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

Development of an efficient and scalable bioprocess for the plant hormone 12-OPDA: Overcoming the hurdles of nature's biosynthesis

Besides its native biological function as a plant hormone, cis-(+)-12-oxo-phytodienoic acid (12-OPDA) serves as a metabolite for the cellular formation of (-)-jasmonic acid and has also been shown to have an influence on mammalian cells. In order to make this biologically active, but at the same time very expensive natural product 12-OPDA broadly accessible for further biological and medicinal research, we developed an efficient bioprocess based on the utilization of a tailor-made whole-cell catalyst by following the principles of its biosynthesis in nature. After process optimization, the three-step one-pot synthesis of 12-OPDA starting from readily accessible α-linolenic acid could be conducted at appropriate technically relevant substrate loadings in the range of 5-20 g L-1. The desired 12-OPDA was obtained with an excellent conversion efficiency, and by means of the developed, efficient downstream-processing, this emulsifying as well as stereochemically labile biosynthetic metabolite 12-OPDA was then obtained with very high chemical purity (>99%) and enantio- and diastereomeric excess (>99% ee, 96% de) as well as negligible side-product formation (<1%). With respect to future technical applications, we also demonstrated the scalability of the production of the whole cell-biocatalyst in a high cell-density fermentation process.

Histone deacetylase OsHDA706 orchestrates rice broad-spectrum antiviral immunity and is impeded by a viral effector

Lysine acetylation is a dynamic post-translational modification of proteins. Extensive studies have revealed that the acetylation modulated by histone acetyltransferases and histone deacetylases (HDACs) plays a crucial role in regulating protein function. However, there has been limited focus on how HDACs regulate jasmonic acid (JA) biosynthesis in plants. Here, we uncover that the protein stability of OsLOX14, a critical enzyme involved in JA biosynthesis, is regulated by a histone deacetylase, OsHDA706, and is hindered by a viral protein. Our results show that OsHDA706 deacetylates OsLOX14 and enhances the stability of OsLOX14, leading to JA accumulation and an improved broad-spectrum rice antiviral defense. Furthermore, we found that the viral protein P2, encoded by the destructive rice stripe virus, disrupts the association of OsHDA706-OsLOX14, promoting viral infection. Overall, our findings reveal how HDAC manipulates the interplay of deacetylation and protein stability of a JA biosynthetic enzyme to enhance plant antiviral responses.

The molecular paradigm of reactive oxygen species (ROS) and reactive nitrogen species (RNS) with different phytohormone signaling pathways during drought stress in plants

Drought is undoubtedly a major environmental constraint that negatively affects agricultural yield and productivity throughout the globe. Plants are extremely vulnerable to drought which imposes several physiological, biochemical and molecular perturbations. Increased generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in different plant organs is one of the inevitable consequences of drought. ROS and RNS are toxic byproducts of metabolic reactions and poise oxidative stress and nitrosative stress that are detrimental for plants. In spite of toxic effects, these potentially active radicals also play a beneficial role in mediating several signal transduction events that lead to plant acclimation and enhanced survival under harsh environmental conditions. The precise understanding of ROS and RNS signaling and their molecular paradigm with different phytohormones, such as auxin, gibberellin, cytokinin, abscisic acid, ethylene, brassinosteroids, strigolactones, jasmonic acid, salicylic acid and melatonin play a pivotal role for maintaining plant fitness and resilience to counteract drought toxicity. Therefore, the present review provides an overview of integrated systemic signaling between ROS, RNS and phytohormones during drought stress based on past and recent advancements and their influential role in conferring protection against drought-induced damages in different plant species. Indeed, it would not be presumptuous to hope that the detailed knowledge provided in this review will be helpful for designing drought-tolerant crop cultivars in the forthcoming times.

Deuterium- and Alkyne-Based Bioorthogonal Raman Probes for In Situ Quantitative Metabolic Imaging of Lipids within Plants

Plants can rapidly respond to different stresses by activating multiple signaling and defense pathways. The ability to directly visualize and quantify these pathways in real time using bioorthogonal probes would have practical applications, including characterizing plant responses to both abiotic and biotic stress. Fluorescence-based labels are widely used for tagging of small biomolecules but are relatively bulky and with potential effects on their endogenous localization and metabolism. This work describes the use of deuterium- and alkyne-derived fatty acid Raman probes to visualize and track the real-time response of plants to abiotic stress within the roots. Relative quantification of the respective signals could be used to track their localization and overall real-time responses in their fatty acid pools due to drought and heat stress without labor-intensive isolation procedures. Their overall usability and low toxicity suggest that Raman probes have great untapped potential in the field of plant bioengineering.

Electrochemically Enabled Total Syntheses of Natural Products

Electrochemical techniques have helped to enable the total synthesis of natural products since the pioneering work of Kolbe in the mid 1800's. The electrochemical toolset grows every day and these new possibilities change the way chemists look at and think about natural products. This review provides a perspective on total syntheses wherein electrochemical techniques enabled the carbon─carbon bond formations in the skeletal assembly of important natural products, discussion of mechanistic details, and representative examples of the bond formations enabled over the last several decades. These bond formations are often distinctly different from those possible with conventional chemistries and allow assemblies complementary to other techniques.

Anti-Inflammatory, Neurotrophic, and Cytotoxic Oxylipins Isolated from Chaenomeles sinensis Twigs

Oxylipins are important biological molecules with diverse roles in human and plants such as pro-/anti-inflammatory, antimicrobial, and regulatory activity. Although there is an increasing number of plant-derived oxylipins, most of their physiological roles in humans remain unclear. Here, we describe the isolation, identification, and biological activities of four new oxylipins, chaenomesters A-D (1-4), along with a known compound (5), obtained from Chaenomeles sinensis twigs. Their chemical structures were determined by spectroscopic (i.e., NMR) and spectrometric (i.e., HRMS) data analysis including ¹H NMR-based empirical rules and homonuclear-decoupled ¹H NMR experiments. Chaenomester D (4), an omega-3 oxylipin, showed a potent inhibitory effect on nitric oxide (NO) production in lipopolysaccharide (LPS)-activated BV-2 cells (NO production, 8.46 ± 0.68 μM), neurotrophic activity in C6 cells through the induction of the secretion of nerve growth factor (NGF, 157.7 ± 2.4%), and cytotoxicity in A549 human cancer cell lines (IC₅₀ = 27.4 μM).

Genotype-Dependent Jasmonic Acid Effect on Pinus sylvestris L. Growth and Induced Systemic Resistance Indicators

Due to temperature changes, forests are expected to encounter more stress than before, both in terms of biotic factors, such as increased insect attacks, and abiotic factors, such as more frequent droughts. Priming trees to respond to these changes faster and more effectively would be beneficial. Induced systemic resistance (ISR) is a mechanism that is turned on when plants encounter unfavorable conditions. Certain elicitors, such as jasmonic acid (JA) are known to induce plants' metabolic response. However, even though studies on ISR in herbaceous species are common and varied ISR elicitors can be used in agriculture, the same cannot be said about trees and forestry enterprises. We aimed to investigate whether JA used in different concentrations could induce metabolic changes (total phenol content, total flavonoid content, photosynthesis pigment content, antioxidant enzyme activity) in Pinus sylvestris seedlings and how this varies between different pine half-sib families (genotypes). After six weeks with a single application of JA, pine seedlings in several pine genetic families exhibited increased antioxidant enzyme activity, total phenol content and carotenoid content that correlated positively with JA concentrations used. Results from other genetic families were varied, but in many cases, there was a significant response to JA, with a noticeable increase as compared to the unaffected group. The impact on chlorophyll content and flavonoids was less noticeable overall. A positive effect on seedling growth parameters was not observed in any of the test cases. We conclude that JA can induce systemic resistance after a single application exogenously in P. sylvestris seedlings and recommend that the use of JA needs to be optimized by selecting appropriate concentrations.

Does Potassium (K+) Contribute to High-Nitrate (NO3-) Weakening of a Plant's Defense System against Necrotrophic Fungi?

