Jasmonate: an oxylipin signal with many roles in plants

Nutrient Elements Promote Disease Resistance in Tomato by Differentially Activating Immune Pathways

Nutrient elements play essential roles in plant growth, development, and reproduction. Balanced nutrition is critical for plant health and the ability to withstand biotic stress. Treatment with essential elements has been shown to induce disease resistance in certain cases. Understanding the functional mechanisms underlying plant immune responses to nutritional elements has the potential to provide new insights into crop improvement. In the present study, we investigated the effect of various elements-potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)-in promoting resistance against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Xanthomonas euvesicatoria in tomato. We demonstrate that spray treatment of essential elements was sufficient to activate immune responses, inducing defense gene expression, cellular leakage, reactive oxygen species, and ethylene production. We report that different defense signaling pathways are required for induction of immunity in response to different elements. Our results suggest that genetic mechanisms that are modulated by nutrient elements can be exploited in agricultural practices to promote disease resistance.

Genome-Wide Association Study of Salt Tolerance-Related Traits during Germination and Seedling Development in an Intermedium-Spike Barley Collection

Increased salinity is one of the major consequences of climatic change affecting global crop production. The early stages in the barley (Hordeum vulgare L.) life cycle are considered the most critical phases due to their contributions to final crop yield. Particularly, the germination and seedling development are sensitive to numerous environmental stresses, especially soil salinity. In this study, we aimed to identify SNP markers linked with germination and seedling development at 150 mM NaCl as a salinity treatment. We performed a genome-wide association study (GWAS) using a panel of 208 intermedium-spike barley (H. vulgare convar. intermedium (Körn.) Mansf.) accessions and their genotype data (i.e., 10,323 SNPs) using the genome reference sequence of “Morex”. The phenotypic results showed that the 150 mM NaCl salinity treatment significantly reduced all recorded germination and seedling-related traits compared to the control treatment. Furthermore, six accessions (HOR 11747, HOR 11718, HOR 11640, HOR 11256, HOR 11275 and HOR 11291) were identified as the most salinity tolerant from the intermedium-spike barley collection. GWAS analysis indicated that a total of 38 highly significantly associated SNP markers under control and/or salinity traits were identified. Of these, two SNP markers on chromosome (chr) 1H, two on chr 3H, and one on chr 4H were significantly linked to seedling fresh and dry weight under salinity stress treatment. In addition, two SNP markers on chr 7H were also significantly associated with seedling fresh and dry weight but under control condition. Under salinity stress, one SNP marker on chr 1H, 5H and 7H were detected for more than one phenotypic trait. We found that in most of the accessions exhibiting the highest salinity tolerance, most of the salinity-related QTLs were presented. These results form the basis for detailed studies, leading to improved salt tolerance breeding programs in barley.

Identifying Soybean Pod Borer (Leguminivora glycinivorella) Resistance QTLs and the Mechanism of Induced Defense Using Linkage Mapping and RNA-Seq Analysis

The soybean pod borer (Leguminivora glycinivorella) (SPB) is a major cause of soybean (Glycine max L.) yield losses in northeast Asia, thus it is desirable to elucidate the resistance mechanisms involved in soybean response to the SPB. However, few studies have mapped SPB-resistant quantitative trait loci (QTLs) and deciphered the response mechanism in soybean. Here, we selected two soybean varieties, JY93 (SPB-resistant) and K6 (SPB-sensitive), to construct F₂ and F_2:3 populations for QTL mapping and collected pod shells before and after SPB larvae chewed on the two parents to perform RNA-Seq, which can identify stable QTLs and explore the response mechanism of soybean to the SPB. The results show that four QTLs underlying SPB damage to seeds were detected on chromosomes 4, 9, 13, and 15. Among them, qESP-9-1 was scanned in all environments, hence it can be considered a stable QTL. All QTLs explained 0.79 to 6.09% of the phenotypic variation. Meanwhile, 2298 and 3509 DEGs were identified for JY93 and K6, respectively, after the SPB attack, and most of these genes were upregulated. Gene Ontology enrichment results indicated that the SPB-induced and differently expressed genes in both parents are involved in biological processes such as wound response, signal transduction, immune response, and phytohormone pathways. Interestingly, secondary metabolic processes such as flavonoid synthesis were only significantly enriched in the upregulated genes of JY93 after SPB chewing compared with K6. Finally, we identified 18 candidate genes related to soybean pod borer resistance through the integration of QTL mapping and RNA-Seq analysis. Seven of these genes had similar expression patterns to the mapping parents in four additional soybean germplasm after feeding by the SPB. These results provide additional knowledge of the early response and induced defense mechanisms against the SPB in soybean, which could help in breeding SPB-resistant soybean accessions.

Jasmonates in plant growth and development and elicitation of secondary metabolites: An updated overview

Secondary metabolites are incontestably key specialized molecules with proven health-promoting effects on human beings. Naturally synthesized secondary metabolites are considered an important source of pharmaceuticals, food additives, cosmetics, flavors, etc., Therefore, enhancing the biosynthesis of these relevant metabolites by maintaining natural authenticity is getting more attention. The application of exogenous jasmonates (JAs) is well recognized for its ability to trigger plant growth and development. JAs have a large spectrum of action that covers seed germination, hypocotyl growth regulation, root elongation, petal expansion, and apical hook growth. This hormone is considered as one of the key regulators of the plant's growth and development when the plant is under biotic or abiotic stress. The JAs regulate signal transduction through cross-talking with other genes in plants and thereby deploy an appropriate metabolism in the normal or stressed conditions. It has also been found to be an effective chemical elicitor for the synthesis of naturally occurring secondary metabolites. This review discusses the significance of JAs in the growth and development of plants and the successful outcomes of jasmonate-driven elicitation of secondary metabolites including flavonoids, anthraquinones, anthocyanin, xanthonoid, and more from various plant species. However, as the enhancement of these metabolites is essentially measured via in vitro cell culture or foliar spray, the large-scale production is significantly limited. Recent advancements in the plant cell culture technology lay the possibilities for the large-scale manufacturing of plant-derived secondary metabolites. With the insights about the genetic background of the metabolite biosynthetic pathway, synthetic biology also appears to be a potential avenue for accelerating their production. This review, therefore, also discussed the potential manoeuvres that can be deployed to synthesis plant secondary metabolites at the large-scale using plant cell, tissue, and organ cultures.

Transcriptome-Wide Identification and Characterization of the JAZ Gene Family in Mentha canadensis L

Jasmonate ZIM-domain (JAZ) proteins are the crucial transcriptional repressors in the jasmonic acid (JA) signaling process, and they play pervasive roles in plant development, defense, and plant specialized metabolism. Although numerous JAZ gene families have been discovered across several plants, our knowledge about the JAZ gene family remains limited in the economically and medicinally important Chinese herb Mentha canadensis L. Here, seven non-redundant JAZ genes named McJAZ1–McJAZ7 were identified from our reported M. canadensis transcriptome data. Structural, amino acid composition, and phylogenetic analysis showed that seven McJAZ proteins contained the typical zinc-finger inflorescence meristem (ZIM) domain and JA-associated (Jas) domain as conserved as those in other plants, and they were clustered into four groups (A-D) and distributed into five subgroups (A1, A2, B1, B2, and D). Quantitative real-time PCR (qRT-PCR) analysis showed that seven McJAZ genes displayed differential expression patterns in M. canadensis tissues, and preferentially expressed in flowers. Furthermore, the McJAZ genes expression was differentially induced after Methyl jasmonate (MeJA) treatment, and their transcripts were variable and up- or down-regulated under abscisic acid (ABA), drought, and salt treatments. Subcellular localization analysis revealed that McJAZ proteins are localized in the nucleus or cytoplasm. Yeast two-hybrid (Y2H) assays demonstrated that McJAZ1-5 interacted with McCOI1a, a homolog of Arabidopsis JA receptor AtCOI1, in a coronatine-dependent manner, and most of McJAZ proteins could also form homo- or heterodimers. This present study provides valuable basis for functional analysis and exploitation of the potential candidate McJAZ genes for developing efficient strategies for genetic improvement of M. canadensis.

