A Bypass in Jasmonate Biosynthesis - the OPR3-independent Formation

Low sucrose availability reduces basal spikelet fertility by inducing abscisic acid and jasmonic acid synthesis in wheat

Within a spike of wheat, the central spikelets usually generate three to four fertile florets, while the basal spikelets generate zero to one fertile floret. The physiological and transcriptional mechanism behind the difference in fertility between the basal and central spikelets is unclear. This study reports a high temporal resolution investigation of transcriptomes, number and morphology of floret primordia, and physiological traits. The W6.5-W7.5 stage was regarded as the boundary to distinguish between fertile and abortive floret primordia; those floret primordia reaching the W6.5-W7.5 stage during the differentiation phase (3-9 d after terminal spikelet stage) usually developed into fertile florets in the next dimorphism phase (12-27 d after terminal spikelet stage), whereas the others aborted. The central spikelets had a greater number of fertile florets than the basal spikelets, which was associated with more floret primordia reaching the W6.5-W7.5 stage. Physiological and transcriptional results demonstrated that the central spikelets had a higher sucrose content and lower abscisic acid (ABA) and jasmonic acid (JA) accumulation than the basal spikelets due to down-regulation of genes involved in ABA and JA synthesis. Collectively, we propose a model in which ABA and JA accumulation is induced under limiting sucrose availability (basal spikelet) through the up-regulation of genes involved in ABA and JA synthesis; this leads to floret primordia in the basal spikelets failing to reach their fertile potential (W6.5-W7.5 stage) during the differentiation phase and then aborting. This fertility repression model may also regulate spikelet fertility in other cereal crops and potentially provides genetic resources to improve spikelet fertility.

Overexpression of PtoMYB99 diminishes poplar tolerance to osmotic stress by suppressing ABA and JA biosynthesis

Drought poses a serious challenge to sustained plant growth and crop yields in the context of global climate change. Drought tolerance in poplars and their underlying mechanisms still remain largely unknown. In this article, we investigated the overexpression of PtoMYB99 - both a drought and abscisic acid (ABA) induced gene constraining drought tolerance in poplars (as compared with wild type poplars). First, we found that PtoMYB99-OE lines exhibited increased stomatal opening and conductance, higher transpiration and photosynthetic rates, as well as reduced levels of ABA and jasmonic acid (JA). Second, PtoMYB99-OE lines accumulated more reactive oxygen species (ROS), including H2O2 and O2-, as well as malonaldehyde (MDA), proline, and soluble sugar under osmotic stress; conversely, the activity of antioxidant enzymes (SOD, POD, and CAT), was weakened in the PtoMYB99-OE lines. Third, the expression of ABA biosynthetic genes, PtoNCED3.1 and PtoNCED3.2, as well as JA biosynthetic genes, PtoOPR3.1 and PtoOPR3.2, was significantly reduced in the PtoMYB99-OE lines under both normal conditions and osmotic stress. Based on our results, we conclude that the overexpression of PtoMYB99 compromises tolerance to osmotic stress in poplar. These findings contribute to the understanding of the role of the MYB genes in drought stress and the biosynthesis of ABA and JA.

Mealybug salivary microbes inhibit induced plant defenses

BACKGROUND

Phenacoccus solenopsis is a polyphagous invasive mealybug that caused serious damage to crops worldwide. Phloem-sucking hemipterans are known to carry symbiotic microbes in their saliva. However, the role of salivary bacteria of P. solenopsis in modulating plant defenses remains limited. Exploring the impact of salivary bacteria on plant defense responses will contribute to the development of new targets for efficient control of invasive mealybugs.

RESULTS

Salivary bacteria of the invasive mealybug P. solenopsis can suppress herbivore-induced plant defenses and thus enhance mealybug fitness. Mealybugs treated with an antibiotic showed decreased weight gain, fecundity and survival. Untreated mealybugs suppressed jasmonic acid (JA)-regulated defenses but activated salicylic acid (SA)-regulated defenses in cotton plants. In contrast, antibiotic-treated mealybugs triggered JA-responsive gene expression and JA accumulation, and showed shortened phloem ingestion. Reinoculating antibiotic-treated mealybugs with Enterobacteriaceae or Stenotrophomonas cultivated from mealybug saliva promoted phloem ingestion and fecundity, and restored the ability of mealybugs to suppress plant defenses. Fluorescence in situ hybridization visualization revealed that Enterobacteriaceae and Stenotrophomonas colonize salivary glands and are secreted into the mesophyll cells and phloem vessels. Exogenous application of the bacterial isolates to plant leaves inhibited JA-responsive gene expression and activated SA-responsive gene expression.

