Jasmonate signaling in plant stress responses and development - active and inactive compounds

GhPLP2 Positively Regulates Cotton Resistance to Verticillium Wilt by Modulating Fatty Acid Accumulation and Jasmonic Acid Signaling Pathway

Patatin-like proteins (PLPs) have non-specific lipid acyl hydrolysis (LAH) activity, which can hydrolyze membrane lipids into fatty acids and lysophospholipids. The vital role of PLPs in plant growth and abiotic stress has been well documented. However, the function of PLPs in plant defense responses against pathogens is still poorly understood. Here, we isolated and identified a novel cotton (Gossypium hirsutum) PLP gene GhPLP2. The expression of GhPLP2 was induced upon treatment with Verticillium dahliae, the signaling molecules jasmonic acid (JA) and ethylene (ETH) in cotton plants. Subcellular localization revealed that GhPLP2 was localized to the plasma membrane. GhPLP2-silenced cotton plants were more susceptible to infection by V. dahliae, while the overexpression of GhPLP2 in Arabidopsis enhanced its resistance to V. dahliae, which was apparent as mild symptoms, and a decrease in the disease index and fungal biomass. The hypersensitive response, deposition of callose, and H₂O₂ accumulation triggered by V. dahliae elicitor were reduced in GhPLP2-silenced cotton plants. The overexpression of GhPLP2 in Arabidopsis resulted in the accumulation of linoleic acid (LA, 18:2) and α-linolenic acid (ALA, 18:3) and facilitated the biosynthesis of JA and JA-mediated defensive responses. GhPLP2 silencing in cotton plants consistently reduced the accumulation of linoleic acid (LA, 18:2) and α-linolenic acid (ALA, 18:3) and suppressed the biosynthesis of JA and the defensive responses mediated by JA. These results indicate that GhPLP2 is involved in the resistance of cotton to V. dahliae by maintaining fatty acid metabolism pools for JA biosynthesis and activating the JA signaling pathway.

GhPLP2 Positively Regulates Cotton Resistance to Verticillium Wilt by Modulating Fatty Acid Accumulation and Jasmonic Acid Signaling Pathway

Patatin-like proteins (PLPs) have non-specific lipid acyl hydrolysis (LAH) activity, which can hydrolyze membrane lipids into fatty acids and lysophospholipids. The vital role of PLPs in plant growth and abiotic stress has been well documented. However, the function of PLPs in plant defense responses against pathogens is still poorly understood. Here, we isolated and identified a novel cotton (Gossypium hirsutum) PLP gene GhPLP2. The expression of GhPLP2 was induced upon treatment with Verticillium dahliae, the signaling molecules jasmonic acid (JA) and ethylene (ETH) in cotton plants. Subcellular localization revealed that GhPLP2 was localized to the plasma membrane. GhPLP2-silenced cotton plants were more susceptible to infection by V. dahliae, while the overexpression of GhPLP2 in Arabidopsis enhanced its resistance to V. dahliae, which was apparent as mild symptoms, and a decrease in the disease index and fungal biomass. The hypersensitive response, deposition of callose, and H₂O₂ accumulation triggered by V. dahliae elicitor were reduced in GhPLP2-silenced cotton plants. The overexpression of GhPLP2 in Arabidopsis resulted in the accumulation of linoleic acid (LA, 18:2) and α-linolenic acid (ALA, 18:3) and facilitated the biosynthesis of JA and JA-mediated defensive responses. GhPLP2 silencing in cotton plants consistently reduced the accumulation of linoleic acid (LA, 18:2) and α-linolenic acid (ALA, 18:3) and suppressed the biosynthesis of JA and the defensive responses mediated by JA. These results indicate that GhPLP2 is involved in the resistance of cotton to V. dahliae by maintaining fatty acid metabolism pools for JA biosynthesis and activating the JA signaling pathway.

Priming of Plant Defenses against Ophiostoma novo-ulmi by Elm (Ulmus minor Mill.) Fungal Endophytes

Some fungal endophytes of forest trees are recognized as beneficial symbionts against stresses. In previous works, two elm endophytes from the classes Cystobasidiomycetes and Eurotiomycetes promoted host resistance to abiotic stress, and another elm endophyte from Dothideomycetes enhanced host resistance to Dutch elm disease (DED). Here, we hypothesize that the combined effect of these endophytes activate the plant immune and/or antioxidant system, leading to a defense priming and/or increased oxidative protection when exposed to the DED pathogen Ophiostoma novo-ulmi. To test this hypothesis, the short-term defense gene activation and antioxidant response were evaluated in DED-susceptible (MDV1) and DED-resistant (VAD2 and MDV2.3) Ulmus minor genotypes inoculated with O. novo-ulmi, as well as two weeks earlier with a mixture of the above-mentioned endophytes. Endophyte inoculation induced a generalized transient defense activation mediated primarily by salicylic acid (SA). Subsequent pathogen inoculation resulted in a primed defense response of variable intensity among genotypes. Genotypes MDV1 and VAD2 displayed a defense priming driven by SA, jasmonic acid (JA), and ethylene (ET), causing a reduced pathogen spread in MDV1. Meanwhile, the genotype MDV2.3 showed lower defense priming but a stronger and earlier antioxidant response. The defense priming stimulated by elm fungal endophytes broadens our current knowledge of the ecological functions of endophytic fungi in forest trees and opens new prospects for their use in the biocontrol of plant diseases.

Function and Mechanism of Jasmonic Acid in Plant Responses to Abiotic and Biotic Stresses

As sessile organisms, plants must tolerate various environmental stresses. Plant hormones play vital roles in plant responses to biotic and abiotic stresses. Among these hormones, jasmonic acid (JA) and its precursors and derivatives (jasmonates, JAs) play important roles in the mediation of plant responses and defenses to biotic and abiotic stresses and have received extensive research attention. Although some reviews of JAs are available, this review focuses on JAs in the regulation of plant stress responses, as well as JA synthesis, metabolism, and signaling pathways. We summarize recent progress in clarifying the functions and mechanisms of JAs in plant responses to abiotic stresses (drought, cold, salt, heat, and heavy metal toxicity) and biotic stresses (pathogen, insect, and herbivore). Meanwhile, the crosstalk of JA with various other plant hormones regulates the balance between plant growth and defense. Therefore, we review the crosstalk of JAs with other phytohormones, including auxin, gibberellic acid, salicylic acid, brassinosteroid, ethylene, and abscisic acid. Finally, we discuss current issues and future opportunities in research into JAs in plant stress responses.

Therapeutic Potential of Jasmonic Acid and Its Derivatives

A modern method of therapeutic use of natural compounds that would protect the body are jasmonates. The main representatives of jasmonate compounds include jasmonic acid and its derivatives, mainly methyl jasmonate. Extracts from plants rich in jasmonic compounds show a broad spectrum of activity, i.e., anti-cancer, anti-inflammatory and cosmetic. Studies of the biological activity of jasmonic acid and its derivatives in mammals are based on their structural similarity to prostaglandins and the compounds can be used as natural therapeutics for inflammation. Jasmonates also constitute a potential group of anti-cancer drugs that can be used alone or in combination with other known chemotherapeutic agents. Moreover, due to their ability to stimulate exfoliation of the epidermis, remove discoloration, regulate the function of the sebaceous glands and reduce the visible signs of aging, they are considered for possible use in cosmetics and dermatology. The paper presents a review of literature data on the biological activity of jasmonates that may be helpful in treatment and prevention.

First Total Synthesis of Phytoprostanes with Prostaglandin-Like Configuration, Evidence for Their Formation in Edible Vegetable Oils and Orienting Study of Their Biological Activity

Phytoprostanes (PhytoP) are natural products, which form in plants under oxidative stress conditions from α-linolenic acid. However, their epimers with relative prostaglandin configuration termed phytoglandins (PhytoG) have never been detected in Nature, likely because of the lack of synthetic reference material. Here, the first asymmetric total synthesis of such compounds, namely of PhytoGF_1α (9-epi-16-F_1t -PhytoP) and its diastereomer ent-16-epi-PhytoGF_1α (ent-9,16-diepi-16-F_1t -PhytoP), has been accomplished. The synthetic strategy is based on radical anion oxidative cyclization, copper(I)-mediated alkyl-alkyl coupling and enantioselective reduction reactions. A UHPLC-MS/MS study using the synthesized compounds as standards indicates PhytoG formation at significant levels during autoxidation of α-linolenic acid in edible vegetable oils. Initial testing of synthetic PhytoGs together with F₁ -PhytoP and 15-F_2t -IsoP derivatives for potential interactions with the PGF_2α (FP) receptor did not reveal significant activity. The notion that PUFA-derived oxidatively formed cyclic metabolites with prostaglandin configuration do not form to a significant extent in biological or food matrices has to be corrected. Strong evidence is provided that oxidatively formed PhytoG metabolites may be ingested with plant-derived food, which necessitates further investigation of their biological profile.

