences for interactions with flower visitors. We synthesize here current knowledge on the specificity of herbivore-induced changes in flower traits, the underlying molecular mechanisms, and the ecological consequences for flower-associated communities. Herbivore-induced changes in flower traits seem to be largely herbivore species-specific. The extensive plasticity observed in flowers influences a highly connected web of interactions within the flower-associated community. We argue that the adaptive value of herbivore-induced plant responses and flower plasticity can be fully understood only from a community perspective rather than from pairwise interactions.

JAZ proteins modulate seed germination through interaction with ABI5 in bread wheat and Arabidopsis

Appropriate regulation of crop seed germination is of significance for agriculture production. In this study, we show that TaJAZ1, most closely related to Arabidopsis JAZ3, negatively modulates abscisic acid (ABA)-inhibited seed germination and ABA-responsive gene expression in bread wheat. Biochemical interaction assays demonstrate that the C-terminal part containing the Jas domain of TaJAZ1 physically interacts with TaABI5. Similarly, Arabidopsis jasmonate-ZIM domain (JAZ) proteins also negatively modulate ABA responses. Further we find that a subset of JAZ proteins could interact with ABI5 using the luciferase complementation imaging assays. Choosing JAZ3 as a representative, we demonstrate that JAZ3 interacts with ABI5 in vivo and represses the transcriptional activation activity of ABI5. ABA application could abolish the enrichment of JAZ proteins in the ABA-responsive gene promoter. Furthermore, we find that ABA application could induce the expression of jasmonate (JA) biosynthetic genes and then increase the JA concentrations partially dependent on the function of ABI5, consequently leading to the degradation of JAZ proteins. This study sheds new light on the crosstalk between JA and ABA in modulating seed germination in bread wheat and Arabidopsis.

Floral plasticity: Herbivore-species-specific-induced changes in flower traits with contrasting effects on pollinator visitation

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant-pollinator interactions. Current knowledge on the full extent of herbivore-induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore-induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species-specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant-mediated interactions with mutualists.

Mutation of ACX1, a Jasmonic Acid Biosynthetic Enzyme, Leads to Petal Degeneration in Chinese Cabbage (Brassica campestris ssp. pekinensis)

Petal color, size, and morphology play important roles in protecting other floral organs, attracting pollinators, and facilitating sexual reproduction in plants. In a previous study, we obtained a petal degeneration mutant (pdm) from the ‘FT’ doubled haploid line of Chinese cabbage and found that the candidate gene for pdm, Bra040093, encodes the enzyme acyl-CoA oxidase1. In this study, we sought to examine the gene networks regulating petal development in pdm plants. We show that the mRNA and protein expression of Bra040093, which is involved in the jasmonic acid (JA) biosynthetic pathway, were significantly lower in the petals of pdm plants than in those of ‘FT’ plants. Similarly, the JA and methyl jasmonate (MeJA) contents of petals were significantly lower in pdm plants than in ‘FT’ plants and we found that exogenous application of these hormones to the inflorescences of pdm plants restored the ‘FT’ phenotype. Comparative analyses of the transcriptomes of ‘FT’, pdm and pdm + JA (pJA) plants revealed 10,160 differentially expressed genes (DEGs) with consistent expression tendencies in ‘FT’ vs. pdm and pJA vs. pdm comparisons. Among these DEGs, we identified 69 DEGs related to floral organ development, 11 of which are involved in petal development regulated by JA. On the basis of qRT-PCR verification, we propose regulatory pathways whereby JA may mediate petal development in the pdm mutant. We demonstrate that mutation of Bra040093 in pdm plants leads to reduced JA levels and that this in turn promotes changes in the expression of genes that are expressed in response to JA, ultimately resulting in petal degeneration. These findings thus indicate that JA is associated with petal development in Chinese cabbage. These results enhance our knowledge on the molecular mechanisms underlying petal development and lay the foundations for further elucidation of the mechanisms associated with floral organ development in Chinese cabbage.

Genome-Wide Identification and Characterization of the JAZ Gene Family in Rubber Tree (Hevea brasiliensis)

Jasmonate signaling plays a vital role in the regulation of secondary laticifer differentiation and natural rubber biosynthesis in Hevea brasiliensis. Jasmonate ZIM-domain (JAZ) proteins are the master regulators of jasmonate signaling. Although several JAZs have been reported in the laticifer cells of H. brasiliensis, the genome-wide screening of HbJAZ members has not yet been explored. In the present study, 18 HbJAZs were identified based on the recent H. brasiliensis genome. Phylogenetic construction revealed that the HbJAZs were clustered into five subgroups and that members within the same subgroup shared highly conserved gene structures and protein motifs. Cis-element analysis of HbJAZ promoters suggested the presence of hormone, stress and development-related cis-elements. HbJAZ1.0, HbJAZ2.0, and HbJAZ5.0 interacted with CORONATINE INSENSITIVE1 (COI1) in the presence of coronatine (COR, a JA mimic). HbJAZ1.0, HbJAZ2.0, HbJAZ5.0, and HbJAZ12.0 could also interact with each other. Of the 18 HbJAZs, transcripts of 15 HbJAZs were present in the vascular cambium region except for that of HbJAZ7.0, HbJAZ8.0d, and HbJAZ13.0. Fourteen of the 15 HbJAZs were significantly up-regulated upon COR treatment. The transcripts of three genes that were absent from vascular cambium region were also absent from the latex. Among the 15 HbJAZs in the latex, the expression patterns of 13 HbJAZs were different between the tapping and ethrel treatments. Eight of the 14 COR-up-regulated HbJAZs in the vascular cambium region were also activated by tapping in latex. Of the eight tapping-activated HbJAZs, 5 HbJAZs were repressed by ethrel application. Based on the computational analyses and gene expression patterns described in this study, the HbJAZ5.0 and HbJAZ10.0b may be associated with laticifer differentiation while the HbJAZ8.0b is a negative regulator for natural rubber biosynthesis in H. brasiliensis.