CONCLUSION

Our findings imply that symbiotic bacteria in the saliva of the mealybug play an important role in manipulating herbivore-induced plant defenses, enabling this important pest to evade induced plant defenses and promoting its performance and destructive effects on crops. © 2023 Society of Chemical Industry.

Biosynthetic Pathways of Hormones in Plants

Phytohormones exhibit a wide range of chemical structures, though they primarily originate from three key metabolic precursors: amino acids, isoprenoids, and lipids. Specific amino acids, such as tryptophan, methionine, phenylalanine, and arginine, contribute to the production of various phytohormones, including auxins, melatonin, ethylene, salicylic acid, and polyamines. Isoprenoids are the foundation of five phytohormone categories: cytokinins, brassinosteroids, gibberellins, abscisic acid, and strigolactones. Furthermore, lipids, i.e., α-linolenic acid, function as a precursor for jasmonic acid. The biosynthesis routes of these different plant hormones are intricately complex. Understanding of these processes can greatly enhance our knowledge of how these hormones regulate plant growth, development, and physiology. This review focuses on detailing the biosynthetic pathways of phytohormones.

12-Oxophytodienoate Reductase Overexpression Compromises Tolerance to Botrytis cinerea in Hexaploid and Tetraploid Wheat

12-Oxophytodienoate reductase is the enzyme involved in the biosynthesis of phytohormone jasmonates, which are considered to be the major regulators of plant tolerance to biotic challenges, especially necrotrophic pathogens. However, we observe compromised tolerance to the necrotrophic fungal pathogen Botrytis cinerea in transgenic hexaploid bread wheat and tetraploid emmer wheat plants overexpressing 12-OXOPHYTODIENOATE REDUCTASE-3 gene from Arabidopsis thaliana, while in Arabidopsis plants themselves, endogenously produced and exogenously applied jasmonates exert a strong protective effect against B. cinerea. Exogenous application of methyl jasmonate on hexaploid and tetraploid wheat leaves suppresses tolerance to B. cinerea and induces the formation of chlorotic damages. Exogenous treatment with methyl jasmonate in concentrations of 100 µM and higher causes leaf yellowing even in the absence of the pathogen, in agreement with findings on the role of jasmonates in the regulation of leaf senescence. Thereby, the present study demonstrates the negative role of the jasmonate system in hexaploid and tetraploid wheat tolerance to B. cinerea and reveals previously unknown jasmonate-mediated responses.

Evolution of wound-activated regeneration pathways in the plant kingdom

Regeneration serves as a self-protective mechanism that allows a tissue or organ to recover its entire form and function after suffering damage. However, the regenerative capacity varies greatly within the plant kingdom. Primitive plants frequently display an amazing regenerative ability as they have developed a complex system and strategy for long-term survival under extreme stress conditions. The regenerative ability of dicot species is highly variable, but that of monocots often exhibits extreme recalcitrance to tissue replenishment. Recent studies have revealed key factors and signals that affect cell fate during plant regeneration, some of which are conserved among the plant lineage. Among these, several members of the ETHYLENE RESPONSE FACTOR (ERF) transcription factors have been implicated in wound signaling, playing crucial roles in the regenerative mechanisms after different types of wounding. An understanding of plant regeneration may ultimately lead to an increased regenerative potential of recalcitrant species, producing more high-yielding, multi-resistant and environmentally friendly crops and ensuring the long-term development of global agriculture.