Database: web application for visualization of the cumulated RNAseq data against the salicylic acid (SA) and methyl jasmonate (MeJA) treatment of Arabidopsis thaliana

BACKGROUND

Plants have adapted to survive under adverse conditions or exploit favorable conditions in response to their environment as sessile creatures. In a way of plant adaptation, plant hormones have been evolved to efficiently use limited resources. Plant hormones including auxin, jasmonic acid, salicylic acid, and ethylene have been studied to reveal their role in plant adaptation against their environment by phenotypic observation with experimental design such as mutation on hormone receptors and treatment / non-treatment of plant hormones along with other environmental conditions. With the development of Next Generation Sequencing (NGS) technology, it became possible to score the total gene expression of the sampled plants and estimate the degree of effect of plant hormones in gene expression. This allowed us to infer the signaling pathway through plant hormones, which greatly stimulated the study of functional genomics using mutants. Due to the continued development of NGS technology and analytical techniques, many plant hormone-related studies have produced and accumulated NGS-based data, especially RNAseq data have been stored in the sequence read archive represented by NCBI, EBI, and DDBJ.

DESCRIPTION

Here, hormone treatment RNAseq data of Arabidopsis (Col0), wild-type genotype, were collected with mock, SA, and MeJA treatments. The genes affected by hormones were identified through a machine learning approach. The degree of expression of the affected gene was quantified, visualized in boxplot using d3 (data-driven-document), and the database was built by Django.

CONCLUSION

Using this database, we created a web application ( http://pgl.gnu.ac.kr/hormoneDB/ ) that lists hormone-related or hormone-affected genes and visualizes the boxplot of the gene expression of selected genes. This web application eventually aids the functional genomics researchers who want to gather the cases of the gene responses by the hormones.

Interactive proteogenomic exploration of response to Fusarium head blight in oat varieties with different resistance

Fusarium species are cereal pathogens that cause the Fusarium Head Blight (FHB) disease. FHB can reduce yield, cause mycotoxin accumulation in the grain and reduce germination efficiency of the harvested seeds. Understanding the biochemical interactions between the host plants and the pathogen is crucial for controlling the disease and for the development of cultivars with improved tolerance to FHB. Here, we studied morphological and proteomic differences between the susceptible oat variety Belinda and the more resistant variety Argamak using variety-specific transcriptome assemblies as references. Measurements of deoxynivalenol toxin levels confirmed the partial resistance in Argamak and the susceptibility in Belinda. To jointly investigate the proteomics- and sequence data, we developed an RShiny-based interface for interactive exploration of the dataset using univariate and multivariate statistics. When applying this interface to the dataset, quantitative protein differences between Belinda and Argamak were detected, and eighteen peptides were found uniquely in Argamak during infection, among them several lipoxygenases. Such proteins can be developed as markers for Fusarium resistance breeding. In conclusion, this study provides the first proteogenomic insight on molecular Fusarium-oat interactions at both morphological and molecular levels and the data are openly available through an interactive interface for further inspection. SIGNIFICANCE: Fusarium head blight causes widespread damage to crops, and chronic and acute toxicity to human and livestock due to the accumulation of toxins during infection. In the present study, two oat varieties with differing resistance were challenged with Fusarium to understand the disease better, and studied both at morphological and molecular levels, identifying proteins which could play a role in the defense mechanism. Furthermore, a proteogenomics approach allows joint profiling of expression and sequence level differences to identify potentially functionally differing mutations. Here such analysis is made openly available through an interactive interface which allows other scientists to draw further findings from the data. This study may both serve as a basis for understanding oat disease response and developing breeding markers for Fusarium resistant oat and future proteogenomic studies using the interactive approach described.

Dragon’s Blood from Dracaena cambodiana in China: Applied History and Induction Techniques toward Formation Mechanism

Dragon’s blood that is extracted from Dracaena plants has been widely used as traditional medicine in various ancient cultures. The application of dragon’s blood has a cherished history in China, even though the original plants were not discovered for some period. Dracaena cochinchinensis and Dracaena cambodiana were successively discovered in southern China during the 1970s–1980s. In the last half of the century, Chinese scientists have extensively investigated the production of dragon’s blood from these two Dracaena species, whereas these results have not been previously systematically summarized, as in the present paper. Herein, we present the applied history in ancient China and artificially induced technologies for dragon’s blood development based on these two Dracaena species, in particular, using tissue cultures seedlings and tender plants of D. cambodiana. Big data research, including transcriptomic and genomic studies, has suggested that dragon’s blood might be a defense substance that is secreted by Dracaena plants in response to (a)biotic stimuli. This review represents an effort to highlight the progress and achievements from applied history as well as induction techniques that are used for the formation of dragon’s blood that have taken place in China. Such knowledge might aid in the global conservation of wild Dracaena species and contribute to understanding dragon blood formation mechanisms, eventually assisting in the efficient utilization of limited Dracaena plant resources for the sustainable production of dragon’s blood.

Jasmonic Acid Signaling Pathway in Response to Abiotic Stresses in Plants

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

A comparison of inducible, ontogenetic, and interspecific sources of variation in the foliar metabolome in tropical trees

Plant interactions with other organisms are mediated by chemistry, yet chemistry varies among conspecific and within individual plants. The foliar metabolome—the suite of small-molecule metabolites found in the leaf—changes during leaf ontogeny and is influenced by the signaling molecule jasmonic acid. Species differences in secondary metabolites are thought to play an important ecological role by limiting the host ranges of herbivores and pathogens, and hence facilitating competitive coexistence among plant species in species-rich plant communities such as tropical forests. Yet it remains unclear how inducible and ontogenetic variation compare with interspecific variation, particularly in tropical trees. Here, we take advantage of novel methods to assemble mass spectra of all compounds in leaf extracts into molecular networks that quantify their chemical structural similarity in order to compare inducible and ontogenetic chemical variation to among-species variation in species-rich tropical tree genera. We ask (i) whether young and mature leaves differ chemically, (ii) whether jasmonic acid-inducible chemical variation differs between young and mature leaves, and (iii) whether interspecific exceeds intraspecific chemical variation for four species from four hyperdiverse tropical tree genera. We observed significant effects of the jasmonic acid treatment for three of eight combinations of species and ontogenetic stage evaluated. Three of the four species also exhibited large metabolomic differences with leaf ontogenetic stage. The profound effect of leaf ontogenetic stage on the foliar metabolome suggests a qualitative turnover in secondary chemistry with leaf ontogeny. We also quantified foliar metabolomes for 45 congeners of the four focal species. Chemical similarity was much greater within than between species for all four genera, even when within-species comparisons included leaves that differed in age and jasmonic acid treatment. Despite ontogenetic and inducible variation within species, chemical differences among congeneric species may be sufficient to partition niche space with respect to chemical defense.

MdHIR4 transcription and translation levels associated with disease in apple are regulated by MdWRKY31

KEY MESSAGE

Here we describe that the regulation of MdWRKY31 on MdHIR4 in transcription and translation levels associated with disease in apple. The phytohormone salicylic acid (SA) is a main factor in apple (Malus domestica) production due to its function in disease resistance. WRKY transcription factors play a vital role in response to stress. An RNA-seq analysis was conducted with 'Royal Gala' seedlings treated with SA to identify the WRKY regulatory mechanism of disease resistance in apple. The analysis indicated that MdWRKY31 was induced. A quantitative real-time polymerase chain reaction (qPCR) analysis demonstrated that the expression of MdWRKY31 was induced by SA and flg22. Ectopic expression of MdWRKY31 in Arabidopsis and Nicotiana benthamiana increased the resistance to flg22 and Pseudomonas syringae tomato (Pst DC3000). A yeast two-hybrid screen was conducted to further analyze the function of MdWRKY31. As a result, hypersensitive-induced reaction (HIR) protein MdHIR4 interacted with MdWRKY31. Biomolecular fluorescence complementation, yeast two-hybrid, and pull-down assays demonstrated the interaction. In our previous study, MdHIR4 conferred decreased resistance to Botryosphaeria dothidea (B. dothidea). A viral vector-based transformation assay indicated that MdWRKY31 evaluated the transcription of SA-related genes, including MdPR1, MdPR5, and MdNPR1 in an MdHIR4-dependent way. A GUS analysis demonstrated that the w-box, particularly w-box2, of the MdHIR4 promoter played a major role in the responses to SA and B. dothidea. Electrophoretic mobility shift assays, yeast one-hybrid assay, and chromatin immunoprecipitation-qPCR demonstrated that MdWRKY31 directly bound to the w-box2 motif in the MdHIR4 promoter. GUS staining activity and a protein intensity analysis further showed that MdWRKY31 repressed MdHIR4 expression. Taken together, our findings reveal that MdWRKY31 regulated plant resistance to B. dothidea through the SA signaling pathway by interacting with MdHIR4.

