Oxylipin Signaling: A Distinct Role for the Jasmonic Acid Precursor cis-(+)-12-Oxo-Phytodienoic Acid (cis-OPDA)

Exploring lipid signaling in plant physiology: From cellular membranes to environmental adaptation

Lipids have evolved as versatile signaling molecules that regulate a variety of physiological processes in plants. Convincing evidence highlights their critical role as mediators in a wide range of plant processes required for survival, growth, development, and responses to environmental conditions such as water availability, temperature changes, salt, pests, and diseases. Understanding lipid signaling as a critical process has helped us expand our understanding of plant biology by explaining how plants sense and respond to environmental cues. Lipid signaling pathways constitute a complex network of lipids, enzymes, and receptors that coordinate important cellular responses and stressing plant biology's changing and adaptable traits. Plant lipid signaling involves a wide range of lipid classes, including phospholipids, sphingolipids, oxylipins, and sterols, each of which contributes differently to cellular communication and control. These lipids function not only as structural components, but also as bioactive molecules that transfer signals. The mechanisms entail the production of lipid mediators and their detection by particular receptors, which frequently trigger downstream cascades that affect gene expression, cellular functions, and overall plant growth. This review looks into lipid signaling in plant physiology, giving an in-depth look and emphasizing its critical function as a master regulator of vital activities.

Broccoli Cultivated with Deep Sea Water Mineral Fertilizer Enhances Anti-Cancer and Anti-Inflammatory Effects of AOM/DSS-Induced Colorectal Cancer in C57BL/6N Mice

This study aimed to determine the alleviating effect of broccoli grown with deep sea water mineral (DSWM) fertilizer extracted from deep sea water on the development of colorectal cancer in C57BL/6N mice treated with AOM/DSS. Naturaldream Fertilizer Broccoli (NFB) cultured with deep sea water minerals (DSWM) showed a higher antioxidant effect and mineral content. In addition, orally administered NFB, showed a level of recovery in the colon and spleen tissues of mice compared with those in normal mice through hematoxylin and eosin (H&E) staining. Orally administered NFB showed the inhibition of the expression of inflammatory cytokine factors IL-1β, IL-6, TNF, IFN-γ, and IL-12 while increasing the expression of IL-10. Furthermore, the expression of inflammatory cytokines and NF-κB in the liver tissue was inhibited, and that of inflammatory enzymes, such as COX-2 and iNOS, was reduced. In the colon tissue, the expression of p53 and p21 associated with cell cycle arrest increased, and that of Bcl-2 associated with apoptosis decreased. Additionally, the expression of Bax, Bad, Bim, Bak, caspase 9, and caspase 3 increased, indicating enhanced activation of apoptosis-related factors. These results demonstrate that oral administration of broccoli cultivated using DSWM significantly restores spleen and colon tissues and simultaneously inhibits the NF-κB pathway while significantly decreasing cytokine expression. Moreover, by inducing cell cycle arrest and activating cell apoptosis, they also suggest alleviating AOM/DSS-induced colon cancer symptoms in C57BL/6N mice.

A Ca2+ sensor BraCBL1.2 involves in BraCRa-mediated clubroot resistance in Chinese cabbage

Clubroot disease caused by Plasmodiophora brassicae (P. brassicae) severely threatens the cultivation of Cruciferous plants, especially Chinese cabbage. Recently, resistance genes in plants have been reported to encode for a Ca2+-permeable channel in the plasma membrane, which can mediate the cytosolic Ca2+ increase in plant cells upon pathogen attack. However, the downstream Ca2+ sensor and decoder are still unknown. In this study, we identified the virulent and avirulent P. brassicae isolates (Pbs) of two near isogenic lines, CR 3-2 and CS 3-2, with CR 3-2 harboring clubroot resistant gene BraCRa. The transcriptomic analysis was then conducted with CR 3-2 after inoculating with virulent isolate PbE and avirulent isolate Pb4. From the differentially expressed genes of transcriptomic data, we identified a Ca2+-sensor encoding gene, BraCBL1.2, that was highly induced in CR 3-2 during infection by Pb4 but not by PbE. Moreover, GUS histochemical staining and subcellular localization analysis revealed that BraCBL1.2 was specifically expressed in the root hair cells of Arabidopsis and encoded a putative Ca2+ sensor localized in the plasma membrane. We also developed an assay to investigate the BraCRa-mediated hypersensitive response (HR) in tobacco leaves. The results suggest that BraCBL1.2 is involved in the BraCRa-mediated plant ETI immune response against P. brassicae. In addition, we verified that overexpression of BraCBL1.2 enhanced clubroot resistance in Arabidopsis. Collectively, our data identified the involvement of a Ca2+ sensor in BraCRa-mediated clubroot resistance in Chinese cabbage, providing a theoretical basis for further research on the resistance of Chinese cabbage to P. brassicae.

Are Arabidopsis thaliana plants able to recover from exposure to gamma radiation? A molecular perspective

Most plant research focuses on the responses immediately after exposure to ionizing irradiation (IR). However, it is as important to investigate how plants recover after exposure since this has a profound effect on future plant growth and development and hence on the long-term consequences of exposure to stress. This study aimed to investigate the IR-induced responses after exposure and during recovery by exposing 1-week old A. thaliana seedlings to gamma dose rates ranging from 27 to 103.7 mGy/h for 2 weeks and allowing them to recover for 4 days. A high-throughput RNAsequencing analysis was carried out. An enrichment of GO terms related to the metabolism of hormones was observed both after irradiation and during recovery at all dose rates. While plants exposed to the lowest dose rate activate defence responses after irradiation, they recover from the IR by resuming normal growth during the recovery period. Plants exposed to the intermediate dose rate invest in signalling and defence after irradiation. During recovery, in the plants exposed to the highest dose rate, fundamental metabolic processes such as photosynthesis and RNA modification were still affected. This might lead to detrimental effects in the long-term or in the next generations of those irradiated plants.

Hormonal involvement in boosting the vegetative vigour underlying caffeine-related improvements in lentil production

Previous studies have shown that caffeine (1,3,7-trimethylxanthine) has some potential for its use as a biostimulant ingredient for boosting lentil production at suboptimal temperatures. However, some limitations to its use include its potential side effects as an emerging contaminant and the current lack of knowledge of its mechanism of action. Here, we aimed to study the mechanisms underlying improved lentil production upon caffeine application. Greenhouse-grown plants treated with caffeine (at 10-5 M, 10-4 M, and 10-3 M) were compared to an untreated, control treatment, and both reproductive and vegetative vigour were evaluated in parallel with endogenous foliar concentrations of phytohormones, including both stress and growth-related hormones. Results showed an enhanced lentil production at the highest caffeine concentration (10-3 M) which might be attributed, at least in part, to a greater vegetative vigour. The hormonal profiling revealed a dual effect. Firstly, there was a specific increase in jasmonoyl-isoleucine (JA-Ile) in the short term, which may provide a priming effect. Secondly, abscisic acid (ABA) content kept at low levels and the active cytokinin (CK) isopentenyl adenine (2-iP) increased and persisted at high levels throughout the reproductive stage. Cytokinin-mediated effects on growth, and more specifically the high CK/ABA ratios in leaves, appeared to mediate caffeine-related effects in boosting vegetative vigour. In conclusion, caffeine emerges as a compelling alkaloid for integration into biostimulant formulations due to its favorable effect in boosting lentil production through an improvement of vegetative vigour. These outcomes appear to be modulated by phytohormones, most notably jasmonates, priming plants for improved performance under suboptimal temperatures, and cytokinins, alongside ABA and its associated ratios, collectively enhancing plant growth and reproductive vigour in challenging conditions.