The wound-activated ERF15 transcription factor drives Marchantia polymorpha regeneration by activating an oxylipin biosynthesis feedback loop

The regenerative potential in response to wounding varies widely among species. Within the plant lineage, the liverwort Marchantia polymorpha displays an extraordinary regeneration capacity. However, its molecular pathways controlling the initial regeneration response are unknown. Here, we demonstrate that the MpERF15 transcription factor gene is instantly activated after wounding and is essential for gemmaling regeneration following tissue incision. MpERF15 operates both upstream and downstream of the MpCOI1 oxylipin receptor by controlling the expression of oxylipin biosynthesis genes. The resulting rise in the oxylipin dinor-12-oxo-phytodienoic acid (dn-OPDA) levels results in an increase in gemma cell number and apical notch organogenesis, generating highly disorganized and compact thalli. Our data pinpoint MpERF15 as a key factor activating an oxylipin biosynthesis amplification loop after wounding, which eventually results in reactivation of cell division and regeneration. We suggest that the genetic networks controlling oxylipin biosynthesis in response to wounding might have been reshuffled over evolution.

The reliance of phytohormone biosynthesis on primary metabolite precursors

There is some debate as to whether phytohormone metabolites should be classified as primary or secondary metabolites. Phytohormones have profound effects on growth - a typical trait of primary metabolites - yet several of them are formed from secondary metabolite precursors. This is further exacerbated by the blurred distinction between primary and secondary metabolism. What is clearer, however, is that phytohormones display distinctive regulatory mechanisms from other metabolites. Moreover, by contrast to microbial and mammalian systems, the majority of plant metabolite receptors characterized to date are hormone receptors. Here, we provide an overview of the metabolic links between primary metabolism and phytohormone biosynthesis in an attempt to complement recent reviews covering the signaling crosstalk between elements of core metabolism and the phytohormones. In doing so, we cover the biosynthesis of both the classical metabolic phytohormones namely auxins, salicylic acid, jasmonate, ethylene, cytokinins, brassinosteroids, gibberellins and abscisic acid as well as recently described plant growth regulators which have been proposed as novel phytohormones namely strigolactones blumenols, zaxinone and β-cyclocitral as well as melatonin. For each hormone, we describe the primary metabolite precursors which fuel its synthesis, act as conjugates or in the case of 2-oxoglutarate act more directly as a co-substrate in the biosynthesis of gibberellin, auxin and salicylic acid. Furthermore, several amino acids operate as hormone conjugates, such as jasmonate-conjugates. In reviewing the biosynthesis of all the phytohormones simultaneously, the exceptional intricacy of the biochemical interplay that underpins their interaction emerges.

Development, validation, and application of an HPLC-MS/MS method for quantification of oxidized fatty acids in plants

Oxylipins constitute a huge class of compounds produced by oxidation of long-chain unsaturated fatty acids either chemically (by radicals such as reactive oxygen species, ROS) or enzymatically (by lipoxygenases, LOX; cyclooxygenases, COX; or cytochrome P450 pathways). This process generates fatty acids peroxides, which can then be further modified in a broad range to epoxy, hydroxy, keto, ether fatty acids, and also hydrolyzed to generate small aldehydes and alcohols. In general, oxylipins are present in almost all living organisms and have a wide range of signaling, metabolic, physiological, and ecological roles depending on the particular organism and on their structure. In plants, oxylipins have been extensively studied over the past 35 years. However, these studies have focused mainly on the jasmonates and so-called green leaves volatiles. The function of early LOX products (like keto and hydroxy fatty acids) is yet not well understood in plants, where they are mainly analyzed by indirect methods or by GC-MS what requires a laborious sample preparation. Here, we developed and validated a straightforward, precise, accurate, and sensitive method for quantifying oxylipins in plant tissues using HPLC-MS/MS, with a one-step extraction procedure using low amount of plant tissues. We successfully applied this method to quantify the oxylipins in different plant species and Arabidopsis thaliana plants treated with various biotic and abiotic stress conditions.

Cold-priming causes dampening of oxylipin biosynthesis and signalling during the early cold- and light-triggering response of Arabidopsis thaliana

Cold-priming uncouples cold and light regulation of otherwise tightly co-regulated genes. In this study, we focused on the early regulatory processes in Arabidopsis within the first 2 h in cold and in high light after a 5-d lag-phase at 20 °C and 24 h cold-priming at 4 °C. Priming quickly modified gene expression in a trigger-specific manner. In the early stress-response phase during cold and high-light triggering, it reduced the regulatory amplitudes of many up- and down-regulated genes. A third of the priming-regulated genes were jasmonate-sensitive, including the full set of genes required for oxylipin biosynthesis. Analysis of wild-type and mutant plants based on qPCR demonstrated that biosynthesis of the jasmonic acid (JA) precursor 12-oxo phytenoic acid (OPDA) relative to the availability of JA dampened the response of the genes for oxylipin biosynthesis. In oxylipin biosynthetic mutants, cold-priming more strongly affected genes involved in the biosynthesis of OPDA than in its conversion to JA. In addition, priming-dependent dampening of the triggering response was more linked to OPDA than to regulation of the JA concentration. Spray application of OPDA prior to triggering counteracted the priming effect. Regulation of the oxylipin hub was controlled by modulation of the oxylipin-sensitivity of the genes for OPDA biosynthesis, but it was insensitive to priming-induced accumulation of thylakoid ascorbate peroxidase, thus identifying a parallel-acting cold-priming pathway.