Arabidopsis Flowers Unlocked the Mechanism of Jasmonate Signaling

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

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

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

Fatty Acid- and Lipid-Mediated Signaling in Plant Defense

Fatty acids and lipids, which are major and essential constituents of all plant cells, not only provide structural integrity and energy for various metabolic processes but can also function as signal transduction mediators. Lipids and fatty acids can act as both intracellular and extracellular signals. In addition, cyclic and acyclic products generated during fatty acid metabolism can also function as important chemical signals. This review summarizes the biosynthesis of fatty acids and lipids and their involvement in pathogen defense.

Structural basis for the regulation of phytohormone receptors

Phytohormones are central players in diverse plant physiological events, such as plant growth, development, and environmental stress and defense responses. The elucidation of their regulatory mechanisms through phytohormone receptors could facilitate the generation of transgenic crops with cultivation advantages and the rational design of growth control chemicals. During the last decade, accumulated structural data on phytohormone receptors have provided critical insights into the molecular mechanisms of phytohormone perception and signal transduction. Here, we review the structural bases of phytohormone recognition and receptor activation. As a common feature, phytohormones regulate the interaction between the receptors and their respective target proteins (also called co-receptors) by two types of regulatory mechanisms, acting as either "molecular glue" or an "allosteric regulator." However, individual phytohormone receptors adopt specific structural features that are essential for activation. In addition, recent studies have focused on the molecular diversity of redundant phytohormone receptors.

The crosstalk between Target of Rapamycin (TOR) and Jasmonic Acid (JA) signaling existing in Arabidopsis and cotton

Target of rapamycin (TOR) acts as an important regulator of cell growth, development and stress responses in most examined diploid eukaryotes. However, little is known about TOR in tetraploid species such as cotton. Here, we show that TORC1-S6K-RPS6, the major signaling components, are conserved and further expanded in cotton genome. Though the cotton seedlings are insensitive to rapamycin, AZD8055, the second-generation inhibitor of TOR, can significantly suppress the growth in cotton. Global transcriptome analysis revealed that genes associated with jasmonic acid (JA) biosynthesis and transduction were significantly altered in AZD8055 treated cotton seedlings, suggesting the potential crosstalk between TOR and JA signaling. Pharmacological and genetic approaches have been employed to get further insights into the molecular mechanism of the crosstalk between TOR and JA. Combination of AZD8055 with methyl jasmonate can synergistically inhibit cotton growth, and additionally JA levels were significantly increased when cotton seedlings were subjected to AZD8055. JA biosynthetic and signaling mutants including jar1, coi1-2 and myc2-2 displayed TOR inhibitor-resistant phenotypes, whereas COI1 overexpression transgenic lines and jaz10 exhibited sensitivity to AZD8055. Consistently, cotton JAZ can partially rescue TOR-suppressed phenotypes in Arabidopsis. These evidences revealed that the crosstalk between TOR and JA pathway operates in cotton and Arabidopsis.

MdHIR proteins repress anthocyanin accumulation by interacting with the MdJAZ2 protein to inhibit its degradation in apples

In higher plants, jasmonate ZIM-domain (JAZ) proteins negatively regulate the biosynthesis of anthocyanins by interacting with bHLH transcription factors. However, it is largely unknown if and how other regulators are involved in this process. In this study, the apple MdJAZ2 protein was characterized in regards to its function in the negative regulation of anthocyanin accumulation and peel coloration. MdJAZ2 was used as a bait to screen a cDNA library using the yeast two-hybrid method. The hypersensitive induced reaction (HIR) proteins, MdHIR2 and MdHIR4, were obtained from this yeast two-hybrid. The ZIM domain of MdJAZ2 and the PHB domain of the MdHIR proteins are necessary for their interactions. The interactions were further verified using an in vitro pull-down assay. Subsequently, immunoblotting assays demonstrated that MdHIR4 enhanced the stability of the MdJAZ2-GUS protein. Finally, a viral vector-based transformation method showed that MdHIR4 inhibited anthocyanin accumulation and fruit coloration in apple by modulating the expression of genes associated with anthocyanin biosynthesis.

Genome-wide characterization of JASMONATE-ZIM DOMAIN transcription repressors in wheat (Triticum aestivum L.)

BACKGROUND

The JASMONATE-ZIM DOMAIN (JAZ) repressor family proteins are jasmonate co-receptors and transcriptional repressor in jasmonic acid (JA) signaling pathway, and they play important roles in regulating the growth and development of plants. Recently, more and more researches on JAZ gene family are reported in many plants. Although the genome sequencing of common wheat (Triticum aestivum L.) and its relatives is complete, our knowledge about this gene family remains vacant.

RESULTS

Fourteen JAZ genes were identified in the wheat genome. Structural analysis revealed that the TaJAZ proteins in wheat were as conserved as those in other plants, but had structural characteristics. By phylogenetic analysis, all JAZ proteins from wheat and other plants were clustered into 11 sub-groups (G1-G11), and TaJAZ proteins shared a high degree of similarity with some JAZ proteins from Aegliops tauschii, Brachypodium distachyon and Oryza sativa. The Ka/Ks ratios of TaJAZ genes ranged from 0.0016 to 0.6973, suggesting that the TaJAZ family had undergone purifying selection in wheat. Gene expression patterns obtained by quantitative real-time PCR (qRT-PCR) revealed differential temporal and spatial regulation of TaJAZ genes under multifarious abiotic stress treatments of high salinity, drought, cold and phytohormone. Among these, TaJAZ7, 8 and 12 were specifically expressed in the anther tissues of the thermosensitive genic male sterile (TGMS) wheat line BS366 and normal control wheat line Jing411. Compared with the gene expression patterns in the normal wheat line Jing411, TaJAZ7, 8 and 12 had different expression patterns in abnormally dehiscent anthers of BS366 at the heading stage 6, suggesting that specific up- or down-regulation of these genes might be associated with the abnormal anther dehiscence in TGMS wheat line.

CONCLUSION

This study analyzed the size and composition of the JAZ gene family in wheat, and investigated stress responsive and differential tissue-specific expression profiles of each TaJAZ gene in TGMS wheat line BS366. In addition, we isolated 3 TaJAZ genes that would be more likely to be involved in the regulation of abnormal anther dehiscence in TGMS wheat line. In conclusion, the results of this study contributed some novel and detailed information about JAZ gene family in wheat, and also provided 3 potential candidate genes for improving the TGMS wheat line.