Plant cytochrome P450s: Role in stress tolerance and potential applications for human welfare

Cytochrome P450s (CYPs) are a versatile group of enzymes and one of the largest families of proteins, controlling various physiological processes via biosynthetic and detoxification pathways. CYPs perform multiple roles through a critical irreversible enzymatic reaction in which an oxygen atom is inserted within hydrophobic molecules, converting them into the reactive and hydro soluble components. During evolution, plants have acquired significantly more number of CYPs and represent about 1% of the encoded genes . CYPs are highly conserved proteins involved in growth, development and tolerance against biotic and abiotic stresses. Furthermore, CYPs reinforce plants' molecular and chemical defense mechanisms by regulating the biosynthesis of secondary metabolites, enhancing reactive oxygen species (ROS) scavenging and controlling biosynthesis and homeostasis of phytohormones, including abscisic acid (ABA) and jasmonates. Thus, they are the critical targets of metabolic engineering for enhancing plant defense against environmental stresses. Additionally, CYPs are also used as biocatalysts in the fields of pharmacology and phytoremediation. Herein, we highlight the role of CYPs in plant stress tolerance and their applications for human welfare.

Molecular Targets and Biological Functions of cAMP Signaling in Arabidopsis

Cyclic AMP (cAMP) is a pivotal signaling molecule existing in almost all living organisms. However, the mechanism of cAMP signaling in plants remains very poorly understood. Here, we employ the engineered activity of soluble adenylate cyclase to induce cellular cAMP elevation in Arabidopsis thaliana plants and identify 427 cAMP-responsive genes (CRGs) through RNA-seq analysis. Induction of cellular cAMP elevation inhibits seed germination, disturbs phytohormone contents, promotes leaf senescence, impairs ethylene response, and compromises salt stress tolerance and pathogen resistance. A set of 62 transcription factors are among the CRGs, supporting a prominent role of cAMP in transcriptional regulation. The CRGs are significantly overrepresented in the pathways of plant hormone signal transduction, MAPK signaling, and diterpenoid biosynthesis, but they are also implicated in lipid, sugar, K⁺, nitrate signaling, and beyond. Our results provide a basic framework of cAMP signaling for the community to explore. The regulatory roles of cAMP signaling in plant plasticity are discussed.

Structure-guided analysis of Arabidopsis JASMONATE-INDUCED OXYGENASE (JOX) 2 reveals key residues for recognition of jasmonic acid substrate by plant JOXs

The jasmonic acid (JA) signaling pathway is used by plants to control wound responses. The persistent accumulation of JA inhibits plant growth, and the hydroxylation of JA to 12-hydroxy-JA by JASMONATE-INDUCED OXYGENASEs (JOXs, also named jasmonic acid oxidases) is therefore vital for plant growth, while structural details of JA recognition by JOXs are unknown. Here, we present the 2.65 Å resolution X-ray crystal structure of Arabidopsis JOX2 in complex with its substrate JA and its co-substrates 2-oxoglutarate and Fe(II). JOX2 contains a distorted double-stranded β helix (DSBH) core flanked by α helices and loops. JA is bound in the narrow substrate pocket by hydrogen bonds with the arginine triad R225, R350, and R354 and by hydrophobic interactions mainly with the phenylalanine triad F157, F317, and F346. The most critical residues for JA binding are F157 and R225, both from the DSBH core, which interact with the cyclopentane ring of JA. The spatial distribution of critical residues for JA binding and the shape of the substrate-binding pocket together define the substrate selectivity of the JOXs. Sequence alignment shows that these critical residues are conserved among JOXs from higher plants. Collectively, our study provides insights into the mechanism by which higher plants hydroxylate the hormone JA.

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.

Jasmonic Acid Signaling and Molecular Crosstalk with Other Phytohormones

Plants continually monitor their innate developmental status and external environment and make adjustments to balance growth, differentiation and stress responses using a complex and highly interconnected regulatory network composed of various signaling molecules and regulatory proteins. Phytohormones are an essential group of signaling molecules that work through a variety of different pathways conferring plasticity to adapt to the everchanging developmental and environmental cues. Of these, jasmonic acid (JA), a lipid-derived molecule, plays an essential function in controlling many different plant developmental and stress responses. In the past decades, significant progress has been made in our understanding of the molecular mechanisms that underlie JA metabolism, perception, signal transduction and its crosstalk with other phytohormone signaling pathways. In this review, we discuss the JA signaling pathways starting from its biosynthesis to JA-responsive gene expression, highlighting recent advances made in defining the key transcription factors and transcriptional regulatory proteins involved. We also discuss the nature and degree of crosstalk between JA and other phytohormone signaling pathways, highlighting recent breakthroughs that broaden our knowledge of the molecular bases underlying JA-regulated processes during plant development and biotic stress responses.

From Spaceflight to Mars g-Levels: Adaptive Response of A. Thaliana Seedlings in a Reduced Gravity Environment Is Enhanced by Red-Light Photostimulation

The response of plants to the spaceflight environment and microgravity is still not well understood, although research has increased in this area. Even less is known about plants' response to partial or reduced gravity levels. In the absence of the directional cues provided by the gravity vector, the plant is especially perceptive to other cues such as light. Here, we investigate the response of Arabidopsis thaliana 6-day-old seedlings to microgravity and the Mars partial gravity level during spaceflight, as well as the effects of red-light photostimulation by determining meristematic cell growth and proliferation. These experiments involve microscopic techniques together with transcriptomic studies. We demonstrate that microgravity and partial gravity trigger differential responses. The microgravity environment activates hormonal routes responsible for proliferation/growth and upregulates plastid/mitochondrial-encoded transcripts, even in the dark. In contrast, the Mars gravity level inhibits these routes and activates responses to stress factors to restore cell growth parameters only when red photostimulation is provided. This response is accompanied by upregulation of numerous transcription factors such as the environmental acclimation-related WRKY-domain family. In the long term, these discoveries can be applied in the design of bioregenerative life support systems and space farming.

Genome-Wide Characterization of Jasmonates Signaling Components Reveals the Essential Role of ZmCOI1a-ZmJAZ15 Action Module in Regulating Maize Immunity to Gibberella Stalk Rot

Gibberella stalk rot (GSR) by Fusarium graminearum causes significant losses of maize production worldwide. Jasmonates (JAs) have been broadly known in regulating defense against pathogens through the homeostasis of active JAs and COI-JAZ-MYC function module. However, the functions of different molecular species of JAs and COI-JAZ-MYC module in maize interactions with Fusarium graminearum and regulation of diverse metabolites remain unknown. In this study, we found that exogenous application of MeJA strongly enhanced resistance to GSR. RNA-seq analysis showed that MeJA activated multiple genes in JA pathways, which prompted us to perform a genome-wide screening of key JA signaling components in maize. Yeast Two-Hybrid, Split-Luciferase, and Pull-down assays revealed that the JA functional and structural mimic coronatine (COR) functions as an essential ligand to trigger the interaction between ZmCOIa and ZmJAZ15. By deploying CRISPR-cas9 knockout and Mutator insertional mutants, we demonstrated that coi1a mutant is more resistant, whereas jaz15 mutant is more susceptible to GSR. Moreover, JA-deficient opr7-5opr8-2 mutant displayed enhanced resistance to GSR compared to wild type. Together, these results provide strong evidence that ZmJAZ15 plays a pivotal role, whereas ZmCOIa and endogenous JA itself might function as susceptibility factors, in maize immunity to GSR.

Changes in Essential Oil Profile of Thymus daenensis Celak., Thymus fedtschenkoi Ronniger., and Thymus vulgaris L. Under Methyl Jasmonate Treatment

BACKGROUND

TThymus plants are well-known medicinal plants and it is believed that the pharmaceutical and therapeutical properties of these plants are related to their essential oils. The quality and quantity of the essential oils, as a secondary metabolite of an aromatic plant, are directly related to the physiological state of the plant. The role of jasmonates in the plant as signal molecules in mediation and up-regulation of plant defense and secondary metabolism processes is well recognized.