Metabolism, signaling, and transport of jasmonates

Biosynthesis/metabolism, perception/signaling, and transport are three essential aspects of the actions of phytohormones. Jasmonates (JAs), including jasmonic acid (JA) and related oxylipins, are implicated in the regulation of a range of ecological interactions, as well as developmental programs to integrate these interactions. Jasmonoyl-isoleucine (JA-Ile) is the most bioactive JAs, and perception of JA-Ile by its coreceptor, the Skp1-Cullin1-F-box-type (SCF) protein ubiquitin ligase complex SCF^COI1-JAZ, in the nucleus derepresses the transcriptional repression of target genes. The biosynthesis and metabolism of JAs occur in the plastid, peroxisome, cytosol, endoplasmic reticulum, and vacuole, whereas sensing of JA-Ile levels occurs in the nucleus. It is increasingly apparent that a number of transporters, particularly members of the jasmonates transporter (JAT) family, located at endomembranes as well as the plasma membrane, constitute a network for modulating and coordinating the metabolic flux and signaling of JAs. In this review, we discuss recent advances in the metabolism, signaling, and especially the transport of JAs, focusing on intracellular compartmentation of these processes. The roles of transporter-mediated cell-cell transport in driving long-distance transport and signaling of JAs are also discussed.

The OPR gene family in watermelon: Genome-wide identification and expression profiling under hormone treatments and root-knot nematode infection

The enzyme 12-oxo-phytodienoic acid reductase (OPR) is important in the jasmonic acid (JA) biosynthesis pathway and thus plays a vital role in plant defence. However, systematic and comprehensive analyses of OPR genes in watermelon and their roles in defence responses are extremely limited. The physicochemical properties, phylogenetic tree, gene structure and cis-acting elements of watermelon OPR genes were analysed using bioinformatics, and qRT-PCR and RNA-Seq were applied to assay expression of OPR genes in watermelon. A total of five OPR family genes were identified in watermelon, which were unevenly distributed across the four chromosomes. Phylogenetic analysis assigned OPR members from different plant species to five subfamilies (OPRI-OPRV). The motif compositions of OPR members were relatively conserved. Expression analysis using qRT-PCR revealed that ClOPR genes, except for ClOPR5, were highly expressed in the flower and fruit. RNA-seq analysis showed that the ClOPR genes had different expression patterns during flesh and rind development. Furthermore, the ClOPR genes, particularly ClOPR2 and ClOPR4, were significantly upregulated by exogenous JA, salicylic acid (SA) and ethylene (ET) treatments. In addition, red light induced expression of ClOPR2 and ClOPR4 in leaves and roots of root-knot nematode (RKN)-infected watermelon plants, suggesting their involvement in red light-induced defence against RKN. These results provide a theoretical basis for elucidating the diverse functions of OPR family genes in watermelon.

Creation of male-sterile lines that can be restored to fertility by exogenous methyl jasmonate for the establishment of a two-line system for the hybrid production of rice (Oryza sativa L.)

Male sterility is widely used in the production of hybrid seeds in rice, but the use of genic male sterility is limited because of the high labour cost for maintaining male-sterile lines. Previous studies using T-DNA insertional mutagenesis demonstrated that disrupting the expression of oxophytodienoic acid reductase 3 (OPR3), which is involved in the jasmonate biosynthesis pathway, results in a kind of male sterility that can be restored to fertility by exogenous jasmonate in Arabidopsis. Here, we created male-sterile mutations by editing the second and fourth exons of OsOPR7 in rice through clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated system 9. The induced mutagenesis at these exons resulted in 31.8% and 23.9% male-sterile plants in the T0 generation, respectively. We screened male-sterile lines that can be restored to fertility by exogenous methyl jasmonate in the T0, T1 and T2 rice populations and characterized the anther and agronomic traits of the transgenic plants. Results showed the successful generation of male-sterile lines through the silencing of OsOPR7, the orthologous gene of Arabidopsis OPR3, in a field crop, paving the way for the establishment of a two-line system for rice hybrid production. The system consists of a male-sterile line that can be maintained by spraying methyl jasmonate and a restoring line that confers pollen.