Origination and selection of ABCDE and AGL6 subfamily MADS-box genes in gymnosperms and angiosperms

BACKGROUND

The morphological diversity of flower organs is closely related to functional divergence within the MADS-box gene family. Bryophytes and seedless vascular plants have MADS-box genes but do not have ABCDE or AGAMOUS-LIKE6 (AGL6) genes. ABCDE and AGL6 genes belong to the subgroup of MADS-box genes. Previous works suggest that the B gene was the first ABCDE and AGL6 genes to emerge in plant but there are no mentions about the probable origin time of ACDE and AGL6 genes. Here, we collected ABCDE and AGL6 gene 381 protein sequences and 361 coding sequences from gymnosperms and angiosperms and reconstructed a complete Bayesian phylogeny of these genes. In this study, we want to clarify the probable origin time of ABCDE and AGL6 genes is a great help for understanding the role of the formation of the flower, which can decipher the forming order of MADS-box genes in the future.

RESULTS

These genes appeared to have been under purifying selection and their evolutionary rates are not significantly different from each other. Using the Bayesian evolutionary analysis by sampling trees (BEAST) tool, we estimated that: the mutation rate of the ABCDE and AGL6 genes was 2.617 × 10-3 substitutions/site/million years, and that B genes originated 339 million years ago (MYA), CD genes originated 322 MYA, and A genes shared the most recent common ancestor with E/AGL6 296 MYA, respectively.

CONCLUSIONS

The phylogeny of ABCDE and AGL6 genes subfamilies differed. The APETALA1 (AP1 or A gene) subfamily clustered into one group. The APETALA3/PISTILLATA (AP3/PI or B genes) subfamily clustered into two groups: the AP3 and PI clades. The AGAMOUS/SHATTERPROOF/SEEDSTICK (AG/SHP/STK or CD genes) subfamily clustered into a single group. The SEPALLATA (SEP or E gene) subfamily in angiosperms clustered into two groups: the SEP1/2/4 and SEP3 clades. The AGL6 subfamily clustered into a single group. Moreover, ABCDE and AGL6 genes appeared in the following order: AP3/PI → AG/SHP/STK → AGL6/SEP/AP1. In this study, we collected candidate sequences from gymnosperms and angiosperms. This study highlights important events in the evolutionary history of the ABCDE and AGL6 gene families and clarifies their evolutionary path.

Rapid plant evolution driven by the interaction of pollination and herbivory

Pollination and herbivory are both key drivers of plant diversity but are traditionally studied in isolation from each other. We investigated real-time evolutionary changes in plant traits over six generations by using fast-cycling Brassica rapa plants and manipulating the presence and absence of bumble bee pollinators and leaf herbivores. We found that plants under selection by bee pollinators evolved increased floral attractiveness, but this process was compromised by the presence of herbivores. Plants under selection from both bee pollinators and herbivores evolved higher degrees of self-compatibility and autonomous selfing, as well as reduced spatial separation of sexual organs (herkogamy). Overall, the evolution of most traits was affected by the interaction of bee pollination and herbivory, emphasizing the importance of the cross-talk between both types of interactions for plant evolution.

Tomato stigma exsertion induced by high temperature is associated with the jasmonate signalling pathway

High temperature (HT) is becoming an increasingly serious factor in limiting crop production with global climate change. During hot seasons, owing to prevailing HT, cultivated tomatoes are prone to exhibiting stigma exsertion, which hampers pollination and causes fruit set failure. However, the underlying regulatory mechanisms of the HT-induced stigma exsertion remain largely unknown. Here, we demonstrate that stigma exsertion induced by HT in cultivated tomato is caused by more seriously shortened stamens than pistils, which is different from the stigma exsertion observed in wild tomato species. Under the HT condition, the different responses of pectin, sugar, expansin, and cyclin cause cell wall remodelling and differentially localized cell division and selective cell enlargement, which further determine the lengths of stamens and pistils. In addition, auxin and jasmonate (JA) are implicated in regulating cell division and cell expansion in stamens and pistils, and exogenous JA instead of auxin treatment can effectively rescue tomato stigma exsertion through regulating the JA/COI1 signalling pathway. Our findings provide a better understanding of stigma exsertions under the HT condition in tomato and uncover a new function of JA in improving plant abiotic stress tolerance.

Crop Pollen Development under Drought: From the Phenotype to the Mechanism

Drought stress induced pollen sterility is a harmful factor that reduces crop yield worldwide. During the reproductive process, the meiotic stage and the mitotic stage in anthers are both highly vulnerable to water deficiency. Drought at these stages causes pollen sterility by affecting the nature and structure of the anthers, including the degeneration of some meiocytes, disorientated microspores, an expanded middle layer and abnormal vacuolizated tapeta. The homeostasis of the internal environment is imbalanced in drought-treated anthers, involving the decreases of gibberellic acid (GA) and auxin, and the increases of abscisic acid (ABA), jasmonic acid (JA) and reactive oxygen species (ROS). Changes in carbohydrate availability, metabolism and distribution may be involved in the effects of drought stress at the reproductive stages. Here, we summarize the molecular regulatory mechanism of crop pollen development under drought stresses. The meiosis-related genes, sugar transporter genes, GA and ABA pathway genes and ROS-related genes may be altered in their expression in anthers to repair the drought-induced injures. It could also be that some drought-responsive genes, mainly expressed in the anther, regulate the expression of anther-related genes to improve both drought tolerance and anther development. A deepened understanding of the molecular regulatory mechanism of pollen development under stress will be beneficial for breeding drought-tolerant crops with high and stable yield under drought conditions.