Relationship between seasonal variation in isoprene emission and plant hormone profiles in the tropical plant Ficus septica

In Ficus septica, the short-term control of isoprene production and, therefore, isoprene emission has been linked to the hormone balance between auxin (IAA) and jasmonic acid (JA). However, the relationship between long-term changes in isoprene emission and that of plant hormones remains unknown. This study tracked isoprene emissions from F. septica leaves, plant hormone concentrations and signalling gene expression, MEP pathway metabolite concentrations, and related enzyme gene expression for 1 year in the field to better understand the role of plant hormones and their long-term control. Seasonality of isoprenes was mainly driven by temperature- and light-dependent variations in substrate availability through the MEP route, as well as transcriptional and post-transcriptional control of isoprene synthase (IspS). Isoprene emissions are seasonally correlated with plant hormone levels. This was especially evident in the cytokinin profiles, which decreased in summer and increased in winter. Only 4-hydroxy-3-methylbut-2-butenyl-4-diphosphate (HMBDP) exhibited a positive connection with cytokinins among the MEP metabolites examined, suggesting that HMBDP and its biosynthetic enzyme, HMBDP synthase (HDS), play a role in channelling of MEP pathway metabolites to cytokinin production. Thus, it is probable that cytokinins have potential feed-forward regulation of isoprene production. Under long-term natural conditions, the hormonal balance of IAA/JA-Ile was not associated with IspS transcripts or isoprene emissions. This study builds on prior work by revealing differences between short- and long-term hormonal modulation of isoprene emissions in the tropical tree F. septica.

ZmEREB57 regulates OPDA synthesis and enhances salt stress tolerance through two distinct signalling pathways in Zea mays

In plant, APETALA2/ethylene-responsive factor (AP2/ERF)-domain transcription factors are important in regulating abiotic stress tolerance. In this study, ZmEREB57 encoding a AP2/ERF transcription factor was identified and its function was investigated in maize. ZmEREB57 is a nuclear protein with transactivation activity induced by several abiotic stress types. Furthermore, two CRISPR/Cas9 knockout lines of ZmEREB57 showed enhanced sensitivity to saline conditions, whereas the overexpression of ZmEREB57 increased salt tolerance in maize and Arabidopsis. DNA affinity purification sequencing (DAP-Seq) analysis revealed that ZmEREB57 notably regulates target genes by binding to promoters containing an O-box-like motif (CCGGCC). ZmEREB57 directly binds to the promoter of ZmAOC2 involved in the synthesis of 12-oxo-phytodienoic acid (OPDA) and jasmonic acid (JA). Transcriptome analysis revealed that several genes involved in regulating stress and redox homeostasis showed differential expression patterns in OPDA- and JA-treated maize seedlings exposed to salt stress compared to those treated with salt stress alone. Analysis of mutants deficient in the biosynthesis of OPDA and JA revealed that OPDA functions as a signalling molecule in the salt response. Our results indicate that ZmEREB57 involves in salt tolerance by regulating OPDA and JA signalling and confirm early observations that OPDA signalling functions independently of JA signalling.

Overlapping Local and Systemic Defense Induced by an Oomycete Fatty Acid MAMP and Brown Seaweed Extract in Tomato

Eicosapolyenoic fatty acids are integral components of oomycete pathogens that can act as microbe-associated molecular patterns to induce disease resistance in plants. Defense-inducing eicosapolyenoic fatty acids include arachidonic acid (AA) and eicosapentaenoic acid and are strong elicitors in solanaceous plants, with bioactivity in other plant families. Similarly, extracts of a brown seaweed, Ascophyllum nodosum, used in sustainable agriculture as a biostimulant of plant growth, may also induce disease resistance. A. nodosum, similar to other macroalgae, is rich in eicosapolyenoic fatty acids, which comprise as much as 25% of total fatty acid composition. We investigated the response of roots and leaves from AA or a commercial A. nodosum extract (ANE) on root-treated tomatoes via RNA sequencing, phytohormone profiling, and disease assays. AA and ANE significantly altered transcriptional profiles relative to control plants, inducing numerous defense-related genes with both substantial overlap and differences in gene expression patterns. Root treatment with AA and, to a lesser extent, ANE also altered both salicylic acid and jasmonic acid levels while inducing local and systemic resistance to oomycete and bacterial pathogen challenge. Thus, our study highlights overlap in both local and systemic defense induced by AA and ANE, with potential for inducing broad-spectrum resistance against pathogens. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Comparative Metabolomic Analysis Reveals the Role of OsHPL1 in the Cold-Induced Metabolic Changes in Rice

Cytochrome P450 (CYP74) family members participate in the generation of oxylipins and play essential roles in plant adaptation. However, the metabolic reprogramming mediated by CYP74s under cold stress remains largely unexplored. Herein, we report how cold-triggered OsHPL1, a member of the CYP74 family, modulates rice metabolism. Cold stress significantly induced the expression of OsHPL1 and the accumulation of OPDA (12-oxo-phytodienoic acid) and jasmonates in the wild-type (WT) plants. The absence of OsHPL1 attenuates OPDA accumulation to a low temperature. Then, we performed a widely targeted metabolomics study covering 597 structurally annotated compounds. In the WT and hpl1 plants, cold stress remodeled the metabolism of lipids and amino acids. Although the WT and hpl1 mutants shared over one hundred cold-affected differentially accumulated metabolites (DAMs), some displayed distinct cold-responding patterns. Furthermore, we identified 114 and 56 cold-responding DAMs, specifically in the WT and hpl1 mutants. In conclusion, our work characterized cold-triggered metabolic rewiring and the metabolic role of OsHPL1 in rice.

Adventitious Root Formation in Plants: The Implication of Hydrogen Peroxide and Nitric Oxide

Adventitious root formation is defined as the formation of new roots on above-ground plant parts and is considered crucial for the survival of a plant under harsh environmental conditions (i.e., flooding, salt stress, and other abiotic stresses) as well as in the nursery industry. Clonal propagation is based on the ability of a plant part to grow and generate a completely new plant, genetically identical to the mother plant, where the plant part came from. Nurseries exploit this potential by multiplying millions of new plants. Most nurseries use cuttings to achieve that, through the induction of adventitious root formation. Many factors have been implicated in the capacity of a cutting to root, with the major role being played by auxins. During the last few decades, intense interest has emerged in the role of other potential rooting co-factors, such as carbohydrates, phenolics, polyamines, and other plant growth regulators, as well as signal molecules, such as reactive oxygen and nitrogen species. Among the latter, hydrogen peroxide and nitric oxide have been found to play significant roles in adventitious root formation. Their production, action, and general implication in rhizogenesis are discussed in this review, in terms of interaction with other molecules and signaling.

Oxylipins and Reactive Carbonyls as Regulators of the Plant Redox and Reactive Oxygen Species Network under Stress

Reactive oxygen species (ROS), and in particular H2O2, serve as essential second messengers at low concentrations. However, excessive ROS accumulation leads to severe and irreversible cell damage. Hence, control of ROS levels is needed, especially under non-optimal growth conditions caused by abiotic or biotic stresses, which at least initially stimulate ROS synthesis. A complex network of thiol-sensitive proteins is instrumental in realizing tight ROS control; this is called the redox regulatory network. It consists of sensors, input elements, transmitters, and targets. Recent evidence revealed that the interplay of the redox network and oxylipins–molecules derived from oxygenation of polyunsaturated fatty acids, especially under high ROS levels–plays a decisive role in coupling ROS generation and subsequent stress defense signaling pathways in plants. This review aims to provide a broad overview of the current knowledge on the interaction of distinct oxylipins generated enzymatically (12-OPDA, 4-HNE, phytoprostanes) or non-enzymatically (MDA, acrolein) and components of the redox network. Further, recent findings on the contribution of oxylipins to environmental acclimatization will be discussed using flooding, herbivory, and establishment of thermotolerance as prime examples of relevant biotic and abiotic stresses.