Regulation of Sixth Seminal Root Formation by Jasmonate in Triticum aestivum L

A well-developed root system is an important characteristic of crop plants, which largely determines their productivity, especially under conditions of water and nutrients deficiency. Being Poaceous, wheat has more than one seminal root. The number of grown seminal roots varies in different wheat accessions and is regulated by environmental factors. Currently, the molecular mechanisms determining the number of germinated seminal roots remain poorly understood. The analysis of the root system development in germinating seeds of genetically modified hexaploid wheat plants with altered activity of jasmonate biosynthesis pathway and seeds exogenously treated with methyl jasmonate revealed the role of jasmonates in the regulation of sixth seminal root development. This regulatory effect strongly depends on the jasmonate concentration and the duration of the exposure to this hormone. The maximum stimulatory effect of exogenously applied methyl jasmonate on the formation of the sixth seminal root was achieved at 200 μM concentration after 48 h of treatment. Further increase in concentration and exposure time does not increase the stimulating effect. While 95% of non-transgenic plants under non-stress conditions possess five or fewer seminal roots, the number of plants with developed sixth seminal root reaches up to 100% when selected transgenic lines are treated with methyl jasmonate.

Deciphering OPDA Signaling Components in the Momilactone-Producing Moss Calohypnum plumiforme

Jasmonic acid (JA) and its biologically active form jasmonoyl-L-isoleucine (JA-Ile) regulate defense responses to various environmental stresses and developmental processes in plants. JA and JA-Ile are synthesized from α-linolenic acids derived from membrane lipids via 12-oxo-phytodienoic acid (OPDA). In the presence of JA-Ile, the COI1 receptor physically interacts with JAZ repressors, leading to their degradation, resulting in the transcription of JA-responsive genes by MYC transcription factors. Although the biosynthesis of JA-Ile is conserved in vascular plants, it is not recognized by COI1 in bryophytes and is not biologically active. In the liverwort Marchantia polymorpha, dinor-OPDA (dn-OPDA), a homolog of OPDA with two fewer carbons, and its isomer dn-iso-OPDA accumulate after wounding and are recognized by COI1 to activate downstream signaling. The moss Calohypnum plumiforme produces the antimicrobial-specialized metabolites, momilactones. It has been reported that JA and JA-Ile are not detected in C. plumiforme and that OPDA, but not JA, can induce momilactone accumulation and the expression of these biosynthetic genes, suggesting that OPDA or its derivative is a biologically active molecule in C. plumiforme that induces chemical defense. In the present study, we investigated the biological functions of OPDA and its derivatives in C. plumiforme. Searching for the components potentially involving oxylipin signaling from transcriptomic and genomic data revealed that two COI1, three JAZ, and two MYC genes were present. Quantification analyses revealed that OPDA and its isomer iso-OPDA accumulated in larger amounts than dn-OPDA and dn-iso-OPDA after wounding. Moreover, exogenously applied OPDA, dn-OPDA, or dn-iso-OPDA induced the transcription of JAZ genes. These results imply that OPDA, dn-OPDA, and/or their isomers potentially act as biologically active molecules to induce the signaling downstream of COI1-JAZ. Furthermore, co-immunoprecipitation analysis showed the physical interaction between JAZs and MYCs, indicating the functional conservation of JAZs in C. plumiforme with other plants. These results suggest that COI1-JAZ-MYC mediated signaling is conserved and functional in C. plumiforme.