Functional identification of apple MdJAZ2 in Arabidopsis with reduced JA-sensitivity and increased stress tolerance

Here, we report the decrease of JA-sensitivity and enhancement of tolerance to salt and PEG stresses in Arabidopsis overexpressing apple MdJAZ2. As signalling molecules, jasmonates (JAs) play significant roles in plant development and stress responses. JAZ proteins are the targets of the SCF^COI1 complex and act as the negative regulators in JA signalling pathway. However, there are no reports regarding the biological function of apple JAZ genes. In this study, one JAZ gene, MdJAZ2 from apple, was functionally characterized in detail. The expression of MdJAZ2 was up-regulated by MeJA and wounding treatments. MdJAZ2-GFP fusion protein was observed in nucleus in transient expression assay. Yeast two-hybrid and bimolecular fluorescence complementation assays revealed that MdJAZ2 could form homo- and heteromers, and also interact with F-box protein MdCOI1. Overexpression of MdJAZ2 conferred impaired JA-sensitivity in transgenic Arabidopsis, including JA-mediated root growth inhibition, susceptibility to the bacterial pathogen Pst DC3000, and the expression of JA response genes. Additionally, MdJAZ2 overexpression also improved tolerance to NaCl and PEG treatments in transgenic Arabidopsis. Together, our findings suggest that apple MdJAZ2 was not only involved in the JA response but also played roles in stress tolerance.

Roles of the Translationally Controlled Tumor Protein (TCTP) in Plant Development

The Translationally Controlled Tumor Protein (TCTP) is a conserved protein which expression was associated with several biochemical and cellular functions. Loss-of-function mutants are lethal both in animals and in plants, making the identification of its exact role difficult. Recent data using the model plant Arabidopsis thaliana provided the first viable adult knockout for TCTP and helped addressing the biological role of TCTP during organ development and the functional conservation between plants and animals. This chapter summarizes our up to date knowledge about the role of TCTP in plants and discuss about conserved functions and mechanisms between plants and animals.

Rhizobacteria activates (+)-δ-cadinene synthase genes and induces systemic resistance in cotton against beet armyworm (Spodoptera exigua)

Gossypol is an important allelochemical produced by the subepidermal glands of some cotton varieties and important for their ability to respond to changing biotic stress by exhibiting antibiosis against some cotton pests. Plant growth-promoting rhizobacteria (PGPR) are root-colonizing bacteria that increase plant growth and often elicit defence against plant pathogens and insect pests. Little is known about the effect of PGPR on cotton plant-insect interactions and the potential biochemical and molecular mechanisms by which PGPR enhance cotton plant defence. Here, we report that PGPR (Bacillus spp.) treated cotton plants showed significantly higher levels of gossypol compared with untreated plants. Similarly, the transcript levels of the genes (i.e. (+)-δ-cadinene synthase gene family) involved in the biosynthesis of gossypol were higher in PGPR-treated plants than in untreated plants. Furthermore, the levels of jasmonic acid, an octadecanoid-derived defence-related phytohormone and the transcript level of jasmonic acid responsive genes were higher in PGPR-treated plants than in untreated plants. Most intriguingly, Spodoptera exigua showed reduced larval feeding and development on PGPR-treated plants. These findings demonstrate that treatment of plants with rhizobacteria may induce significant biochemical and molecular changes with potential ramifications for plant-insect interactions.

TaOPR2 encodes a 12-oxo-phytodienoic acid reductase involved in the biosynthesis of jasmonic acid in wheat (Triticum aestivum L.)

The 12-oxo-phytodienoic acid reductases (OPRs) are involved in the various processes of growth and development in plants, and classified into the OPRⅠ and OPRⅡ subgroups. In higher plants, only OPRⅡ subgroup genes take part in the biosynthesis of endogenous jasmonic acid. In this study, we isolated a novel OPRⅡ subgroup gene named TaOPR2 (GeneBank accession: KM216389) from the thermo-sensitive genic male sterile (TGMS) wheat cultivar BS366. TaOPR2 was predicted to encode a protein with 390 amino acids. The encoded protein contained the typical oxidored_FMN domain, the C-terminus peroxisomal-targeting signal peptide, and conserved FMN-binding sites. TaOPR2 was mapped to wheat chromosome 7B and located on peroxisome. Protein evolution analysis revealed that TaOPR2 belongs to the OPRⅡ subgroup and shares a high degree of identity with other higher plant OPR proteins. The quantitative real-time PCR results indicated that the expression of TaOPR2 is inhibited by abscisic acid (ABA), salicylic acid (SA), gibberellic acid (GA3), low temperatures and high salinity. In contrast, the expression of TaOPR2 can be induced by wounding, drought and methyl jasmonate (MeJA). Furthermore, the transcription level of TaOPR2 increased after infection with Puccinia striiformis f. sp. tritici and Puccinia recondite f. sp. tritici. TaOPR2 has NADPH-dependent oxidoreductase activity. In addition, the constitutive expression of TaOPR2 can rescue the male sterility phenotype of Arabidopsis mutant opr3. These results suggest that TaOPR2 is involved in the biosynthesis of jasmonic acid (JA) in wheat.

Brassinosteroids Regulate Root Growth, Development, and Symbiosis

Brassinosteroids (BRs) are natural plant hormones critical for growth and development. BR deficient or signaling mutants show significantly shortened root phenotypes. However, for a long time, it was thought that these phenotypes were solely caused by reduced cell elongation in the mutant roots. Functions of BRs in regulating root development have been largely neglected. Nonetheless, recent detailed analyses, revealed that BRs are not only involved in root cell elongation but are also involved in many aspects of root development, such as maintenance of meristem size, root hair formation, lateral root initiation, gravitropic response, mycorrhiza formation, and nodulation in legume species. In this review, current findings on the functions of BRs in mediating root growth, development, and symbiosis are discussed.

OPDA Has Key Role in Regulating Plant Susceptibility to the Root-Knot Nematode Meloidogyne hapla in Arabidopsis

Jasmonic acid (JA) is a plant hormone that plays important roles in regulating plant defenses against necrotrophic pathogens and herbivorous insects, but the role of JA in mediating the plant responses to root-knot nematodes has been unclear. Here we show that an application of either methyl jasmonate (MeJA) or the JA-mimic coronatine (COR) on Arabidopsis significantly reduced the number of galls caused by the root-knot nematode Meloidogyne hapla. Interestingly, the MeJA-induced resistance was independent of the JA-receptor COI1 (CORONATINE INSENSITIVE 1). The MeJA-treated plants accumulated the JA precursor cis-(+)-12-oxo-phytodienoic acid (OPDA) in addition to JA/JA-Isoleucine, indicating a positive feedback loop in JA biosynthesis. Using mutants in the JA-biosynthetic pathway, we found that plants deficient in the biosynthesis of JA and OPDA were hyper-susceptible to M. hapla. However, the opr3 mutant, which cannot convert OPDA to JA, exhibited wild-type levels of nematode galling. In addition, mutants in the JA-biosynthesis and perception which lie downstream of opr3 also displayed wild-type levels of galling. The data put OPR3 (OPDA reductase 3) as the branch point between hyper-susceptibility and wild-type like levels of disease. Overall, the data suggests that the JA precursor, OPDA, plays a role in regulating plant defense against nematodes.

Activated expression of AtEDT1/HDG11 promotes lateral root formation in Arabidopsis mutant edt1 by upregulating jasmonate biosynthesis

Root architecture is crucial for plants to absorb water and nutrients. We previously reported edt1 (edt1D) mutant with altered root architecture that contributes significantly to drought resistance. However, the underlying molecular mechanisms are not well understood. Here we report one of the mechanisms underlying EDT1/HDG11-conferred altered root architecture. Root transcriptome comparison between the wild type and edt1D revealed that the upregulated genes involved in jasmonate biosynthesis and signaling pathway were enriched in edt1D root, which were confirmed by quantitative RT-PCR. Further analysis showed that EDT1/HDG11, as a transcription factor, bound directly to the HD binding sites in the promoters of AOS, AOC3, OPR3, and OPCL1, which encode four key enzymes in JA biosynthesis. We found that the jasmonic acid level was significantly elevated in edt1D root compared with that in the wild type subsequently. In addition, more auxin accumulation was observed in the lateral root primordium of edt1D compared with that of wild type. Genetic analysis of edt1D opcl1 double mutant also showed that HDG11 was partially dependent on JA in regulating LR formation. Taken together, overexpression of EDT1/HDG11 increases JA level in the root of edt1D by directly upregulating the expressions of several genes encoding JA biosynthesis enzymes to activate auxin signaling and promote lateral root formation.