OBJECTIVE

With the aim of increasing the performance and stimulating secondary metabolites, this study evaluates the influence of the foliar application of MJ on essential oil content and composition of three different Thymus species, whether as an elicitor or an activator Method: The experiment was arranged in a randomized block design with MJ treatments in four levels (0, 30, 60, 100 mM) and three replications Results: Compared to the control, the essential oil content of all three species increased in all treatment levels. However, the changes in essential oil composition were different. Under MJ treatments, the amount of sesquiterpenes (especially caryophyllene oxide) increased in T. daenensis and T. fedtschenkoi. In addition, the amount of thymol in T. daenensis, thymol, and γ-terpinene in T. vulgaris increased, whereas carvacrol methyl ether in T. daenensis and p-cymene in T. vulgaris decreased.

CONCLUSION

IIt seems the type of plant species has a specific role in determining the response. There were no interpretable changes between treatment levels.

Characterization of a Plant Nuclear Matrix Constituent Protein in Liverwort

The nuclear lamina (NL) is a complex network of nuclear lamins and lamina-associated nuclear membrane proteins, which scaffold the nucleus to maintain structural integrity. In animals, type V intermediate filaments are the main constituents of NL. Plant genomes do not encode any homologs of these intermediate filaments, yet plant nuclei contain lamina-like structures that are present in their nuclei. In Arabidopsis thaliana, CROWDED NUCLEI (CRWN), which are required for maintaining structural integrity of the nucleus and specific perinuclear chromatin anchoring, are strong candidates for plant lamin proteins. Recent studies revealed additional roles of Arabidopsis Nuclear Matrix Constituent Proteins (NMCPs) in modulating plants' response to pathogen and abiotic stresses. However, detailed analyses of Arabidopsis NMCP activities are challenging due to the presence of multiple homologs and their functional redundancy. In this study, we investigated the sole NMCP gene in the liverwort Marchantia polymorpha (MpNMCP). We found that MpNMCP proteins preferentially were localized to the nuclear periphery. Using CRISPR/Cas9 techniques, we generated an MpNMCP loss-of-function mutant, which displayed reduced growth rate and curly thallus lobes. At an organelle level, MpNMCP mutants did not show any alteration in nuclear morphology. Transcriptome analyses indicated that MpNMCP was involved in regulating biotic and abiotic stress responses. Additionally, a highly repetitive genomic region on the male sex chromosome, which was preferentially tethered at the nuclear periphery in wild-type thalli, decondensed in the MpNMCP mutants and located in the nuclear interior. This perinuclear chromatin anchoring, however, was not directly controlled by MpNMCP. Altogether, our results unveiled that NMCP in plants have conserved functions in modulating stress responses.

Ultraviolet Radiation From a Plant Perspective: The Plant-Microorganism Context

Ultraviolet (UV) radiation directly affects plants and microorganisms, but also alters the species-specific interactions between them. The distinct bands of UV radiation, UV-A, UV-B, and UV-C have different effects on plants and their associated microorganisms. While UV-A and UV-B mainly affect morphogenesis and phototropism, UV-B and UV-C strongly trigger secondary metabolite production. Short wave (<350 nm) UV radiation negatively affects plant pathogens in direct and indirect ways. Direct effects can be ascribed to DNA damage, protein polymerization, enzyme inactivation and increased cell membrane permeability. UV-C is the most energetic radiation and is thus more effective at lower doses to kill microorganisms, but by consequence also often causes plant damage. Indirect effects can be ascribed to UV-B specific pathways such as the UVR8-dependent upregulated defense responses in plants, UV-B and UV-C upregulated ROS accumulation, and secondary metabolite production such as phenolic compounds. In this review, we summarize the physiological and molecular effects of UV radiation on plants, microorganisms and their interactions. Considerations for the use of UV radiation to control microorganisms, pathogenic as well as non-pathogenic, are listed. Effects can be indirect by increasing specialized metabolites with plant pre-treatment, or by directly affecting microorganisms.

Knockdown of the DUF647 family member RUS4 impairs stamen development and pollen maturation in Arabidopsis

ROOT UV-B SENSITIVE4 (RUS4) encodes a Domain of Unknown Function647 (DUF647) protein, whose function is poorly understood. We have previously shown the artificial microRNA knockdown Arabidopsis RUS4 plants, referred to as amiR-RUS4, have severely reduced male fertility with a defect in anther dehiscence. Here, we show that amiR-RUS4 plants are also defective in pollen maturation and germination. Promoter-reporter analysis shows that RUS4 is highly expressed in tapetal layer, developing microspores, mature and germinating pollen, strongly suggesting its role in the process of pollen maturation. As the translational RUS4-GFP fusion protein has been localized to the chloroplasts where the first step of jasmonic acid (JA) biosynthesis takes place, leading to the hypothesis that RUS4 may be involved in JA-mediated stamen development. We show that expression of several JA metabolic genes increased markedly in flower buds of the amiR-RUS4 plants compared to that of the wild-type. We further show that transcript abundance of a clade of the JA-responsive MYB transcript factor genes, especially MYB108, reduced significantly in stamens of amiR-RUS4 plants relative to the wild-type; these MYB transcript factors have been shown to be required for JA-mediated stamen and pollen maturation. Our data suggest that RUS4 may play a role in coordinating anther dehiscence and pollen maturation by affecting the expression of JA-related genes.

Effects of exogenous methyl jasmonate on the synthesis of endogenous jasmonates and the regulation of photosynthesis in citrus

Methyl jasmonate (MeJA) is an airborne signaling phytohormone that can induce changes in endogenous jasmonates (JAs) and cause photosynthetic responses. However, the response of these two aspects of citrus plants at different MeJA concentrations is still unclear. Four MeJA concentrations were used in two citrus varieties, Huangguogan (C. reticulata × C. sinensis) and Shiranuhi [C. reticulata × (C. reticulata × C. sinensis)], to investigate the effects of MeJA dose on the endogenous JAs pathway and photosynthetic capacity. We observed that MeJA acted in a dose-dependent manner, and its stimulation in citrus leaves showed a bidirectional character at different concentrations. This work demonstrates that MeJA at only a concentration of 2.2 mM or less contributed to the activation of magnesium protoporphyrin IX methyltransferase (ChlM, EC 2.1.1.11) and protochlorophyllide oxidoreductase (POR, EC 1.3.1.11) and the simultaneous accumulation of Chl a and Chl b, which in turn contributed to an improved photosynthetic capacity and PSII photochemistry efficiency of citrus. Meanwhile, the inhibition of endogenous JAs synthesis by exogenous MeJA was observed. This was achieved by reducing the ratio of monogalactosyl diacylglycerol (MGDG) to diagalactosyl diacylglycerol (DGDG) and inhibiting the activities of key enzymes in JAs synthesis, especially 12-oxo-phytodienoic acid reductase (OPR, EC 1.3.1.42). Another noteworthy finding is that there may exist a JA-independent pathway that could regulate 12-oxo-phytodienoic acid (OPDA) synthesis. This study jointly analyzed the internal hormone regulation mechanism and the external physiological response, as well as revealed the effects of exogenous MeJA on promoting the photosynthesis and inhibiting the endogenous JAs synthesis.

De novo transcriptome analysis of the critically endangered alpine Himalayan herb Nardostachys jatamansi reveals the biosynthesis pathway genes of tissue-specific secondary metabolites

The study is the first report on de novo transcriptome analysis of Nardostachys jatamansi, a critically endangered medicinal plant of alpine Himalayas. Illumina GAIIx sequencing of plants collected during end of vegetative growth (August) yielded 48,411 unigenes. 74.45% of these were annotated using UNIPROT. GO enrichment analysis, KEGG pathways and PPI network indicated simultaneous utilization of leaf photosynthates for flowering, rhizome fortification, stress response and tissue-specific secondary metabolites biosynthesis. Among the secondary metabolite biosynthesis genes, terpenoids were predominant. UPLC-PDA analysis of in vitro plants revealed temperature-dependent, tissue-specific differential distribution of various phenolics. Thus, as compared to 25 °C, the phenolic contents of both leaves (gallic acid and rutin) and roots (p-coumaric acid and cinnamic acid) were higher at 15 °C. These phenolics accounted for the therapeutic properties reported in the plant. In qRT-PCR of in vitro plants, secondary metabolite biosynthesis pathway genes showed higher expression at 15 °C and 14 h/10 h photoperiod (conditions representing end of vegetative growth period). This provided cues for in vitro modulation of identified secondary metabolites. Such modulation of secondary metabolites in in vitro systems can eliminate the need for uprooting N. jatamansi from wild. Hence, the study is a step towards effective conservation of the plant.