In this opinion article, we have analyzed the relevancy of a hypothesis which is based on the idea that in Arabidopsis thaliana jasmonic acid, a (JA)-mediated defense system against necrotrophic fungi is weakened when NO₃^- supply is high. Such a hypothesis is based on the fact that when NO₃^- supply is high, it induces an increase in the amount of bioactive ABA which induces the sequestration of the phosphatase ABI2 (PP2C) into the PYR/PYL/RCAR receptor. Consequently, the Ca sensors CBL1/9-CIPK23 are not dephosphorylated by ABI2, thus remaining able to phosphorylate targets such as AtNPF6.3 and AtKAT1, which are NO₃^- and K⁺ transporters, respectively. Therefore, the impact of phosphorylation on the regulation of these two transporters, could (1) reduce NO₃^- influx as in its phosphorylated state AtNPF6.3 shifts to low capacity state and (2) increase K⁺ influx, as in its phosphorylated state KAT1 becomes more active. It is also well known that in roots, K⁺ loading in the xylem and its transport to the shoot is activated in the presence of NO₃^-. As such, the enrichment of plant tissues in K⁺ can impair a jasmonic acid (JA) regulatory pathway and the induction of the corresponding biomarkers. The latter are known to be up-regulated under K⁺ deficiency and inhibited when K⁺ is resupplied. We therefore suggest that increased K⁺ uptake and tissue content induced by high NO₃^- supply modifies the JA regulatory pathway, resulting in a weakened JA-mediated plant's defense system against necrotrophic fungi.

Phytohormone profiles and related gene expressions after endodormancy release in developing Pinus tabuliformis male strobili

Development after endo-dormancy release ensures perennial plants, such as forest trees, proper response to environmental changes and enhances their adaptability. In northern hemisphere, megasporophore and microsporophore of conifers undergo dormancy to complete their development. Here combined with transcriptome data, we used high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (ESI-HPLC-MS/MS) to quantitatively analyse the various hormones (Abscisic Acid (ABA), 3-Indoleacetic acid (IAA), Gibberellins (GAs), Cytokinin (CTK), Jasmonic acid (JA) and Salicylic acid (SA)) of Chinese pine (Pinus tabuliformis Carr.) male strobili after endo-dormancy release. More specifically, we analysed endogenous hormones and their related-genes and verified the important role of ABA in plants growth and development. We observed rapid decrease in ABA content after dormancy release, resulting in reducing the inhibitory effect on male strobili growth. Similarly, rapid drop in ABA/GA ratio was observed and was associated with the start of male strobili growth and development. Combined with transcriptome data, we found that HAB2-SnRK2.10 played a central role in the ABA pathway in the entire network of hormones regulating male strobili development. Due to external environment warming, the differentially expressed HAB2-SnRK gene led to ABA content rapid decline, thus initiating male strobili growth. We constructed a network of hormone-regulated development to understand the interactions between hormones after male strobili dormancy release of male strobili. This study provided essential foundations for studying megasporophore and microsporophore growth mechanism after endo-dormancy and offered new ideas for flower development in gymnosperms and angiosperms.

Effects of Preharvest Methyl Jasmonate and Salicylic Acid Treatments on Growth, Quality, Volatile Components, and Antioxidant Systems of Chinese Chives

Methyl jasmonate (MeJA) and salicylic acid (SA) regulate the production of biologically active compounds in plants and stimulate the accumulation of plant aromatic substances. However, the underlying mechanisms of how MeJA and SA influence characteristic flavor compounds and the antioxidant activity of vegetables are poorly understood. Five MeJA and SA concentrations were used to investigate the dose-dependent effects of these phytohormones on the dry and fresh weight; chlorophyll abundance; the contents of vitamin C, soluble protein, and sugar, nitrate, total phenols, flavonoids, volatile components, and enzymatically produced pyruvic acid; and antioxidant activity in Chinese chive. We found that MeJA and SA at concentrations of 500 and 150 μM, respectively, significantly increased the levels of total chlorophyll, phenols and flavonoids, vitamin C, and volatile components and significantly reduced the accumulation of nitrate. In addition, compared with the control, 500 μM of MeJA significantly increased the soluble sugar and protein content, and 150 μM SA significantly increased the dry and fresh weight of Chinese chive. Furthermore, these concentrations of MeJA and SA significantly increased the enzymatic pyruvate content and the amount of sulfide and aromatic volatile compounds and improved the characteristic flavor compounds. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity, Trolox-equivalent antioxidant capacity, and ferric-reducing antioxidant capacity were significantly improved after a preharvest treatment with 500 μM MeJA and 150 μM SA, which could improve the antioxidant activity, thus improving the postharvest quality and preservation characteristics of Chinese chives. Taken together, a preharvest treatment with 500 μM MeJA and 150 μM SA is optimal to improve the growth, quality, antioxidant activity, and flavor of Chinese chive, thereby enhancing its commercial value.

A Jasmonate-Induced Defense Elicitation in Mature Leaves Reduces Carbon Export and Alters Sink Priority in Grape (Vitis vinifera Chardonnay)

This work aims to understand how Vitis vinifera (Chardonnay) vines prioritise the export and distribution of recently fixed photoassimilate between root tissue, fruit, and defence, following the elicitation of a defence response. Jasmonic acid (JA) and its methyl ester, MeJA, are endogenous plant hormones, known collectively as jasmonates, that have signalling roles in plant defence and consequently are often used to prime plant defence systems. Here, we use exogenous jasmonate application to mature source leaves of Chardonnay grapevines to elucidate the prioritisation strategy of carbon allocation between plant defence and growth. Our results demonstrate that jasmonate application to Chardonnay leaves can elicit a defence response to Botrytis cinerea, but the effect was localised to the jasmonate-treated area. We found no evidence of a systemic defence response in non-treated mature leaves or young growing tissue. JA application reduced the photosynthetic rate of the treated leaf and reduced the export rate of recently fixed carbon-11 from the leaf. Following JA application, a greater proportion of available recently fixed carbon was allocated to the roots, suggesting an increase in sink strength of the roots. Relative sink strength of the berries did not change; however, an increase in berry sugar was observed seven days after JA treatment. We conclude that the data provide evidence for a “high sugar resistance” model in the mature treated leaves of the vine, since the export of carbon was reduced to ensure an elevated defence response in the treated leaf. The increase in berry sugar concentration seven days after treatment can be explained by the initial prioritisation of a greater portion of the exported carbon to storage in the roots, making it available for remobilisation to the berries once the challenge to defence had passed.

Role of jasmonic acid in plants: the molecular point of view

Recent updates in JA biosynthesis, signaling pathways and the crosstalk between JA and others phytohormones in relation with plant responses to different stresses. In plants, the roles of phytohormone jasmonic acid (JA), amino acid conjugate (e.g., JA-Ile) and their derivative emerged in last decades as crucial signaling compounds implicated in stress defense and development in plants. JA has raised a great interest, and the number of researches on JA has increased rapidly highlighting the importance of this phytohormone in plant life. First, JA was considered as a stress hormone implicated in plant response to biotic stress (pathogens and herbivores) which confers resistance to biotrophic and hemibiotrophic pathogens contrarily to salicylic acid (SA) which is implicated in plant response to necrotrophic pathogens. JA is also implicated in plant responses to abiotic stress (such as soil salinity, wounding and UV). Moreover, some researchers have recently revealed that JA controls several physiological processes like root growth, growth of reproductive organs and, finally, plant senescence. JA is also involved in the biosynthesis of various metabolites (e.g., phytoalexins and terpenoids). In plants, JA signaling pathways are well studied in few plants essentially Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa L. confirming the crucial role of this hormone in plants. In this review, we highlight the last foundlings about JA biosynthesis, JA signaling pathways and its implication in plant maturation and response to environmental constraints.

Network-guided search for genetic heterogeneity between gene pairs

MOTIVATION

Correlating genetic loci with a disease phenotype is a common approach to improve our understanding of the genetics underlying complex diseases. Standard analyses mostly ignore two aspects, namely genetic heterogeneity and interactions between loci. Genetic heterogeneity, the phenomenon that genetic variants at different loci lead to the same phenotype, promises to increase statistical power by aggregating low-signal variants. Incorporating interactions between loci results in a computational and statistical bottleneck due to the vast amount of candidate interactions.