Comparative transcriptome analysis of the petal degeneration mutant pdm in Chinese cabbage (Brassica campestris ssp. pekinensis) using RNA-Seq

Flowering, which plays a crucial role in the growth and development of flowering plants, is a crucial point from vegetative growth to reproductive growth. The goal of this study was to examine the differences between the transcriptomes of the Chinese cabbage mutant pdm and the corresponding wild-type line 'FT'. We performed transcriptome analysis on mRNA isolated from flower buds of pdm and 'FT' using Illumina RNA sequencing (RNA-Seq) data. A total of 117 differentially expressed genes (DEGs) were detected. Among the DEGs, we identified a number of genes involved in floral development and flowering, including an F-box protein gene, EARLY FLOWERING 4 (ELF4), and transcription factors BIGPETAL (BPE) and MYB21 (v-myb avian myeloblastosis viral oncogene homolog); differential expression of these genes could potentially explain the difference in the flowers between pdm and 'FT'. In addition, the expression patterns of 20 DEGs, including 12 floral development and flowering-related genes and eight randomly selected genes, were validated by qRT-PCR, and the results were highly concordant with the RNA-Seq results. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed to better understand the functions of these DEGs. We also identified a large number of single nucleotide polymorphism and insertion/deletion markers, which will be a rich resource for future marker development and breeding research in Chinese cabbage. Also, our analysis revealed numerous novel transcripts and alternative splicing events. The transcriptome analysis provides valuable information for furthering our understanding of the molecular mechanisms that regulate the flowering process, and establishes a solid foundation for future genetic and functional genomic studies in Chinese cabbage.

Friends or foes: new insights in jasmonate and ethylene co-actions

One strategy for sessile plants to adapt to their surrounding environment involves the modulation of their various internal phytohormone signaling and distributions when the plants sense environmental change. There are currently dozens of identified phytohormones in plant cells and they act in concert to regulate plant growth, development, metabolism and defense. It has been determined that phytohormones often act together to achieve certain physiological functions. Thus, the study of hormone-hormone interactions is becoming a competitive research field for deciphering the underlying regulatory mechanisms. Among phytohormones, jasmonate and ethylene present a fascinating case of synergism and antagonism. They are commonly recognized as defense hormones that act synergistically. Plants impaired in jasmonate and/or ethylene signaling are susceptible to infections by necrotrophic fungi, suggesting that these two hormones are both required for defense. Moreover, jasmonate and ethylene also act antagonistically, such as in the regulation of apical hook development and wounding responses. Here, we highlight the recent breakthroughs in the understanding of jasmonate-ethylene co-actions and point out the potential power of studying protein-protein interactions for systematically exploring signal cross-talk.

The Physcomitrella patens unique alpha-dioxygenase participates in both developmental processes and defense responses

BACKGROUND

Plant α-dioxygenases catalyze the incorporation of molecular oxygen into polyunsaturated fatty acids leading to the formation of oxylipins. In flowering plants, two main groups of α-DOXs have been described. While the α-DOX1 isoforms are mainly involved in defense responses against microbial infection and herbivores, the α-DOX2 isoforms are mostly related to development. To gain insight into the roles played by these enzymes during land plant evolution, we performed biochemical, genetic and molecular analyses to examine the function of the single copy moss Physcomitrella patens α-DOX (Ppα-DOX) in development and defense against pathogens.

RESULTS

Recombinant Ppα-DOX protein catalyzed the conversion of fatty acids into 2-hydroperoxy derivatives with a substrate preference for α-linolenic, linoleic and palmitic acids. Ppα-DOX is expressed during development in tips of young protonemal filaments with maximum expression levels in mitotically active undifferentiated apical cells. In leafy gametophores, Ppα-DOX is expressed in auxin producing tissues, including rhizoid and axillary hairs. Ppα-DOX transcript levels and Ppα-DOX activity increased in moss tissues infected with Botrytis cinerea or treated with Pectobacterium carotovorum elicitors. In B. cinerea infected leaves, Ppα-DOX-GUS proteins accumulated in cells surrounding infected cells, suggesting a protective mechanism. Targeted disruption of Ppα-DOX did not cause a visible developmental alteration and did not compromise the defense response. However, overexpressing Ppα-DOX, or incubating wild-type tissues with Ppα-DOX-derived oxylipins, principally the aldehyde heptadecatrienal, resulted in smaller moss colonies with less protonemal tissues, due to a reduction of caulonemal filament growth and a reduction of chloronemal cell size compared with normal tissues. In addition, Ppα-DOX overexpression and treatments with Ppα-DOX-derived oxylipins reduced cellular damage caused by elicitors of P. carotovorum.

CONCLUSIONS

Our study shows that the unique α-DOX of the primitive land plant P. patens, although apparently not crucial, participates both in development and in the defense response against pathogens, suggesting that α-DOXs from flowering plants could have originated by duplication and successive functional diversification after the divergence from bryophytes.

Jasmonates: Emerging Players in Controlling Temperature Stress Tolerance

The sedentary life of plants has forced them to live in an environment that is characterized by the presence of numerous challenges in terms of biotic and abiotic stresses. Phytohormones play essential roles in mediating plant physiology and alleviating various environmental perturbations. Jasmonates are a group of oxylipin compounds occurring ubiquitously in the plant kingdom that play pivotal roles in response to developmental and environmental cues. Jasmonates (JAs) have been shown to participate in unison with key factors of other signal transduction pathway, including those involved in response to abiotic stress. Recent findings have furnished large body of information suggesting the role of jasmonates in cold and heat stress. JAs have been shown to regulate C-repeat binding factor (CBF) pathway during cold stress. The interaction between the integrants of JA signaling and components of CBF pathway demonstrates a complex relationship between the two. JAs have also been shown to counteract chilling stress by inducing ROS avoidance enzymes. In addition, several lines of evidence suggest the positive regulation of thermotolerance by JA. The present review provides insights into biosynthesis, signal transduction pathway of jasmonic acid and their role in response to temperature stress.

Oxylipins in moss development and defense

Oxylipins are oxygenated fatty acids that participate in plant development and defense against pathogen infection, insects, and wounding. Initial oxygenation of substrate fatty acids is mainly catalyzed by lipoxygenases (LOXs) and α-dioxygenases but can also take place non-enzymatically by autoxidation or singlet oxygen-dependent reactions. The resulting hydroperoxides are further metabolized by secondary enzymes to produce a large variety of compounds, including the hormone jasmonic acid (JA) and short-chain green leaf volatiles. In flowering plants, which lack arachidonic acid, oxylipins are produced mainly from oxidation of polyunsaturated C18 fatty acids, notably linolenic and linoleic acids. Algae and mosses in addition possess polyunsaturated C20 fatty acids including arachidonic and eicosapentaenoic acids, which can also be oxidized by LOXs and transformed into bioactive compounds. Mosses are phylogenetically placed between unicellular green algae and flowering plants, allowing evolutionary studies of the different oxylipin pathways. During the last years the moss Physcomitrella patens has become an attractive model plant for understanding oxylipin biosynthesis and diversity. In addition to the advantageous evolutionary position, functional studies of the different oxylipin-forming enzymes can be performed in this moss by targeted gene disruption or single point mutations by means of homologous recombination. Biochemical characterization of several oxylipin-producing enzymes and oxylipin profiling in P. patens reveal the presence of a wider range of oxylipins compared to flowering plants, including C18 as well as C20-derived oxylipins. Surprisingly, one of the most active oxylipins in plants, JA, is not synthesized in this moss. In this review, we present an overview of oxylipins produced in mosses and discuss the current knowledge related to the involvement of oxylipin-producing enzymes and their products in moss development and defense.

