Inverse correlation between jasmonic acid and salicylic acid during early wound response in rice

Dissecting the role of salicylic acid in mediating stress response in mungbean cultivars concurrently exposed to Macrophomina phaseolina infection and drought stress

The combined stress studies provide fundamental knowledge that could assist in producing multiple stress resilient crops. The fungal phytopathogen, Macrophomina phaseolina is a major limiting factor in the productivity of the crop, Vigna radiata (mungbean). This fungal species tends to flourish under hot and dry conditions. Therefore, in this study the salicylic acid (SA) mediated stress responses in contrasting mungbean cultivars (Shikha and RMG-975) exposed to combined M. phaseolina infection (F) and drought stress (D) have been elucidated. The combined stress was applied to ten days seedlings in three orders i.e. drought followed by fungal infection (DF), drought followed by fungal infection with extended water deficit (DFD) and fungal infection followed by drought stress (FD). The severity of infection was analyzed using ImageJ analysis. Besides, the concentration of SA has been correlated with the phenylpropanoid pathway products, expression of pathogenesis-related proteins (β-1,3-glucanase and chitinase) and the specific activity of certain related enzymes (phenylalanine ammonia lyase, lipoxygenase and glutathione-S-transferase). The data revealed that the cultivar RMG-975 was relatively more tolerant than Shikha under individual stresses. However, the former became more susceptible to the infection under DFD treatment while the latter showed tolerance. Otherwise, the crown rot severity was reduced in both the cultivars under other combined treatments. The stress response analysis suggested that enhanced chitinase expression is vital for tolerance against both, the pathogen and drought stress. Also, it was noted that plants treat each stress combination differently and the role of SA was more prominently visible under individual stress conditions.

Decoding early stress signaling waves in living plants using nanosensor multiplexing

Increased exposure to environmental stresses due to climate change have adversely affected plant growth and productivity. Upon stress, plants activate a signaling cascade, involving multiple molecules like H2O2, and plant hormones such as salicylic acid (SA) leading to resistance or stress adaptation. However, the temporal ordering and composition of the resulting cascade remains largely unknown. In this study we developed a nanosensor for SA and multiplexed it with H2O2 nanosensor for simultaneous monitoring of stress-induced H2O2 and SA signals when Brassica rapa subsp. Chinensis (Pak choi) plants were subjected to distinct stress treatments, namely light, heat, pathogen stress and mechanical wounding. Nanosensors reported distinct dynamics and temporal wave characteristics of H2O2 and SA generation for each stress. Based on these temporal insights, we have formulated a biochemical kinetic model that suggests the early H2O2 waveform encodes information specific to each stress type. These results demonstrate that sensor multiplexing can reveal stress signaling mechanisms in plants, aiding in developing climate-resilient crops and pre-symptomatic stress diagnoses.

Lipidomics, transcription analysis, and hormone profiling unveil the role of CsLOX6 in MeJA biosynthesis during black tea processing

Jasmonates, such as jasmonic acid (JA) and methyl jasmonate (MeJA), are crucial aspect of black tea quality. However, lipids species, hormones, and genes regulated mechanism in the jasmonate biosynthesis during black tea processing are lacking. In this study, we employed lipidomics, hormone metabolism analysis, and transcriptome profiling of genes associated with the MeJA biosynthesis pathway to investigate these factors. The contents of lipids GLs, PLs, and TAG are decreased, accompanied by the main lipids species reduced during black tea processing. Galactolipids, primarily 34:3/36:6/36:3 DGDG and 36:6/36:5/36:4 MGDG, are transformed into massive MeJA and JA in black tea processing, accompanied by the decreased SA, MeSA, IAA, and BA and increased zeatin. Additionally, the transcriptional activity of the primary genes in MeJA biosynthesis pathway exhibited downregulated trends except for AOS and OPR and non-primary genes tend to be a little high or have fluctuation of expression. Coordinated expression of main CsHPL (TEA008699), CsAOS (TEA001041), and CsJMT (TEA015791) control the flow of lipids degradation and MeJA production. A strong infected reduction of a key lipoxygenase gene, CsLOX6 (TEA009423), in tea buds significantly reduced the level of jasmonates and expression of downstream genes, accompanied by SA, MeSA level rising, and ABA declining. We have identified a key CsLOX6, as well as established galactolipids, mainly 34:3/36:6/36:3 DGDG and 36:6/36:5/36:4 MGDG, sources for MeJA biosynthesis regulated by dynamics hormone and controlled by coordinated expressed CsHPL (TEA008699), CsAOS (TEA001041), and CsJMT (TEA015791). Our findings provide a theoretical basis for breeding high-quality black tea and offer valuable insights for improving processing methods.

Early transcriptomic responses of rice leaves to herbivory by Spodoptera frugiperda

During herbivory, chewing insects deposit complex oral secretions (OS) onto the plant wound. Understanding how plants respond to the different cues of herbivory remains an active area of research. In this study, we used an herbivory-mimick experiment to investigate the early transcriptional response of rice plants leaves to wounding, OS, and OS microbiota from Spodoptera frugiperda larvae. Wounding induced a massive early response associated to hormones such as jasmonates. This response switched drastically upon OS treatment indicating the activation of OS specific pathways. When comparing native and dysbiotic OS treatments, we observed few gene regulation. This suggests that in addition to wounding the early response in rice is mainly driven by the insect compounds of the OS rather than microbial. However, microbiota affected genes encoding key phytohormone synthesis enzymes, suggesting an additional modulation of plant response by OS microbiota.

Arbuscular mycorrhizal fungi-mediated activation of plant defense responses in direct seeded rice (Oryza sativa L.) against root-knot nematode Meloidogyne graminicola

Rhizosphere is the battlefield of beneficial and harmful (so called phytopathogens) microorganisms. Moreover, these microbial communities are struggling for their existence in the soil and playing key roles in plant growth, mineralization, nutrient cycling and ecosystem functioning. In the last few decades, some consistent pattern have been detected so far that link soil community composition and functions with plant growth and development; however, it has not been studied in detail. AM fungi are model organisms, besides potential role in nutrient cycling; they modulate biochemical pathways directly or indirectly which lead to better plant growth under biotic and abiotic stress conditions. In the present investigations, we have elucidated the AM fungi-mediated activation of plant defense responses against Meloidogyne graminicola causing root-knot disease in direct seeded rice (Oryza sativa L.). The study describes the multifarious effects of Funneliformis mosseae, Rhizophagus fasciculatus, and Rhizophagus intraradices inoculated individually or in combination under glasshouse conditions in rice plants. It was found that F. mosseae, R. fasciculatus and R. intraradices when applied individually or in combination modulated the biochemical and molecular mechanisms in the susceptible and resistant inbred lines of rice. AM inoculation significantly increased various plant growth attributes in plants with simultaneous decrease in the root-knot intensity. Among these, the combined application of F. mosseae, R. fasciculatus, and R. intraradices was found to enhance the accumulation and activities of biomolecules and enzymes related to defense priming as well as antioxidation in the susceptible and resistant inbred lines of rice pre-challenged with M. graminicola. The application of F. mosseae, R. fasciculatus and R. intraradices, induced the key genes involved in plant defense and signaling and it has been demonstrated for the first time. Results of the present investigation advocated that the application of F. mosseae, R. fasciculatus and R. intraradices, particularly a combination of all three, not only helped in the control of root-knot nematodes but also increased plant growth as well as enhances the gene expression in rice. Thus, it proved to be an excellent biocontrol as well as plant growth-promoting agent in rice even when the crop is under biotic stress of the root-knot nematode, M. graminicola.