Ethylene and Jasmonates Signaling Network Mediating Secondary Metabolites under Abiotic Stress

Plants are sessile organisms that face environmental threats throughout their life cycle, but increasing global warming poses an even more existential threat. Despite these unfavorable circumstances, plants try to adapt by developing a variety of strategies coordinated by plant hormones, resulting in a stress-specific phenotype. In this context, ethylene and jasmonates (JAs) present a fascinating case of synergism and antagonism. Here, Ethylene Insensitive 3/Ethylene Insensitive-Like Protein1 (EIN3/EIL1) and Jasmonate-Zim Domain (JAZs)-MYC2 of the ethylene and JAs signaling pathways, respectively, appear to act as nodes connecting multiple networks to regulate stress responses, including secondary metabolites. Secondary metabolites are multifunctional organic compounds that play crucial roles in stress acclimation of plants. Plants that exhibit high plasticity in their secondary metabolism, which allows them to generate near-infinite chemical diversity through structural and chemical modifications, are likely to have a selective and adaptive advantage, especially in the face of climate change challenges. In contrast, domestication of crop plants has resulted in change or even loss in diversity of phytochemicals, making them significantly more vulnerable to environmental stresses over time. For this reason, there is a need to advance our understanding of the underlying mechanisms by which plant hormones and secondary metabolites respond to abiotic stress. This knowledge may help to improve the adaptability and resilience of plants to changing climatic conditions without compromising yield and productivity. Our aim in this review was to provide a detailed overview of abiotic stress responses mediated by ethylene and JAs and their impact on secondary metabolites.

Light-induced stomatal opening in Arabidopsis is negatively regulated by chloroplast-originated OPDA signaling

Stomatal movement is orchestrated by diverse signaling cascades and metabolic activities in guard cells. Light triggers the opening of the pores through the phototropin-mediated pathway, which leads to the activation of plasma membrane H⁺-ATPase and thereby facilitates potassium accumulation through K_in⁺ channels. However, it remains poorly understood how phototropin signaling is fine-tuned to prevent excessive stomatal opening and consequent water loss. Here, we show that the stomatal response to light is negatively regulated by 12-oxo-phytodienoic acid (OPDA), an oxylipin metabolite produced through enzymatic oxygenation of polyunsaturated fatty acids (PUFAs). We identify a set of phospholipase-encoding genes, phospholipase (PLIP)1/2/3, which are transactivated rapidly in guard cells upon illumination in a phototropin-dependent manner. These phospholipases release PUFAs from the chloroplast membrane, which is oxidized by guard-cell lipoxygenases and further metabolized to OPDA. The OPDA-deficient mutants had wider stomatal pores, whereas mutants containing elevated levels of OPDA showed the opposite effect on stomatal aperture. Transmembrane solute fluxes that drive stomatal aperture were enhanced in lox6-1 guard cells, indicating that OPDA signaling ultimately impacts on activities of proton pumps and K_in⁺ channels. Interestingly, the accelerated stomatal kinetics in lox6-1 leads to increased plant growth without cost in water or macronutrient use. Together, our results reveal a new role for chloroplast membrane oxylipin metabolism in stomatal regulation. Moreover, the accelerated stomatal opening kinetics in OPDA-deficient mutants benefits plant growth and water use efficiency.

Comparative Transcriptomics Profiling of Perennial Ryegrass Infected with Wild Type or a ΔvelA Epichloë festucae Mutant Reveals Host Processes Underlying Mutualistic versus Antagonistic Interactions

Epichloë species form bioprotective endophytic symbioses with many cool-season grasses, including agriculturally important forage grasses. Despite its importance, relatively little is known about the molecular details of the interaction and the regulatory genes involved. VelA is a key global regulator in fungal secondary metabolism and development. In previous studies, we showed the requirement of velA for E. festucae to form a mutualistic interaction with Lolium perenne. We showed that VelA regulates the expression of genes encoding proteins involved in membrane transport, fungal cell wall biosynthesis, host cell wall degradation, and secondary metabolism, along with several small-secreted proteins in Epichloë festucae. Here, by a comparative transcriptomics analysis on perennial ryegrass seedlings and mature plants, which are endophyte free or infected with wild type (mutualistic interaction) or mutant ΔvelA E. festucae (antagonistic or incompatible interaction), regulatory effects of the endophytic interaction on perennial ryegrass development was studied. We show that ΔvelA mutant associations influence the expression of genes involved in primary metabolism, secondary metabolism, and response to biotic and abiotic stresses compared with wild type associations, providing an insight into processes defining mutualistic versus antagonistic interactions.

Lipoxygenase (LOX) in Sweet and Hot Pepper (Capsicum annuum L.) Fruits during Ripening and under an Enriched Nitric Oxide (NO) Gas Atmosphere

Lipoxygenases (LOXs) catalyze the insertion of molecular oxygen into polyunsaturated fatty acids (PUFA) such as linoleic and linolenic acids, being the first step in the biosynthesis of a large group of biologically active fatty acid (FA)-derived metabolites collectively named oxylipins. LOXs are involved in multiple functions such as the biosynthesis of jasmonic acid (JA) and volatile molecules related to the aroma and flavor production of plant tissues, among others. Using sweet pepper (Capsicum annuum L.) plants as a model, LOX activity was assayed by non-denaturing polyacrylamide gel electrophoresis (PAGE) and specific in-gel activity staining. Thus, we identified a total of seven LOX isozymes (I to VII) distributed among the main plant organs (roots, stems, leaves, and fruits). Furthermore, we studied the FA profile and the LOX isozyme pattern in pepper fruits including a sweet variety (Melchor) and three autochthonous Spanish varieties that have different pungency levels (Piquillo, Padrón, and Alegría riojana). It was observed that the number of LOX isozymes increased as the capsaicin content increased in the fruits. On the other hand, a total of eight CaLOX genes were identified in sweet pepper fruits, and their expression was differentially regulated during ripening and by the treatment with nitric oxide (NO) gas. Finally, a deeper analysis of the LOX IV isoenzyme activity in the presence of nitrosocysteine (CysNO, a NO donor) suggests a regulatory mechanism via S-nitrosation. In summary, our data indicate that the different LOX isozymes are differentially regulated by the capsaicin content, fruit ripening, and NO.

OPDA, more than just a jasmonate precursor

The oxylipin 12-oxo-phytodienoic acid (OPDA) is known as a biosynthetic precursor of the important plant hormone jasmonic acid. However, OPDA is also a signaling molecule with functions independent of jasmonates. OPDA involvement in diverse biological processes, from plant defense and stress responses to growth regulation and development, has been documented across plant species. OPDA is synthesized in the plastids from alpha-linolenic acid, and OPDA binding to plastidial cyclophilins activates TGA transcription factors upstream of genes associated with stress responses. Here, we summarize what is known about OPDA metabolism and signaling while briefly discussing its jasmonate dependent and independent roles. We also describe open questions, such as the OPDA protein interactome and biological roles of OPDA conjugates.

Insights into the Jasmonate Signaling in Basal Land Plant Revealed by the Multi-Omics Analysis of an Antarctic Moss Pohlia nutans Treated with OPDA

12-oxo-phytodienoic acid (OPDA) is a biosynthetic precursor of jasmonic acid and triggers multiple biological processes from plant development to stress responses. However, the OPDA signaling and relevant regulatory networks were largely unknown in basal land plants. Using an integrated multi-omics technique, we investigated the global features in metabolites and transcriptional profiles of an Antarctic moss (Pohlia nutans) in response to OPDA treatment. We detected 676 metabolites based on the widely targeted metabolomics approach. A total of 82 significantly changed metabolites were observed, including fatty acids, flavonoids, phenolic acids, amino acids and derivatives, and alkaloids. In addition, the transcriptome sequencing was conducted to uncover the global transcriptional profiles. The representative differentially expressed genes were summarized into functions including Ca2+ signaling, abscisic acid signaling, jasmonate signaling, lipid and fatty acid biosynthesis, transcription factors, antioxidant enzymes, and detoxification proteins. The integrated multi-omics analysis revealed that the pathways of jasmonate and ABA signaling, lipid and fatty acid biosynthesis, and flavonoid biosynthesis might dominate the molecular responses to OPDA. Taken together, these observations provide insights into the molecular evolution of jasmonate signaling and the adaptation mechanisms of Antarctic moss to terrestrial habitats.