Label-free comparative proteomic and physiological analysis provides insight into leaf color variation of the golden-yellow leaf mutant of Lagerstroemia indica

GL1 is a golden-yellow leaf mutant that cultivated from natural bud-mutation of Lagerstroemia indica and has a very low level of photosynthetic pigment under sunlight. GL1 can gradually increase its pigment content and turn into pale-green leaf when shading under sunshade net (referred as Re-GL1). The mechanisms that cause leaf color variation are complicated and are not still unclear. Here, we have used a label-free comparative proteomics to investigate differences in proteins abundance and analyze the specific biological process associated with mechanisms of leaf color variation in GL1. A total of 245 and 160 proteins with different abundance were identified in GL1 vs WT and GL1 vs Re-GL1, respectively. Functional classification analysis revealed that the proteins with different abundance mainly related to photosynthesis, heat shock proteins, ribosome proteins, and oxidation-reduction. The proteins that the most significantly contributed to leaf color variation were photosynthetic proteins of PSII and PSI, which directly related to photooxidation and determined the photosynthetic performance of photosystem. Further analysis demonstrated that low jasmonic acid content was needed to golden-yellow leaf GL1. These findings lay a solid foundation for future studies into the molecular mechanisms that underlie leaf color formation of GL1. BIOLOGICAL SIGNIFICANCE: The natural bud mutant GL1 of L. indica is an example through changing leaf color to cope with complex environment. However, the molecular mechanism of leaf color variation are largely elusive. The proteins with different abundance identified from a label-free comparative proteomics revealed a range of biological processes associated with leaf color variation, including photosynthesis, oxidation-reduction and jasmonic acid signaling. The photooxidation and low level of jasmonic acid played a primary role in GL1 adaptation in golden-yellow leaf. These findings provide possible pathway or signal for the molecular mechanism associated with leaf color formation and as a valuable resource for signal transaction of chloroplast.

Genome-Wide Analysis of OPR Family Genes in Cotton Identified a Role for GhOPR9 in Verticillium dahliae Resistance

The 12-oxo-phytodienoic acid reductases (OPRs) have been proven to play a major role in plant development and growth. Although the classification and functions of OPRs have been well understood in Arabidopsis, tomato, rice, maize, and wheat, the information of OPR genes in cotton genome and their responses to biotic and abiotic stresses have not been reported. In this study, we found 10 and 9 OPR genes in Gossypium hirsutum and Gossypium barbadense, respectively. They were classified into three groups, based on the similar gene structure and conserved protein motifs. These OPR genes just located on chromosome 01, chromosome 05, and chromosome 06. In addition, the whole genome duplication (WGD) or segmental duplication events contributed to the evolution of the OPR gene family. The analyses of cis-acting regulatory elements of GhOPRs showed that the functions of OPR genes in cotton might be related to growth, development, hormone, and stresses. Expression patterns showed that GhOPRs were upregulated under salt treatment and repressed by polyethylene glycol 6000 (PEG6000). The expression patterns of GhOPRs were different in leaf, root, and stem under V. dahliae infection. GhOPR9 showed a higher expression level than other OPR genes in cotton root. The virus-induced gene silencing (VIGS) analysis suggested that knockdown of GhOPR9 could increase the susceptibility of cotton to V. dahliae infection. Furthermore, GhOPR9 also modulated the expressions of jasmonic acid (JA) pathway-regulated genes under the V. dahliae infection. Overall, our results provided the evolution and potential functions of the OPR genes in cotton. These findings suggested that GhOPR9 might play an important role in cotton resistance to V. dahliae.

The β-ketoacyl-CoA synthase KCS13 regulates the cold response in cotton by modulating lipid and oxylipin biosynthesis

Cold stress is a key environmental factor that affects plant development and productivity. In this study, RNA-seq in cotton following cold-stress treatment resulted in the identification of 5239 differentially expressed genes (DEGs) between two cultivars with differing sensitivity to low temperatures, among which GhKCS13 was found to be involved in the response. Transgenic plants overexpressing GhKCS13 showed increased sensitivity to cold stress. KEGG analysis of 418 DEGs in both GhKCS13-overexpressing and RNAi lines after treatment at 4 °C indicated that lipid biosynthesis and linoleic acid metabolism were related to cold stress. ESI-MS/MS analysis showed that overexpression of GhKCS13 led to modifications in the composition of sphingolipids and glycerolipids in the leaves, which might alter the fluidity of the cell membrane under cold conditions. In particular, differences in levels of jasmonic acid (JA) in GhKCS13 transgenic lines suggested that, together with lysophospholipids, it might mediate the cold-stress response. Our results suggest that overexpression of GhKCS13 probably causes remodeling of lipids in the endoplasmic reticulum and biosynthesis of lipid-derived JA in chloroplasts, which might account for the increased sensitivity to cold stress in the transgenic plants. Complex interactions between lipid components, lipid signaling molecules, and JA appear to determine the response to cold stress in cotton.

Role of Cytochrome P450 Enzymes in Plant Stress Response

Cytochrome P450s (CYPs) are the largest enzyme family involved in NADPH- and/or O₂-dependent hydroxylation reactions across all the domains of life. In plants and animals, CYPs play a central role in the detoxification of xenobiotics. In addition to this function, CYPs act as versatile catalysts and play a crucial role in the biosynthesis of secondary metabolites, antioxidants, and phytohormones in higher plants. The molecular and biochemical processes catalyzed by CYPs have been well characterized, however, the relationship between the biochemical process catalyzed by CYPs and its effect on several plant functions was not well established. The advent of next-generation sequencing opened new avenues to unravel the involvement of CYPs in several plant functions such as plant stress response. The expression of several CYP genes are regulated in response to environmental stresses, and they also play a prominent role in the crosstalk between abiotic and biotic stress responses. CYPs have an enormous potential to be used as a candidate for engineering crop species resilient to biotic and abiotic stresses. The objective of this review is to summarize the latest research on the role of CYPs in plant stress response.

Methyl Jasmonate Applications From Flowering to Ripe Fruit Stages of Strawberry (Fragaria × ananassa 'Camarosa') Reinforce the Fruit Antioxidant Response at Post-harvest

Preharvest applications of methyl jasmonate (MeJA) have been shown to improve post-harvest fruit quality in strawberry fruit. However, the effectiveness of consecutive field applications at different phenological stages on the reinforcement of the antioxidant capacity remains to be analyzed. To determine the best antioxidant response of strawberry (Fragaria × ananassa 'Camarosa') fruit to different numbers and timing of MeJA applications, we performed three differential preharvest treatments (M1, M2, and M3) consisted of successive field applications of 250 μmol L^-1 MeJA at flowering (M3), large green (M2 and M3), and ripe fruit stages (M1, M2, and M3). Then, we analyzed their effects on fruit quality parameters [firmness, skin color, soluble solids content/titratable acidity (SSC/TA) ratio, fruit weight at harvest, and weight loss] along with anthocyanin and proanthocyanidin (PA) accumulation; the antioxidant-related enzymatic activity of catalase (CAT), guaiacol peroxidase (POX), and ascorbate peroxidase (APX); the total flavonoid and phenolic contents, antioxidant capacity, and ascorbic acid content (AAC) during post-harvest storage (0, 24, 48, and 72 h). We also evaluated the effect on lignin, total carbon and nitrogen (%C and N), lipid peroxidation, and C and N isotopes signatures on fruits. Remarkably, the results indicated that MeJA treatment increases anthocyanin and PA contents as well as CAT activity in post-harvest storage, depending on the number of preharvest MeJA applications. Also, M3 fruit showed a higher AAC compared to control at 48 and 72 h. Noticeably, the anthocyanin content and CAT activity were more elevated in M3 treatment comparing with control at all post-harvest times. In turn, APX activity was found higher on all MeJA-treated fruit independent of the number of applications. Unlike, MeJA applications did not generate variations on fruit firmness and weight, lignin contents,% C and N, and in lipid peroxidation and water/nitrogen use efficiency according to C and N isotope discrimination. Finally, we concluded that an increasing number of MeJA applications (M3 treatment) improve anthocyanin, PA, AAC, and CAT activity that could play an essential role against reactive oxygen species, which cause stress that affects fruits during post-harvest storage.

Evolution of Plant Hormone Response Pathways

This review focuses on the evolution of plant hormone signaling pathways. Like the chemical nature of the hormones themselves, the signaling pathways are diverse. Therefore, we focus on a group of hormones whose primary perception mechanism involves an Skp1/Cullin/F-box-type ubiquitin ligase: auxin, jasmonic acid, gibberellic acid, and strigolactone. We begin with a comparison of the core signaling pathways of these four hormones, which have been established through studies conducted in model organisms in the Angiosperms. With the advent of next-generation sequencing and advanced tools for genetic manipulation, the door to understanding the origins of hormone signaling mechanisms in plants beyond these few model systems has opened. For example, in-depth phylogenetic analyses of hormone signaling components are now being complemented by genetic studies in early diverging land plants. Here we discuss recent investigations of how basal land plants make and sense hormones. Finally, we propose connections between the emergence of hormone signaling complexity and major developmental transitions in plant evolution.