Rice peroxygenase catalyzes lipoxygenase-dependent regiospecific epoxidation of lipid peroxides in the response to abiotic stressors

The peroxygenase pathway plays pivotal roles in plant responses to oxidative stress and other environmental stressors. Analysis of a network of co-expressed stress-regulated rice genes demonstrated that expression of OsPXG9 is negatively correlated with expression of genes involved in jasmonic acid biosynthesis. DNA sequence analysis and structure/function studies reveal that OsPXG9 is a caleosin-like peroxygenase with amphipathic α-helices that localizes to lipid droplets in rice cells. Enzymatic studies demonstrate that 12-epoxidation is slightly more favorable with 9(S)-hydroperoxyoctadecatrienoic acid than with 9(S)-hydroperoxyoctadecadienoic acid as substrate. The products of 12-epoxidation are labile, and the epoxide ring is hydrolytically cleaved into corresponding trihydroxy compounds. On the other hand, OsPXG9 catalyzed 15-epoxidation of 13(S)-hydroperoxyoctadecatrienoic acid generates a relatively stable epoxide product. Therefore, the regiospecific 12- or 15-epoxidation catalyzed by OsPXG9 strongly depends on activation of the 9- or 13- peroxygenase reaction pathways, with their respective preferred substrates. The relative abundance of products in the 9-PXG and 13-PXG pathways suggest that the 12-epoxidation involves intramolecular oxygen transfer while the 15-epoxidation can proceed via intramolecular or intermolecular oxygen transfer. Expression of OsPXG9 is up-regulated by abiotic stimuli such as drought and salt stress, but it is down-regulated by biotic stimuli such as flagellin 22 and salicylic acid. The results suggest that the primary function of OsPXG9 is to modulate the level of lipid peroxides to facilitate effective defense responses to abiotic and biotic stressors.

N-Acetylcysteine Priming Alleviates the Transplanting Injury of Machine-Transplanted Rice by Comprehensively Promoting Antioxidant and Photosynthetic Systems

The stress of transplanting injury adversely affects rice growth and productivity worldwide. N-acetylcysteine (NAC), the precursor of glutathione, is a potent ROS scavenger with powerful antioxidant activity. Previous studies on the application of NAC in plants mainly focused on alleviating the stress of heavy metals, UV-B, herbicides, etc. However, the role of NAC in alleviating transplanting injury is still not clear. A barrel experiment was carried out to explain the mechanism of NAC regulating the transplanting injury to machine-transplanted rice during the recovery stage. The results showed that NAC priming shortened the time of initiation of tillering and increased the tiller numbers within 3 weeks after transplanting. In addition, NAC priming increased the chlorophyll content, net photosynthetic rate, and sucrose content, thereby improving the dry weight at the recovery stage, especially root dry weight. At the same time, NAC priming significantly increased the activity of ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT), and superoxide dismutase (SOD). In addition, it also regulated flavonoids and total phenols contents to reduce hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, especially at the initial days after transplanting. These results suggest that NAC priming improves the tolerance of rice seedlings against transplanting injury by enhancing photosynthesis and antioxidant systems at initial days after transplanting, thereby promoting the accumulation of dry matter and tillering for higher yield returns.

Regulation and integration of plant jasmonate signaling: a comparative view of monocot and dicot

The phytohormone jasmonate plays a pivotal role in various aspects of plant life, including developmental programs and defense against pests and pathogens. A large body of knowledge on jasmonate biosynthesis, signal transduction as well as its functions in diverse plant processes has been gained in the past two decades. In addition, there exists extensive crosstalk between jasmonate pathway and other phytohormone pathways, such as salicylic acid (SA) and gibberellin (GA), in co-regulation of plant immune status, fine-tuning the balance of plant growth and defense, and so on, which were mostly learned from studies in the dicotyledonous model plants Arabidopsis thaliana and tomato but much less in monocot. Interestingly, existing evidence suggests both conservation and functional divergence in terms of core components of jasmonate pathway, its biological functions and signal integration with other phytohormones, between monocot and dicot. In this review, we summarize the current understanding on JA signal initiation, perception and regulation, and highlight the distinctive characteristics in different lineages of plants.

A Comparative Transcriptomic Meta-Analysis Revealed Conserved Key Genes and Regulatory Networks Involved in Drought Tolerance in Cereal Crops

Drought affects plant growth and development, causing severe yield losses, especially in cereal crops. The identification of genes involved in drought tolerance is crucial for the development of drought-tolerant crops. The aim of this study was to identify genes that are conserved key players for conferring drought tolerance in cereals. By comparing the transcriptomic changes between tolerant and susceptible genotypes in four Gramineae species, we identified 69 conserved drought tolerant-related (CDT) genes that are potentially involved in the drought tolerance of all of the analysed species. The CDT genes are principally involved in stress response, photosynthesis, chlorophyll biogenesis, secondary metabolism, jasmonic acid signalling, and cellular transport. Twenty CDT genes are not yet characterized and can be novel candidates for drought tolerance. The k-means clustering analysis of expression data highlighted the prominent roles of photosynthesis and leaf senescence-related mechanisms in differentiating the drought response between tolerant and sensitive genotypes. In addition, we identified specific transcription factors that could regulate the expression of photosynthesis and leaf senescence-related genes. Our analysis suggests that the balance between the induction of leaf senescence and maintenance of photosynthesis during drought plays a major role in tolerance. Fine-tuning of CDT gene expression modulation by specific transcription factors can be the key to improving drought tolerance in cereals.

Transcriptomics of tapping and healing process in frankincense tree during resin production

Frankincense tree (Boswellia sacra Fluek) has been poorly known on how it responds to tapping and wound-recovery process at molecular levels. Here, we used RNA-sequencing analysis to profile transcriptome of B. sacra after 30 min, 3 h and 6 h of post-tapping. Results showed 5525 differentially expressed genes (DEGs) that were related to terpenoid biosynthesis, phytohormonal regulation, cellular transport, and cell-wall synthesis. Plant-growth-regulators were applied exogenously which showed regulation of endogenous jasmonates and resulted in rapid recovery of cell-wall integrity by significantly up-regulated gene expression of terpenoid biosynthesis (germacrene-D synthase, B-amyrin synthase, and squalene epioxidase-1) and cell-wall synthesis (xyloglucan endotransglucosylase, cellulose synthase-A, and cell-wall hydrolase) compared to control. These findings suggest that tapping immediately activated several cell-developmental and regeneration processes, alongwith defense-induced terpenoid metabolism, to improve the healing process in epidermis. Exogenous growth regulators, especially jasmonic acid, can drastically help tree recovery from tissue degeneration and might help in tree conservation purposes.