Metabolic profiling and gene expression analyses provide insights into cold adaptation of an Antarctic moss Pohlia nutans

Antarctica is the coldest, driest, and most windy continent on earth. The major terrestrial vegetation consists of cryptogams (mosses and lichens) and two vascular plant species. However, the molecular mechanism of cold tolerance and relevant regulatory networks were largely unknown in these Antarctic plants. Here, we investigated the global alterations in metabolites and regulatory pathways of an Antarctic moss (Pohlia nutans) under cold stress using an integrated multi-omics approach. We found that proline content and several antioxidant enzyme activities were significantly increased in P. nutans under cold stress, but the contents of chlorophyll and total flavonoids were markedly decreased. A total of 559 metabolites were detected using ultra high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). We observed 39 and 71 differentially changed metabolites (DCMs) after 24 h and 60 h cold stress, indicating that several major pathways were differentially activated for producing fatty acids, alkaloids, flavonoids, terpenoids, and phenolic acids. In addition, the quantitative transcriptome sequencing was conducted to uncover the global transcriptional profiles of P. nutans under cold stress. The representative differentially expressed genes (DEGs) were identified and summarized to the function including Ca²⁺ signaling, ABA signaling, jasmonate signaling, fatty acids biosynthesis, flavonoid biosynthesis, and other biological processes. The integrated dataset analyses of metabolome and transcriptome revealed that jasmonate signaling, auxin signaling, very-long-chain fatty acids and flavonoid biosynthesis pathways might contribute to P. nutans acclimating to cold stress. Overall, these observations provide insight into Antarctic moss adaptations to polar habitats and the impact of global climate change on Antarctic plants.

Comparison of the pathway structures influencing the temporal response of salicylate and jasmonate defence hormones in Arabidopsis thaliana

Defence phytohormone pathways evolved to recognize and counter multiple stressors within the environment. Salicylic acid responsive pathways regulate the defence response to biotrophic pathogens whilst responses to necrotrophic pathogens, herbivory, and wounding are regulated via jasmonic acid pathways. Despite their contrasting roles in planta, the salicylic acid and jasmonic acid defence networks share a common architecture, progressing from stages of biosynthesis, to modification, regulation, and response. The unique structure, components, and regulation of each stage of the defence networks likely contributes, in part, to the speed, establishment, and longevity of the salicylic acid and jasmonic acid signaling pathways in response to hormone treatment and various biotic stressors. Recent advancements in the understanding of the Arabidopsis thaliana salicylic acid and jasmonic acid signaling pathways are reviewed here, with a focus on how the structure of the pathways may be influencing the temporal regulation of the defence responses, and how biotic stressors and the many roles of salicylic acid and jasmonic acid in planta may have shaped the evolution of the signaling networks.

Genome-wide association study reveals that GhTRL1 and GhPIN8 affect cotton root development

Two regions located at chromosome A05 and D04 were found to be significantly associated with 0-0.5 mm and 0.5-2 mm diameter roots, respectively, and two candidate genes related to root development were identified. Roots absorb water and nutrients, and play an important role in plant growth. However, there are few genetic developmental studies on cotton root structural traits. In this study, we used 200 upland cotton (Gossypium hirsutum L.) varieties to analyze the phenotypic variation of 43 traits. A total of 2001 related single-nucleotide polymorphism (SNP) sites located within or near 1046 genes were detected through a genome-wide association study (GWAS). The 32 root traits were linked to SNPs that corresponded to 317 nonrepetitive genes. For SNPs associated with root length and 0-0.5 mm diameter root traits, a significant peak appeared on chromosome A05 (between 21.91 and 22.24 Mb). For SNPs associated with root surface area, root volume and 0.5-2 mm diameter root traits, a significant peak appeared on chromosome D04 (between 7.35 and 7.70 Mb). Within these two key regions, SNPs were detected in the promoter and coding regions of two candidate genes, GhTRL1-A05 and GhPIN8-D04. The expression levels of these two genes also changed significantly according to transcriptome sequencing and quantitative real-time PCR (qRT-PCR). After silencing the GhTRL1 and GhPIN8 genes via virus-induced gene silencing (VIGS), we found that the plants expressing TRV2::GhTRL1 and TRV2::GhPIN8 had a reduced root length, surface area. Moreover, the contents of cis-12-oxo-phytodienoic acid (cis-OPDA), isopentenyl adenosine (iPR) and cis-zeatin (cZ) in the roots of the plants expressing TRV2::GhTRL1 decreased. This study contributes to the cultivation and improvement of cotton varieties.

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.

Integrated transcriptome and metabolome analyses reveal the adaptation of Antarctic moss Pohlia nutans to drought stress

Most regions of the Antarctic continent are experiencing increased dryness due to global climate change. Mosses and lichens are the dominant vegetation of the ice-free areas of Antarctica. However, the molecular mechanisms of these Antarctic plants adapting to drought stress are less documented. Here, transcriptome and metabolome analyses were employed to reveal the responses of an Antarctic moss (Pohlia nutans subsp. LIU) to drought stress. We found that drought stress made the gametophytes turn yellow and curled, and enhanced the contents of malondialdehyde and proline, and the activities of antioxidant enzymes. Totally, 2,451 differentially expressed genes (DEGs) were uncovered under drought treatment. The representative DEGs are mainly involved in ROS-scavenging and detoxification, flavonoid metabolism pathway, plant hormone signaling pathway, lipids metabolism pathway, transcription factors and signal-related genes. Meanwhile, a total of 354 differentially changed metabolites (DCMs) were detected in the metabolome analysis. Flavonoids and lipids were the most abundant metabolites and they accounted for 41.53% of the significantly changed metabolites. In addition, integrated transcriptome and metabolome analyses revealed co-expression patterns of flavonoid and long-chain fatty acid biosynthesis genes and their metabolites. Finally, qPCR analysis demonstrated that the expression levels of stress-related genes were significantly increased. These genes included those involved in ABA signaling pathway (NCED3, PP2C, PYL, and SnAK2), jasmonate signaling pathway (AOC, AOS, JAZ, and OPR), flavonoid pathway (CHS, F3',5'H, F3H, FLS, FNS, and UFGT), antioxidant and detoxifying functions (POD, GSH-Px, Prx and DTX), and transcription factors (ERF and DREB). In summary, we speculated that P. nutans were highly dependent on ABA and jasmonate signaling pathways, ROS scavenging, flavonoids and fatty acid metabolism in response to drought stress. These findings present an important knowledge for assessing the impact of coastal climate change on Antarctic basal plants.

Chitooligosaccharide elicitor and oxylipins synergistically elevate phytoalexin production in rice

We show that in rice, the amino acid-conjugates of JA precursor, OPDA, may function as a non-canonical signal for the production of phytoalexins in coordination with the innate chitin signaling. The core oxylipins, jasmonic acid (JA) and JA-Ile, are well-known as potent regulators of plant defense against necrotrophic pathogens and/or herbivores. However, recent studies also suggest that other oxylipins, including 12-oxo-phytodienoic acid (OPDA), may contribute to plant defense. Here, we used a previously characterized metabolic defense marker, p-coumaroylputrescine (CoP), and fungal elicitor, chitooligosaccharide, to specifically test defense role of various oxylipins in rice (Oryza sativa). While fungal elicitor triggered a rapid production of JA, JA-Ile, and their precursor OPDA, rice cells exogenously treated with the compounds revealed that OPDA, rather than JA-Ile, can stimulate the CoP production. Next, reverse genetic approach and oxylipin-deficient rice mutant (hebiba) were used to uncouple oxylipins from other elicitor-triggered signals. It appeared that, without oxylipins, residual elicitor signaling had only a minimal effect but, in synergy with OPDA, exerted a strong stimulatory activity towards CoP production. Furthermore, as CoP levels were compromised in the OPDA-treated Osjar1 mutant cells impaired in the oxylipin-amino acid conjugation, putative OPDA-amino acid conjugates emerged as hypothetical regulators of CoP biosynthesis. Accordingly, we found several OPDA-amino acid conjugates in rice cells treated with exogenous OPDA, and OPDA-Asp was detected, although in small amounts, in the chitooligosaccharide-treated rice. However, as synthetic OPDA-Asp and OPDA-Ile, so far, failed to induce CoP in cells, it suggests that yet another presumed OPDA-amino acid form(s) could be acting as novel regulator(s) of phytoalexins in rice.