Jasmonic Acid at the Crossroads of Plant Immunity and Pseudomonas syringae Virulence

Sensing of pathogen infection by plants elicits early signals that are transduced to affect defense mechanisms, such as effective blockage of pathogen entry by regulation of stomatal closure, cuticle, or callose deposition, change in water potential, and resource acquisition among many others. Pathogens, on the other hand, interfere with plant physiology and protein functioning to counteract plant defense responses. In plants, hormonal homeostasis and signaling are tightly regulated; thus, the phytohormones are qualified as a major group of signaling molecules controlling the most widely tinkered regulatory networks of defense and counter-defense strategies. Notably, the phytohormone jasmonic acid mediates plant defense responses to a wide array of pathogens. In this review, we present the synopsis on the jasmonic acid metabolism and signaling, and the regulatory roles of this hormone in plant defense against the hemibiotrophic bacterial pathogen Pseudomonas syringae. We also elaborate on how this pathogen releases virulence factors and effectors to gain control over plant jasmonic acid signaling to effectively cause disease. The findings discussed in this review may lead to ideas for the development of crop cultivars with enhanced disease resistance by genetic manipulation.

Identification, molecular characterization and expression of JAZ genes in Lycoris aurea

Jasmonates (JAs) are key phytohormones involved in regulation of plant growth and development, stress responses, and secondary metabolism. It has been reported that treatments with JAs could increase the contents of Amaryllidaceae alkaloids in Amaryllidaceae plants. Jasmonate ZIM (zinc-finger inflorescence meristem) domain (JAZ) proteins are key components in JA signal processes. However, JAZ proteins have not been characterized in genus Lycoris. In this study, we identified and cloned seven differentially expressed JAZ genes (namely LaJAZ1–LaJAZ7) from Lycoris aurea. Bioinformatic analyses revealed that these seven LaJAZ proteins contain the ZIM domain and JA-associated (Jas, also named CCT_2) motif. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis revealed that these LaJAZ genes display different expression patterns in L. aurea tissues, and most of them are inducible when treated with methyl jasmonate (MeJA) treatment. Subcellular localization assay demonstrated that LaJAZ proteins are localized in the cell nucleus or cytoplasm. In addition, LaJAZ proteins could interact with each other to form homodimer and/or heterodimer. The findings in this study may facilitate further functional research of the LaJAZ genes, especially the potential regulatory mechanism of plant secondary metabolites including Amaryllidaceae alkaloids in L. aurea.

cis-12-Oxo-phytodienoic acid represses Arabidopsis seed germination in shade conditions

Light-dependent seed germination is induced by gibberellins (GA) and inhibited by abscisic acid (ABA). The widely accepted view of the GA/ABA ratio controlling germination does not, however, explain the fact that seeds deficient in ABA still germinate poorly under shade conditions that repress germination. In Arabidopsis, MOTHER-OF-FT-AND-TFL1 (MFT) acts as a key negative regulator of germination, modulating GA and ABA responses under shade conditions. Under full light the oxylipin cis-12-oxo-phytodienoic acid (OPDA), a precursor of the stress-related phytohormone jasmonic acid, interacts with ABA and MFT to repress germination. Here, we show that under shade conditions both OPDA and ABA repress germination to varying extents. We demonstrate that the level of shade-induced MFT expression influences the ability of OPDA and/or ABA to fully repress germination. We also found that MFT expression decreases with seed age and this again correlates with the response of seeds to OPDA and ABA. We conclude that OPDA plays an essential role alongside ABA in repressing germination in response to shade and the combined effect of these phytohormones is integrated to a significant extent through MFT.

Tobacco transcription repressors NtJAZ: Potential involvement in abiotic stress response and glandular trichome induction

Members of the Jasmonate ZIM domain (JAZ) proteins act as transcriptional repressors in the jasmonate (JA) hormonal response. To characterize the potential roles of JAZ gene family in plant development and abiotic stress response, fifteen JAZs were identified based on the genome of Nicotiana tabacum. Structural analysis confirmed the presence of single Jas and TIFY motif. Tissue expression pattern analysis indicated that NtJAZ-2, -3, -5, and -10 were highly expressed in roots and NtJAZ-11 was expressed only in the cotyledons. The transcript level of NtJAZ-3, -5, -9, and -10 in the stem epidermis was higher than that in the stem without epidermis. Dynamic expression of NtJAZs exposed to abiotic stress and phytohormone indicated that the expression of most NtJAZs was activated by salicylic acid, methyl jasmonate, gibberellic acid, cold, salt, and heat stresses. With abscisic acid treatment, NtJAZ-1, -2, and -3 were not activated; NtJAZ-4, -5, and -6 were up-regulated; and the remaining NtJAZ genes were inhibited. With drought stress, the expression of NtJAZ-1, -2, -3, -4, -5, -6, -7, and -8 was up-regulated, whereas the transcript of the remaining genes was inhibited. Moreover, high concentration MeJA (more than 1 mM MeJA) had an effect on secreting trichome induction, but inhabited the plant growth. Nine NtJAZs may play important role in secreting trichome induction. These results indicate that the JAZ proteins are convergence points for various phytohormone signal networks, which are involved in abiotic stress responses.