Abscisic acid stimulates wound suberisation in kiwifruit (Actinidia chinensis) by regulating the production of jasmonic acid, cytokinin and auxin

Wounding induces a cascade of correlative physiological responses that lead to the repair of damaged tissue. In this study, the effect of wounding on suberin, endogenous hormones and their metabolic genes expression was observed during the wound healing of kiwifruit (Actinidia chinensis Planch.). In addition, the role of abscisic acid (ABA) in wound suberisation was investigated by analysing the coordinated regulation between ABA and other hormones. The wound healing process in kiwifruit could be divided into two stages including: (1) initial accumulation of suberin polyphenolic (SPP) and long carbon chain suberin polyaliphatic monomers (LSPA) before 24h; and (2) massive synthesis of SPP and very long carbon chain suberin polyaliphatic monomers (VLSPA) after 24h. ABA content rapidly increased and induced the jasmonic acid (JA) biosynthesis at the early stage of wound healing. ABA level gradually decreased with the expression of AchCYP707A genes, while the contents of trans-zeatin (t-ZT) and indole-3-acetic acid (IAA) steadily increased at the late stage of wound healing. Exogenous ABA stimulated JA and suberin monomers accumulation, but suppressed both t-ZT and IAA biosynthesis. The role of ABA in wound healing of kiwifruit might be involved in the coordination of both JA-mediated suberin monomers biosynthesis and t-ZT- and IAA-mediated formation of suberised cells via an interaction mechanism.

Bacterial leaf streak 1 encoding a mitogen-activated protein kinase confers resistance to bacterial leaf streak in rice

Bacterial leaf streak (BLS) is a major bacterial disease of rice. Utilization of host genetic resistance has become one of the most important strategies for controlling BLS. However, only a few resistance genes have been characterized. Previously, a recessive BLS resistance gene bls1 was roughly mapped on chromosome 6. Here, we further delineated bls1 to a 21 kb region spanning four genes. Genetic analysis confirmed that the gene encoding a mitogen-activated protein kinase (OsMAPK6) is the target of the allelic genes BLS1 and bls1. Overexpression of BLS1 weakened resistance to the specific Xanthomonas oryzae pv. oryzicola (Xoc) strain JZ-8, while low expression of bls1 increased resistance. However, both overexpression of BLS1 and low expression of bls1 could increase no-race-specific broad-spectrum resistance. These results indicate that BLS1 and bls1 negatively regulate race-specific resistance to Xoc strain JZ-8 but positively and negatively control broad-spectrum resistance, respectively. Subcellular localization demonstrated that OsMAPK6 was localized in the nucleus. RGA4, which is known to mediate resistance to Xoc, is the potential target of OsMAPK6. Overexpression of BLS1 and low expression of bls1 showed increase in salicylic acid and induced expression of defense-related genes, simultaneously increasing broad-spectrum resistance. Moreover, low expression of bls1 showed increase an in jasmonic acid and abscisic acid, in company with an increase in resistance to Xoc strain JZ-8. Collectively, our study provides new insights into the understanding of BLS resistance and facilitates the development of rice host-resistant cultivars.

Both Allene Oxide Synthases Genes Are Involved in the Biosynthesis of Herbivore-Induced Jasmonic Acid and Herbivore Resistance in Rice

Allene oxide synthase (AOS) is the second enzyme in the biosynthesis of the plant defensive hormone jasmonic acid (JA). In rice, there are two AOSs, OsAOS1 and OsAOS2. However, the role of these two AOS genes in herbivore-induced defenses in rice remains unidentified. We cloned the two rice AOS genes and observed that the transcript level of both OsAOS1 and OsAOS2 was enhanced by mechanical wounding, the infestation of the striped stem borer (SSB) (Chilo suppressalis) or brown planthopper (BPH) (Niaparvata lugens), and treatment with JA; however, OsAOS1 responded more rapidly to SSB infestation and JA treatment than did OsAOS2. The antisense expression of OsAOS1 (as-aos1) or OsAOS2 (as-aos2) decreased levels of SSB- or BPH-induced JA, which, in turn, reduced the production of SSB-induced trypsin protease inhibitor (TrypPI) and volatiles as well as the resistance of rice to SSB. In contrast, BPH preferred to feed and oviposit on wild-type (WT) plants over as-aos1 and as-aos2 plants. Moreover, the survival of BPH nymphs on as-aos1 or as-aos2 lines was significantly lower than on WT plants. The increased resistance of as-aos1 or as-aos2 plants to BPH correlated with higher levels of BPH-induced H₂O₂ and SA. These results indicate that OsAOS1 and OsAOS2 are both involved in herbivore-induced JA biosynthesis and play a vital role in determining the resistance of rice to chewing and phloem-feeding herbivores.

Mayetiola destructor (Diptera: Cecidmyiidae) host preference and survival on small grains with respect to leaf reflectance and phytohormone concentrations

The Hessian fly Mayetiola destructor (Diptera: Cecidmyiidae) is a major pest of wheat, globally. We conducted a series of laboratory choice and no-choice assays to quantify Hessian fly host preference for barley (cv. Champion), oat (cv. Cayuse), susceptible (cv. Alturas), and resistant (cv. Hollis) wheat. In addition, larval survivorship and adult emergence were compared among the evaluated host plants. We then examined whether insect preference for a host can be explained by differences in plant spectral reflectance. Further, larval survivorship and adult emergence were compared among host plants in relation to phytohormone concentrations. Hessian flies laid more eggs on wheat compared to either oat or barley. Spectral reflectance measurements of leaves were similar between susceptible and resistant wheat cultivars but different from those of barley and oat. Our results suggested that higher reflectance in the near-infrared range and lower reflectance in the visible range may be used by females for host selection. Hessian fly larvae were unable to develop into the pupal stage on resistant wheat and oat. No significant difference in larval survivorship was detected between the susceptible wheat and barley. However, adult emergence was significantly higher on barley than the susceptible wheat. Phytohormonal evaluations revealed that salicylic acid (SA) may be an important contributor to plant defense response to larval feeding as relatively higher concentrations of SA were present in oat and resistant wheat. While resistance in the resistant wheat is achieved only through antibiosis, both antibiosis and antixenosis were in effect rendering oat as a non-host for Hessian flies.