Untargeted Metabolomics Profiling of Arabidopsis WT, lbr-2-2 and bak1-4 Mutants Following Treatment with Two LPS Chemotypes

Plants perceive pathogenic threats from the environment that have evaded preformed barriers through pattern recognition receptors (PRRs) that recognise microbe-associated molecular patterns (MAMPs). The perception of and triggered defence to lipopolysaccharides (LPSs) as a MAMP is well-studied in mammals, but little is known in plants, including the PRR(s). Understanding LPS-induced secondary metabolites and perturbed metabolic pathways in Arabidopsis will be key to generating disease-resistant plants and improving global plant crop yield. Recently, Arabidopsis LPS-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI)-related proteins (LBP/BPI related-1) and (LBP/BPI related-2) were shown to perceive LPS from Pseudomonas aeruginosa and trigger defence responses. In turn, brassinosteroid insensitive 1 (BRI1)-associated receptor kinase 1 (BAK1) is a well-established co-receptor for several defence-related PRRs in plants. Due to the lack of knowledge pertaining to LPS perception in plants and given the involvement of the afore-mentioned proteins in MAMPs recognition, in this study, Arabidopsis wild type (WT) and mutant (lbr2-2 and bak1-4) plants were pressure-infiltrated with LPSs purified from Pseudomonas syringae pv. tomato DC3000 (Pst) and Xanthomonas campestris pv. campestris 8004 (Xcc). Metabolites were extracted from the leaves at four time points over a 24 h period and analysed by UHPLC-MS, generating distinct metabolite profiles. Data analysed using unsupervised and supervised multivariate data analysis (MVDA) tools generated results that reflected time- and treatment-related variations after both LPS chemotypes treatments. Forty-five significant metabolites were putatively annotated and belong to the following groups: glucosinolates, hydroxycinnamic acid derivatives, flavonoids, lignans, lipids, oxylipins, arabidopsides and phytohormones, while metabolic pathway analysis (MetPA) showed enrichment of flavone and flavanol biosynthesis, phenylpropanoid biosynthesis, alpha-linolenic acid metabolism and glucosinolate biosynthesis. Distinct metabolite accumulations depended on the LPS chemotype and the genetic background of the lbr2-2 and bak1-4 mutants. This study highlights the role of LPSs in the reprogramming Arabidopsis metabolism into a defensive state, and the possible role of LBR and BAK1 proteins in LPSs perception and thus plant defence against pathogenic bacteria.

Distribution analysis of jasmonic acid-related compounds in developing Glycine max L. (soybean) seeds using mass spectrometry imaging and liquid chromatography-mass spectrometry

INTRODUCTION

Jasmonic acid (JA) and its precursors are oxylipins derived from α-linolenic acid (αLA) and hexadecatrienoic acid, and regulate seed development. However, their spatial distribution in the developing Glycine max L. (soybean) seeds has not been elucidated.

OBJECTIVE

To investigate the distribution of JA-related compounds in the developing soybean seeds using desorption electrospray ionisation-mass spectrometry imaging (DESI-MSI) and liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) analyses.

METHODS

Cryosections of developing seeds were prepared using adhesive films, and subjected to DESI-MSI analysis. Verification of the DESI-MSI ion images were performed using DESI-tandem MSI (MS/MSI), LC-ESI-MS and tandem MS (MS/MS).

RESULTS

In the DESI-MSI mass spectrum, peaks matching the chemical formulae of αLA, 12-oxo-phytodienoic acid (OPDA), and 3-oxo-2-(2-(Z)-pentenyl)-cyclopentane-1-octanoic acid (OPC-8:0) were detected. These compounds were mainly distributed in the seed coat, especially near the hilum. This was consistent with the quantitative results obtained by LC-ESI-MS. While, DESI-MS/MSI and LC-ESI-MS/MS suggested the presence of isomers for OPDA and OPC-8:0. The effect of isomers on the DESI-MSI ion images was small for OPDA, and considerable for OPC-8:0.

CONCLUSION

These results demonstrated that free αLA, OPDA, and OPC-8:0 were the abundant JA-related compounds mainly distributed in the seed coat of the developing soybeans. OPDA and OPC-8:0 might exert a biological role in the seed coat. To the best of my knowledge, this is the first report on the accumulation of OPDA and OPC-8:0 in the seed coat. The combination of DESI-MSI and LC-ESI-MS is a useful tool for distribution analysis of JA-related compounds in the developing seeds.

Silencing of a Pseudo-nitzschia arenysensis lipoxygenase transcript leads to reduced oxylipin production and impaired growth

Because of their importance as chemical mediators, the presence of a rich and varied family of lipoxygenase (LOX) products, collectively named oxylipins, has been investigated thoroughly in diatoms, and the involvement of these products in important processes such as bloom regulation has been postulated. Nevertheless, little information is available on the enzymes and pathways operating in these protists. Exploiting transcriptome data, we identified and characterized a LOX gene, PaLOX, in Pseudo-nitzschia arenysensis, a marine diatom known to produce different species of oxylipins by stereo- and regio-selective oxidation of eicosapentaenoic acid (EPA) at C12 and C15. PaLOX RNA interference correlated with a decrease of the lipid-peroxidizing activity and oxylipin synthesis, as well as with a reduction of growth of P. arenysensis. In addition, sequence analysis and structure models of the C-terminal part of the predicted protein closely fitted with the data for established LOXs from other organisms. The presence in the genome of a single LOX gene, whose downregulation impairs both 12- and 15-oxylipins synthesis, together with the in silico 3D protein modelling suggest that PaLOX encodes for a 12/15S-LOX with a dual specificity, and provides additional support to the correlation between cell growth and oxylipin biosynthesis in diatoms.

Unravelling the Molecular Regulation Mechanisms of Slow Ripening Trait in Prunus persica

Fruit development is a complex process that involves the interplay of cell division, expansion, and differentiation. As a model to study fruit development, nectarines incapable of ripening were described as slow ripening. Slow ripening fruits remained firm and exhibited no rise in CO₂ or ethylene production rates for one month or more at 20 °C. Different studies suggest that this trait is controlled by a single gene (NAC072). Transcriptome analysis between normal and slow ripening fruits showed a total of 157, 269, 976, and 5.224 differentially expressed genes in each fruit developmental stage analyzed (T1, T2, T3, and T7, respectively), and no expression of NAC072 was found in the slow ripening individuals. Using this transcriptomic information, we identified a correlation of NAC072 with auxin-related genes and two genes associated with terpene biosynthesis. On the other hand, significant differences were observed in hormonal biosynthetic pathways during fruit development between the normal and slow ripening individuals (gibberellin, ethylene, jasmonic acid and abscisic acid). These results suggest that the absence of NAC072 by the direct or indirect expression control of auxins or terpene-related genes prevents normal peach fruit development.

Kaolin and Jasmonic acid improved cotton productivity under water stress conditions

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

Identification of Fungal Pathogens to Control Postharvest Passion Fruit (Passiflora edulis) Decays and Multi-Omics Comparative Pathway Analysis Reveals Purple Is More Resistant to Pathogens than a Yellow Cultivar

Production of passion fruit (Passiflora edulis) is restricted by postharvest decay, which limits the storage period. We isolated, identified, and characterized fungal pathogens causing decay in two passion fruit cultivars during two fruit seasons in China. Morphological characteristics and nucleotide sequences of ITS-rDNA regions identified eighteen isolates, which were pathogenic on yellow and purple fruit. Fusarium kyushuense, Fusarium concentricum, Colletotrichum truncatum, and Alternaria alternata were the most aggressive species. Visible inspections and comparative analysis of the disease incidences demonstrated that wounded and non-wounded yellow fruit were more susceptible to the pathogens than the purple fruit. Purple cultivar showed higher expression levels of defense-related genes through expression and metabolic profiling, as well as significantly higher levels of their biosynthesis pathways. We also found fungi with potential beneficial features for the quality of fruits. Our transcriptomic and metabolomics data provide a basis to identify potential targets to improve the pathogen resistance of the susceptible yellow cultivar. The identified fungi and affected features of the fruit of both cultivars provide important information for the control of pathogens in passion fruit industry and postharvest storage.