RESULTS

We propose a novel method SiNIMin that addresses these two aspects by finding pairs of interacting genes that are, upon combination, associated with a phenotype of interest under a model of genetic heterogeneity. We guide the interaction search using biological prior knowledge in the form of protein-protein interaction networks. Our method controls type I error and outperforms state-of-the-art methods with respect to statistical power. Additionally, we find novel associations for multiple Arabidopsis thaliana phenotypes, and, with an adapted variant of SiNIMin, for a study of rare variants in migraine patients.

AVAILABILITY AND IMPLEMENTATION

Code available at https://github.com/BorgwardtLab/SiNIMin.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Jasmonates and Plant Salt Stress: Molecular Players, Physiological Effects, and Improving Tolerance by Using Genome-Associated Tools

Soil salinity is one of the most limiting stresses for crop productivity and quality worldwide. In this sense, jasmonates (JAs) have emerged as phytohormones that play essential roles in mediating plant response to abiotic stresses, including salt stress. Here, we reviewed the mechanisms underlying the activation and response of the JA-biosynthesis and JA-signaling pathways under saline conditions in Arabidopsis and several crops. In this sense, molecular components of JA-signaling such as MYC2 transcription factor and JASMONATE ZIM-DOMAIN (JAZ) repressors are key players for the JA-associated response. Moreover, we review the antagonist and synergistic effects between JA and other hormones such as abscisic acid (ABA). From an applied point of view, several reports have shown that exogenous JA applications increase the antioxidant response in plants to alleviate salt stress. Finally, we discuss the latest advances in genomic techniques for the improvement of crop tolerance to salt stress with a focus on jasmonates.

Temporal Changes and Correlations between Quality Loss Parameters, Antioxidant Properties and Enzyme Activities in Apricot Fruit Treated with Methyl Jasmonate and Salicylic Acid during Cold Storage and Shelf-Life

The apricot storability is one of the largest challenges, which the apricot industry has to face all over the world; therefore, finding options for prolonging fruit quality during cold storage (CS) and shelf-life (SL) will help to decrease postharvest losses of apricot. The aim of this apricot fruit work was to study the temporal changes and correlations of 10 quality parameters (quality losses, antioxidant properties and enzyme activities) in the postharvest treatments of methyl jasmonate (MeJA) and salicylic acid (SA) under 1 °C CS (7, 14 and 21 days) and 25 °C SL (4 and 8 days after the 21-day CS) treatments. MeJA and SA significantly decreased the quality loss of chilling injury (CI) and fruit decay (FD) at all dates for both storage conditions. MeJA- and SA-treated fruits increased total antioxidant capacity (TAC), total soluble phenolic compounds (TSPC) and carotenoids contents (TCC) at all dates of both storage treatments. In contrast, the ascorbic acid content (AAC) increased only until days 14 and 4 in the CS and SL treatments, respectively. Among enzyme activity parameters, the activities of phenylalanine ammonia-lyase (PAL), peroxidase and superoxide dismutase (SOD) were significantly increased in the MeJA and SA treatments in all dates of both storage treatments. Catalase (CAT) activity increased in the SA and control treatments, while it decreased in the MeJA treatment in both storage conditions. In both the MeJA and the SA treatments, six pair-variables (FD vs. CI, PAL vs. CAT, PAL vs. SOD, TAC vs. SOD, TAC vs. FD, and AAC vs. CI) were significant in Pearson correlation and regression analyses among the 45 parameters pairs. Principal component analyses explained 89.3% of the total variance and PC1 accounted for 55.6% of the variance and correlated with the CI, FD, TAC, TSPC, TCC, PAL and SOD, indicating strong connections among most parameters. In conclusion, MeJA and SA are practically useful and inexpensive techniques to maintain quality attributes of CI, FD, TAC, TSPC, TCC, PAL, POD and SOD in apricot fruit during both CS and SL conditions.

Induction of Salt Tolerance in Arabidopsis thaliana by Volatiles From Bacillus amyloliquefaciens FZB42 via the Jasmonic Acid Signaling Pathway

Previously, we showed that Bacillus amyloliquefaciens FZB42 can confer salt tolerance in plants by root inoculation under salt stress condition, and the FZB42 volatile organic compounds (VOCs) promoted plant growth and development under non-salt stress condition. In the present study, we investigated the mechanism that allows FZB42 VOCs to confer salt tolerance in Arabidopsis without colonization of plant roots. We found that FZB42 VOCs significantly increased the biomass of Arabidopsis and also maintained the leaf chlorophyll content under salt stress condition. Physiological tests showed that the plant anti-oxidation system was activated by FZB42 VOCs, where higher peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) activities were detected in plants exposed to FZB42 VOCs compared with non-exposed plants. In addition, FZB42 VOCs increased the leaf total soluble sugars (TSS) content but decreased the proline content compared with the non-exposed plants. Moreover, FZB42 VOCs significantly decreased the Na⁺ contents of the whole plants and induced the expression of genes (NHX1; Na⁺/H⁺ exchanger 1 and HKT1; high-affinity K⁺ transporter 1) that function to alleviate Na⁺ toxicity. Furthermore, analysis of mutants with defects in specific hormone pathways showed that FZB42 VOCs induced salt tolerance in plants by modulating jasmonic acid (JA) signaling, which was confirmed by the up-regulation of JA synthesis, defense-related genes, and JA biosynthesis inhibitor tests. The results of this study provide new insights into the molecular mechanism related to the interactions between plant growth-promoting rhizobacteria and plants under salt stress condition.

From a Biosynthetic Pathway toward a Biocatalytic Process and Chemocatalytic Modifications: Three-Step Enzymatic Cascade to the Plant Metabolite cis-(+)-12-OPDA and Metathesis-Derived Products

A biotechnological approach toward the plant metabolite and regulator cis-(+)-12-oxophytodienoic acid (cis-(+)-12-OPDA) in a one-pot process with >99% conversion, at least 90% selectivity and ≤10% of side products as well as a high diastereoselectivity (leading to d.r. of at least 90:10) is reported. The optimized organic-synthetic enzyme cascade for preparing this bioactive and commercial molecule with pharmaceutical relevance on a gram per L scale is designed based on its biosynthetic pathway starting from cheap and readily accessible linolenic acid. Toward this end, a recombinant biocatalyst system has been prepared for carrying out the most critical two key steps in a tailored manner, thus avoiding sensitive intermediate decomposition. Furthermore, cis-(+)-12-OPDA is successfully modified via a cross-alkene metathesis reaction with conversions of up to >99%, leading to a compound library of new cis-(+)-12-OPDA derivatives with different substitution pattern of the side chain at the 2-position. By means of such a combined biotechnological and chemocatalytic route, a straightforward approach to a structurally unique oxylipin library is realized, which would be highly difficult or not accessible by pure chemical and biotechnological methods, respectively.

Jasmonate and Ethylene-Regulated Ethylene Response Factor 22 Promotes Lanolin-Induced Anthocyanin Biosynthesis in 'Zaosu' Pear (Pyrus bretschneideri Rehd.) Fruit

Anthocyanin contributes to the coloration of pear fruit and enhances plant defenses. Members of the ethylene response factor (ERF) family play vital roles in hormone and stress signaling and are involved in anthocyanin biosynthesis. Here, PbERF22 was identified from the lanolin-induced red fruit of ‘Zaosu’ pear (Pyrus bretschneideri Rehd.) using a comparative transcriptome analysis. Its expression level was up- and down-regulated by methyl jasmonate and 1-methylcyclopropene plus lanolin treatments, respectively, which indicated that PbERF22 responded to the jasmonate- and ethylene-signaling pathways. In addition, transiently overexpressed PbERF22 induced anthocyanin biosynthesis in ‘Zaosu’ fruit, and a quantitative PCR analysis further confirmed that PbERF22 facilitated the expression of anthocyanin biosynthetic structural and regulatory genes. Moreover, a dual luciferase assay showed that PbERF22 enhanced the activation effects of PbMYB10 and PbMYB10b on the PbUFGT promoter. Therefore, PbERF22 responses to jasmonate and ethylene signals and regulates anthocyanin biosynthesis. This provides a new perspective on the correlation between jasmonate–ethylene crosstalk and anthocyanin biosynthesis.