Functional characterisation of the transcriptome from leaf tissue of the fluoroacetate-producing plant, Dichapetalum cymosum, in response to mechanical wounding

Dichapetalum cymosum produces the toxic fluorinated metabolite, fluoroacetate, presumably as a defence mechanism. Given the rarity of fluorinated metabolites in nature, the biosynthetic origin and function of fluoroacetate have been of particular interest. However, the mechanism for fluorination in D. cymosum was never elucidated. More importantly, there is a severe lack in knowledge on a genetic level for fluorometabolite-producing plants, impeding research on the subject. Here, we report on the first transcriptome for D. cymosum and investigate the wound response for insights into fluorometabolite production. Mechanical wounding studies were performed and libraries of the unwounded (control) and wounded (30 and 60 min post wounding) plant were sequenced using the Illumina HiSeq platform. A combined reference assembly generated 77,845 transcripts. Using the SwissProt, TrEMBL, GO, eggNOG, KEGG, Pfam, EC and PlantTFDB databases, a 69% annotation rate was achieved. Differential expression analysis revealed the regulation of 364 genes in response to wounding. The wound responses in D. cymosum included key mechanisms relating to signalling cascades, phytohormone regulation, transcription factors and defence-related secondary metabolites. However, the role of fluoroacetate in inducible wound responses remains unclear. Bacterial fluorinases were searched against the D. cymosum transcriptome but transcripts with homology were not detected suggesting the presence of a potentially different fluorinating enzyme in plants. Nevertheless, the transcriptome produced in this study significantly increases genetic resources available for D. cymosum and will assist with future research into fluorometabolite-producing plants.

Antibacterial activity and rice-induced resistance, mediated by C15surfactin A, in controlling rice disease caused by Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) is an important pathogen in rice. C₁₅surfactin A, produced by Bacillus velezensis HN-2, displayed antibacterial activity against Xoo and effectively inhibited its infection of rice. The median inhibitory concentration of C₁₅surfactin A was 9.27 μg/mL. Scanning electron and transmission electron microscopy examination showed that C₁₅surfactin A caused significant damage to the cell wall structure of Xoo cells. On the other hand, dramatic increases in the activity of phenylalanine ammonia-lyase (Pal) and H₂O₂ content were observed in rice leaves inoculated with Xoo from 0 h to 72 h. Quantitative PCR assays indicated that C₁₅surfactin A exposure upregulated the expression of the genes Pr1a, CatA, and Pal. The results showed that C₁₅surfactin A could inhibit the growth of Xoo and effectively induce rice resistance to Xoo by triggering a hypersensitive reaction (HR) via mediation of the activities of antioxidant-related enzymes. Taken together, C₁₅surfactin A has strong antibiotic activity against Xoo and effectively induces rice resistance to Xoo. These results highlight the potential of C₁₅surfactin A as a biocontrol agent against Xoo in rice.

Feeding on tea GH19 chitinase enhances tea defense responses induced by regurgitant derived from Ectropis grisescens

Multiple isoforms of chitinases participate in plant defense against outside invaders. However, the functions of hydrolase family 19 (GH19) chitinases on pest control remain largely unknown. Here we reported the isolation and functional analysis of a gene CsChi19, which encodes a GH19 endochitinase protein of 332 amino acid residues from tea plant (Camellia sinensis). CsChi19 expression levels were upregulated in response to mechanical wounding, infestation by two important pests: the tea geometrid Ectropis grisescens and the tea green leafhopper Empoasca (Matsumurasca) onukii, a fungal pathogen Colletotrichum fructicola, and treatment with two phytohormones: jasmonic acid (JA) and salicylic acid. CsChi19 was heterologously expressed in Escherichia coli, and its catalytic function was further elucidated. The protein could hydrolyze colloidal chitin, and the optimum temperature and pH for its activity was 40°C and pH 5.0. CsChi19 were found to be toxic to tea pests when they were fed on artificial diets containing this protein. Interestingly, the regurgitant derived from E. grisescens fed with artificial diets containing CsChi19 protein induced stronger expression of CsMPK3, more JA burst, more accumulation of defense-related secondary metabolites, and more emission of volatiles than the regurgitant derived from E. grisescens fed only with artificial diets. Our results provide first evidence that CsChi19 is involved in mediating a novel defense mechanism of tea plant through altering the composition of the regurgitant.

Uptake of pharmaceuticals acts as an abiotic stress and triggers variation of jasmonates in Malabar spinach (Basella alba. L)

In recent years, pharmaceuticals have received increasing attentions because of their potential risks to the environment, but researches focusing on their impacts on defense system of living plants are still lacking. As an important class of phytohormones, jasmonates play crucial roles in plant defense system against environmental stress. In order to investigate the effect of pharmaceuticals uptake on endogenous jasmonates, an in vivo solid phase microextraction (SPME) method was established to simultaneously detect and monitor both pharmaceuticals and jasmonates in living plants. The proposed method exhibited wide linear ranges, high sensitivity (limits of detection ranging 0.0043-0.035 ng g^-1 for pharmaceuticals and 0.091-0.22 ng g^-1 for jasmonates, respectively), and satisfactory reproducibility (relative standard deviation of intrafiber ranging 4.2%-8.6% and interfiber ranging 5.2%-8.2%, respectively). Subsequently, this method was successfully applied to track the concentrations of each pharmaceutical and corresponding jasmonates in living Malabar spinach plants (Basella alba. L) exposed to three common pharmaceuticals (i.e. gemfibrozil, mefenamic acid and tolfenamic acid) over 15 days. In result, all pharmaceuticals appeared to trigger intensive biosynthesis of jasmonic acid (JA) (3.1-9.4 times of control) while reduced the concentration of methyl jasmonate (MeJA) (18.3%-38.1% of control). We inferred that uptake of pharmaceuticals acted as an abiotic stress and stimulated the plant defense response because of the variation of jasmonates. To the best of our knowledge, this is the first study applying SPME to detect and track both pharmaceuticals and phytohormones in living plants, which not only provided a glimpse to the adverse effect of pharmaceuticals on plants as well as the regulation of endogenous jasmonates, but also set a promising template for future in vivo analysis of xenobiotics and plant endogenous substances.

A Disease Resistance Elicitor Laminarin Enhances Tea Defense against a Piercing Herbivore Empoasca (Matsumurasca) onukii Matsuda

The tea plant (Camellia sinensis) suffers heavily from a harmful piercing pest, the tea green leafhopper (TLH) Empoasca (Matsumurasca) onukii Matsuda. In the present study, we studied the effect of an efficient elicitor of plant disease resistance, the β-1,3-glucan laminarin, on the induced defense against TLH in tea plants. Defense responses elicited by laminarin in tea include the activation of mitogen-activated protein kinases and WRKY, the burst of H₂O₂, salicylic acid, and abscisic acid, and the accumulation of direct-defense chemicals (including chitinase, phenylalanine ammonia lyase, callose, polyphenol oxidase, and flavonol synthase), as well as the production of volatile compounds. The laminarin-treated tea plants reduced the performance of TLH and enhanced the attractiveness to the egg parasitoid wasp of TLH, Stethynium empoascae Subba Rao. In the field experiment, laminarin application effectively reduced the number of TLH by attracting parasitoids. These results suggest that laminarin can induce protection against TLH by regulating signaling pathways in tea plant. Our study also proposes an environment friendly strategy for the integrated management of an economically important piercing pest.