Elevated O₃ enhances the attraction of whitefly-infested tomato plants to Encarsia formosa

We experimentally examined the effects of elevated O₃ and whitefly herbivory on tomato volatiles, feeding and oviposition preferences of whiteflies and behavioural responses of Encarsia formosa to these emissions on two tomato genotypes, a wild-type (Wt) and a jasmonic acid (JA) defence-enhanced genotype (JA-OE, 35S). The O₃ level and whitefly herbivory significantly increased the total amount of volatile organic compounds (VOCs), monoterpenes, green leaf volatiles (GLVs), and aldehyde volatiles produced by tomato plants. The 35S plants released higher amount of total VOCs and monoterpene volatiles than Wt plants under O₃+herbivory treatments. The feeding and oviposition bioassays showed that control plants were preferred by adult whiteflies whereas the 35S plants were not preferred by whiteflies. In the Y-tube tests, O₃+herbivory treatment genotypes were preferred by adult E. Formosa. The 35S plants were preferred by adult E. formosa under O₃, herbivory and O₃+herbivory treatments. Our results demonstrated that elevated O₃ and whitefly herbivory significantly increased tomato volatiles, which attracted E. formosa and reduced whitefly feeding. The 35S plants had a higher resistance to B. tabaci than Wt plant. Such changes suggest that the direct and indirect defences of resistant genotypes, such as 35S, could strengthen as the atmospheric O₃ concentration increases.

An in-advance stable isotope labeling strategy for relative analysis of multiple acidic plant hormones in sub-milligram Arabidopsis thaliana seedling and a single seed

A sensitive and reliable in-advance stable isotope labeling strategy was developed for simultaneous relative quantification of 8 acidic plant hormones in sub-milligram amount of plant materials. Bromocholine bromide (BETA) and its deuterated counterpart D9-BETA were used to in-advance derivatize control and sample extracts individually, which were then combined and subjected to solid-phase extraction (SPE) purification followed by UPLC-MS/MS analysis. Relative quantification of target compounds was obtained by calculation of the peak area ratios of BETA/D9-BETA labeled plant hormones. The in-advance stable isotope labeling strategy realized internal standard-based relative quantification of multiple kinds of plant hormones independent of availability of internal standard of every analyte with enhanced sensitivity of 1-3 orders of magnitude. Meanwhile, the in-advance labeling contributes to higher sample throughput and more reliability. The method was successfully applied to determine 8 plant hormones in 0.8mg DW (dry weight) of seedlings and 4 plant hormones from single seed of Arabidopsis thaliana. The results show the potential of the method in relative quantification of multiple plant hormones in tiny plant tissues or organs, which will advance the knowledge of the crosstalk mechanism of plant hormones.

Smart plants: memory and communication without brains

The immobility of plants is consistent with their principal function: collecting light to provide photosynthetic substrate for the biological system. Their immobility does impose limitations on some basic requirements, such as the need for pollination, for seed dispersal, and for protection against herbivores. Meeting these 3 needs will logically necessitate some ability for plant communication - at least a capability for beneficial adaptive behavior. Three types of plant behavior provide evidence of memory and communication abilities: a capability for memory, a capability for measuring time, and extensive evidence of chemical signaling systems. These may provide benefits for genetic outcrossing, seed dispersal and protection - beneficial adaptive behaviors. The chemical signaling system constitutes a wireless communication network that draws mobile animals into assisting plant functions that require mobility. Plants share their chemical signaling systems most frequently with insects and birds. These beneficial adaptable behaviors may be interpreted as some type of consciousness.

Role of tomato lipoxygenase D in wound-induced jasmonate biosynthesis and plant immunity to insect herbivores

In response to insect attack and mechanical wounding, plants activate the expression of genes involved in various defense-related processes. A fascinating feature of these inducible defenses is their occurrence both locally at the wounding site and systemically in undamaged leaves throughout the plant. Wound-inducible proteinase inhibitors (PIs) in tomato (Solanum lycopersicum) provide an attractive model to understand the signal transduction events leading from localized injury to the systemic expression of defense-related genes. Among the identified intercellular molecules in regulating systemic wound response of tomato are the peptide signal systemin and the oxylipin signal jasmonic acid (JA). The systemin/JA signaling pathway provides a unique opportunity to investigate, in a single experimental system, the mechanism by which peptide and oxylipin signals interact to coordinate plant systemic immunity. Here we describe the characterization of the tomato suppressor of prosystemin-mediated responses8 (spr8) mutant, which was isolated as a suppressor of (pro)systemin-mediated signaling. spr8 plants exhibit a series of JA-dependent immune deficiencies, including the inability to express wound-responsive genes, abnormal development of glandular trichomes, and severely compromised resistance to cotton bollworm (Helicoverpa armigera) and Botrytis cinerea. Map-based cloning studies demonstrate that the spr8 mutant phenotype results from a point mutation in the catalytic domain of TomLoxD, a chloroplast-localized lipoxygenase involved in JA biosynthesis. We present evidence that overexpression of TomLoxD leads to elevated wound-induced JA biosynthesis, increased expression of wound-responsive genes and, therefore, enhanced resistance to insect herbivory attack and necrotrophic pathogen infection. These results indicate that TomLoxD is involved in wound-induced JA biosynthesis and highlight the application potential of this gene for crop protection against insects and pathogens.

Two-way plant mediated interactions between root-associated microbes and insects: from ecology to mechanisms

Plants are members of complex communities and function as a link between above- and below-ground organisms. Associations between plants and soil-borne microbes commonly occur and have often been found beneficial for plant fitness. Root-associated microbes may trigger physiological changes in the host plant that influence interactions between plants and aboveground insects at several trophic levels. Aboveground, plants are under continuous attack by insect herbivores and mount multiple responses that also have systemic effects on belowground microbes. Until recently, both ecological and mechanistic studies have mostly focused on exploring these below- and above-ground interactions using simplified systems involving both single microbe and herbivore species, which is far from the naturally occurring interactions. Increasing the complexity of the systems studied is required to increase our understanding of microbe-plant-insect interactions and to gain more benefit from the use of non-pathogenic microbes in agriculture. In this review, we explore how colonization by either single non-pathogenic microbe species or a community of such microbes belowground affects plant growth and defense and how this affects the interactions of plants with aboveground insects at different trophic levels. Moreover, we review how plant responses to foliar herbivory by insects belonging to different feeding guilds affect interactions of plants with non-pathogenic soil-borne microbes. The role of phytohormones in coordinating plant growth, plant defenses against foliar herbivores while simultaneously establishing associations with non-pathogenic soil microbes is discussed.

A trichome-specific linoleate lipoxygenase expressed during pyrethrin biosynthesis in pyrethrum

The lipid precursor alcohols of pyrethrins-jasmolone, pyrethrolone and cinerolone-have been proposed as sharing parts of the oxylipin pathway with jasmonic acid. This implies that one of the first committed steps of pyrethrin biosynthesis is catalyzed by a lipoxygenase, catalyzing the hydroperoxidation of linolenic acid at position 13. Previously, we showed that the expression and activity of chrysanthemyl diphosphate synthase (TcCDS), the enzyme catalyzing the first committed step in the biosynthesis of the acid moiety of pyrethrins, is trichome-specific and developmentally regulated in flowers. In the present study we characterized the expression pattern of 25 lipoxygenase EST contigs, and subsequently carried out the molecular cloning of two pyrethrum lipoxygenases, TcLOX1 and TcLOX2, that have a similar pattern to TcCDS. Only recombinant TcLOX1 catalyzed the peroxidation of the linolenic acid substrate. Just as TcCDS, TcLOX1, are exclusively expressed in trichomes. Phylogenetic analysis showed that the enzyme shared the highest homology with chloroplast-localized 13-type-lipoxygenases that are involved in maintaining basal levels of jasmonate.