Interactions between sucrose and jasmonate signalling in the response to cold stress

BACKGROUND

Jasmonates play an important role in plant stress and defence responses and are also involved in the regulation of anthocyanin synthesis in response to sucrose availability. Here we explore the signalling interactions between sucrose and jasmonates in response to cold stress in Arabidopsis.

RESULTS

Sucrose and cold treatments increased anthocyanin content additively. Comprehensive profiling of phytohormone contents demonstrated that jasmonates, salicylic acid and abscisic acid contents increased in response to sucrose treatment in plants grown on agar, but remained considerably lower than in plants grown in compost. The gibberellin GA3 accumulated in response to sucrose treatment but only at warm temperature. The role of jasmonate signalling was explored using the jasmonate response mutants jar1-1 and coi1-16. While the jar1-1 mutant lacked jasmonate-isoleucine and jasmonate-leucine, it accumulated 12-oxo-phytodienoic acid at low temperature on agar medium. Altered patterns of abscisic acid accumulation and higher sugar contents were found in the coi1-16 mutant when grown in compost. Both mutants were able to accumulate anthocyanin and to cold acclimate, but the jar-1-1 mutant showed a larger initial drop in whole-rosette photosystem II efficiency upon transfer to low temperature.

CONCLUSIONS

Hormone contents are determined by interactions between temperature and sucrose supply. Some of these effects may be caused indirectly through senescence initiation in response to sucrose availability. During cold stress, the adjustments of hormone contents may compensate for impaired jasmonate signalling, enabling cold acclimation and anthocyanin accumulation in Arabidopsis jasmonate response mutants, e.g. through antagonistic interactions between gibberellin and jasmonate signalling.

Gossypium hirsutum Salt Tolerance Is Enhanced by Overexpression of G. arboreum JAZ1

Gossypium arboreum possesses many favorable traits including robust defense against biotic and abiotic stress although it has been withdrawn from the market because of lower yield and fiber quality compared to G. hirsutum (upland cotton). It is therefore important to explore and utilize the beneficial genes of G. arboretum for G. hirsutum cultivar breeding. Here, the function of G. arboreum JAZ1 in tolerance to salt stress was determined through loss-of-function analysis. GaJAZ1can interact with GaMYC2 to repress expression of downstream genes whose promoters contain a G-box cis element, affecting plant tolerance to salinity stress. The experimental data from NaCl treatments and a 2 year continuous field trial with natural saline-alkaline soil showed that the ectopically overexpressed GaJAZ1 significantly increased salt tolerance in upland cotton compared to the wild type, showing higher growth vigor with taller plants, increased fresh weight, and more bolls, which is due to reprogrammed expression of tolerance-related genes and promotion of root development. High-throughput RNA sequencing of GaJAZ1 transgenic and wild-type plants showed many differentially expressed genes involved in JA signaling and biosynthesis, salt stress-related genes, and hormone-related genes, suggesting that overexpressing GaJAZ1 can reprogram the expression of defense-related genes in G. hirsutum plants to increase tolerance to salt stress. The research provides a foundation to explore and utilize favorable genes from Gossypium species for upland cotton cultivar breeding.

JA-Ile-macrolactone 5b Induces Tea Plant (Camellia sinensis) Resistance to Both Herbivore Ectropis obliqua and Pathogen Colletotrichum camelliae

Jasmonates (JAs), the group of lipid-derived hormones, were found to control the defense responses in a myriad of plants. Meaningfully, the macrolactones of 12-hydroxy jasmonate isoleucine (12OH-JA-Ile) were reported to induce the defensive response of wild tobacco. However, little to nothing has been known about the elicitation effect of JA-Ile-macrolactones on woody plants to harmful organisms, let alone its underlying mechanisms. Here, we first optimized the synthetic routine using mild toxic reagent isobutyl chloroformate instead of ethyl chloroformate for conjugation, and we used acetonitrile (MeCN) instead of ethyl alcohol for the better dissolution of p-toluenesulfonic acid (p-TsOH) to gain JA-Ile-macrolactones. JA-Ile-macrolactone 5b-treated tea plants significantly inhibited the larvae weight gain of Ectropis obliqua larvae and the lesions caused by Colletotrichum camelliae. Furthermore, the expression level of CsOPR3 was significantly upregulated in 5b-treated leaves. Meanwhile, 5b reduced the accumulation of eriodictyol 7-O-glucuronide (EDG) in tea plants, which was confirmed to promote the growth rate of E. obliqua larvae by artificial diet assay. In conclusion, our study proved that the exogenous application of 5b could induce the tea plant resistance both to herbivore E. obliqua and pathogen C. camelliae, and EDG was identified as one of the secondary metabolites that could influence the growth rate of E. obliqua, but it did not directly influence the infection of C. camelliae in vitro. Further research should be carried out to clarify the mechanism through which 5b induces tea plant resistance to C. camelliae.

Functions of Jasmonic Acid in Plant Regulation and Response to Abiotic Stress

Jasmonic acid (JA) is an endogenous growth-regulating substance, initially identified as a stress-related hormone in higher plants. Similarly, the exogenous application of JA also has a regulatory effect on plants. Abiotic stress often causes large-scale plant damage. In this review, we focus on the JA signaling pathways in response to abiotic stresses, including cold, drought, salinity, heavy metals, and light. On the other hand, JA does not play an independent regulatory role, but works in a complex signal network with other phytohormone signaling pathways. In this review, we will discuss transcription factors and genes involved in the regulation of the JA signaling pathway in response to abiotic stress. In this process, the JAZ-MYC module plays a central role in the JA signaling pathway through integration of regulatory transcription factors and related genes. Simultaneously, JA has synergistic and antagonistic effects with abscisic acid (ABA), ethylene (ET), salicylic acid (SA), and other plant hormones in the process of resisting environmental stress.

Chitosan-Based Layer-by-Layer Assembly: Towards Application on Quality Maintenance of Lemon Fruits

We fabricated a novel chitosan-carboxymethyl cellulose (CMC) layer-by-layer assembly system to facilitate the postharvest quality of the fresh produce. Fourier transform infrared spectroscopy (FTIR), TA-XT2 texture analyzer, water vapor permeability (WVP) analyzer, and scanning electron microscopy (SEM) were applied to compare the properties of chitosan and layer-by-layer assembly. The strategy involved the optimization of water vapor permeability, puncture strength, and elasticity properties of multiplayer polymer coating. Results showed that the lemon (Citrus limon (L.) Burm. f.), coated by chitosan-CMC layer-by-layer assembly, displayed significantly higher lemon firmness and vitamin C content with excellent morphology, as well as inhibited weight loss and flesh browning. This study could provide support for quality maintenance in the fruit and vegetable industry and make a significant contribution to the utilization of the natural polysaccharide as a viable resource.

Jasmonic Acid Signaling Pathway in Response to Abiotic Stresses in Plants

Plants as immovable organisms sense the stressors in their environment and respond to them by means of dedicated stress response pathways. In response to stress, jasmonates (jasmonic acid, its precursors and derivatives), a class of polyunsaturated fatty acid-derived phytohormones, play crucial roles in several biotic and abiotic stresses. As the major immunity hormone, jasmonates participate in numerous signal transduction pathways, including those of gene networks, regulatory proteins, signaling intermediates, and proteins, enzymes, and molecules that act to protect cells from the toxic effects of abiotic stresses. As cellular hubs for integrating informational cues from the environment, jasmonates play significant roles in alleviating salt stress, drought stress, heavy metal toxicity, micronutrient toxicity, freezing stress, ozone stress, CO₂ stress, and light stress. Besides these, jasmonates are involved in several developmental and physiological processes throughout the plant life. In this review, we discuss the biosynthesis and signal transduction pathways of the JAs and the roles of these molecules in the plant responses to abiotic stresses.

Preharvest application of methyl jasmonate increases crop yield, fruit quality and bioactive compounds in pomegranate 'Mollar de Elche' at harvest and during postharvest storage

BACKGROUND

Previous reports have addressed the effectiveness of postharvest methyl jasmonate (MeJA) treatments on maintaining quality properties of pomegranate fruit during storage. However, there is no literature regarding the effects of preharvest MeJA treatments on pomegranate 'Mollar de Elche' crop yield, fruit ripening, quality attributes and bioactive compounds content (at harvest or after long-term storage), which were evaluated in this research.