The OsJAZ1 degron modulates jasmonate signaling sensitivity during rice development

Jasmonates (JAs) are crucial to the coordination of plant stress responses and development. JA signaling depends on JASMONATE-ZIM DOMAIN (JAZ) proteins that are destroyed by the SCF^COI1-mediated 26S proteasome when the JAZ co-receptor COI1 binds active JA or the JA-mimicking phytotoxin coronatine (COR). JAZ degradation releases JAZ-interacting transcription factors that can execute stress and growth responses. The JAZ proteins typically contain Jas motifs that undergo conformational changes during JA signal transduction and that are important for the JAZ-COI1 interaction and JAZ protein degradation. However, how alterations in the Jas motif and, in particular, the JAZ degron part of the motif, influence protein stability and plant development have not been well explored. To clarify this issue, we performed bioassays and genetic experiments to uncover the function of the OsJAZ1 degron in rice JA signaling. We found that substitution or deletion of core segments of the degron altered the OsJAZ1-OsCOI1b interaction in a COR-dependent manner. We show that these altered interactions function as a regulator for JA signaling during flower and root development. Our study therefore expands our understanding of how the JAZ degron functions, and provides the means to change the sensitivity and specificity of JA signaling in rice.

Identification and Analysis of a CPYC-Type Glutaredoxin Associated with Stress Response in Rubber Trees

Glutaredoxins (GRXs) are a class of small oxidoreductases which modulate various biological processes in plants. Here, we isolated a GRX gene from the rubber tree (Hevea brasiliensis Müll. Arg.), named as HbSRGRX1, which encoded 107 amino acid residues with a CPYC active site. Phylogenetic analysis displayed that HbSRGRX1 was more correlated with GRXs from Manihot esculenta Crantz. and Ricinus communis L. HbSRGRX1 was localized in the nuclei of tobacco cells, and its transcripts were preferentially expressed in male flowers and in the high-yield variety Reyan 7-33-97 with strong resistance against cold. The expression levels of HbSRGRX1 significantly decreased in tapping panel dryness (TPD) trees. Furthermore, HbSRGRX1 was regulated by wounding, hydrogen peroxide (H2O2), and multiple hormones. Altogether, these results suggest important roles of HbSRGRX1 in plant development and defense response to TPD and multiple stresses.

The involvement of a herbivore-induced acyl-CoA oxidase gene, CsACX1, in the synthesis of jasmonic acid and its expression in flower opening in tea plant (Camellia sinensis)

The biosynthesis of jasmonic acid (JA) in plant peroxisomes requires the action of acyl-CoA oxidase (ACX; EC 1.3.3.6). Multiple isoforms of ACXs have been identified in various annual herbaceous plants, but the genes encoding these enzymes in perennial woody plants are yet to be fully investigated. In this study, an ACX gene named CsACX1 (GeneBank accession: KX650077.1) was isolated from tea plant (Camellia sinensis L.). CsACX1 was predicted to consist of 664 amino acid residues. Transcriptional analysis revealed that CsACX1 can be induced by mechanical wounding, JA application, and infestation by the tea geometrid Ectropis obliqua Prout and the tea green leafhopper Empoasca (Matsumurasca) onukii Matsuda. To further elucidate the function of CsACX1, it was heterologously expressed in a bacterial system and characterized. Recombinant CsACX1 showed preference for C₁₂ ∼ C₁₆-CoA substrates. The constitutive expression of CsACX1 can rescue wound-related JA biosynthesis in Arabidopsis mutant acx1. CsACX1 was expressed in different organs, predominantly in flowers. Notably, CsACX1 transcripts were detected up-regulated during flower opening, and the JA levels were correlated with CsACX1 expression. All these results enrich our knowledge of the regulatory pathway involved in the JA biosynthesis in tea, and helps further understand the defense mechanism of tea plant against insects.

Chemical regulators of plant hormones and their applications in basic research and agriculture*

Plant hormones are small molecules that play versatile roles in regulating plant growth, development, and responses to the environment. Classic methodologies, including genetics, analytic chemistry, biochemistry, and molecular biology, have contributed to the progress in plant hormone studies. In addition, chemical regulators of plant hormone functions have been important in such studies. Today, synthetic chemicals, including plant growth regulators, are used to study and manipulate biological systems, collectively referred to as chemical biology. Here, we summarize the available chemical regulators and their contributions to plant hormone studies. We also pose questions that remain to be addressed in plant hormone studies and that might be solved with the help of chemical regulators.

Transcriptome analysis of Jatropha curcas L. flower buds responded to the paclobutrazol treatment

Jatropha seeds can be used to produce high-quality biodiesel due to their high oil content. However, Jatropha produces low numbers of female flowers, which limits seed yield. Paclobutrazol (PCB), a plant growth retardant, can increase number of Jatropha female flowers and seed yield. However, the underlying mechanisms of flower development after PCB treatment are not well understood. To identify the critical genes associated with flower development, the transcriptome of flower buds following PCB treatment was analyzed. Scanning Electron Microscope (SEM) analysis revealed that the flower developmental stage between PCB-treated and control flower buds was similar. Based on the presence of sex organs, flower buds at 0, 4, and 24 h after treatment were chosen for global transcriptome analysis. In total, 100,597 unigenes were obtained, 174 of which were deemed as interesting based on their response to PCB treatment. Our analysis showed that the JcCKX5 and JcTSO1 genes were up-regulated at 4 h, suggesting roles in promoting organogenic capacity and ovule primordia formation in Jatropha. The JcNPGR2, JcMGP2-3, and JcHUA1 genes were down-regulated indicating that they may contribute to increased number of female flowers and amount of seed yield. Expression of cell division and cellulose biosynthesis-related genes, including JcGASA3, JcCycB3;1, JcCycP2;1, JcKNAT7, and JcCSLG3 was decreased, which might have caused the compacted inflorescences. This study represents the first report combining SEM-based morphology, qRT-PCR and transcriptome analysis of PCB-treated Jatropha flower buds at different stages of flower development.