iTRAQ-based mitochondrial proteome analysis of the molecular mechanisms underlying postharvest senescence of Zizania latifolia

To explore the molecular mechanisms underlying postharvest senescence of Zizania latifolia, the changes in the mitochondrial proteome of plants treated with or without (control) 1-methyleyelopropene and ethylene during storage at room temperature for 0, 3 and 6 days were investigated using isobaric tags for relative and absolute quantitation (iTRAQ) labeling combined with two-dimensional liquid chromatography-tandem mass spectrometry. A total of 1,390 proteins with two or more peptides were identified, of which 211 showed a significant (p < .05) change (at least twofold) in relative abundance. Monitoring the parallel reaction validated the reliability and accuracy of the iTRAQ results. Bioinformatics and functional analysis of these differentially expressed proteins (DEPs) revealed that postharvest senescence of Z. latifolia could be attributed to (a) strengthened pentose phosphate pathway, (b) imbalanced protein, amino acid, organic acid, and fatty acid metabolism, (c) disordered energy homeostasis, (d) exacerbated oxidative damage, (e) RNA degradation, (f) activation of the Ca²⁺ , mitogen-activated protein kinase, and jasmonic acid signaling pathways, (g) programed cell death, (h) excessive biosynthesis of secondary metabolites, or (i) degradation of cell structure. Our findings provide integrated insight into the molecular mechanisms of postharvest senescence during storage as well as the DEPs that show promise as targets for controlling senescence-induced quality deterioration of Z. latifolia. PRACTICAL APPLICATIONS: Postharvest senescence is the most important factor that causes fast quality deterioration of Zizania latifolia. The understanding of the processes leading to postharvest senescence of Z. latifolia is essential in enhancing the commercial value and extending the shelf life of the product. It is currently believed that the mitochondrial metabolism is closely related to postharvest senescence. For this, the changes of proteome in Z. latifolia mitochondria treated with or without (control) 1-MCP and ETH during storage at room temperature were investigated. Results showed that a variety of physiobiochemical responses occur during postharvest senescence of Z. latifolia. 1-MCP treatment significantly inhibited the changes of these physiobiochemical processes, finally, retarding the postharvest senescence of Z. latifolia. ETH treatment had opposite effects on proteome changes compared with 1-MCP treatment. Taken together, these results enrich the understanding of the molecular mechanisms of postharvest senescence of Z. latifolia.

Jasmonate-Inducible R2R3-MYB Transcription Factor Regulates Capsaicinoid Biosynthesis and Stamen Development in Capsicum

Jasmonates (JAs) play an important role in plant developmental processes and regulate the biosynthesis of various specialized metabolites, and transcription factors are crucial in mediating JA signaling to regulate these processes. Capsaicinoids (Caps) are intriguing specialized metabolites produced uniquely by Capsicum species that give their fruits a pungent flavor to defend against herbivory and pathogens. In this study, we identify a R2R3-MYB transcription factor CaMYB108 and demonstrate its roles in regulating the biosynthesis of Caps and stamen development. Transcriptional analysis indicated that CaMYB108 was preferentially expressed in the flower and fruit, while the subcellular localization of CaMYB108 was shown to be the nucleus. Virus-induced gene silencing of CaMYB108 led to the expression of capsaicinoid biosynthetic genes (CBGs), and the contents of Caps dramatically reduce. Moreover, the CaMYB108-silenced plants showed delayed anther dehiscence and reduced pollen viability. Transient overexpression of CaMYB108 caused the expression of CBGs to be upregulated, and the Caps content significantly increased. The results of dual-luciferase reporter assays showed that CaMYB108 targeted CBG promoters. In addition, the expression of CaMYB108 and CBGs was inducible by methyl jasmonate and was consistent with the increased content of Caps. Overall, our results indicate that CaMYB108 is involved in the regulation of Caps biosynthesis and stamen development.

Comparative proteomic analysis of two sesame genotypes with contrasting salinity tolerance in response to salt stress

Sesame is one of the most important oilseed crops and has high nutritional value. The yield and quality of sesame are severely affected by high salinity in coastal and semi-arid/arid regions. In this study, the phenotypic, physiological, and proteomic changes induced by salt treatment were analyzed in salt-tolerant (G441) and salt-sensitive (G358) seedlings. Phenotypic and physiological results indicated that G441 had an enhanced capacity to withstand salinity stress compared to G358. Proteomic analysis revealed a strong induction of salt-responsive protein species in sesame, mainly related to catalytic, hydrolase, oxidoreductase, and binding activities. Pathway enrichment analysis showed that more salt-responsive proteins in G441 were involved in tyrosine metabolism, carbon fixation in photosynthetic organisms, carbon metabolism, alpha-linolenic acid metabolism, biosynthesis of amino acids, photosynthesis, and glutathione metabolism. Furthermore, G441 displayed unique differentially accumulated proteins in seedlings functioning as heat shock proteins, abscisic acid receptor PYL2-like, calcium-dependent protein kinases, serine/threonine-protein phosphatases, nucleoredoxin, and antioxidant enzymes. Quantitative real-time PCR analysis revealed that some of the proteins were also regulated by salinity stress at the transcript level. Our findings provide important information on salinity responses in plants and may constitute useful resources for enhancing salinity tolerance in sesame. SIGNIFICANCE: Our study identified potential biological pathways and salt-responsive protein species related to transducing stress signals and scavenging reactive oxygen species under salt stress. These findings will provide possible participants/pathways/proteins that contribute to salt tolerance and may serve as the basis for improving salinity tolerance in sesame and other plants.

A Pivotal Role of Hormones in Regulating Cotton Fiber Development

Cotton is the main source of renewable fiber in the world and is primarily used for textile production. Cotton fibers are single cells differentiated from the ovule epidermis and are an excellent model system for studying cell elongation, polyploidization, and cell wall biosynthesis. Plant hormones, which are present in relatively low concentrations, play important roles in various developmental processes, and recently, multiple reports have revealed the pivotal roles of hormones in regulating cotton fiber development. For example, exogenous application of hormones has been shown to promote the initiation and growth of fiber cells. However, a comprehensive understanding about phytohormone regulating fiber development is still unknown. Here, we focus on recent advances in elucidating the roles of multiple phytohormones in the control of fiber development, namely auxin, gibberellin, brassinosteroid, ethylene, cytokinin, abscisic acid, and strigolactones. We not only review the identification of genes involved in hormone biosynthetic and signaling pathways but also discuss the mechanisms of these phytohormones in regulating the initiation and elongation of fiber cells in cotton. Auxin, gibberellin, brassinosteroid, ethylene, jasmonic acid, and strigolactones play positive roles in fiber development, whereas cytokinin and abscisic acid inhibit fiber growth. Our aim is to provide a comprehensive review of the role of phytohormones in cotton fiber development that will serve as the basis for further elucidation of the mechanisms by which plant hormones regulate fiber growth.

Hormonal Orchestration of Bud Dormancy Cycle in Deciduous Woody Perennials

Woody perennials enter seasonal dormancy to avoid unfavorable environmental conditions. Plant hormones are the critical mediators regulating this complex process, which is subject to the influence of many internal and external factors. Over the last two decades, our knowledge of hormone-mediated dormancy has increased considerably, primarily due to advancements in molecular biology, omics, and bioinformatics. These advancements have enabled the elucidation of several aspects of hormonal regulation associated with bud dormancy in various deciduous tree species. Plant hormones interact with each other extensively in a context-dependent manner. The dormancy-associated MADS (DAM) transcription factors appear to enable hormones and other internal signals associated with the transition between different phases of bud dormancy. These proteins likely hold a great potential in deciphering the underlying mechanisms of dormancy initiation, maintenance, and release. In this review, a recent understanding of the roles of plant hormones, their cross talks, and their potential interactions with DAM proteins during dormancy is discussed.