RESULTS

Preharvest MeJA treatments (1, 5, and 10 mmol L^-1 ) increased pomegranate crop yield. MeJA at 1 and 5 mmol L^-1 accelerated the on-tree ripening process, while it was delayed with 10 mmol L^-1 . Losses in fruit weight, firmness and organic acids during storage at 10 °C were delayed in MeJA treated fruit, leading to quality maintenance. In addition, MeJA treatments improved arils colour due to increased concentration of total and individual anthocyanins, at harvest and during storage. Total phenolic and ascorbic acid contents and total antioxidant activity [hydrophilic (H-TAA) and lipophilic (L-TAA) fractions] were also higher in arils from treated pomegranate fruits than in controls.

CONCLUSION

Preharvest treatments with MeJA could be a promising tool to improve pomegranate crop yield, fruit quality and its content in bioactive compounds at harvest and during storage. The higher effects were obtained with MeJA at 5 mmol L^-1 dose, which could be the selected treatment for practical application purposes. © 2019 Society of Chemical Industry.

Novel crosstalk between ethylene- and jasmonic acid-pathway responses to a piercing-sucking insect in rice

Ethylene (ET) and jasmonic acid (JA) play important roles in plant defenses against biotic stresses. Crosstalk between JA and ET has been well studied in mediating pathogen resistance, but its roles in piercing-sucking insect resistance are unclear. The brown planthopper (BPH; Nilaparvata lugens) is the most notorious piercing-sucking insect specific to rice (Oryza sativa) that severely affects yield. A genetic analysis revealed that OsEBF1 and OsEIL1, which are in the ET signaling pathway, positively and negatively regulated BPH resistance, respectively. Molecular and biochemical analyses revealed direct interactions between OsEBF1 and OsEIL1. OsEBF1, an E3 ligase, mediated the degradation of OsEIL1 through the ubiquitination pathway, indicating the negative regulation of the ET-signaling pathway in response to BPH infestation. An RNA sequencing analysis revealed that a JA biosynthetic pathway-related gene, OsLOX9, was downregulated significantly in the oseil1 mutant. Biochemical analyses, including yeast one-hybrid, dual luciferase, and electrophoretic mobility shift assay, confirmed the direct regulation of OsLOX9 by OsEIL1. This study revealed the synergistic and negative regulation of JA and ET pathways in response to piercing-sucking insect attack. The synergistic mechanism was realized by transcriptional regulation of OsEIL1 on OsLOX9. OsEIL1-OsLOX9 is a novel crosstalk site in these two phytohormone signaling pathways.

α-Ionone, an Apocarotenoid, Induces Plant Resistance to Western Flower Thrips, Frankliniella occidentalis, Independently of Jasmonic Acid

Apocarotenoids, such as β-cyclocitral, α-ionone, β-ionone, and loliolide, are derived from carotenes via chemical or enzymatic processes. Recent studies revealed that β-cyclocitral and loliolide play an important role in various aspects of plant physiology, such as stress responses, plant growth, and herbivore resistance. However, information on the physiological role of α-ionone is limited. We herein investigated the effects of α-ionone on plant protection against herbivore attacks. The pretreatment of whole tomato (Solanum lycopersicum) plants with α-ionone vapor decreased the survival rate of western flower thrips (Frankliniella occidentalis) without exhibiting insecticidal activity. Exogenous α-ionone enhanced the expression of defense-related genes, such as basic β-1,3-glucanase and basic chitinase genes, in tomato leaves, but not that of jasmonic acid (JA)- or loliolide-responsive genes. The pretreatment with α-ionone markedly decreased egg deposition by western flower thrips in the JA-insensitive Arabidopsis (Arabidopsis thaliana) mutant coi1-1. We also found that common cutworm (Spodoptera litura) larvae fed on α-ionone-treated tomato plants exhibited a reduction in weight. These results suggest that α-ionone induces plant resistance to western flower thrips through a different mode of action from that of JA and loliolide.

Conjunctive Analyses of BSA-Seq and BSR-Seq to Reveal the Molecular Pathway of Leafy Head Formation in Chinese Cabbage

As the storage organ of Chinese cabbage, the leafy head was harvested as a commercial product due to its edible value. In this study, the bulked segregant analysis (BSA) and bulked segregant RNA-Seq (BSR) were performed with F2 separation progeny to study the molecular mechanism of leafy head formation in Chinese cabbage. BSA-Seq analysis located four candidate regions containing 40 candidate genes, while BSR-Seq analysis revealed eight candidate regions containing 607 candidate genes. The conjunctive analyses of these two methods identified that Casein kinase gene BrCKL8 (Bra035974) is the common candidate gene related with leafy head formation in Chinese cabbage, and it showed high expression levels at the three segments of heading type plant leaves. The differentially expressed genes (DEGs) between two set pairs of cDNA sequencing bulks were divided into two categories: one category was related with five hormone pathways (Auxin, Ethylene, Abscisic acid, Jasmonic acid and Gibberellin), the other category was composed of genes that associate with the calcium signaling pathway. Moreover, a series of upregulated transcriptional factors (TFs) were also identified by the association analysis of BSR-Seq analysis. The leafy head development was regulated by various biological processes and effected by diverse external environment factors, so our research will contribute to the breeding of perfect leaf-heading types of Chinese cabbage.

A Meta-Analysis of Comparative Transcriptomic Data Reveals a Set of Key Genes Involved in the Tolerance to Abiotic Stresses in Rice

Several environmental factors, such as drought, salinity, and extreme temperatures, negatively affect plant growth and development, which leads to yield losses. The tolerance or sensitivity to abiotic stressors are the expression of a complex machinery involving molecular, biochemical, and physiological mechanisms. Here, a meta-analysis on previously published RNA-Seq data was performed to identify the genes conferring tolerance to chilling, osmotic, and salt stresses, by comparing the transcriptomic changes between tolerant and susceptible rice genotypes. Several genes encoding transcription factors (TFs) were identified, suggesting that abiotic stress tolerance involves upstream regulatory pathways. A gene co-expression network defined the metabolic and signalling pathways with a prominent role in the differentiation between tolerance and susceptibility: (i) the regulation of endogenous abscisic acid (ABA) levels, through the modulation of genes that are related to its biosynthesis/catabolism, (ii) the signalling pathways mediated by ABA and jasmonic acid, (iii) the activity of the "Drought and Salt Tolerance" TF, involved in the negative regulation of stomatal closure, and (iv) the regulation of flavonoid biosynthesis by specific MYB TFs. The identified genes represent putative key players for conferring tolerance to a broad range of abiotic stresses in rice; a fine-tuning of their expression seems to be crucial for rice plants to cope with environmental cues.

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.

Pre-harvest methyl jasmonate treatments increase antioxidant systems in lemon fruit without affecting yield or other fruit quality parameters

BACKGROUND

Jasmonic acid (JA) and its volatile derivative methyl jasmonate (MeJA) are hormones involved in the regulation of many processes in plants and act (when applied as a post- or pre-harvest treatment) to increase fruit bioactive compounds with antioxidant potential. However, there is no literature available regarding the effect of pre-harvest MeJA treatment on lemon fruit antioxidant systems, which was the aim of the present study.

RESULTS

MeJA treatment (0.1, 0.5 and 1.0 mmol L^-1 ) increased antioxidant compounds, such as phenolics, in the juice and flavedo of 'Fino' and 'Verna' lemons at harvest, with the most effective concentration being 0.1 mmol L^-1 in both cultivars. In addition, catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) activities were also increased by MeJA treatment, with the highest increases being also found with 0.1 mmol L^-1 . The increases in APX and CAT were maintained from one treatment to another during fruit development on the tree, whereas the increase on POD disappeared after 8-10 days of each treatment. For both antioxidant systems, the highest increases were found in lemon harvested at the commercial ripening stage. By contrast, crop yield, fruit ripening process and quality parameters were generally not affected by MeJA treatment.

CONCLUSION

Preharvest MeJA treatment could be a useful tool for increasing antioxidant potential and the health beneficial effects of lemon fruit consumption, given the relationship between these properties and phenolic content. Moreover, the increased concentration of phenolics and the activity of antioxidant enzymes in the flavedo of MeJA treated fruit could increase lemon tolerance to chilling injury and decay during postharvest storage. © 2019 Society of Chemical Industry.