Comparative transcriptomic analysis identifies genes responsible for fruit count and oil yield in the oil tea plant Camellia chekiangoleosa

Fruit yield is an important trait for horticultural crops. However, the limited fruit yield of Camellia chekiangoleosa, a novel promising oil tree, restricts the production of oil. The breeding improvement is little due to its long generation time and lack of available genomic sequence. We identified distinct fruit count phenotypes, high-yield (HY) and low-yield (LY). To understand the underlying genetic basis, we focused on global gene discovery and expression levels in floral buds, which affect fruit count. A total of 140,299 de novo assembled unigenes were obtained using RNA-seq technology, and more genes were expressed in HY than in LY. 2395 differentially expressed genes (DEGs) were identified and enriched in membrane, energy metabolism, secondary metabolism, fatty acid biosynthesis and metabolism, and 18 other metabolic pathways. Of the DEGs, twelve identified transcription factors, including AP2, mostly involve in inflorescence and flower development and in hormone networks. Key DEGs in fatty acid biosynthesis (Fab) FabB, FabF, FabZ, and AccD were highly expressed in floral buds and associated with high oil yield in fruits. We hypothesized that a potential link exists between fruit count and its oil yield. These findings help to elucidate the molecular cues affecting fruit count and oil yield.

Jasmonate signaling makes flowers attractive to pollinators and repellant to florivores in nature

Flowers are required for the Darwinian fitness of flowering plants, but flowers' advertisements for pollination services can attract florivores. Previous glasshouse work with Nicotiana attenuata revealed the role of jasmonate (JA) signaling in flower development, advertisement and defense. However, whether JA signaling mediates flowers' filtering of floral visitors in nature remained unknown. This field study revealed that silencing JA signaling resulted in flowers that produce less nectar and benzyl acetone, two pollinator-attractive traits. Meanwhile, flowers of defenseless plants were highly attacked by a suite of native herbivores, and damage to buds in native plants correlated negatively with their JA-Ile levels.

MSD1 regulates pedicellate spikelet fertility in sorghum through the jasmonic acid pathway

Grain number per panicle (GNP) is a major determinant of grain yield in cereals. However, the mechanisms that regulate GNP remain unclear. To address this issue, we isolate a series of sorghum [Sorghum bicolor (L.) Moench] multiseeded (msd) mutants that can double GNP by increasing panicle size and altering floral development so that all spikelets are fertile and set grain. Through bulk segregant analysis by next-generation sequencing, we identify MSD1 as a TCP (Teosinte branched/Cycloidea/PCF) transcription factor. Whole-genome expression profiling reveals that jasmonic acid (JA) biosynthetic enzymes are transiently activated in pedicellate spikelets. Young msd1 panicles have 50% less JA than wild-type (WT) panicles, and application of exogenous JA can rescue the msd1 phenotype. Our results reveal a new mechanism for increasing GNP, with the potential to boost grain yield, and provide insight into the regulation of plant inflorescence architecture and development.

Inflorescence architecture affects crop grain yield. Here, the authors deploy whole-genome sequencing-based bulk segregant analysis to identify the causal gene of a sorghum multi-seeded (msd) mutant and suggest MSD1 regulating the fertility of the pedicellate spikelets through jasmonic acid pathway.

Detection of Epistasis for Flowering Time Using Bayesian Multilocus Estimation in a Barley MAGIC Population

Gene-by-gene interactions, also known as epistasis, regulate many complex traits in different species. With the availability of low-cost genotyping it is now possible to study epistasis on a genome-wide scale. However, identifying genome-wide epistasis is a high-dimensional multiple regression problem and needs the application of dimensionality reduction techniques. Flowering Time (FT) in crops is a complex trait that is known to be influenced by many interacting genes and pathways in various crops. In this study, we successfully apply Sure Independence Screening (SIS) for dimensionality reduction to identify two-way and three-way epistasis for the FT trait in a Multiparent Advanced Generation Inter-Cross (MAGIC) barley population using the Bayesian multilocus model. The MAGIC barley population was generated from intercrossing among eight parental lines and thus, offered greater genetic diversity to detect higher-order epistatic interactions. Our results suggest that SIS is an efficient dimensionality reduction approach to detect high-order interactions in a Bayesian multilocus model. We also observe that many of our findings (genomic regions with main or higher-order epistatic effects) overlap with known candidate genes that have been already reported in barley and closely related species for the FT trait.

E3 Ubiquitin Ligases: Ubiquitous Actors in Plant Development and Abiotic Stress Responses

Understanding the precise regulatory mechanisms of plant development and stress responses at the post-translational level is currently a topic of intensive research. Protein ubiquitination, including the sequential performances of ubiquitin-activating (E1), ubiquitin-conjugating (E2) and ubiquitin ligase (E3) enzymes, is a refined post-translational modification ubiquitous in all eukaryotes. Plants are an integral part of our ecosystem and, as sessile organisms, the ability to perceive internal and external signals and to adapt well to various environmental challenges is crucial for their survival. Over recent decades, extensive studies have demonstrated that protein ubiquitination plays key roles in multiple plant developmental stages (e.g. seed dormancy and germination, root growth, flowering time control, self-incompatibility and chloroplast development) and several abiotic stress responses (e.g. drought and high salinity), by regulating the abundance, activities or subcellular localizations of a variety of regulatory polypeptides and enzymes. Importantly, diverse E3 ligases are involved in these regulatory pathways by mediating phytohormone and light signaling or other pathways. In this updated review, we mainly summarize recent advances in our understanding of the regulatory roles of protein ubiquitination in plant development and plant-environment interactions, and primarily focus on different types of E3 ligases because they play critical roles in determining substrate specificity.