Molecular Characterization and Overexpression of SmJMT Increases the Production of Phenolic Acids in Salvia miltiorrhiza

Jasmonic acid (JA) carboxyl methyltransferase (JMT), a key enzyme in jasmonate-regulated plant responses, may be involved in plant defense and development by methylating JA to MeJA, thus influencing the concentrations of MeJA in plant. In this study, we isolated the JMT gene from Salvia miltiorrhiza, an important medicinal plant widely used to treat cardiovascular disease. We present a genetic manipulation strategy to enhance the production of phenolic acids by overexpresion SmJMT in S. miltiorrhiza. Global transcriptomic analysis using RNA sequencing showed that the expression levels of genes involved in the biosynthesis pathway of phenolic acids and MeJA were upregulated in the overexpression lines. In addition, the levels of endogenous MeJA, and the accumulation of rosmarinic acid (RA) and salvianolic acid (Sal B), as well as the concentrations of total phenolics and total flavonoids in transgenic lines, were significantly elevated compared with the untransformed control. Our results demonstrate that overexpression of SmJMT promotes the production of phenolic acids through simultaneously activating genes encoding key enzymes involved in the biosynthesis pathway of phenolic acids and enhancing the endogenous MeJA levels in S. miltiorrhiza.

Phytohormones enhanced drought tolerance in plants: a coping strategy

Drought stress is a severe environmental constraint among the emerging problems. Plants are highly vulnerable to drought stress and a severe decrease in yield was recorded in the last few decades. So, it is highly desirable to understand the mechanism of drought tolerance in plants and consequently enhance the tolerance against drought stress. Phytohormones are known to play vital roles in regulating various phenomenons in plants to acclimatize to varying drought environment. Abscisic acid (ABA) is considered the main hormone which intensifies drought tolerance in plants through various morpho-physiological and molecular processes including stomata regulation, root development, and initiation of ABA-dependent pathway. In addition, jasmonic acid (JA), salicylic acid (SA) ethylene (ET), auxins (IAA), gibberellins (GAs), cytokinins (CKs), and brassinosteroids (BRs) are also very important phytohormones to congregate the challenges of drought stress. However, these hormones are usually cross talk with each other to increase the survival of plants in drought conditions. On the other hand, the transgenic approach is currently the most accepted technique to engineer the genes responsible for the synthesis of phytohormones in drought stress response. Our present review highlights the regulatory circuits of phytohormones in drought tolerance mechanism.

Contrasting nutrient-disease relationships: Potassium gradients in barley leaves have opposite effects on two fungal pathogens with different sensitivities to jasmonic acid

Understanding the interactions between mineral nutrition and disease is essential for crop management. Our previous studies with Arabidopsis thaliana demonstrated that potassium (K) deprivation induced the biosynthesis of jasmonic acid (JA) and increased the plant's resistance to herbivorous insects. Here, we addressed the question of how tissue K affects the development of fungal pathogens and whether sensitivity of the pathogens to JA could play a role for the K-disease relationship in barley (Hordeum vulgare cv. Optic). We report that K-deprived barley plants showed increased leaf concentrations of JA and other oxylipins. Furthermore, a natural tip-to-base K-concentration gradient within leaves of K-sufficient plants was quantitatively mirrored by the transcript levels of JA-responsive genes. The local leaf tissue K concentrations affected the development of two economically important fungi in opposite ways, showing a positive correlation with powdery mildew (Blumeria graminis) and a negative correlation with leaf scald (Rhynchosporium commune) disease symptoms. B. graminis induced a JA response in the plant and was sensitive to methyl-JA treatment whereas R. commune initiated no JA response and was JA insensitive. Our study challenges the view that high K generally improves plant health and suggests that JA sensitivity of pathogens could be an important factor in determining the exact K-disease relationship.

Effects of overproduced ethylene on the contents of other phytohormones and expression of their key biosynthetic genes

Ethylene is involved in regulation of various aspects of plant growth and development. Physiological and genetic analyses have indicated the existence of crosstalk between ethylene and other phytohormones, including auxin, cytokinin (CK), abscisic acid (ABA), gibberellin (GA), salicylic acid (SA), jasmonic acid (JA), brassinosteroid (BR) and strigolactone (SL) in regulation of different developmental processes. However, the effects of ethylene on the biosynthesis and contents of these hormones are not fully understood. Here, we investigated how overproduction of ethylene may affect the contents of other plant hormones using the ethylene-overproducing mutant ethylene-overproducer 1 (eto1-1). The contents of various hormones and transcript levels of the associated biosynthetic genes in the 10-day-old Arabidopsis eto1-1 mutant and wild-type (WT) plants were determined and compared. Higher levels of CK and ABA, while lower levels of auxin, SA and GA were observed in eto1-1 plants in comparison with WT, which was supported by the up- or down-regulation of their biosynthetic genes. Although we could not quantify the BR and SL contents in Arabidopsis, we observed that the transcript levels of the potential rate-limiting BR and SL biosynthetic genes were increased in the eto1-1 versus WT plants, suggesting that BR and SL levels might be enhanced by ethylene overproduction. JA level was not affected by overproduction of ethylene, which might be explained by unaltered expression level of the proposed rate-limiting JA biosynthetic gene allene oxide synthase. Taken together, our results suggest that ET affects the levels of auxin, CK, ABA, SA and GA, and potentially BR and SL, by influencing the expression of genes involved in the rate-limiting steps of their biosynthesis.

The Commonly Used Bactericide Bismerthiazol Promotes Rice Defenses against Herbivores

Chemical elicitors that enhance plant resistance to pathogens have been extensively studied, however, chemical elicitors that induce plant defenses against insect pests have received little attention. Here, we found that the exogenous application of a commonly used bactericide, bismerthiazol, on rice induced the biosynthesis of constitutive and/or elicited jasmonic acid (JA), jasmonoyl-isoleucine conjugate (JA-Ile), ethylene and H₂O₂ but not salicylic acid. These activated signaling pathways altered the volatile profile of rice plants. White-backed planthopper (WBPH, Sogatella furcifera) nymphs and gravid females showed a preference for feeding and/or oviposition on control plants: survival rates were better and more eggs were laid than on bismerthiazol-treated plants. Moreover, bismerthiazol treatment also increased both the parasitism rate of WBPH eggs laid on plants in the field by Anagrus nilaparvatae, and also the resistance of rice to the brown planthopper (BPH) Nilaparvata lugens and the striped stem borer (SSB) Chilo suppressalis. These findings suggest that the bactericide bismerthiazol can induce the direct and/or indirect resistance of rice to multiple insect pests, and so can be used as a broad-spectrum chemical elicitor.

Molecular characterization of rice arsenic-induced RING finger E3 ligase 2 (OsAIR2) and its heterogeneous overexpression in Arabidopsis thaliana

Arsenic (As) accumulation adversely affects the growth and productivity of plants and poses a serious threat to human health and food security. In this study, we identified one As-responsive Really Interesting New Gene (RING) E3 ubiquitin ligase gene from rice root tissues during As stress. We named it Oryza sativa As-Induced RING E3 ligase 2 (OsAIR2). Expression of OsAIR2 was induced under various abiotic stress conditions, including heat, salt, drought and As exposure. Results of an in vitro ubiquitination assay showed that OsAIR2 possesses an E3 ligase activity. Within the cell, OsAIR2 was found to be localized to the Golgi apparatus. Using yeast two-hybrid (Y2H) assay, the 3-ketoacyl-CoA thiolase (KAT) protein was identified as an interaction partner. We found that the O. sativa KAT1 (OsKAT1) is localized to the cytosol and peroxisomes. Moreover, in vitro pull-down assay verified the physical interaction between OsAIR2 and OsKAT1. Interestingly, in vitro ubiquitination assay and in vivo proteasomal degradation assay revealed that OsAIR2 ubiquitinates OsKAT1 and promotes the degradation of OsKAT1 via the 26S proteasome degradation pathway. Heterogeneous overexpression of OsAIR2 in Arabidopsis improved the seed germination and increased the root length under arsenate stress conditions. Therefore, these results suggest that OsAIR2 may be associated with the plant response to As stress and acts as a positive regulator of As stress tolerance.