Jasmonate signaling in plant development and defense response to multiple (a)biotic stresses

Plants frequently live in environments characterized by the presence of simultaneous and different stresses. The intricate and finely tuned molecular mechanisms activated by plants in response to abiotic and biotic environmental factors are not well understood, and less is known about the integrative signals and convergence points activated by plants in response to multiple (a)biotic stresses. Phytohormones play a key role in plant development and response to (a)biotic stresses. Among these, one of the most important signaling molecules is an oxylipin, the plant hormone jasmonic acid. Oxylipins are derived from oxygenation of polyunsaturated fatty acids. Jasmonic acid and its volatile derivative methyl jasmonate have been considered for a long time to be the bioactive forms due to their physiological effects and abundance in the plant. However, more recent studies showed unambiguously that they are only precursors of the active forms represented by some amino acid conjugates. Upon developmental or environmental stimuli, jasmonates are synthesized and accumulate transiently. Upon perception, jasmonate signal transduction process is finely tuned by a complex mechanism comprising specific repressor proteins which in turn control a number of transcription factors regulating the expression of jasmonate responsive genes. We discuss the latest discoveries about the role of jasmonates in plants resistance mechanism against biotic and abiotic stresses. Finally, the deep interplay of different phytohormones in stresses signaling will be also discussed.

(10E,12E,14E)-9,16-Dioxoocta-deca-10,12,14-trienoic acid

The title octa-deca-trienoic acid derivative, C(18)H(26)O(4), was isolated from Silene maritima With. (Caryophyllaceae), the first time this natural compound has been found in the Caryophyllales order. This fatty acid has an 18-carbon backbone with three double bonds on trans (E) conformation and two carbonyl. In the crystal, molecules are linked via pairs of O-H⋯O hydrogen bonds, forming inversion dimers.

Lichen Depsides and Depsidones Reduce Symptoms of Diseases Caused by Tobacco Mosaic Virus (TMV) in Tobacco Leaves

Two depsides and five depsidones, isolated from lichens, were tested to determine their in vivo protective effects on tobacco leaves challenged with Tobacco Mosaic Virus (TMV). The results indicate that most of these compounds are able to reduce either the number and/or the size of necrotic lesions following virus infection. Pannarin, 1′-chloro-pannarin and stictic acid provided the more effective protective results, reducing by at least 45% the number and size of lesions. Real Time PCR assays were used to explore the target of action against TMV by examining the response behavior of genes involved in the plant defense mechanism. The application of the lichen substances did not lead to changes in the transcriptional levels of pathogen-related ( PR1a), allene oxide synthase 2 ( AOS2) or oxophytodienoate reductase ( OPR3) genes. Thus, the protection observed in the tobacco leaves treated with the lichen compounds may be mediated by a mechanism which does not involved the SA- or JA-mediated defensive plant response. A possible structure-activity relationship is presented.

Root-localized phytochrome chromophore synthesis is required for photoregulation of root elongation and impacts root sensitivity to jasmonic acid in Arabidopsis

Plants exhibit organ- and tissue-specific light responses. To explore the molecular basis of spatial-specific phytochrome-regulated responses, a transgenic approach for regulating the synthesis and accumulation of the phytochrome chromophore phytochromobilin (PΦB) was employed. In prior experiments, transgenic expression of the BILIVERDIN REDUCTASE (BVR) gene was used to metabolically inactivate biliverdin IXα, a key precursor in the biosynthesis of PΦB, and thereby render cells accumulating BVR phytochrome deficient. Here, we report analyses of transgenic Arabidopsis (Arabidopsis thaliana) lines with distinct patterns of BVR accumulation dependent upon constitutive or tissue-specific, promoter-driven BVR expression that have resulted in insights on a correlation between root-localized BVR accumulation and photoregulation of root elongation. Plants with BVR accumulation in roots and a PΦB-deficient elongated hypocotyl2 (hy2-1) mutant exhibit roots that are longer than those of wild-type plants under white illumination. Additional analyses of a line with root-specific BVR accumulation generated using a GAL4-dependent bipartite enhancer-trap system confirmed that PΦB or phytochromes localized in roots directly impact light-dependent root elongation under white, blue, and red illumination. Additionally, roots of plants with constitutive plastid-localized or root-specific cytosolic BVR accumulation, as well as phytochrome chromophore-deficient hy1-1 and hy2-1 mutants, exhibit reduced sensitivity to the plant hormone jasmonic acid (JA) in JA-dependent root inhibition assays, similar to the response observed for the JA-insensitive mutants jar1 and myc2. Our analyses of lines with root-localized phytochrome deficiency or root-specific phytochrome depletion have provided novel insights into the roles of root-specific PΦB, or phytochromes themselves, in the photoregulation of root development and root sensitivity to JA.

Diverting the flux of the JA pathway in Nicotiana attenuata compromises the plant's defense metabolism and fitness in nature and glasshouse

A plant's inducible defenses against herbivores as well as certain developmental processes are known to be controlled by the jasmonic acid (JA) pathway. We have previously shown that ectopically expressing Arabidopsis thaliana JA O-methyltransferase in Nicotiana attenuata (35S-jmt) strongly reduces the herbivory-elicited jasmonate bursts by acting as metabolic sink that redirects free JA towards methylation; here we examine the consequences of this metabolic sink on N. attenuata's secondary metabolism and performance in nature. In the glasshouse, 35S-jmt plants produced fewer seed capsules due to shorter floral styles, which could be restored to wild type (WT) levels after hand-pollination, and were more susceptible to Manduca sexta larvae attack. When transplanted into the Great Basin Desert in Utah, 35S-jmt plants grew as well as WT empty vector, but were highly attacked by native herbivores of different feeding guilds: leaf chewers, miners, and single cell feeders. This greater susceptibility was strongly associated with reduced emissions of volatile organic compounds (hexenylesters, monoterpenes and sesquiterpenes) and profound alterations in the production of direct defenses (trypsin proteinase inhibitors [TPI], nicotine, diterpene glycosides [DTGs] and phenylpropanoid-polyamine conjugates) as revealed by a combination of targeted and metabolomics analyses of field collected samples. Complementation experiments with JA-Ile, whose formation is outcompeted in 35S-jmt plants by the methylation reaction, restored the local TPI activation to WT levels and partially complemented nicotine and DTG levels in elicited but not systemic leaves. These findings demonstrate that MeJA, the major JA metabolite in 35S-jmt plants, is not an active signal in defense activation and highlights the value of creating JA sinks to disrupt JA signaling, without interrupting the complete octadecanoid pathway, in order to investigate the regulation of plants' defense metabolism in nature.

GsTIFY10, a novel positive regulator of plant tolerance to bicarbonate stress and a repressor of jasmonate signaling

Recent discoveries show that TIFY family genes are plant-specific genes involved in the response to several abiotic stresses, also acting as key regulators of jasmonate signaling in Arabidopsis thaliana. However, there is limited information about this gene family in wild soybean, nor is its role in plant bicarbonate stress adaptation completely understood. Here, we isolated and characterized a novel TIFY family gene, GsTIFY10, from Glycine soja. GsTIFY10 could be induced by bicarbonate, salinity stress and the phytohormone JA, both in the leaves and roots of wild soybean. Over-expression of GsTIFY10 in Arabidopsis resulted in enhanced plant tolerance to bicarbonate stress during seed germination, early seedling and adult seedling developmental stages, and the expression levels of some bicarbonate stress response and stress-inducible marker genes were significantly higher in the GsTIFY10 overexpression lines than in wild-type plants. It was also found that GsTIFY10 could repress JA signal transduction. The roots of plants overexpressing GsTIFY10 grew longer than wild-type in the presence of MeJA, and some JA response and JA biosynthesis marker genes were suppressed in the GsTIFY10 overexpression lines. Subcellular localization studies using a GFP fusion protein showed that GsTIFY10 is localized to the nucleus. These results suggest that the newly isolated wild soybean GsTIFY10 is a positive regulator of plant bicarbonate stress tolerance and is also a repressor of jasmonate signaling, from hormone perception to transcriptional activity.