Flower-specific jasmonate signaling regulates constitutive floral defenses in wild tobacco

Optimal defense (OD) theory predicts that within a plant, tissues are defended in proportion to their fitness value and risk of predation. The fitness value of leaves varies greatly and leaves are protected by jasmonate (JA)-inducible defenses. Flowers are vehicles of Darwinian fitness in flowering plants and are attacked by herbivores and pathogens, but how they are defended is rarely investigated. We used Nicotiana attenuata, an ecological model plant with well-characterized herbivore interactions to characterize defense responses in flowers. Early floral stages constitutively accumulate greater amounts of two well-characterized defensive compounds, the volatile (E)-α-bergamotene and trypsin proteinase inhibitors (TPIs), which are also found in herbivore-induced leaves. Plants rendered deficient in JA biosynthesis or perception by RNA interference had significantly attenuated floral accumulations of defensive compounds known to be regulated by JA in leaves. By RNA-seq, we found a JAZ gene, NaJAZi, specifically expressed in early-stage floral tissues. Gene silencing revealed that NaJAZi functions as a flower-specific jasmonate repressor that regulates JAs, (E)-α-bergamotene, TPIs, and a defensin. Flowers silenced in NaJAZi are more resistant to tobacco budworm attack, a florivore. When the defensin was ectopically expressed in leaves, performance of Manduca sexta larvae, a folivore, decreased. NaJAZi physically interacts with a newly identified NINJA-like protein, but not the canonical NINJA. This NINJA-like recruits the corepressor TOPLESS that contributes to the suppressive function of NaJAZi on floral defenses. This study uncovers the defensive function of JA signaling in flowers, which includes components that tailor JA signaling to provide flower-specific defense.

Jasmonic acid deficiency leads to scattered floret opening time in cytoplasmic male sterile rice Zhenshan 97A

Cytoplasmic male sterile (CMS) rice has been widely used for hybrid rice seed production in China. However, CMS rice suffers from undesirable flowering habits including scattered floret opening time (FOT), which causes different FOTs among parental rice plants and greatly reduces hybrid rice seed production. Little is known about the mechanism of scattered FOT in CMS rice. Our results demonstrate that scattered FOT in CMS rice Zhenshan 97A (ZS97A) resulted from the lack of a driving force to open florets, which was directly caused by retarded lodicule expansion. Our results indicate that retarded lodicule expansion in ZS97A was caused by reduced water accumulation due to retarded accumulation of osmotic regulation substances (ORSs). Further, the retardation in accumulation of ORSs and water were caused by jasmonic acid (JA) deficiency, resulting from down-regulation of OsAOC expression. Applying JA restored scattered FOT in ZS97A by promoting ORS and water accumulation, and inducing the expansion of the lodicules. Taken together, JA deficiency inhibited lodicule expansion by retarding the accumulation of ORSs and water, leading to scattered FOT in CMS rice ZS97A.

Genome-wide identification and characterization of JAZ gene family in upland cotton (Gossypium hirsutum)

Plant JAZ (Jasmonate ZIM-domain) proteins play versatile roles in multiple aspects of plant development and defense. However, little is known about the JAZ family in allotetraploid upland cotton (Gossypium hirsutum) so far. In this study, 30 non-redundant JAZ genes were identified in upland cotton through genome-wide screening. Phylogenetic analysis revealed that the 30 proteins in cotton JAZ family are further divided into five groups (I - V), and members in the same group share highly conserved motif structures. Subcellular localization assay demonstrated that GhJAZ proteins are localized in the cell nucleus. Quantitative RT-PCR analysis indicated that GhJAZs display different expression patterns in cotton tissues, and most of them could be induced by Jasmonic (JA). Furthermore, some GhJAZ genes are preferentially expressed in cotton ovules and fibers, and showed differential expression in ovules of wild type cotton and fiberless mutant (fl) during fiber initiation. GhJAZ proteins could interact with each other to form homodimer or heterodimer, and they also interacted with some JA signaling regulators and the proteins involved in cotton fiber initiation. Collectively, our data suggested that some GhJAZ proteins may play important roles in cotton fiber initiation and development by regulating JA signaling as well as some fiber-related proteins.

Mapping and application of the twin-grain1 gene in rice

The map-based cloning and application of a flower organ number gene twin - grain1 provide great potential for improving seed production in hybrid rice. A new germplasm for high-yield rice breeding, the twin-grain1 (tg1) mutant with more than one grain in a glume, was obtained from the Zhejing 22 rice variety via physical mutagenesis. The mapping results showed that TG1 is allelic to FLORAL ORGAN NUMBER2 (FON2)/FLORAL ORGAN NUMBER4 (FON4), a flower organ number gene located at 88.7 cM on chromosome 11. The novel tg1 gene allele was introgressed into the cytoplasmic male sterility (CMS) line Zhejing 22A, giving rise to a new CMS line Zhejing 22-tg1A. The Zhejing 22-tg1A line showed enhanced glume opening and stigma exsertion, which increased the outcrossing rate in hybrid rice. A small-scale hybrid rice seed production test demonstrated that the grain yield of the Zhejing 22-tg1A/Zhejinghui 5 line was significantly increased compared to that of the Zhejing 22A/Zhejinghui 5 line. The plot yield evaluation of the F₁ hybrid lines showed a higher yield for the Zhejing 22-tg1A/Zhejinghui 5 line than that of the Zhejing 22A/Zhejinghui 5 line. The results implied great potentials for the tg1 gene in hybrid rice breeding.