Identification and Analysis of Jasmonate Pathway Genes in Coffea canephora (Robusta Coffee) by In Silico Approach

BACKGROUND

Coffea canephora is the commonly cultivated coffee species in the world along with Coffea arabica. Different pests and pathogens affect the production and quality of the coffee. Jasmonic acid (JA) is a plant hormone which plays an important role in plants growth, development, and defense mechanisms, particularly against insect pests. The key enzymes involved in the production of JA are lipoxygenase, allene oxide synthase, allene oxide cyclase, and 12-oxo-phytodienoic reductase. There is no report on the genes involved in JA pathway in coffee plants.

OBJECTIVE

We made an attempt to identify and analyze the genes coding for these enzymes in C. canephora.

MATERIALS AND METHODS

First, protein sequences of jasmonate pathway genes from model plant Arabidopsis thaliana were identified in the National Center for Biotechnology Information (NCBI) database. These protein sequences were used to search the web-based database Coffee Genome Hub to identify homologous protein sequences in C. canephora genome using Basic Local Alignment Search Tool (BLAST).

RESULTS

Homologous protein sequences for key genes were identified in the C. canephora genome database. Protein sequences of the top matches were in turn used to search in NCBI database using BLAST tool to confirm the identity of the selected proteins and to identify closely related genes in species. The protein sequences from C. canephora database and the top matches in NCBI were aligned, and phylogenetic trees were constructed using MEGA6 software and identified the genetic distance of the respective genes. The study identified the four key genes of JA pathway in C. canephora, confirming the conserved nature of the pathway in coffee. The study expected to be useful to further explore the defense mechanisms of coffee plants.

CONCLUSION

JA is a plant hormone that plays an important role in plant defense against insect pests. Genes coding for the 4 key enzymes involved in the production of JA viz., LOX, AOS, AOC, and OPR are identified in C. canephora (robusta coffee) by bioinformatic approaches confirming the conserved nature of the pathway in coffee. The findings are useful to understand the defense mechanisms of C. canephora and coffee breeding in the long run.

SUMMARY

JA is a plant hormone that plays an important role in plant defense against insect pests. Genes coding for the 4 key enzymes involved in the production of JA viz., LOX, AOS, AOC and OPR were identified and analyzed in C. canephora (robusta coffee) by in silico approach. The study has confirmed the conserved nature of JA pathway in coffee; the findings are useful to further explore the defense mechanisms of coffee plants. Abbreviations used:C. canephora: Coffea canephora; C. arabica: Coffea arabica; JA: Jasmonic acid; CGH: Coffee Genome Hub; NCBI: National Centre for Biotechnology Information; BLAST: Basic Local Alignment Search Tool; A. thaliana: Arabidopsis thaliana; LOX: Lipoxygenase, AOS: Allene oxide synthase; AOC: Allene oxide cyclase; OPR: 12 oxo phytodienoic reductase.

Phytohormone Behavior in the Model Environment of Plant and Human Lipid Membranes

Interactions between three auxins (indole-3-acetic acid (IAA), 2-naphthoxyacetic acid (BNOA), and 2,4-dichlorophenoxyacetic acid (2,4-D)) and model two-dimensional lipid systems mimicking plant and human cell membranes were investigated in monolayers formed at the air/water solution interface. The analysis was based on the recorded π-A isotherm characteristics complemented with Brewster angle microscopy. The influence of auxins on model membranes was discussed on the basis of condensation changes, modification of mutual lipid-lipid interactions in the mixed films, and morphological alteration of the surface domains on the microscopic scale. It was demonstrated that the lipid composition and mutual proportion of the artificial membranes together with sterol to main the phospholipid ratio play a crucial role in the context of auxin behavior in the membrane-mimicking environment. Apart from specific molecular interactions between studied phytohormones represented by auxins and lipids, the condensation of the investigated monolayers was found to be a regulative factor of model systems' susceptibility toward auxin action. Two effects were recognized: fluidizing of monolayers being in the liquid state (model membranes) and initialization of the three-dimensional structure formation in ordered sterol films at high surface pressure. The influence of auxin molecules on lipid interactions in the monolayer and diminishing of the film condensation was the largest for BNOA, due to the presence of the most bulky nonpolar, aromatic fragment in the molecule. It was also demonstrated that auxins interact with model plant membranes more selectively, stronger, and at markedly lower concentration than with the human membrane models.

Effects of alginate oligomer on the expression of cell cycle- and stress-related genes in Chlamydomonas reinhardtii

Enzymatically prepared alginate oligomer (AO) promoted the growth of Chlamydomonas reinhardtii in a concentration-dependent manner. AO at 2.5 mg/mL induced increase in expression levels of cyclin A, cyclin B, and cyclin D in C. reinhardtii. CuSO₄ at 100 μM suppressed the growth of C. reinhardtiin, and AO at 2.5 mg/mL significantly alleviated the toxicity of CuSO₄. Increased intracellular reactive oxygen species level in C. reinhardtii induced by CuSO₄ was reduced by AO. After cultivation with CuSO₄ at 100 μM, expression levels of ascorbate peroxidase and superoxide dismutase in C. reinhardtii were increased, and AO reduced the increased levels of these enzymes. These results suggest that AO exhibits beneficial effects on C. reinhardtii through influencing the expression of various genes not only at normal growth condition but also under CuSO₄ stress.

Jasmonic acid involves in grape fruit ripening and resistant against Botrytis cinerea

Fruit ripening is a complex process that is regulated by a signal network. Whereas the regulatory mechanism of abscisic acid has been studied extensively in non-climacteric fruit, little is know about other signaling pathways involved in this process. In this study, we performed that plant hormone jasmonic acid plays an important role in grape fruit coloring and softening by increasing the transcription levels of several ripening-related genes, such as the color-related genes PAL1, DFR, CHI, F3H, GST, CHS, and UFGT; softening-related genes PG, PL, PE, Cell, EG1, and XTH1; and aroma-related genes Ecar, QR, and EGS. Lastly, the fruit anthocyanin, phenol, aroma, and cell wall materials were changed. Jasmonic acid positively regulated its biosynthesis pathway genes LOS, AOS, and 12-oxophytodienoate reductase (OPR) and signal pathway genes COI1 and JMT. RNA interference of grape jasmonic acid pathway gene VvAOS in strawberry fruit appeared fruit un-coloring phenotypes; exogenous jasmonic acid rescued this phenotypes. On the contrary, overexpression of grape jasmonic acid receptor VvCOI1 in the strawberry fruit accelerated the fruit-ripening process and induced some plant defense-related gene expression level. Furthermore, jasmonic acid treatment or strong jasmonic acid signal pathway in strawberry fruit make the fruit resistance against Botrytis cinerea.

Jasmonates: Multifunctional Roles in Stress Tolerance

Jasmonates (JAs) [Jasmonic acid (JA) and methyl jasmonates (MeJAs)] are known to take part in various physiological processes. Exogenous application of JAs so far tested on different plants under abiotic stresses particularly salinity, drought, and temperature (low/high) conditions have proved effective in improving plant stress tolerance. However, its extent of effectiveness entirely depends on the type of plant species tested or its concentration. The effects of introgression or silencing of different JA- and Me-JA-related genes have been summarized in this review, which have shown a substantial role in improving crop yield and quality in different plants under stress or non-stress conditions. Regulation of JAs synthesis is impaired in stressed as well as unstressed plant cells/tissues, which is believed to be associated with a variety of metabolic events including signal transduction. Although, mitogen activated protein kinases (MAPKs) are important components of JA signaling and biosynthesis pathways, nitric oxide, ROS, calcium, ABA, ethylene, and salicylic acid are also important mediators of plant growth and development during JA signal transduction and synthesis. The exploration of other signaling molecules can be beneficial to examine the details of underlying molecular mechanisms of JA signal transduction. Much work is to be done in near future to find the proper answers of the questions like action of JA related metabolites, and identification of universal JA receptors etc. Complete signaling pathways involving MAPKs, CDPK, TGA, SIPK, WIPK, and WRKY transcription factors are yet to be investigated to understand the complete mechanism of action of JAs.