Omega hydroxylated JA-Ile is an endogenous bioactive jasmonate that signals through the canonical jasmonate signaling pathway

Jasmonates are fatty acid derivatives that control several plant processes including growth, development and defense. Despite the chemical diversity of jasmonates, only jasmonoyl-L-isoleucine (JA-Ile) has been clearly characterized as the endogenous ligand of the jasmonate co-receptors (COI1-JAZs) in higher plants. Currently, it is accepted that ω-hydroxylation of JA-Ile leads to inactivation of the molecule. This study shows that ω-hydroxylated JA-Ile (12-OH-JA-Ile) retains bioactivity and signals through the canonical JA-pathway. The results suggest that 12-OH-JA-Ile differentially activates a subset of JA-Ile co-receptors that may control and/or modulate particular jasmonate dependent responses. It is proposed that after a strong immune response mediated by JA-Ile, the ω-hydroxylated form modulates JA-Ile activated processes thereby improving plant resilience.

Secondary sulfur metabolism in cellular signalling and oxidative stress responses

The sulfur metabolism pathway in plants produces a variety of compounds that are central to the acclimation response to oxidative stresses such as drought and high light. Primary sulfur assimilation provides the amino acid cysteine, which is utilized in protein synthesis and as a precursor for the cellular redox buffer glutathione. In contrast, the secondary sulfur metabolism pathway produces sulfated compounds such as glucosinolates and sulfated peptides, as well as a corresponding by-product 3'-phosphoadenosine 5'-phosphate (PAP). Emerging evidence over the past decade has shown that secondary sulfur metabolism also has a crucial engagement during oxidative stress. This occurs across various cellular, tissue, and organismal levels including chloroplast-to-nucleus retrograde signalling events mediated by PAP, modulation of hormonal signalling by sulfated compounds and PAP, control of physiological responses such as stomatal closure, and potential regulation of plant growth. In this review, we examine the contribution of the different components of plant secondary metabolism to oxidative stress homeostasis, and how this pathway is metabolically regulated. We further outline the key outstanding questions in the field that are necessary to understand how and why this 'specialized' metabolic pathway plays significant roles in plant oxidative stress tolerance.

Biosynthesis of Jasmonates from Linoleic Acid by the Fungus Fusarium oxysporum. Evidence for a Novel Allene Oxide Cyclase

Fusarium oxysporum f. sp. tulipae (FOT) secretes (+)-7-iso-jasmonoyl-(S)-isoleucine ((+)-JA-Ile) to the growth medium together with about 10 times less 9,10-dihydro-(+)-7-iso-JA-Ile. Plants and fungi form (+)-JA-Ile from 18:3n-3 via 12-oxophytodienoic acid (12-OPDA), which is formed sequentially by 13S-lipoxygenase, allene oxide synthase (AOS), and allene oxide cyclase (AOC). Plant AOC does not accept linoleic acid (18:2n-6)-derived allene oxides and dihydrojasmonates are not commonly found in plants. This raises the question whether 18:2n-6 serves as the precursor of 9,10-dihydro-JA-Ile in Fusarium, or whether the latter arises by a putative reductase activity operating on the n-3 double bond of (+)-JA-Ile or one of its precursors. Incubation of pentadeuterated (d₅ ) 18:3n-3 with mycelia led to the formation of d₅ -(+)-JA-Ile whereas d₅ -9,10-dihydro-JA-Ile was not detectable. In contrast, d₅ -9,10-dihydro-(+)-JA-Ile was produced following incubation of [17,17,18,18,18-² H₅ ]linoleic acid (d₅ -18:2n-6). Furthermore, 9(S),13(S)-12-oxophytoenoic acid, the 15,16-dihydro analog of 12-OPDA, was formed upon incubation of unlabeled or d₅ -18:2n-6. Appearance of the α-ketol, 12-oxo-13-hydroxy-9-octadecenoic acid following incubation of unlabeled or [¹³ C₁₈ ]-labeled 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid confirmed the involvement of AOS and the biosynthesis of the allene oxide 12,13(S)-epoxy-9,11-octadecadienoic acid. The lack of conversion of this allene oxide by AOC in higher plants necessitates the conclusion that the fungal AOC is distinct from the corresponding plant enzyme.

Jasmonate action in plant defense against insects

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

Regulatory-Associated Protein of TOR 1B (RAPTOR1B) regulates hormonal switches during seed germination in Arabidopsis thaliana

Target of Rapamycin (TOR) regulates multiple growth- and metabolic-related processes in Arabidopsis thaliana as in all other eukaryotes. While several of these processes have been investigated in diverse Arabidopsis growth stages, little is known about hormonal and metabolic regulation of TOR during seed germination. This is mainly due to the fact that Arabidopsis knockout lines of TOR are embryo lethal. Here, we utilized the knockout lines of TOR-interacting protein, REGULATORY-ASSOCIATED PROTEIN OF TOR 1B (RAPTOR1B), to perform comprehensive hormone profiling during seed germination. We previously reported that RAPTOR1B positively regulates seed germination by maintaining the nutritional and hormonal balance. In the current analysis, dry and imbibed seeds as well as germinated seeds were subjected to detailed hormone analysis. Accordingly, the abscisic acid content of dry and imbibed raptor1b seeds was higher than that of WT, while the amounts of gibberellins were comparable after stratification. Further analysis showed that raptor1b seeds maintained higher levels of indole-3-acetic acid and jasmonates, namely jasmonic acid (JA) and 12-oxo-phytodienoic acid, even after stratification. The combination of this hormonal perturbation seems to be the driving factor for the observed delayed germination phenotypes in raptor1b seeds.

Genome-Wide Identification and Characterization of the OPR Gene Family in Wheat (Triticum aestivum L.)

The 12-oxo-phytodienoic acid reductases (OPRs), which belong to the old yellow enzyme (OYE) family, are flavin mononucleotide (FMN)-dependent oxidoreductases with critical functions in plants. Despite the clear characteristics of growth and development, as well as the defense responses in Arabidopsis, tomato, rice, and maize, the potential roles of OPRs in wheat are not fully understood. Here, forty-eight putative OPR genes were found and classified into five subfamilies, with 6 in sub. I, 4 in sub. II, 33 in sub. III, 3 in sub. IV, and 2 in sub. V. Similar gene structures and conserved protein motifs of TaOPRs in wheat were identified in the same subfamilies. An analysis of cis-acting elements in promoters revealed that the functions of OPRs in wheat were mostly related to growth, development, hormones, biotic, and abiotic stresses. A total of 14 wheat OPR genes were identified as tandem duplicated genes, while 37 OPR genes were segmentally duplicated genes. The expression patterns of TaOPRs were tissue- and stress-specific, and the expression of TaOPRs could be regulated or induced by phytohormones and various stresses. Therefore, there were multiple wheat OPR genes, classified into five subfamilies, with functional diversification and specific expression patterns, and to our knowledge, this was the first study to systematically investigate the wheat OPR gene family. The findings not only provide a scientific foundation for the comprehensive understanding of the wheat OPR gene family, but could also be helpful for screening more candidate genes and breeding new varieties of wheat, with a high yield and stress resistance.

Early Brassica Crops Responses to Salinity Stress: A Comparative Analysis Between Chinese Cabbage, White Cabbage, and Kale

Soil salinity is severely affecting crop productivity in many countries, particularly in the Mediterranean area. To evaluate early plant responses to increased salinity and characterize tolerance markers, three important Brassica crops - Chinese cabbage (Brassica rapa ssp. pekinensis), white cabbage (B. oleracea var. capitata) and kale (B. oleracea var. acephala) were subjected to short-term (24 h) salt stress by exposing them to NaCl at concentrations of 50, 100, or 200 mM. Physiological (root growth, photosynthetic performance parameters, and Na+/K+ ratio) and biochemical parameters (proline content and lipid peroxidation as indicated by malondialdehyde, MDA, levels) in the plants' roots and leaves were then measured. Photosynthetic parameters such as the total performance index PItotal (describing the overall efficiency of PSI, PSII and the intersystem electron transport chain) appeared to be the most salinity-sensitive parameter and informative stress marker. This parameter was decreased more strongly in Chinese cabbage than in white cabbage and kale. It indicated that salinity reduced the capacity of the photosynthetic system for efficient energy conversion, particularly in Chinese cabbage. In parallel with the photosynthetic impairments, the Na+/K+ ratio was highest in Chinese cabbage leaves and lowest in kale leaves while kale root is able to keep high Na+/K+ ratio without a significant increase in MDA. Thus Na+/K+ ratio, high in root and low in leaves accompanying with low MDA level is an informative marker of salinity tolerance. The crops' tolerance was positively correlated with levels of the stress hormone abscisic acid (ABA) and negatively correlated with levels of jasmonic acid (JA), and jasmonoyl-L-isoleucine (JA-Ile). Furthermore, salinity induced contrasting changes in levels of the growth-promoting hormones brassinosteroids (BRs). The crop's tolerance was positively correlated with levels of BR precursor typhasterol while negatively with the active BR brassinolide. Principal Component Analysis revealed correlations in observed changes in phytohormones, biochemical, and physiological parameters. Overall, the results show that kale is the most tolerant of the three species and Chinese cabbage the most sensitive to salt stress, and provide holistic indications of the spectrum of tolerance mechanisms involved.