OsLRR-RLK1, an early responsive leucine-rich repeat receptor-like kinase, initiates rice defense responses against a chewing herbivore

Plants are constantly exposed to a variety of environmental stresses, including herbivory. How plants perceive herbivores on a molecular level is poorly understood. Leucine-rich repeat receptor-like kinases (LRR-RLKs), the largest subfamily of RLKs, are essential for plants to detect external stress signals, and may therefore also be involved in herbivore perception. Here, we employed RNA interference silencing, phytohormone profiling and complementation, as well as herbivore resistance assays, to investigate the requirement of an LRR-RLK for the initiation of rice (Oryza sativa) defenses against the chewing herbivore striped stem borer (SSB) Chilo suppressalis. We discovered a plasma membrane-localized LRR-RLK, OsLRR-RLK1, whose transcription is strongly up-regulated by SSB attack and treatment with oral secretions of Spodoptera frugiperda. OsLRR-RLK1 acts upstream of mitogen-activated protein kinase (MPK) cascades, and positively regulates defense-related MPKs and WRKY transcription factors. Moreover, OsLRR-RLK1 is a positive regulator of SSB-elicited, but not wound-elicited, levels of jasmonic acid and ethylene, trypsin protease inhibitor activity and plant resistance towards SSB. OsLRR-RLK1 therefore plays an important role in herbivory-induced defenses of rice. Given the well-documented role of LRR-RLKs in the perception of stress-related molecules, we speculate that OsLRR-RLK1 may be involved in the perception of herbivory-associated molecular patterns.

The role of Euglena gracilis paramylon in modulating xylem hormone levels, photosynthesis and water-use efficiency in Solanum lycopersicum L

β-1,3-glucans such as paramylon act as elicitors in plants, modifying the hormonal levels and the physiological responses. Plant hormones affect all phases of the plant life cycle and their responses to environmental stresses, both biotic and abiotic. The aim of this study was to investigate the effects of a root treatment with Euglena gracilis paramylon on xylem hormonal levels, photosynthetic performance and dehydration stress in tomato (Solanum lycopersicum). Paramylon granules were processed to obtain the linear fibrous structures capable to interact with tomato cell membrane. Modulation of hormone levels (abscisic acid, jasmonic acid and salicylic acid) and related physiological responses such as CO₂ assimilation rate, stomatal and mesophyll conductance, intercellular CO₂ concentration, transpiration rate, water-use efficiency, quantum yield of photosystem II and leaf water potential were investigated. The results indicate a clear dose-dependent effect of paramylon on the hormonal content of xylem sap, photosynthetic performance and dehydration tolerance. Paramylon has the capability to enhance plant defense capacity against abiotic stress, such as drought, by modulating the conductance to CO₂ diffusion from air to the carboxylation sites and improving the water-use efficiency.

Allelic diversity in an NLR gene BPH9 enables rice to combat planthopper variation

Brown planthopper (BPH), Nilaparvata lugens Stål, is one of the most devastating insect pests of rice (Oryza sativa L.). Currently, 30 BPH-resistance genes have been genetically defined, most of which are clustered on specific chromosome regions. Here, we describe molecular cloning and characterization of a BPH-resistance gene, BPH9, mapped on the long arm of rice chromosome 12 (12L). BPH9 encodes a rare type of nucleotide-binding and leucine-rich repeat (NLR)-containing protein that localizes to the endomembrane system and causes a cell death phenotype. BPH9 activates salicylic acid- and jasmonic acid-signaling pathways in rice plants and confers both antixenosis and antibiosis to BPH. We further demonstrated that the eight BPH-resistance genes that are clustered on chromosome 12L, including the widely used BPH1, are allelic with each other. To honor the priority in the literature, we thus designated this locus as BPH1/9 These eight genes can be classified into four allelotypes, BPH1/9-1, -2, -7, and -9 These allelotypes confer varying levels of resistance to different biotypes of BPH. The coding region of BPH1/9 shows a high level of diversity in rice germplasm. Homologous fragments of the nucleotide-binding (NB) and leucine-rich repeat (LRR) domains exist, which might have served as a repository for generating allele diversity. Our findings reveal a rice plant strategy for modifying the genetic information to gain the upper hand in the struggle against insect herbivores. Further exploration of natural allelic variation and artificial shuffling within this gene may allow breeding to be tailored to control emerging biotypes of BPH.

Suppression of Jasmonic Acid-Mediated Defense by Viral-Inducible MicroRNA319 Facilitates Virus Infection in Rice

MicroRNAs (miRNAs) are pivotal modulators of plant development and host-virus interactions. However, the roles and action modes of specific miRNAs involved in viral infection and host susceptibility remain largely unclear. In this study, we show that Rice ragged stunt virus (RRSV) infection caused increased accumulation of miR319 but decreased expression of miR319-regulated TCP (TEOSINTE BRANCHED/CYCLOIDEA/PCF) genes, especially TCP21, in rice plants. Transgenic rice plants overexpressing miR319 or downregulating TCP21 exhibited disease-like phenotypes and showed significantly higher susceptibility to RRSV in comparison with the wild-type plants. In contrast, only mild disease symptoms were observed in RRSV-infected lines overexpressing TCP21 and especially in the transgenic plants overexpressing miR319-resistant TCP21. Both RRSV infection and overexpression of miR319 caused the decreased endogenous jasmonic acid (JA) levels along with downregulated expression of JA biosynthesis and signaling-related genes in rice. However, treatment of rice plants with methyl jasmonate alleviated disease symptoms caused by RRSV and reduced virus accumulation. Taken together, our results suggest that the induction of miR319 by RRSV infection in rice suppresses JA-mediated defense to facilitate virus infection and symptom development.

Comparing the defence-related gene expression changes upon root-knot nematode attack in susceptible versus resistant cultivars of rice

Rice is one of the major staple food crops in the world and an excellent model system for studying monocotyledonous plants. Diseases caused by nematodes in rice are well documented and among them, root-knot nematode (RKN), Meloidogyne graminicola, causes extensive yield decline. It is therefore necessary to identify novel sources of natural resistance to RKN in rice and to investigate the rice-RKN interaction in detail to understand the basal plant defence mechanisms and nematode manipulation of the host physiology. To this end, six different cultivars of rice were initially screened for RKN infection and development; Pusa 1121 and Vandana were found to be most susceptible and resistant to RKN infection, respectively. In order to investigate the role of major hormone-regulated plant defence pathways in compatible/incompatible rice-RKN interaction, some well-identified marker genes involved in salicylate/jasmonate/ethylene pathway were evaluated for their differential expression through qRT-PCR. In general, our study shows a remarkable discrepancy in the expression pattern of those genes between compatible and incompatible rice-RKN interaction. As most information on the molecular interplay between plants and nematodes were generated on dicotyledonous plants, the current study will strengthen our basic understanding of plant-nematode interaction in the monocot crops, which will aid in defining future strategies for best plant health measures.