Transcriptome analysis of sweet orange trees infected with 'Candidatus Liberibacter asiaticus' and two strains of Citrus Tristeza Virus

BACKGROUND

Huanglongbing (HLB) and tristeza, are diseases of citrus caused by a member of the α-proteobacteria, 'Candidatus Liberibacter asiaticus' (CaLas), and Citrus tristeza virus (CTV) respectively. HLB is a devastating disease, but CTV strains vary from very severe to very mild. Both CaLas and CTV are phloem-restricted. The CaLas-B232 strain and CTV-B6 cause a wide range of severe and similar symptoms. The mild strain CTV-B2 doesn't induce significant symptoms or damage to plants.

RESULTS

Transcriptome profiles obtained through RNA-seq revealed 611, 404 and 285 differentially expressed transcripts (DETs) after infection with CaLas-B232, CTV-B6 and CTV-B2. These DETs were components of a wide range of pathways involved in circadian rhythm, cell wall modification and cell organization, as well as transcription factors, transport, hormone response and secondary metabolism, signaling and stress response. The number of transcripts that responded to both CTV-B6 and CaLas-B232 was much larger than the number of transcripts that responded to both strains of CTV or to both CTV-B2 and CaLas-B232. A total of 38 genes were assayed by RT-qPCR and the correlation coefficients between Gfold and RT-qPCR were 0.82, 0.69, 0.81 for sweet orange plants infected with CTV-B2, CTV-B6 and CaLas-B232, respectively.

CONCLUSIONS

The number and composition of DETs reflected the complexity of symptoms caused by the pathogens in established infections, although the leaf tissues sampled were asymptomatic. There were greater similarities between the sweet orange in response to CTV-B6 and CaLas-B232 than between the two CTV strains, reflecting the similar physiological changes caused by both CTV-B6 and CaLas-B232. The circadian rhythm system of plants was perturbed by all three pathogens, especially by CTV-B6, and the ion balance was also disrupted by all three pathogens, especially by CaLas-B232. Defense responses related to cell wall modification, transcriptional regulation, hormones, secondary metabolites, kinases and stress were activated by all three pathogens but with different patterns. The transcriptome profiles of Citrus sinensis identified host genes whose expression is affected by the presence of a pathogen in the phloem without producing symptoms (CTV-B2), and host genes whose expression leads to induction of symptoms in the plant (CTV-B6, CaLas-B232).

Production of 3-Oxo-2-(2'-pentenyl)-cyclopentane-1-octanoic Acid in the Fungus Aspergillus oryzae: A Step Towards Heterologous Production of Pyrethrins in Fungi

Pyrethrins are natural insecticides, which accumulate to high concentrations in pyrethrum (Chrysanthemum cinerariaefolium) flowers. Synthetic pyrethroids are more stable, more efficacious and cheaper, but contemporary requirements for safe and environmentally friendly pesticides encourage a return to the use of natural pyrethrins, and this would be favoured by development of an efficient route to their production by microbial fermentation. The biosynthesis of pyrethrins involves ester linkage between an acid moiety (chrysanthemoyl or pyrethroyl, synthesised via the mevalonic acid pathway from glucose), and an alcohol (pyrethrolone). Pyrethrolone is generated from 3-oxo-2-(2'-pentenyl)-cyclopentane-1-octanoic acid, which originates from α-linolenic acid via the jasmonic acid biosynthetic cascade. The first four genes in this cascade, encoding lipoxygenase 2, allene-oxide synthase, allene-oxide cyclase 2 and 12-oxophytodienoic acid reductase 3, were amplified from an Arabidopsis thaliana cDNA library, cloned in a purpose-built fungal multigene expression vector and expressed in Aspergillus oryzae. HPLC-MS analysis of the transgenic fungus homogenate gave good evidence for the presence of 3-oxo-2-(2'-pentenyl)-cyclopentane-1-octanoic acid.

MADS1, a novel MADS-box protein, is involved in the response of Nicotiana benthamiana to bacterial harpin(Xoo)

MADS-box transcription factor genes are well known for their role in floral organ and seed development. In this study, a novel MADS-box-containing gene, designated NbMADS1, was isolated from leaves of Nicotiana benthamiana. The full-length cDNA was 666 bp and encoded a putative polypeptide of 221 aa with a mass of 24.3 kDa. To assess the role of NbMADS1 in the defence response to bacterial harpin(Xoo), an elicitor of the hypersensitive response, a loss-of-function experiment was performed in N. benthamiana plants using virus-induced gene silencing. Analyses of electrolyte leakage revealed more extensive cell death in the control plants than in NbMADS1-silenced plants. The NbMADS1-silenced plants showed impaired harpin(Xoo)-induced stomatal closure, decreased harpin(Xoo)-induced production of hydrogen peroxide (H2O2) and nitric oxide (NO) in guard cells, and reduced harpin(Xoo)-induced resistance to Phytophthora nicotianae. The compromised stomatal closure observed in the NbMADS1-silenced plants was inhibited by the application of H2O2 and sodium nitroprusside (an NO donor). Taken together, these results demonstrate that the NbMADS1-H2O2-NO pathway mediates multiple harpin(Xoo)-triggered responses, including stomatal closure, hypersensitive cell death, and defence-related gene expression, suggesting that NbMADS1 plays an important role in regulating the response to harpin(Xoo) in N. benthamiana plants.

Global poplar root and leaf transcriptomes reveal links between growth and stress responses under nitrogen starvation and excess

Nitrogen (N) starvation and excess have distinct effects on N uptake and metabolism in poplars, but the global transcriptomic changes underlying morphological and physiological acclimation to altered N availability are unknown. We found that N starvation stimulated the fine root length and surface area by 54 and 49%, respectively, decreased the net photosynthetic rate by 15% and reduced the concentrations of NH4+, NO3(-) and total free amino acids in the roots and leaves of Populus simonii Carr. in comparison with normal N supply, whereas N excess had the opposite effect in most cases. Global transcriptome analysis of roots and leaves elucidated the specific molecular responses to N starvation and excess. Under N starvation and excess, gene ontology (GO) terms related to ion transport and response to auxin stimulus were enriched in roots, whereas the GO term for response to abscisic acid stimulus was overrepresented in leaves. Common GO terms for all N treatments in roots and leaves were related to development, N metabolism, response to stress and hormone stimulus. Approximately 30-40% of the differentially expressed genes formed a transcriptomic regulatory network under each condition. These results suggest that global transcriptomic reprogramming plays a key role in the morphological and physiological acclimation of poplar roots and leaves to N starvation and excess.

Combination of transcriptomic and metabolomic analyses reveals a JAZ repressor in the jasmonate signaling pathway of Salvia miltiorrhiza

Jasmonates (JAs) are plant-specific key signaling molecules that respond to various stimuli and are involved in the synthesis of secondary metabolites. However, little is known about the JA signal pathway, especially in economically significant medicinal plants. To determine the functions of novel genes that participate in the JA-mediated accumulation of secondary metabolites, we examined the metabolomic and transcriptomic signatures from Salvia miltiorrhiza. For the metabolome, 35 representative metabolites showing significant changes in rates of accumulation were extracted and identified. We also screened out 2131 differentially expressed unigenes, of which 30 were involeved in the phenolic secondary metabolic pathway, while 25 were in the JA biosynthesis and signal pathways. Among several MeJA-induced novel genes, SmJAZ8 was selected for detailed functional analysis. Transgenic plants over-expressing SmJAZ8 exhibited a JA-insensitive phenotype, suggesting that the gene is a transcriptional regulator in the JA signal pathway of S. miltiorrhiza. Furthermore, this transgenic tool revealed that JAZ genes have novel function in the constitutive accumulation of secondary metabolites. Based on these findings, we propose that the combined strategy of transcriptomic and metabolomic analyses is valuable for efficient discovery of novel genes in plants.

Fine mapping of Rcr1 and analyses of its effect on transcriptome patterns during infection by Plasmodiophora brassicae

BACKGROUND

The protist Plasmodiophora brassicae is a biotrophic soil-borne pathogen that causes clubroot on Brassica crops worldwide. Clubroot disease is a serious threat to the 8 M ha of canola (Brassica napus) grown annually in western Canada. While host resistance is the key to clubroot management, sources of resistance are limited.