Fast Quenching the Burst of Host Salicylic Acid Is Common in Early Strawberry/Colletotrichum fructicola Interaction

The fungus Colletotrichum fructicola (a species of C. gloeosporioides complex) causes devastating anthracnose in strawberry. Like other species of the genus Colletotrichum, it uses a composite strategy including both the biotrophic and necrotrophic processes for pathogenesis. Host-derived hormones are central regulators of immunity, among which salicylic acid (SA) is the core defense one against biotrophic and hemibiotrophic pathogens. However, the manner and timing of pathogen manipulation of SA are largely elusive in strawberry. To achieve better understanding of the early challenges that SA-mediated defense experiences during strawberry/C. fructicola interaction, dynamic changes of SA levels were followed through the high-performance liquid chromatography method. A very early burst of free SA at 1 h postinoculation (hpi) followed by a fast quenching during the next 12 h was noticed, although rhythm variations were present in two hosts. Transcriptional characterization of genes related to SA pathway in two varieties on C. fructicola inoculation revealed that these genes were differentially expressed, although they were all induced at different time points. At the same time, three types of genes encoding homologous effectors interfering with SA accumulation were found to be first inhibited but sequentially activated during the first 24 hpi. Furthermore, subcellular localization analysis suggests that CfShy1 is a weapon of C. fructicola for strawberry invasion. Based on these results, we propose that the infection strategy that C. fructicola utilizes on strawberry is specialized, which is implemented through the optimized expression of a specific set of effector genes. Transcriptional characterization of host genes supports that de novo SA biosynthesis and the free SA release from methyl salicylate might contribute equally to the intricate control of SA homeostasis in strawberry. C. fructicola manipulation of SA-dependent resistance in strawberry might be closely related to multihormonal interplay among SA, jasmonic acid, abscisic acid, and cytokinin.

Characterization of Non-heading Mutation in Heading Chinese Cabbage (Brassica rapa L. ssp. pekinensis)

Heading is a key agronomic trait of Chinese cabbage. A non-heading mutant with flat growth of heading leaves (fg-1) was isolated from an EMS-induced mutant population of the heading Chinese cabbage inbred line A03. In fg-1 mutant plants, the heading leaves are flat similar to rosette leaves. The epidermal cells on the adaxial surface of these leaves are significantly smaller, while those on the abaxial surface are much larger than in A03 plants. The segregation of the heading phenotype in the F2 and BC1 population suggests that the mutant trait is controlled by a pair of recessive alleles. Phytohormone analysis at the early heading stage showed significant decreases in IAA, ABA, JA and SA, with increases in methyl IAA and trans-Zeatin levels, suggesting they may coordinate leaf adaxial-abaxial polarity, development and morphology in fg-1. RNA-sequencing analysis at the early heading stage showed a decrease in expression levels of several auxin transport (BrAUX1, BrLAXs, and BrPINs) and responsive genes. Transcript levels of important ABA responsive genes, including BrABF3, were up-regulated in mid-leaf sections suggesting that both auxin and ABA signaling pathways play important roles in regulating leaf heading. In addition, a significant reduction in BrIAMT1 transcripts in fg-1 might contribute to leaf epinastic growth. The expression profiles of 19 genes with known roles in leaf polarity were significantly different in fg-1 leaves compared to wild type, suggesting that these genes might also regulate leaf heading in Chinese cabbage. In conclusion, leaf heading in Chinese cabbage is controlled through a complex network of hormone signaling and abaxial-adaxial patterning pathways. These findings increase our understanding of the molecular basis of head formation in Chinese cabbage.

Mimosine accumulation in Leucaena leucocephala in response to stress signaling molecules and acute UV exposure

Mimosine is a non-protein amino acid of Fabaceae, such as Leucaena spp. and Mimosa spp. Several relevant biological activities have been described for this molecule, including cell cycle blocker, anticancer, antifungal, antimicrobial, herbivore deterrent and allelopathic activities, raising increased economic interest in its production. In addition, information on mimosine dynamics in planta remains limited. In order to address this topic and propose strategies to increase mimosine production aiming at economic uses, the effects of several stress-related elicitors of secondary metabolism and UV acute exposure were examined on mimosine accumulation in growth room-cultivated seedlings of Leucaena leucocephala spp. glabrata. Mimosine concentration was not significantly affected by 10 ppm salicylic acid (SA) treatment, but increased in roots and shoots of seedlings treated with 84 ppm jasmonic acid (JA) and 10 ppm Ethephon (an ethylene-releasing compound), and in shoots treated with UV-C radiation. Quantification of mimosine amidohydrolase (mimosinase) gene expression showed that ethephon yielded variable effect over time, whereas JA and UV-C did not show significant impact. Considering the strong induction of mimosine accumulation by acute UV-C exposure, additional in situ ROS localization, as well as in vitro antioxidant assays were performed, suggesting that, akin to several secondary metabolites, mimosine may be involved in general oxidative stress modulation, acting as a hydrogen peroxide and superoxide anion quencher.

Interference between arsenic-induced toxicity and hypoxia

Plants often face combinatorial stresses in their natural environment. Here, arsenic (As) toxicity was combined with hypoxia (Hpx) in the roots of Arabidopsis thaliana as it often occurs in nature. Arsenic inhibited growth of both roots and leaves, whereas root growth almost entirely ceased in Hpx. Growth efficiently resumed, and Hpx marker transcripts decreased upon reaeration. Compromised recovery from HpxAs treatment following reaeration indicated some persistent effects of combined stresses despite lower As accumulation. Root glutathione redox potential turned more oxidized in Hpx and most strongly in HpxAs. The more oxidizing root cell redox potential and the lowered glutathione amounts may be conducive to the growth arrest of plants exposed to HpxAs. The stresses elicited changes in elemental and transcriptomic composition. Thus, calcium, magnesium, and phosphorous amounts decreased in rosettes, but the strongest decline was seen for potassium. The reorganized potassium-related transcriptome supports the conclusion that disturbed potassium homeostasis contributes to the growth phenotype. In a converse manner, photosynthesis-related parameters were hardly affected, whereas accumulated carbohydrates under all stresses and anthocyanins under Hpx exclude carbohydrate limitation. The study demonstrates the existence of both synergistic since mutually aggravating effects and antagonistic effects of single and combined stresses.

Untargeted Metabolomics Reveal Defensome-Related Metabolic Reprogramming in Sorghum bicolor against Infection by Burkholderia andropogonis

Burkholderia andropogonis is the causal agent of bacterial leaf stripe, one of the three major bacterial diseases affecting Sorghum bicolor. However, the biochemical aspects of the pathophysiological host responses are not well understood. An untargeted metabolomics approach was designed to understand molecular mechanisms underlying S. bicolor⁻B. andropogonis interactions. At the 4-leaf stage, two sorghum cultivars (NS 5511 and NS 5655) differing in disease tolerance, were infected with B. andropogonis and the metabolic changes monitored over time. The NS 5511 cultivar displayed delayed signs of wilting and lesion progression compared to the NS 5655 cultivar, indicative of enhanced resistance. The metabolomics results identified statistically significant metabolites as biomarkers associated with the sorghum defence. These include the phytohormones salicylic acid, jasmonic acid, and zeatin. Moreover, metabolic reprogramming in an array of chemically diverse metabolites that span a wide range of metabolic pathways was associated with the defence response. Signatory biomarkers included aromatic amino acids, shikimic acid, metabolites from the phenylpropanoid and flavonoid pathways, as well as fatty acids. Enhanced synthesis and accumulation of apigenin and derivatives thereof was a prominent feature of the altered metabolomes. The analyses revealed an intricate and dynamic network of the sorghum defence arsenal towards B. andropogonis in establishing an enhanced defensive capacity in support of resistance and disease suppression. The results pave the way for future analysis of the biosynthesis of signatory biomarkers and regulation of relevant metabolic pathways in sorghum.