Evolution of jasmonate biosynthesis and signaling mechanisms

Jasmonates are phytohormones that modulate a wide spectrum of plant physiological processes, especially defense against herbivores and necrotrophs. The molecular mechanisms of jasmonate biosynthesis and signaling have been well characterized in model plants. In this review, we provide an in-depth analysis and overview of the origin and evolution of the jasmonate biosynthesis and signaling pathways. Furthermore, we discuss the striking parallels between jasmonate and auxin signaling mechanisms, which reveals a common ancestry of these signaling mechanisms. Finally, we highlight the importance of studying jasmonate biosynthesis and signaling in lower plants.

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.

Jasmonate regulates leaf senescence and tolerance to cold stress: crosstalk with other phytohormones

Plants are challenged with numerous abiotic stresses, such as drought, cold, heat, and salt stress. These environmental stresses are major causes of crop failure and reduced yields worldwide. Phytohormones play essential roles in regulating various plant physiological processes and alleviating stressful perturbations. Jasmonate (JA), a group of oxylipin compounds ubiquitous in the plant kingdom, acts as a crucial signal to modulate multiple plant processes. Recent studies have shown evidence supporting the involvement of JA in leaf senescence and tolerance to cold stress. Concentrations of JA are much higher in senescent leaves compared with those in non-senescent ones. Treatment with exogenous JA induces leaf senescence and expression of senescence-associated genes. In response to cold stress, exogenous application of JA enhances Arabidopsis freezing tolerance with or without cold acclimation. Consistently, biosynthesis of endogenous JA is activated in response to cold exposure. JA positively regulates the CBF (C-REPEAT BINDING FACTOR) transcriptional pathway to up-regulate downstream cold-responsive genes and ultimately improve cold tolerance. JA interacts with other hormone signaling pathways (such as auxin, ethylene, and gibberellin) to regulate leaf senescence and tolerance to cold stress. In this review, we summarize recent studies that have provided insights into JA-mediated leaf senescence and cold-stress tolerance.

Transcriptional analysis of mating and pre-infection stages of the anther smut, Microbotryum lychnidis-dioicae

Microbotryum lychnidis-dioicae is an obligate biotrophic parasite of the wildflower species Silene latifolia. This dikaryotic fungus, commonly known as an anther smut, requires that haploid, yeast-like sporidia of opposite mating types fuse and differentiate into dikaryotic hyphae that penetrate host tissue as part of the fungal life cycle. Mating occurs under conditions of cool temperatures and limited nutrients. Further development requires host cues or chemical mimics, including a variety of lipids, e.g. phytols. To identify global changes in transcription associated with developmental shifts, RNA-Seq was conducted at several in vitro stages of fungal propagation, i.e. haploid cells grown independently on rich and nutrient-limited media, mated cells on nutrient-limited media as well as a time course of such mated cells exposed to phytol. Comparison of haploid cells grown under rich and nutrient-limited conditions identified classes of genes probably associated with general nutrient availability, including components of the RNAi machinery. Some gene enrichment patterns comparing the nutrient-limited and mated transcriptomes suggested gene expression changes associated with the mating programme (e.g. homeodomain binding proteins, secreted proteins, proteins unique to M. lychnidis-dioicae¸ multicopper oxidases and RhoGEFs). Analysis for phytol treatment compared with mated cells alone allowed identification of genes likely to be involved in the dikaryotic switch (e.g. oligopeptide transporters). Gene categories of particular note in all three conditions included those in the major facilitator superfamily, proteins containing PFAM domains of the secretory lipase family as well as proteins predicted to be secreted, many of which have the hallmarks of fungal effectors with potential roles in pathogenicity.

Interactions between FLORAL ORGAN NUMBER4 and floral homeotic genes in regulating rice flower development

The floral meristem (FM) is self-maintaining at the early stages of flower development, but it is terminated when a fixed number of floral organs are produced. The FLORAL ORGAN NUMBER4 (FON4; also known as FON2) gene, an ortholog of Arabidopsis CLAVATA3 (CLV3), is required for regulating FM size and determinacy in rice. However, its interactions with floral homeotic genes remain unknown. Here, we report the genetic interactions between FON4 and floral homeotic genes OsMADS15 (an A-class gene), OsMADS16 (also called SUPERWOMAN1, SPW1, a B-class gene), OsMADS3 and OsMADS58 (C-class genes), OsMADS13 (a D-class gene), and OsMADS1 (an E-class gene) during flower development. We observed an additive phenotype in the fon4 double mutant with the OsMADS15 mutant allele dep (degenerative palea). The effect on the organ number of whorl 2 was enhanced in fon4 spw1. Double mutant combinations of fon4 with osmads3, osmads58, osmads13, and osmads1 displayed enhanced defects in FM determinacy and identity, respectively, indicating that FON4 and these genes synergistically control FM activity. In addition, the expression patterns of all the genes besides OsMADS13 had no obvious change in the fon4 mutant. This work reveals how the meristem maintenance gene FON4 genetically interacts with C, D, and E floral homeotic genes in specifying FM activity in monocot rice.