RESULTS

To identify new sources of clubroot resistance (CR), we fine mapped a CR gene (Rcr1) from B. rapa ssp. chinensis to the region between 24.26 Mb and 24.50 Mb on the linkage group A03, with several closely linked markers identified. Transcriptome analysis was conducted using RNA sequencing on a segregating F1 population inoculated with P. brassicae, with 2,212 differentially expressed genes (DEGs) identified between plants carrying and not carrying Rcr1. Functional annotation of these DEGs showed that several defense-related biological processes, including signaling and metabolism of jasmonate and ethylene, defensive deposition of callose and biosynthesis of indole-containing compounds, were up-regulated significantly in plants carrying Rcr1 while genes involved in salicylic acid metabolic and signaling pathways were generally not elevated. Several DEGs involved in metabolism potentially related to clubroot symptom development, including auxin biosynthesis and cell growth/development, showed significantly lower expression in plants carrying Rcr1.

CONCLUSION

The CR gene Rcr1 and closely linked markers will be highly useful for breeding new resistant canola cultivars. The identification of DEGs between inoculated plants carrying and not carrying Rcr1 is an important step towards understanding of specific metabolic/signaling pathways in clubroot resistance mediated by Rcr1. This information may help judicious use of CR genes with complementary resistance mechanisms for durable clubroot resistance.

The action of peroxyl radicals, powerful deleterious reagents, explains why neither cholesterol nor saturated fatty acids cause atherogenesis and age-related diseases

Cells respond to alterations in their membrane structure by activating hydrolytic enzymes. Thus, polyunsaturated fatty acids (PUFAs) are liberated. Free PUFAs react with molecular oxygen to give lipid hydroperoxide molecules (LOOHs). In case of severe cell injury, this physiological reaction switches to the generation of lipid peroxide radicals (LOO(·)). These radicals can attack nearly all biomolecules such as lipids, carbohydrates, proteins, nucleic acids and enzymes, impairing their biological functions. Identical cell responses are triggered by manipulation of food, for example, heating/grilling and particularly homogenization, representing cell injury. Cholesterol as well as diets rich in saturated fat have been postulated to accelerate the risk of atherosclerosis while food rich in unsaturated fatty acids has been claimed to lower this risk. However, the fact is that LOO(·) radicals generated from PUFAs can oxidize cholesterol to toxic cholesterol oxides, simulating a reduction in cholesterol level. In this review it is shown how active LOO(·) radicals interact with biomolecules at a speed transcending usual molecule-molecule reactions by several orders of magnitude. Here, it is explained how functional groups are fundamentally transformed by an attack of LOO(·) with an obliteration of essential biomolecules leading to pathological conditions. A serious reconsideration of the health and diet guidelines is required.

Expression of a functional jasmonic acid carboxyl methyltransferase is negatively correlated with strawberry fruit development

The volatile metabolite methyl jasmonate (MeJA) plays an important role in intra- and interplant communication and is involved in diverse biological processes. In this study, we report the cloning and functional characterization of a S-adenosyl-l-methionine:jasmonic acid carboxyl methyltransferase (JMT) from Fragaria vesca and Fragaria×ananassa. Biochemical assays and comprehensive transcript analyses showed that JMT has been erroneously annotated as gene fusion with a carboxyl methyltransferase (CMT) (gene15184) in the first published genome sequence of F. vesca. Recombinant FvJMT catalyzed the formation of MeJA with KM value of 22.3μM while FvCMT and the fusion protein were almost inactive. Activity of JMT with benzoic acid and salicylic acid as substrates was less than 1.5% of that with JA. Leucine at position 245, an amino acid missing in other JMT sequences is essential for activity of FvJMT. In accordance with MeJA levels, JMT transcript levels decreased steadily during strawberry fruit ripening, as did the expression levels of JA biosynthesis and regulatory genes. It appears that CMT has originated by a recent duplication of JMT and lost its enzymatic activity toward JA. In the newest version of the strawberry genome sequence (June 2014) CMT and JMT are annotated as separate genes in accordance with differential temporal and spatial expression patterns of both genes in Fragaria sp. In conclusion, MeJA, the inactive derivative of JA, is probably involved in early steps of fruit development by modulating the levels of the active plant hormone JA.

Hormones, polyamines, and cell wall metabolism during oil palm fruit mesocarp development and ripening

Oil palm is one of the most productive oil-producing crops and can store up to 90% oil in its fruit mesocarp. Oil palm fruit is a sessile drupe consisting of a fleshy mesocarp from which palm oil is extracted. Biochemical changes in the mesocarp cell walls, polyamines, and hormones at different ripening stages of oil palm fruits were studied, and the relationship between the structural and the biochemical metabolism of oil palm fruits during ripening is discussed. Time-course analysis of the changes in expression of polyamines, hormones, and cell-wall-related genes and metabolites provided insights into the complex processes and interactions involved in fruit development. Overall, a strong reduction in auxin-responsive gene expression was observed from 18 to 22 weeks after pollination. High polyamine concentrations coincided with fruit enlargement during lipid accumulation and latter stages of maturation. The trend of abscisic acid (ABA) concentration was concordant with GA₄ but opposite to the GA₃ profile such that as ABA levels increase the resulting elevated ABA/GA₃ ratio clearly coincides with maturation. Polygalacturonase, expansin, and actin gene expressions were also observed to increase during fruit maturation. The identification of the master regulators of these coordinated processes may allow screening for oil palm variants with altered ripening profiles.

Brassinosteroid-related transcription factor BIL1/BZR1 increases plant resistance to insect feeding

The plant steroid hormones brassinosteroids (BRs) play important roles in plant growth and responses to stresses. The up-regulation of pathogen resistance by BR signaling has been analyzed, but the relationship between BR and insect herbivores remains largely unclear. BIL1/BZR1 is a BR master transcription factor known to be involved in the regulation of plant development through work conducted on a gain of function mutation. Here, we analyzed the function of BIL1/BZR1 in response to insect feeding and demonstrated that resistance against thrip feeding was increased in the bil1-1D/bzr1-1D mutant compared to wild-type. We generated Lotus japonicus transgenic plants that over-express the Arabidopsis bil1/bzr1 mutant, Lj-bil1/bzr1-OX. The Lj-bil1/bzr1-OX plants showed increased resistance to thrip feeding. The expression levels of the jasmoninc acid (JA)-inducible VSP genes were increased in both Arabidopsis bil1-1D/bzr1-1D mutants and L. japonicus Lj-bil1/bzr1-OX plants. The resistance to thrip feeding caused by the BIL1/BZR1 gene may involve JA signaling.

ALY proteins participate in multifaceted Nep1Mo-triggered responses in Nicotiana benthamiana and Arabidopsis thaliana

Previously, it was found that Nep1Mo (a Nep1-like protein from Magnaporthe oryzae) could trigger a variety of plant responses, including stomatal closure, hypersensitive cell death (HCD), and defence-related gene expression, in Nicotiana benthamiana. In this study, it was found that Nep1Mo-induced cell death could be inhibited by the virus-induced gene silencing of NbALY916 in N. benthamiana. NbALY916-silenced plants showed impaired Nep1Mo-induced stomatal closure, decreased Nep1Mo-induced production of hydrogen peroxide (H2O2) and nitric oxide (NO) in guard cells, and reduced Nep1Mo-induced resistance against Phytophthora nicotianae. It also found that the deletion of AtALY4, an orthologue of NbALY916 in Arabidopsis thaliana, impaired Nep1Mo-triggered stomatal closure, HCD, and defence-related gene expression. The compromised stomatal closure observed in the NbALY916-silenced plants and AtALY4 mutants was inhibited by the application of H2O2 and sodium nitroprusside (an NO donor), and both Nep1Mo and H2O2 stimulated guard cell NO synthesis. Conversely, NO-induced stomatal closure was found not to require H2O2 synthesis; and NO treatment did not induce H2O2 production in guard cells. Taken together, these results demonstrate that the NbAlY916/AtAlY4-H2O2-NO pathway mediates multiple Nep1Mo-triggered responses, including stomatal closure, HCD, and defence-related gene expression.