Whole genomes and transcriptomes reveal adaptation and domestication of pistachio

BACKGROUND

Pistachio (Pistacia vera), one of the most important commercial nut crops worldwide, is highly adaptable to abiotic stresses and is tolerant to drought and salt stresses.

RESULTS

Here, we provide a draft de novo genome of pistachio as well as large-scale genome resequencing. Comparative genomic analyses reveal stress adaptation of pistachio is likely attributable to the expanded cytochrome P450 and chitinase gene families. Particularly, a comparative transcriptomic analysis shows that the jasmonic acid (JA) biosynthetic pathway plays an important role in salt tolerance in pistachio. Moreover, we resequence 93 cultivars and 14 wild P. vera genomes and 35 closely related wild Pistacia genomes, to provide insights into population structure, genetic diversity, and domestication. We find that frequent genetic admixture occurred among the different wild Pistacia species. Comparative population genomic analyses reveal that pistachio was domesticated about 8000 years ago and suggest that key genes for domestication related to tree and seed size experienced artificial selection.

CONCLUSIONS

Our study provides insight into genetic underpinning of local adaptation and domestication of pistachio. The Pistacia genome sequences should facilitate future studies to understand the genetic basis of agronomically and environmentally related traits of desert crops.

Overexpression of Arabidopsis OPR3 in Hexaploid Wheat (Triticum aestivum L.) Alters Plant Development and Freezing Tolerance

Jasmonates are plant hormones that are involved in the regulation of different aspects of plant life, wherein their functions and molecular mechanisms of action in wheat are still poorly studied. With the aim of gaining more insights into the role of jasmonic acid (JA) in wheat growth, development, and responses to environmental stresses, we have generated transgenic bread wheat plants overexpressing Arabidopsis 12-OXOPHYTODIENOATE REDUCTASE 3 (AtOPR3), one of the key genes of the JA biosynthesis pathway. Analysis of transgenic plants showed that AtOPR3 overexpression affects wheat development, including germination, growth, flowering time, senescence, and alters tolerance to environmental stresses. Transgenic wheat plants with high AtOPR3 expression levels have increased basal levels of JA, and up-regulated expression of ALLENE OXIDE SYNTHASE, a jasmonate biosynthesis pathway gene that is known to be regulated by a positive feedback loop that maintains and boosts JA levels. Transgenic wheat plants with high AtOPR3 expression levels are characterized by delayed germination, slower growth, late flowering and senescence, and improved tolerance to short-term freezing. The work demonstrates that genetic modification of the jasmonate pathway is a suitable tool for the modulation of developmental traits and stress responses in wheat.

Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds

: Jasmonic acid (JA) and its related derivatives are ubiquitously occurring compounds of land plants acting in numerous stress responses and development. Recent studies on evolution of JA and other oxylipins indicated conserved biosynthesis. JA formation is initiated by oxygenation of α-linolenic acid (α-LeA, 18:3) or 16:3 fatty acid of chloroplast membranes leading to 12-oxo-phytodienoic acid (OPDA) as intermediate compound, but in Marchantiapolymorpha and Physcomitrellapatens, OPDA and some of its derivatives are final products active in a conserved signaling pathway. JA formation and its metabolic conversion take place in chloroplasts, peroxisomes and cytosol, respectively. Metabolites of JA are formed in 12 different pathways leading to active, inactive and partially active compounds. The isoleucine conjugate of JA (JA-Ile) is the ligand of the receptor component COI1 in vascular plants, whereas in the bryophyte M. polymorpha COI1 perceives an OPDA derivative indicating its functionally conserved activity. JA-induced gene expressions in the numerous biotic and abiotic stress responses and development are initiated in a well-studied complex regulation by homeostasis of transcription factors functioning as repressors and activators.