Emission Timetable and Quantitative Patterns of Wound-Induced Volatiles Across Different Leaf Damage Treatments in Aspen (Populus Tremula)

Plant-feeding herbivores can generate complex patterns of foliar wounding, but it is unclear how wounding-elicited volatile emissions scale with the severity of different wounding types, and there is no common protocol for wounding experiments. We investigated the rapid initial response to wounding damage generated by different numbers of straight cuts and punctures through leaf lamina as well as varying area of lamina squeezing in the temperate deciduous tree Populus tremula. Wounding-induced volatile emission time-courses were continuously recorded by a proton-transfer-reaction time-of-flight mass-spectrometer. After the mechanical wounding, an emission cascade was rapidly elicited resulting in sequential emissions of key stress volatiles methanol, acetaldehyde, and volatiles of the lipoxygenase pathway, collectively constituting more than 97% of the total emission. The maximum emission rates, reached after one to three minutes after wounding, and integrated emissions during the burst were strongly correlated with the severity in all damage treatments. For straight cuts and punch hole treatments, the emissions per cut edge length were constant, indicating a direct proportionality. Our results are useful for screening wounding-dependent emission capacities.

Two thiadiazole compounds promote rice defence against Xanthomonas oryzae pv. oryzae by suppressing the bacterium's production of extracellular polysaccharides

Thiazole, isothiazole, thiadiazole, and their derivatives are used to control various human, animal and plant diseases. In addition to having direct anti-microbial and anti-fungal properties, these compounds are thought to induce host defences, but the mechanism of defence induction remains poorly understood. This article reports that the thiadiazoles of zinc thiazole and bismerthiazol induce H2 O2 accumulation, up-regulation of defence-related genes, callose deposition and hypersensitive response-like cell death in rice leaves infected with Xanthomonas oryaze pv. oryzae (Xoo) strain ZJ173, but not in non-infected leaves. These defence responses in Xoo-infected leaves were suppressed by the exogenous application of catalase, which reduces H2 O2 accumulation. The application of extracellular polysaccharides (EPSs) extracted from strain ZJ173 significantly compromised rice defence against ZJ173 with or without thiadiazole treatment. The EPS-deficient Xoo mutant ∆gumH triggered a stronger defence than its parent strain ZJ173. The thiadiazole treatments reduced EPS production by strain ZJ173, but not by the thiadiazole-resistant strain 2-1-1, which is thiadiazole resistant in vivo, but not in vitro; moreover, enhanced defence was not detected in thiadiazole-treated rice inoculated with 2-1-1. Based on these data, we infer that zinc thiazole and bismerthiazol promote rice defence against Xoo by inhibiting the production of bacterial EPS.

Comparative analysis of antiviral responses in Brachypodium distachyon and Setaria viridis reveals conserved and unique outcomes among C3 and C4 plant defenses

Viral diseases cause significant losses in global agricultural production, yet little is known about grass antiviral defense mechanisms. We previously reported on host immune responses triggered by Panicum mosaic virus (PMV) and its satellite virus (SPMV) in the model C3 grass Brachypodium distachyon. To aid comparative analyses of C3 and C4 grass antiviral defenses, here, we establish B. distachyon and Setaria viridis (a C4 grass) as compatible hosts for seven grass-infecting viruses, including PMV and SPMV, Brome mosaic virus, Barley stripe mosaic virus, Maize mild mottle virus, Sorghum yellow banding virus, Wheat streak mosaic virus (WSMV), and Foxtail mosaic virus (FoMV). Etiological and molecular characterization of the fourteen grass-virus pathosystems showed evidence for conserved crosstalk among salicylic acid (SA), jasmonic acid, and ethylene pathways in B. distachyon and S. viridis. Strikingly, expression of PHYTOALEXIN DEFICIENT4, an upstream modulator of SA signaling, was consistently suppressed during most virus infections in B. distachyon and S. viridis. Hierarchical clustering analyses further identified unique antiviral responses triggered by two morphologically similar viruses, FoMV and WSMV, and uncovered other host-dependent effects. Together, the results of this study establish B. distachyon and S. viridis as models for the analysis of plant-virus interactions and provide the first framework for conserved and unique features of C3 and C4 grass antiviral defenses.

Regulation of jasmonic acid biosynthesis by silicon application during physical injury to Oryza sativa L

We investigated the effects of silicon (Si) application on rice plants (Oryza sativa L.) and its responses in the regulation of jasmonic acid (JA) during wounding stress. Endogenous JA was significantly higher in wounded rice plants than in non-wounded. In contrast, Si treatment significantly reduced JA synthesis as compared to non-Si applications under wounding stress. mRNA expression of O. sativa genes showed down-regulation of lipoxygenase, allene oxide synthase 1, allene oxide synthase 2, 12-oxophytodienoate reductase 3, and allene oxide cyclase upon Si application and wounding stress as compared to non-Si-treated wounded rice plants. The physical injury-induced-oxidative stress was modulated by Si treatments, which resulted in higher catalase, peroxidase, and polyphenol oxidase activities as compared with non-Si-treated plants under wounding stress. The higher Si accumulation in rice plants also reduced the level of lipid peroxidation, which helped the rice plants to protect it from wounding stress. In conclusion, Si accumulation in rice plants mitigated the adverse effects of wounding through regulation of antioxidants and JA.

Differential activation of sporamin expression in response to abiotic mechanical wounding and biotic herbivore attack in the sweet potato

BACKGROUND

Plants respond differently to mechanical wounding and herbivore attack, using distinct pathways for defense. The versatile sweet potato sporamin possesses multiple biological functions in response to stress. However, the regulation of sporamin gene expression that is activated upon mechanical damage or herbivore attack has not been well studied.

RESULTS

Biochemical analysis revealed that different patterns of Reactive oxygen species (ROS) and antioxidant mechanism exist between mechanical wounding (MW) and herbivore attack (HA) in the sweet potato leaf. Using LC-ESI-MS (Liquid chromatography electrospray ionization mass spectrometry analysis), only the endogenous JA (jasmonic acid) level was found to increase dramatically after MW in a time-dependent manner, whereas both endogenous JA and SA (salicylic acid) increase in parallel after HA. Through yeast one-hybrid screening, two transcription factors IbNAC1 (no apical meristem (NAM), Arabidopsis transcription activation factor (ATAF), and cup-shaped cotyledon (CUC)) and IbWRKY1 were isolated, which interact with the sporamin promoter fragment of SWRE (sporamin wounding-responsive element) regulatory sequences. Exogenous application of MeJA (methyl jasmonate), SA and DIECA (diethyldithiocarbamic acid, JAs biosynthesis inhibitor) on sweet potato leaves was employed, and the results revealed that IbNAC1 mediated the expression of sporamin through a JA-dependent signaling pathway upon MW, whereas both IbNAC1 and IbWRKY1 coordinately regulated sporamin expression through JA- and SA-dependent pathways upon HA. Transcriptome analysis identified MYC2/4 and JAZ2/TIFY10A (jasmonate ZIM/tify-domain), the repressor and activator of JA and SA signaling among others, as the genes that play an intermediate role in the JA and SA pathways, and these results were further validated by qRT-PCR (quantitative real-time polymerase chain reaction).