Transcriptomic Analysis Reveals Mechanisms of Sterile and Fertile Flower Differentiation and Development in Viburnum macrocephalum f. keteleeri

Sterile and fertile flowers are an important evolutionary developmental (evo-devo) phenotype in angiosperm flowers, playing important roles in pollinator attraction and sexual reproductive success. However, the gene regulatory mechanisms underlying fertile and sterile flower differentiation and development remain largely unknown. Viburnum macrocephalum f. keteleeri, which possesses fertile and sterile flowers in a single inflorescence, is a useful candidate species for investigating the regulatory networks in differentiation and development. We developed a de novo-assembled flower reference transcriptome. Using RNA sequencing (RNA-seq), we compared the expression patterns of fertile and sterile flowers isolated from the same inflorescence over its rapid developmental stages. The flower reference transcriptome consisted of 105,683 non-redundant transcripts, of which 5,675 transcripts showed significant differential expression between fertile and sterile flowers. Combined with morphological and cytological changes between fertile and sterile flowers, we identified expression changes of many genes potentially involved in reproductive processes, phytohormone signaling, and cell proliferation and expansion using RNA-seq and qRT-PCR. In particular, many transcription factors (TFs), including MADS-box family members and ABCDE-class genes, were identified, and expression changes in TFs involved in multiple functions were analyzed and highlighted to determine their roles in regulating fertile and sterile flower differentiation and development. Our large-scale transcriptional analysis of fertile and sterile flowers revealed the dynamics of transcriptional networks and potentially key components in regulating differentiation and development of fertile and sterile flowers in Viburnum macrocephalum f. keteleeri. Our data provide a useful resource for Viburnum transcriptional research and offer insights into gene regulation of differentiation of diverse evo-devo processes in flowers.

A Factor Linking Floral Organ Identity and Growth Revealed by Characterization of the Tomato Mutant unfinished flower development (ufd)

Floral organogenesis requires coordinated interactions between genes specifying floral organ identity and those regulating growth and size of developing floral organs. With the aim to isolate regulatory genes linking both developmental processes (i.e., floral organ identity and growth) in the tomato model species, a novel mutant altered in the formation of floral organs was further characterized. Under normal growth conditions, floral organ primordia of mutant plants were correctly initiated, however, they were unable to complete their development impeding the formation of mature and fertile flowers. Thus, the growth of floral buds was blocked at an early stage of development; therefore, we named this mutant as unfinished flower development (ufd). Genetic analysis performed in a segregating population of 543 plants showed that the abnormal phenotype was controlled by a single recessive mutation. Global gene expression analysis confirmed that several MADS-box genes regulating floral identity as well as other genes participating in cell division and different hormonal pathways were affected in their expression patterns in ufd mutant plants. Moreover, ufd mutant inflorescences showed higher hormone contents, particularly ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and strigol compared to wild type. Such results indicate that UFD may have a key function as positive regulator of the development of floral primordia once they have been initiated in the four floral whorls. This function should be performed by affecting the expression of floral organ identity and growth genes, together with hormonal signaling pathways.

Expression profiles of genes involved in jasmonic acid biosynthesis and signaling during growth and development of carrot

Jasmonates (JAs) are recognized as essential regulators in response to environmental stimuli and plant development. Carrot is an Apiaceae vegetable with great value and undergoes significant size changes over the course of plant growth. However, JA accumulation and its potential roles in carrot growth remain unclear. Here, methyl JA (MeJA) levels and expression profiles of JA-related genes were analyzed in carrot roots and leaves at five developmental stages. MeJA levels in the roots and leaves were the highest at the first stage and decreased as carrot growth proceeded. Transcript levels of several JA-related genes (Dc13-LOX1, Dc13-LOX2, DcAOS, DcAOC, DcOPR2, DcOPR3, DcOPCL1, DcJAR1, DcJMT, DcCOI1, DcJAZ1, DcJAZ2, DcMYC2, DcCHIB/PR3, DcLEC, and DcVSP2) were not well correlated with MeJA accumulation during carrot root and leaf development. In addition, some JA-related genes (DcJAR1, DcJMT, DcCOI1, DcMYC2, and DcVSP2) showed differential expression between roots and leaves. These results suggest that JAs may regulate carrot plant growth in stage-dependent and organ-specific manners. Our work provides novel insights into JA accumulation and its potential roles during carrot growth and development.

Jasmonate regulates juvenile-to-adult phase transition in rice

Juvenile-to-adult phase transition is an important shift for the acquisition of adult vegetative characteristics and subsequent reproductive competence. We identified a recessive precocious (pre) mutant exhibiting a long leaf phenotype in rice. The long leaf phenotype is conspicuous in the second to the fourth leaves, which are juvenile and juvenile-to-adult transition leaves. We found that morphological and physiological traits, such as midrib formation, shoot meristem size, photosynthetic rate and plastochron, in juvenile and juvenile-to-adult transition stages of the pre mutant have precociously acquired adult characteristics. In agreement with these results, expression patterns of miR156 and miR172, which are microRNAs regulating phase change, support the accelerated juvenile-to-adult phase change in the pre mutant. The mutated gene encodes an allene oxide synthase (OsAOS1), which is a key enzyme for the biosynthesis of jasmonic acid (JA). The pre mutant showed a low level of JA and enhanced sensitivity to gibberellic acid, which promotes the phase change in some plant species. We also show that prolonged plastochron in the pre mutant is caused by accelerated PLASTOCHRON1 (PLA1) function. The present study reveals a substantial role of JA as a negative regulator of vegetative phase change.

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.