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.

Fungal Jasmonate as a Novel Morphogenetic Signal for Pathogenesis

A key question that has remained unanswered is how pathogenic fungi switch from vegetative growth to infection-related morphogenesis during a disease cycle. Here, we identify a fungal oxylipin analogous to the phytohormone jasmonic acid (JA), as the principal regulator of such a developmental switch to isotropic growth and pathogenicity in the rice-blast fungus Magnaporthe oryzae. Using specific inhibitors and mutant analyses, we determined the molecular function of intrinsic jasmonates during M. oryzae pathogenesis. Loss of 12-Oxo-phytodienoic Acid (OPDA) Reductase and/or consequent reduction of jasmonate biosynthesis, prolonged germ tube growth and caused delayed initiation and improper development of infection structures in M. oryzae, reminiscent of phenotypic defects upon impaired cyclic AMP (cAMP) signaling. Chemical- or genetic-complementation completely restored proper vegetative growth and appressoria in opr1Δ. Mass spectrometry-based quantification revealed increased OPDA accumulation and significantly decreased jasmonate levels in opr1Δ. Most interestingly, exogenous jasmonate restored proper appressorium formation in pth11Δ that lacks G protein/cAMP signaling; but failed to do so in the Mitogen-activated protein (MAP) kinase mutants. Epistasis analysis placed jasmonate upstream of the cAMP pathway in rice blast. Mechanistically, intrinsic jasmonate orchestrates timely cessation of the vegetative phase and induces pathogenic development via a complex regulatory interaction with the cAMP-PKA cascade and redox signaling in rice blast.

Herbivore-induced and constitutive volatiles are controlled by different oxylipin-dependent mechanisms in rice

Despite the importance of volatile organic compounds (VOCs) for plants, control mechanisms for their basal and stress-induced biosynthesis and release remain unclear. We sampled and characterized headspace and internal leaf volatile pools in rice (Oryza sativa), after a simulated herbivory treatment, which triggers an endogenous jasmonate burst. Certain volatiles, such as linalool, were strongly upregulated by simulated herbivory stress. In contrast, other volatiles, such as β-caryophyllene, were constitutively emitted and fluctuated according to time of day. Transcripts of the linalool synthase gene transiently increased 1-3 h after exposure of rice to simulated herbivory, whereas transcripts of caryophyllene synthase peaked independently at dawn. Unexpectedly, although emission and accumulation patterns of rice inducible and constitutive VOCs were substantially different, both groups of volatiles were compromised in jasmonate-deficient hebiba mutants, which lack the allene oxide cyclase (AOC) gene. This suggests that rice employs at least two distinct oxylipin-dependent mechanisms downstream of AOC to control production of constitutive and herbivore-induced volatiles. Levels of the JA precursor, 12-oxo-phytodienoic acid (OPDA), were correlated with constitutive volatile levels suggesting that OPDA or its derivatives could be involved in control of volatile emission in rice.

Unique localization of jasmonic acid-related compounds in developing Phaseolus vulgaris L. (common bean) seeds revealed through desorption electrospray ionization-mass spectrometry imaging

Jasmonic acid (JA) and its precursors are oxylipins derived from α-linolenic acid (αLA). Presumably, they are involved in the regulation of seed embryogenesis, dormancy, and germination. However, their spatial localization in the developing Phaseolus vulgaris L. (common bean) seeds has not been fully elucidated. Therefore, desorption electrospray ionization-mass spectrometry imaging (DESI-MSI) was performed to investigate their localization in the developing seeds. Peaks corresponding to the chemical formulae of αLA and 3-oxo-2-(2-(Z)-pentenyl)-cyclopentane-1-octanoic acid (OPC-8:0) were localized mainly in the radicle and seed coat, while that of 12-oxo-phytodienoic acid (OPDA) in the seed coat. This was consistent with the quantitative results obtained using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analysis. In contrast, DESI-tandem MSI (MS/MSI) and LC-ESI-MS/MS analyses showed that the effects of isomers on the DESI-MSI ion images were small for αLA and OPDA, but not for OPC-8:0. This indicated that DESI-MSI could accurately visualize αLA and OPDA, while DESI-MS/MSI was necessary to visualize OPC-8:0. The results demonstrated that free αLA and OPC-8:0 were abundant in the radicle and seed coat, while free OPDA was accumulated in the seed coat. Interestingly, the localization pattern of OPDA was similar to that of JA. In addition, compared to the concentrations of OPDA, the concentration of OPC-8:0 was lower in the seed coat and higher in the radicle. These results suggest that OPDA and/or JA play a biological role mainly in the seed coat, while OPC-8:0 is biologically active mainly in the radicle. Therefore, DESI-MSI coupled with LC-ESI-MS is a useful tool for spatial analysis of JA-related compounds in developing common bean seeds.

Hormesis-Inducing Essential Oil Nanodelivery System Protects Plants against Broad Host-Range Necrotrophs

Botrytis cinerea, a broad host-range necrotrophic (BHN) phytopathogen, establishes compatible interactions with hosts by deploying multigene infection strategies, rendering simply inherited resistance ineffective to fight off this pathogen. Since essential oils (EOs) serve as intermediators during phytobiome communication, we hypothesize that they have the potential to enhance the quantitative disease resistance against BHN by eliciting the adaptive stress response (hormesis) in plants. However, using EOs is challenging due to their poor solubility in water. Nanoemulsification of EOs enhances not only the solubility of EOs but also their potency and stability. Here, we demonstrate the potential use of essential oil nanoemulsions (EONEs) to control infections caused by BHN. Using basic engineering principles of nanocarrier design, we demonstrate the efficacy of a robust EONEs design for controlling B. cinerea infection in a model plant, Arabidopsis thaliana. Our nanoemulsion delivery system significantly enhanced the disease resistance of the host by reducing the necrotic area by up to 50% compared to untreated plants. RNA-seq analysis indicated that successful treatments upregulated autophagy, ROS scavenging, and activation of the jasmonic acid signaling pathway.

Interactions between zinc and Phomopsis longicolla infection in roots of Glycine max

Phomopsis. longicolla is a hemibiotrophic fungus causing significant soybean yield loss worldwide. To reveal the role of zinc in plant-pathogen interactions, soybean seedlings were grown hydroponically with a range of Zn concentrations, 0.06 µM (deficient, Zn0), 0.4 µM (optimal growth), 1.5 µM, 4 µM, 12 µM, and toxic 38 μM, and were subsequently inoculated with P. longicolla via the roots. In vivo analysis of metal distribution in tissues by micro-X-ray fluorescence showed local Zn mobilization in the root maturation zone in all treatments. Decreased root and pod biomass, and photosynthetic performance in infected plants treated with 0.4 µM Zn were accompanied with accumulation of Zn, jasmonoyl-L-isoleucine (JA-Ile), jasmonic acid, and cell wall-bound syringic acid (cwSyA) in roots. Zn concentration in roots of infected plants treated with 1.5 µM Zn was seven-fold higher than in the 0.4 µM Zn treatment, which together with accumulation of JA-Ile, cwSyA, cell wall-bound vanilic acid and leaf jasmonates contributed to maintaining photosynthesis and pod biomass. Host-pathogen nutrient competition and phenolics accumulation limited the infection in Zn-deficient plants. The low infection rate in Zn 4 µM-treated roots correlated with salicylic and 4-hydroxybenzoic acid, and cell wall-bound p-coumaric acid accumulation. Zn toxicity promoted pathogen invasion and depleted cell wall-bound phenolics. The results show that manipulation of Zn availability improves soybean resistance to P. longicolla by stimulating phenolics biosynthesis and stress-inducible phytohormones.