CONCLUSION

This work has improved our understanding of the differential regulatory mechanism of sporamin expression. Our study illustrates that sweet potato sporamin expression is differentially induced upon abiotic MW and biotic HA that involves IbNAC1 and IbWRKY1 and is dependent on the JA and SA signaling pathways. Thus, we established a model to address the plant-wounding response upon physical and biotic damage.

Ultraviolet-B induced changes in morphological, physiological and biochemical parameters of two cultivars of pea (Pisum sativum L.)

Increase in perception of solar ultraviolet-B (UV-B) radiation on Earth's surface due to anthropogenic activities has potential in causing detrimental effects on plants. The present study was performed to evaluate the effect of elevated UV-B on Pisum sativum L., a leguminous plant with emphasis on nitrogen metabolism, flavonoids and hormonal changes. Elevated UV-B (ambient+7.2 kJ m(-2) day(-1)) negatively affected the growth, biomass, yield and its quality by generating oxidative stress directly or due to elevation of salicylic acid in two cultivars with higher magnitude being observed in HUP-2 as compared to HUDP-15. The increased accumulation of flavonoids (quercetin and kaempferol) under elevated UV-B neither provided sufficient protection to the photosynthetic machinery nor helped in elevation of biological nitrogen fixation. Nitrogen fixation and its assimilation were negatively affected under elevated UV-B as observed by the decline in nitrogenase, nitrate reductase, nitrite reductase activities and leghaemoglobin contents. Higher accumulation of salicylic acid in HUP-2 might be associated with its higher degree of sensitivity against UV-B, while higher induction of jasmonic acid and antioxidative enzymes (superoxide dismutase, catalase and ascorbate peroxidase activities) provided resistance to HUDP-15 against applied stress vis-a-vis exhibited less reduction in biomass, yield and quality of produce.

Making sense of hormone-mediated defense networking: from rice to Arabidopsis

Phytohormones are not only essential for plant growth and development but also play central roles in triggering the plant immune signaling network. Historically, research aimed at elucidating the defense-associated role of hormones has tended to focus on the use of experimentally tractable dicot plants such as Arabidopsis thaliana. Emerging from these studies is a picture whereby complex crosstalk and induced hormonal changes mold plant health and disease, with outcomes largely dependent on the lifestyle and infection strategy of invading pathogens. However, recent studies in monocot plants are starting to provide additional important insights into the immune-regulatory roles of hormones, often revealing unique complexities. In this review, we address the latest discoveries dealing with hormone-mediated immunity in rice, one of the most important food crops and an excellent model for molecular genetic studies in monocots. Moreover, we highlight interactions between hormone signaling, rice defense and pathogen virulence, and discuss the differences and similarities with findings in Arabidopsis. Finally, we present a model for hormone defense networking in rice and describe how detailed knowledge of hormone crosstalk mechanisms can be used for engineering durable rice disease resistance.

The Hordeum vulgare signalling protein MAP kinase 4 is a regulator of biotic and abiotic stress responses

Mitogen activated protein kinase (MAP kinase) signal transduction pathways are important eukaryotic mechanisms for regulating cellular responses to stress. The objective of this work was to investigate the role of the barley MAP kinase HvMPK4 (a homologue of the Arabidopsis MAP kinase AtMPK1) in the plant response to biotic and abiotic stress. Transgenic barley plants bearing antisense or overexpression constructs for HvMPK4 were produced, and RNA blot analysis showed that HvMPK4 gene expression was much reduced in the antisense lines and approximately double in the overexpression lines. Three independent lines of each construct were tested for their response to a fungal pathogen and to salt treatment. The antisense lines were more resistant to the hemibiotrophic fungal pathogen Magnaporthe grisea, and showed enhanced levels of salicylic acid (SA) and of hydrogen peroxide following infection; HvMPK4 is thus a negative regulator of SA production post infection. The overexpression lines had constitutively higher levels of jasmonic acid and enhanced levels of ethylene following infection but were not more resistant to the pathogen. However the overexpression lines showed greater tolerance to abiotic stress, as following 2 weeks of salt treatment these lines showed less reduction in fresh and dry weight, accumulated less salt in the leaves and contained enhanced levels of the osmoprotectant amino acid, proline.

Hormone defense networking in rice: tales from a different world

Recent advances in plant immunity research underpin the pivotal role of small-molecule hormones in regulating the plant defense signaling network. Although most of our understanding comes from studies of dicot plants such as Arabidopsis thaliana, new studies in monocots are providing additional insights into the defense-regulatory role of phytohormones. Here, we review the roles of both classical and more recently identified stress hormones in regulating immunity in the model monocot rice (Oryza sativa) and highlight the importance of hormone crosstalk in shaping the outcome of rice-pathogen interactions. We also propose a defense model for rice that does not support a dichotomy between the pathogen lifestyle and the effectiveness of the archetypal defense hormones salicylic acid (SA) and jasmonic acid (JA).

Quantification of jasmonic and salicylic acids in rice seedling leaves

Jasmonic acid (JA) and salicylic acid (SA) are critical signaling components involved in various aspects of plant growth, development, and defense. Their constitutive levels vary from plant to plant and also from tissue to tissue within the same plant. Moreover, their quantitative levels change when plant is exposed to biotic and abiotic stresses. To better understand the JA- and SA-mediated signaling and metabolic pathways, it is important to precisely quantify their levels in plants/tissues/organs. However, their extraction and quantification are not trivial and still technically challenging. An effort has been made in various laboratories to develop a simple and standard procedure that can be utilized for quantification of JA and SA. Here, we present the experimental procedure and our decade of experience on extracting and quantifying them in an absolute manner in leaves of rice seedlings. We must mention that this method has been applied to both monocotyledonous and dicotyledonous plants for absolute quantification of JA and SA. As collaboration is the key towards rapid progress in science and technology, we are always open to sharing our experience in this field with any active research group with an aim to improve the procedure further and eventually to connect the importance of their (JA and SA) quantitative levels with networks of signaling and metabolic pathways in plants.