Ectopic expression of AtJMT in Nicotiana attenuata: creating a metabolic sink has tissue-specific consequences for the jasmonate metabolic network and silences downstream gene expression

To create a metabolic sink in the jasmonic acid (JA) pathway, we generated transgenic Nicotiana attenuata lines ectopically expressing Arabidopsis (Arabidopsis thaliana) jasmonic acid O-methyltransferase (35S-jmt) and additionally silenced in other lines the N. attenuata methyl jasmonate esterase (35S-jmt/ir-mje) to reduce the deesterification of methyl jasmonate (MeJA). Basal jasmonate levels did not differ between transgenic and wild-type plants; however, after wounding and elicitation with Manduca sexta oral secretions, the bursts of JA, jasmonoyl-isoleucine (JA-Ile), and their metabolites that are normally observed in the lamina, midvein, and petiole of elicited wild-type leaves were largely absent in both transformants but replaced by a burst of endogenous MeJA that accounted for almost half of the total elicited jasmonate pools. In these plants, MeJA became a metabolic sink that affected the jasmonate metabolic network and its spread to systemic leaves, with major effects on 12-oxo-phytodieonic acid, JA, and hydroxy-JA in petioles and on JA-Ile in laminas. Alterations in the size of jasmonate pools were most obvious in systemic tissues, especially petioles. Expression of threonine deaminase and trypsin proteinase inhibitor, two JA-inducible defense genes, was strongly decreased in both transgenic lines without influencing the expression of JA biosynthesis genes that were uncoupled from the wounding and elicitation with M. sexta oral secretions-elicited JA-Ile gradient in elicited leaves. Taken together, this study provides support for a central role of the vasculature in the propagation of jasmonates and new insights into the versatile spatiotemporal characteristics of the jasmonate metabolic network.

C12 derivatives of the hydroperoxide lyase pathway are produced by product recycling through lipoxygenase-2 in Nicotiana attenuata leaves

In response to diverse stresses, the hydroperoxide lyase (HPL) pathway produces C(6) aldehydes and 12-oxo-(9Z )-dodecenoic acid ((9Z )-traumatin). Since the original characterization of (10E )-traumatin and traumatic acid, little has been added to our knowledge of the metabolism and fluxes associated with the conversion of (9Z )-traumatin into diverse products in response to wounding and herbivory. A liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method was developed to quantify C(12) derivatives of the HPL pathway and to determine their metabolism after wounding and simulated herbivory in Nicotiana attenuata leaves. Ninety-eight per cent of the (9Z )-traumatin produced was converted to 9-hydroxy-(10E )-traumatin (9-OH-traumatin); two-thirds by product recycling through lipoxygenase-2 (NaLOX2) activity and one-third by nonenzymatic oxidation. Thirty-eight per cent of the de novo produced 9-OH-traumatin was conjugated to glutathione, consistent with this oxylipin being a reactive electrophile species. 12-OH-(9Z )-dodecenoic and dodecenedioic acids also showed rapid increases after wounding and simulated herbivory and a role for C(12) derivatives as signals in these processes was consistent with their ability to elicit substantial changes in gene expression. These results underscore the importance of metabolite reflux through LOX2, an insight which creates new opportunities for a functional understanding of C(12) derivatives of the HPL pathway in the regulation of stress responses.

The basic helix-loop-helix transcription factor MYC2 directly represses PLETHORA expression during jasmonate-mediated modulation of the root stem cell niche in Arabidopsis

The root stem cell niche, which in the Arabidopsis thaliana root meristem is an area of four mitotically inactive quiescent cells (QCs) and the surrounding mitotically active stem cells, is critical for root development and growth. We report here that during jasmonate-induced inhibition of primary root growth, jasmonate reduces root meristem activity and leads to irregular QC division and columella stem cell differentiation. Consistently, jasmonate reduces the expression levels of the AP2-domain transcription factors PLETHORA1 (PLT1) and PLT2, which form a developmentally instructive protein gradient and mediate auxin-induced regulation of stem cell niche maintenance. Not surprisingly, the effects of jasmonate on root stem cell niche maintenance and PLT expression require the functioning of MYC2/JASMONATE INSENSITIVE1, a basic helix-loop-helix transcription factor that involves versatile aspects of jasmonate-regulated gene expression. Gel shift and chromatin immunoprecipitation experiments reveal that MYC2 directly binds the promoters of PLT1 and PLT2 and represses their expression. We propose that MYC2-mediated repression of PLT expression integrates jasmonate action into the auxin pathway in regulating root meristem activity and stem cell niche maintenance. This study illustrates a molecular framework for jasmonate-induced inhibition of root growth through interaction with the growth regulator auxin.

Brassinosteroid enhances jasmonate-induced anthocyanin accumulation in Arabidopsis seedlings

Jasmonate (JA) regulates plant development, mediates defense responses, and induces anthocyanin biosynthesis as well. Previously, we isolated the psc1 mutant that partially suppressed coi1 insensitivity to JA, and found that brassinosteroid (BR) was involved in JA signaling and negatively regulated JA inhibition of root growth in Arabidopsis. In this study it was shown that JA-induced anthocyanin accumulation was reduced in BR mutants or in wild type treated with brassinazole, an inhibitor of BR biosynthesis, whereas it was induced by an application of exogenous BR. It was also shown that the 'late' anthocyanin biosynthesis genes including DFR, LDOX, and UF3GT, were induced slightly by JA in the BR mutants relative to wild type. Furthermore, the expression level of JA-induced Myb/bHLH transcription factors such as PAP1, PAP2, and GL3, which are components of the WD-repeat/Myb/bHLH transcriptional complexes that mediate the 'late' anthocyanin biosynthesis genes, was lower in the BR mutants than that in wild type. These results suggested that BR affects JA-induced anthocyanin accumulation by regulating the 'late' anthocyanin biosynthesis genes and this regulation might be mediated by the WD-repeat/Myb/bHLH transcriptional complexes.

Characterization of HbEREBP1, a wound-responsive transcription factor gene in laticifers of Hevea brasiliensis Muell. Arg

AP2/ERF transcription factors play an important role in regulation of the cross-talk between ethylene and jasmonate signaling pathways mediating defense responses of plants to biotic and abiotic stresses. In this study, an AP2/ERF transcription factor gene was isolated and characterized from laticifers of rubber tree by using RACE and real time PCR. The full length cDNA, referred to as HbEREBP1, was 1,095 bp in length and contained a 732 bp open reading frame encoding a putative protein of 243 amino acid residues. The molecular mass of the putative protein is 26.4 kDa with a pI of 9.46. The deduced amino acid sequence had a specific domain of AP2 superfamily and an ethylene-responsive element binding factor-associated amphiphilic repression motif, sharing 42.4, 39.1, and 38.0% identity with that of AtERF11, AtERF4, and AtERF8 in Arabidopsis, respectively. HbEREBP1 expression was down-regulated by tapping and mechanical wounding in the laticifers of adult trees. It was also down-regulated at early stage while up-regulated at late stage upon treatment with exogenous ethephon or methyl jasmonate, which was reverse to the case of defense genes in laticifers of epicormic shoots of rubber tree. Our results suggest that HbEREBP1 may be a negative regulator of defense genes in laticifers.

Systemin/Jasmonate-mediated systemic defense signaling in tomato

Wound-inducible proteinase inhibitors (PIs) in tomato plants provide a useful model system to elucidate the signal transduction pathways that regulate systemic defense response. Among the proposed intercellular signals for wound-induced PIs expression are the peptide systemin and the oxylipin-derived phytohormone jasmonic acid (JA). An increasing body of evidence indicates that systemin and JA work in the same signaling pathway to activate the expression of PIs and other defense-related genes. However, relatively less is known about how these signals interact to promote cell-to-cell communication over long distances. Genetic analysis of the systemin/JA signaling pathway in tomato plants provides a unique opportunity to study, in a single experimental system, the mechanism by which peptide and oxylipin signals interact to coordinate systemic expression of defense-related genes. Previously, it has been proposed that systemin is the long-distance mobile signal for defense gene expression. Recently, grafting experiments with tomato mutants defective in JA biosynthesis and signaling provide new evidence that JA, rather than systemin, functions as the systemic wound signal, and that the biosynthesis of JA is regulated by the peptide systemin. Further understanding of the systemin/JA signaling pathway promises to provide new insights into the basic mechanisms governing plant defense to biotic stress.