Understanding Plant Social Networking System: Avoiding Deleterious Microbiota but Calling Beneficials

Plant association with microorganisms elicits dramatic effects on the local phytobiome and often causes systemic and transgenerational modulation on plant immunity against insect pests and microbial pathogens. Previously, we introduced the concept of the plant social networking system (pSNS) to highlight the active involvement of plants in the recruitment of potentially beneficial microbiota upon exposure to insects and pathogens. Microbial association stimulates the physiological responses of plants and induces the development of their immune mechanisms while interacting with multiple enemies. Thus, beneficial microbes serve as important mediators of interactions among multiple members of the multitrophic, microscopic and macroscopic communities. In this review, we classify the steps of pSNS such as elicitation, signaling, secreting root exudates, and plant protection; summarize, with evidence, how plants and beneficial microbes communicate with each other; and also discuss how the molecular mechanisms underlying this communication are induced in plants exposed to natural enemies. Collectively, the pSNS modulates robustness of plant physiology and immunity and promotes survival potential by helping plants to overcome the environmental and biological challenges.

Brachypodium Phenylalanine Ammonia Lyase (PAL) Promotes Antiviral Defenses against Panicum mosaic virus and Its Satellites

Brachypodium distachyon has recently emerged as a premier model plant for monocot biology, akin to Arabidopsis thaliana We previously reported genome-wide transcriptomic and alternative splicing changes occurring in Brachypodium during compatible infections with Panicum mosaic virus (PMV) and its satellite virus (SPMV). Here, we dissected the role of Brachypodium phenylalanine ammonia lyase 1 (PAL1), a key enzyme for phenylpropanoid and salicylic acid (SA) biosynthesis and the induction of plant defenses. Targeted metabolomics profiling of PMV-infected and PMV- plus SPMV-infected (PMV/SPMV) Brachypodium plants revealed enhanced levels of multiple defense-related hormones and metabolites such as cinnamic acid, SA, and fatty acids and lignin precursors during disease progression. The virus-induced accumulation of SA and lignin was significantly suppressed upon knockdown of B. distachyon PAL1 (BdPAL1) using RNA interference (RNAi). The compromised SA accumulation in PMV/SPMV-infected BdPAL1 RNAi plants correlated with weaker induction of multiple SA-related defense gene markers (pathogenesis related 1 [PR-1], PR-3, PR-5, and WRKY75) and enhanced susceptibility to PMV/SPMV compared to that of wild-type (WT) plants. Furthermore, exogenous application of SA alleviated the PMV/SPMV necrotic disease phenotypes and delayed plant death caused by single and mixed infections. Together, our results support an antiviral role for BdPAL1 during compatible host-virus interaction, perhaps as a last resort attempt to rescue the infected plant.IMPORTANCE Although the role of plant defense mechanisms against viruses are relatively well studied in dicots and in incompatible plant-microbe interactions, studies of their roles in compatible interactions and in grasses are lagging behind. In this study, we leveraged the emerging grass model Brachypodium and genetic resources to dissect Panicum mosaic virus (PMV)- and its satellite virus (SPMV)-compatible grass-virus interactions. We found a significant role for PAL1 in the production of salicylic acid (SA) in response to PMV/SPMV infections and that SA is an essential component of the defense response preventing the plant from succumbing to viral infection. Our results suggest a convergent role for the SA defense pathway in both compatible and incompatible plant-virus interactions and underscore the utility of Brachypodium for grass-virus biology.

The Grapevine E3 Ubiquitin Ligase VriATL156 Confers Resistance against the Downy Mildew Pathogen Plasmopara viticola

Downy mildew, caused by Plasmopara viticola, is one of the most severe diseases of grapevine (Vitis vinifera L.). Genetic resistance is an effective and sustainable control strategy, but major resistance genes (encoding receptors for specific pathogen effectors) introgressed from wild Vitis species, although effective, may be non-durable because the pathogen can evolve to avoid specific recognition. Previous transcriptomic studies in the resistant species Vitis riparia highlighted the activation of signal transduction components during infection. The transfer of such components to V. vinifera might confer less specific and therefore more durable resistance. Here, we describe the generation of transgenic V. vinifera lines constitutively expressing the V. riparia E3 ubiquitin ligase gene VriATL156. Phenotypic and molecular analysis revealed that the transgenic plants were less susceptible to P. viticola than vector-only controls, confirming the role of this E3 ubiquitin ligase in the innate immune response. Two independent transgenic lines were selected for detailed analysis of the resistance phenotype by RNA-Seq and microscopy, revealing the profound reprogramming of transcription to achieve resistance that operates from the earliest stages of pathogen infection. The introduction of VriATL156 into elite grapevine cultivars could therefore provide an effective and sustainable control measure against downy mildew.

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.

Untargeted Metabolomic Analyses Reveal Chemical Complexity of Dioecious Cannabis Flowers

Cannabis is a mostly dioecious multi-use flowering plant genus. Sexual dimorphism is an important characteristic in Cannabis-based commercial production systems, which has consequences for fibre, seed, and the yield of secondary metabolites, such as phytocannabinoid and terpenes for therapeutic uses. Beyond the obvious morphological differences between male and female plants, metabolic variation among dioecious flowers is largely undefined. Here, we report a pilot metabolomic study comparing staminate (male) and pistillate (female) unisexual flowers. Enrichment of the α-linolenic acid pathway and consensus evaluation of the jasmonic acid (JA) related compound 12-oxo-phytodienoicacid (OPDA) among differentially abundant metabolites suggests that oxylipin signalling is associated with secondary metabolism and sex expression in female flowers. Several putative phytocannabinoid-like compounds were observed to be upregulated in female flowers, but full identification was not possible due to the limitation of available databases. Targeted analysis of 14 phytocannabinoids using certified reference standards (cannabidiolic acid (CBDA), cannabidiol (CBD), Δ9-tetrahydrocannabinolic acid A (Δ9-THCAA), Δ9-tetrahydrocannabinol (Δ9-THC), cannabichromenic acid (CBCA), cannabichromene (CBC), cannabigerolic acid (CBGA), cannabigerol (CBG), cannabinolic acid (CBNA), cannabinol (CBN), cannabidivarinic acid (CBDVA), cannabidivarin (CBDV), tetrahydrocannabivarinic acid (THCVA), and tetrahydrocannabivarin (THCV)) showed a higher total phytocannabinoid content in female flowers compared with the male flowers, as expected. In summary, the development of a phytocannabinoid-specific accurate-mass MSn fragmentation spectral library and gene pool representative metabolome has the potential to improve small molecule compound annotation and accelerate understanding of metabolic variation underlying phenotypic diversity in Cannabis.

12-oxo-Phytodienoic Acid: A Fuse and/or Switch of Plant Growth and Defense Responses?

12-oxo-Phytodienoic acid (OPDA) is a primary precursor of (-)-jasmonic acid (JA), able to trigger autonomous signaling pathways that regulate a unique subset of jasmonate-responsive genes, activating and fine-tuning defense responses, as well as growth processes in plants. Recently, a number of studies have illuminated the physiol-molecular activities of OPDA signaling in plants, which interconnect the regulatory loop of photosynthesis, cellular redox homeostasis, and transcriptional regulatory networks, together shedding new light on (i) the underlying modes of cellular interfaces between growth and defense responses (e.g., fitness trade-offs or balances) and (ii) vital information in genetic engineering or molecular breeding approaches to upgrade own survival capacities of plants. However, our current knowledge regarding its mode of actions is still far from complete. This review will briefly revisit recent progresses on the roles and mechanisms of OPDA and information gaps within, which help in understanding the phenotypic and environmental plasticity of plants.