Dynamics of Jasmonate Metabolism upon Flowering and across Leaf Stress Responses in Arabidopsis thaliana

The jasmonic acid (JA) signaling pathway plays important roles in adaptation of plants to environmental cues and in specific steps of their development, particularly in reproduction. Recent advances in metabolic studies have highlighted intricate mechanisms that govern enzymatic conversions within the jasmonate family. Here we analyzed jasmonate profile changes upon Arabidopsis thaliana flower development and investigated the contribution of catabolic pathways that were known to turnover the active hormonal compound jasmonoyl-isoleucine (JA-Ile) upon leaf stress. We report a rapid decline of JA-Ile upon flower opening, concomitant with the massive accumulation of its most oxidized catabolite, 12COOH-JA-Ile. Detailed genetic analysis identified CYP94C1 as the major player in this process. CYP94C1 is one out of three characterized cytochrome P450 enzymes that define an oxidative JA-Ile turnover pathway, besides a second, hydrolytic pathway represented by the amido-hydrolases IAR3 and ILL6. Expression studies combined with reporter gene analysis revealed the dominant expression of CYP94C1 in mature anthers, consistent with the established role of JA signaling in male fertility. Significant CYP94B1 expression was also evidenced in stamen filaments, but surprisingly, CYP94B1 deficiency was not associated with significant changes in JA profiles. Finally, we compared global flower JA profiles with those previously reported in leaves reacting to mechanical wounding or submitted to infection by the necrotrophic fungus Botrytis cinerea. These comparisons revealed distinct dynamics of JA accumulation and conversions in these three biological systems. Leaf injury boosts a strong and transient JA and JA-Ile accumulation that evolves rapidly into a profile dominated by ω-oxidized and/or Ile-conjugated derivatives. In contrast, B. cinerea-infected leaves contain mostly unconjugated jasmonates, about half of this content being ω-oxidized. Finally, developing flowers present an intermediate situation where young flower buds show detectable jasmonate oxidation (probably originating from stamen metabolism) which becomes exacerbated upon flower opening. Our data illustrate that in spite conserved enzymatic routes, the jasmonate metabolic grid shows considerable flexibility and dynamically equilibrates into specific blends in different physiological situations.

A Genome-Wide Analysis Reveals Stress and Hormone Responsive Patterns of TIFY Family Genes in Brassica rapa

The TIFY family is a plant-specific group of proteins with a diversity of functions and includes four subfamilies, viz. ZML, TIFY, PPD, and JASMONATE ZIM-domain (JAZ) proteins. TIFY family members, particularly JAZ subfamily proteins, play roles in biological processes such as development and stress and hormone responses in Arabidopsis, rice, chickpea, and grape. However, there is no information about this family in any Brassica crop. This study identifies 36 TIFY genes in Brassica rapa, an economically important crop species in the Brassicaceae. An extensive in silico analysis of phylogenetic grouping, protein motif organization and intron-exon distribution confirmed that there are four subfamilies of BrTIFY proteins. Out of 36 BrTIFY genes, we identified 21 in the JAZ subfamily, seven in the TIFY subfamily, six in ZML and two in PPD. Extensive expression profiling of 21 BrTIFY JAZs in various tissues, especially in floral organs and at different flower growth stages revealed constitutive expression patterns, which suggest that BrTIFY JAZ genes are important during growth and development of B. rapa flowers. A protein interaction network analysis also pointed to association of these proteins with fertility and defense processes of B. rapa. Using a low temperature-treated whole-genome microarray data set, most of the JAZ genes were found to have variable transcript abundance between the contrasting inbred lines Chiifu and Kenshin of B. rapa. Subsequently, the expression of all 21 BrTIFY JAZs in response to cold stress was characterized in the same two lines via qPCR, demonstrating that nine genes were up-regulated. Importantly, the BrTIFY JAZs showed strong and differential expression upon JA treatment, pointing to their probable involvement in JA-mediated growth regulatory functions, especially during flower development and stress responses. Additionally, BrTIFY JAZs were induced in response to salt, drought, Fusarium, ABA, and SA treatments, and six genes (BrTIFY3a, 3b, 6a, 9a, 9b, and 9c) were identified to have co-responsive expression patterns. The extensive annotation and transcriptome profiling reported in this study will be useful for understanding the involvement of TIFY genes in stress resistance and different developmental functions, which ultimately provides the basis for functional characterization and exploitation of the candidate TIFY genes for genetic engineering of B. rapa.

Comparative Transcriptome Analysis between Gynoecious and Monoecious Plants Identifies Regulatory Networks Controlling Sex Determination in Jatropha curcas

Most germplasms of the biofuel plant Jatropha curcas are monoecious. A gynoecious genotype of J. curcas was found, whose male flowers are aborted at early stage of inflorescence development. To investigate the regulatory mechanism of transition from monoecious to gynoecious plants, a comparative transcriptome analysis between gynoecious and monoecious inflorescences were performed. A total of 3,749 genes differentially expressed in two developmental stages of inflorescences were identified. Among them, 32 genes were involved in floral development, and 70 in phytohormone biosynthesis and signaling pathways. Six genes homologous to KNOTTED1-LIKE HOMEOBOX GENE 6 (KNAT6), MYC2, SHI-RELATED SEQUENCE 5 (SRS5), SHORT VEGETATIVE PHASE (SVP), TERMINAL FLOWER 1 (TFL1), and TASSELSEED2 (TS2), which control floral development, were considered as candidate regulators that may be involved in sex differentiation in J. curcas. Abscisic acid, auxin, gibberellin, and jasmonate biosynthesis were lower, whereas cytokinin biosynthesis was higher in gynoecious than that in monoecious inflorescences. Moreover, the exogenous application of gibberellic acid (GA₃) promoted perianth development in male flowers and partly prevented pistil development in female flowers to generate neutral flowers in gynoecious inflorescences. The arrest of stamen primordium at early development stage probably causes the abortion of male flowers to generate gynoecious individuals. These results suggest that some floral development genes and phytohormone signaling pathways orchestrate the process of sex determination in J. curcas. Our study provides a basic framework for the regulation networks of sex determination in J. curcas and will be helpful for elucidating the evolution of the plant reproductive system.