1H Nuclear Magnetic Resonance and Liquid Chromatography Coupled with Mass Spectrometry-Based Metabolomics Reveal Enhancement of Growth-Promoting Metabolites in Onion Seedlings Treated with Green-Synthesized Nanomaterials

Seed priming is a promising approach to improve germination, emergence, and seedling growth by triggering pre-germinative metabolism and enhancing seedling vigor. Recently, nanopriming gained importance in seed improvement as a result of the small size and unique physicochemical characteristics of nanomaterials. In the present study, silver and gold nanoparticles were synthesized using onion extracts as the reducing agent. Similarly, the agro-food industrial byproducts citrus seed oil and curcumin-removed turmeric oleoresin were used for the preparation of nanoemulsions. For seed priming, these green-synthesized nanomaterials were incubated with seeds of two onion (Allium cepa L.) cultivars (Legend and 50147) for 72 h, and then the plants were grown in a greenhouse for 3 weeks. Seed priming with these nanomaterials increased seed germination and seedling emergence. One-dimensional ¹H nuclear magnetic resonance and liquid chromatography coupled with mass spectrometry metabolomics studies showed that different nanopriming treatments distinctly altered the metabolome of onion seedlings. Seed priming treatments significantly inhibited plant hormones and growth regulators, such as abscisic acid and cis-(+)-12-oxo-phytodienoic acid, and enhanced germination stimulators, such as γ-aminobutyric acid and zeatin, in onion seeds and seedlings. Therefore, these priming treatments have positive impact on improving seed performance and plant growth.

Chitosan Induces Plant Hormones and Defenses in Tomato Root Exudates

In this work, we use electrophysiological and metabolomic tools to determine the role of chitosan as plant defense elicitor in soil for preventing or manage root pests and diseases sustainably. Root exudates include a wide variety of molecules that plants and root microbiota use to communicate in the rhizosphere. Tomato plants were treated with chitosan. Root exudates from tomato plants were analyzed at 3, 10, 20, and 30 days after planting (dap). We found, using high performance liquid chromatography (HPLC) and excitation emission matrix (EEM) fluorescence, that chitosan induces plant hormones, lipid signaling and defense compounds in tomato root exudates, including phenolics. High doses of chitosan induce membrane depolarization and affect membrane integrity. 1H-NMR showed the dynamic of exudation, detecting the largest number of signals in 20 dap root exudates. Root exudates from plants irrigated with chitosan inhibit ca. twofold growth kinetics of the tomato root parasitic fungus Fusarium oxysporum f. sp. radicis-lycopersici. and reduced ca. 1.5-fold egg hatching of the root-knot nematode Meloidogyne javanica.

CYP20-3 deglutathionylates 2-CysPRX A and suppresses peroxide detoxification during heat stress

In plants, growth-defense trade-offs occur because of limited resources, which demand prioritization towards either of them depending on various external and internal factors. However, very little is known about molecular mechanisms underlying their occurrence. Here, we describe that cyclophilin 20-3 (CYP20-3), a 12-oxo-phytodienoic acid (OPDA)-binding protein, crisscrosses stress responses with light-dependent electron reactions, which fine-tunes activities of key enzymes in plastid sulfur assimilations and photosynthesis. Under stressed states, OPDA, accumulates in the chloroplasts, binds and stimulates CYP20-3 to convey electrons towards serine acetyltransferase 1 (SAT1) and 2-Cys peroxiredoxin A (2CPA). The latter is a thiol-based peroxidase, protecting and optimizing photosynthesis by reducing its toxic byproducts (e.g., H2O2). Reduction of 2CPA then inactivates its peroxidase activity, suppressing the peroxide detoxification machinery, whereas the activation of SAT1 promotes thiol synthesis and builds up reduction capacity, which in turn triggers the retrograde regulation of defense gene expressions against abiotic stress. Thus, we conclude that CYP20-3 is a unique metabolic hub conveying resource allocations between plant growth and defense responses (trade-offs), ultimately balancing optimal growth phonotype.

OPDA and ABA accumulation in Pb-stressed Zygophyllum fabago can be primed by salicylic acid and coincides with organ-specific differences in accumulation of phenolics

Salicylic acid (SA) is a well-known priming agent that is widely used to protect plants against stressing agents, including heavy metals as Pb. A better understanding of the mechanisms that enable plants to counteract Pb toxicity would help to select strategies for land reclamation programs. Here we used a metallicolous population of Zygophyllum fabago to assess the extent to which SA pretreatment modulates Pb-induced changes in phenol metabolism and stress-related phytohormone levels in roots and leaves. Our data revealed that accumulation of different phytohormones, lignin, soluble and wall-bound phenolics as well as peroxidase (PRX) activity in Pb-stressed plants differed after SA-pretreatment. Exposure to Pb led to the induction of soluble and cell wall-bound PRX activities, particularly those involved in the oxidation of coniferyl alcohol and ferulic acid, while pretreatment with SA reduced the Pb-induced stimulation of PRX activities in roots but increased them in leaves. SA-treatment by itself induced accumulation of ABA and the JA-precursor 12-oxo-phytodienoic acid (OPDA) in the roots. Pb in turn inhibited these SA-induced effects with the exception of OPDA accumulation that was primed by the pretreatment. The SA treatment also induced accumulation of OPDA in leaves but suppressed the accumulation of JA-Ile although with relatively small absolute changes. Notably, Pb-induced accumulation of ABA was primed in the leaves of SA-pretreated plants. Together our data suggest that priming of OPDA accumulation in the roots and of ABA in the leaves by SA-pretreatment may play important regulatory roles, possibly via regulating PRX activities, for Pb stress in plants.

Hormonal interplay in the regulation of fruit ripening and cold acclimation in avocados

Avocados (Persea americana Mill.) are climacteric fruits, the ripening of which during postharvest at room temperature is strongly ethylene dependent. However, the role of other phytohormones in the modulation of postharvest ripening of avocados is still poorly understood. The optimal ripening state of avocados is attained a few days after harvest depending on the genotype, growing region and initial maturity stage of the fruit, and cold temperature storage is commonly used to delay this process. Here, we hypothesized that the ripening of avocados at room temperature may be governed not only by ethylene, but also by other phytohormones. With this aim, we analyzed the hormonal profiling of avocados subjected to either 4 °C and 25 °C during 10 days of postharvest. A biphasic response was observed during postharvest ripening of avocados at room temperature. While ethylene alone appeared to govern fruit ripening during the first transfer from cold to room temperature, a complex hormonal interplay occurred during ripening of avocados leading to a progressive fruit softening at room temperatures. Aside from ethylene, auxin, gibberellins, jasmonates and ABA appeared to be involved in avocado fruit ripening during postharvest at room temperature. Cold storage for a period of 10 days inhibited this hormonal response related to ripening. Furthermore, avocados stored at cold temperatures underwent a quick response in order to tolerate cold stress leading to changes in endogenous ABA and jasmonates. We conclude that a complex hormonal interplay, rather than ethylene alone, modulates postharvest ripening of avocados and that cold storage can effectively be employed as a technique to prevent avocados from a rapid ripening thanks to the cold stress tolerance mechanisms deployed by fruits through multiple hormonal regulation.

Simple liquid chromatography-electrospray ionization ion trap mass spectrometry method for the quantification of galacto-oxylipin arabidopsides in plant samples

A simple and sensitive method to quantify five different arabidopsides by HPLC—ion trap mass spectrometry in complex plant samples was developed and validated. Arabidopsides are oxidized galactolipids first described in Arabidopsis thaliana but also produced by other plant species under stress conditions. External calibration was performed using arabidopsides purified from freeze-thawed Arabidopsis leaves. Lipids were extracted and pre-purified on an SPE silica column before HPLC–MS analysis. Arabidopsides were separated on a C18 column using a gradient of mQ water and acetonitrile:mQ water (85:15) supplemented with formic acid (0.2%) and ammonium formate (12 mM). The method was validated according to European commission decision 2002/657/CE. LOD, LOQ, linearity, intra-day and inter-day precision and accuracy, selectivity, matrix effects and recoveries were determined for the five metabolites. The established method is highly selective in a complex plant matrix. LOD and LOQ were, respectively, in the range 0.098–0.78 and 0.64–1.56 µM, allowing the arabidopside quantification from 25.6–62.4 nmol/g fresh weight. Calibration curve correlation coefficients were higher than 0.997. Matrix effects ranged from -2.09% to 6.10% and recoveries between 70.7% and 109%. The method was successfully applied to complex plant matrixes: Arabidopsis thaliana and Nasturtium officinale.