Brassinosteroids suppress rice defense against root-knot nematodes through antagonism with the jasmonate pathway

The importance of phytohormone balance is increasingly recognized as central to the outcome of plant-pathogen interactions. Next to their well-known developmental role, brassinosteroids (BR) were recently found to be involved in plant innate immunity. In this study, we examined the role of BR in rice (Oryza sativa) innate immunity during infection with the root-knot nematode Meloidogyne graminicola, and we studied the inter-relationship with the jasmonate (JA) pathway. Exogenous epibrassinolide (BL) supply at low concentrations induced susceptibility in the roots whereas high concentrations of BL enforced systemic defense against this nematode. Upon high exogenous BL supply on the shoot, quantitative reverse-transcription polymerase chain reaction (qRT-PCR) confirmed a strong feedback inhibitory effect, leading to reduced BR biosynthesis in the root. Moreover, we demonstrate that the immune suppressive effect of BR is at least partly due to negative cross-talk with the JA pathway. Mutants in the BR biosynthesis or signaling pathway accumulate slightly higher levels of the immediate JA-precursor 12-oxo-phytodienoic acid, and qRT-PCR data showed that the BR and JA pathway are mutually antagonistic in rice roots. Collectively, these results suggest that the balance between the BR and JA pathway is an effective regulator of the outcome of the rice-M. graminicola interaction.

Evolution of jasmonate and salicylate signal crosstalk

The evolution of land plants approximately 470 million years ago created a new adaptive zone for natural enemies (attackers) of plants. In response to attack, plants evolved highly effective, inducible defense systems. Two plant hormones modulating inducible defenses are salicylic acid (SA) and jasmonic acid (JA). Current thinking is that SA induces resistance against biotrophic pathogens and some phloem feeding insects and JA induces resistance against necrotrophic pathogens, some phloem feeding insects and chewing herbivores. Signaling crosstalk between SA and JA commonly manifests as a reciprocal antagonism and may be adaptive, but this remains speculative. We examine evidence for and against adaptive explanations for antagonistic crosstalk, trace its phylogenetic origins and provide a hypothesis-testing framework for future research on the adaptive significance of SA-JA crosstalk.

Transgenic expression of dual positional maize lipoxygenase-1 leads to the regulation of defense-related signaling molecules and activation of the antioxidative enzyme system in rice

Effects of transgenic expression of dual positional maize lipoxygenase-1 on the defense system were analyzed in rice. The activities of hydroperoxidelyase and antioxidative enzymes (superoxide dismutase, catalase, peroxidase) were increased and high levels of aldehydes including malondialdehyde were produced. The constitutive level of jasmonic was slightly increased and the constitutive salicylic acid level was decreased. Kinetic analysis of wound response indicated that the levels of jasmonic acid and salicylic acid are inversely correlated in nully transgenic rice plants, suggesting that there is an antagonistic interaction between jasmonic acid and salicylic acid. Microarray analysis indicated that several defense-related genes encoding antioxidative enzymes and pathogen-related proteins were up-regulated, and the resistance to rice blast fungus was enhanced in transgenic rice. Taken together, our results suggest that maize lipoxygenase-1 expressed in the cytoplasm plays an important role for the regulation of defense system including the antioxidative enzymes in transgenic rice, and that these effects may be mediated by reactive oxygen species generated through the enzyme-initiated catalytic peroxidation mechanism of maize lipoxygenase-1.

The broad-leaf herbicide 2,4-dichlorophenoxyacetic acid turns rice into a living trap for a major insect pest and a parasitic wasp

Synthetic chemical elicitors of plant defense have been touted as a powerful means for sustainable crop protection. Yet, they have never been successfully applied to control insect pests in the field. We developed a high-throughput chemical genetics screening system based on a herbivore-induced linalool synthase promoter fused to a β-glucuronidase (GUS) reporter construct to test synthetic compounds for their potential to induce rice defenses. We identified 2,4-dichlorophenoxyacetic acid (2,4-D), an auxin homolog and widely used herbicide in monocotyledonous crops, as a potent elicitor of rice defenses. Low doses of 2,4-D induced a strong defensive reaction upstream of the jasmonic acid and ethylene pathways, resulting in a marked increase in trypsin proteinase inhibitor activity and volatile production. Induced plants were more resistant to the striped stem borer Chilo suppressalis, but became highly attractive to the brown planthopper Nilaparvata lugens and its main egg parasitoid Anagrus nilaparvatae. In a field experiment, 2,4-D application turned rice plants into living traps for N. lugens by attracting parasitoids. Our findings demonstrate the potential of auxin homologs as defensive signals and show the potential of the herbicide to turn rice into a selective catch crop for an economically important pest.

Influence of short-term silicon application on endogenous physiohormonal levels of Oryza sativa L. under wounding stress

The current study was conducted in order to investigate the short-term effects (6, 12, and 24 h) of silicon (Si) on the endogenous hormonal composition of rice (Oryza sativa L. cv. Dongjin-beyo), with and without wounding stress. Si applied in different concentrations (0.5, 1.0, and 2.0 mM) significantly promoted shoot length, plant biomass, and chlorophyll content of rice plants. Plants treated with different concentrations of sole Si for 6, 12, and 24 h had higher endogenous jasmonic acid contents than control. However, a combined application of wounding stress and Si induced a significantly small quantity of endogenous jasmonic acid as compared with control. On the contrary, endogenous salicylic acid level was significantly higher in sole Si-treated plants, while after wounding stress, a similar trend was observed yet again. After 6, 12, and 24 h of Si applications, with and without wounding stress, ethylene levels were significantly lower in comparison to their respective controls. The findings of the present study perpetrate the beneficial role of Si on the growth and development of rice plant by relieving physical injury and stress. Si also affects endogenous jasmonic acid and ethylene levels, while an inverse correlation exists between jasmonic acid and salicylic acid under wounding stress conditions.

Mining for treatment-specific and general changes in target compounds and metabolic fingerprints in response to herbivory and phytohormones in Plantago lanceolata

Induction studies focusing on target metabolites may not reveal metabolic changes occurring in plants after various challenges. By contrast, metabolic fingerprinting can be a powerful tool to find patterns that are either treatment-specific or general and was therefore used to depict plant responses after various challenges. Plants of Plantago lanceolata were challenged by mechanical damage, specialist herbivores (aphids or sawfly larvae), generalist herbivores (Lepidopteran caterpillars) or phytohormones (jasmonic or salicylic acid). After 3 d of treatment, local and systemic leaves were analyzed for characteristic target metabolites (iridoid glucosides and verbascoside) by gas chromatography coupled with mass spectrometry (GC-MS) and for metabolic fingerprints by liquid chromatography coupled with time of flight mass spectrometry (LC-TOF-MS). Whereas only marginal changes in target metabolite concentrations were found, metabolic fingerprints were substantially affected especially by generalist and phytohormone treatments. By contrast, mechanical damage and specialist herbivory caused fewer changes. Responses to generalists partly overlapped with the changes caused by jasmonic acid, but many additional peaks were up-regulated. Furthermore, many peaks were co-induced by jasmonic and salicylic acid. The surprisingly high co-induction of peaks by both phytohormones suggests that the signaling pathways regulate a set of common targets. Furthermore, only metabolic fingerprinting could reveal that herbivores induce additional species-specific pathways beyond these phytohormone responses.

RSOsPR10 expression in response to environmental stresses is regulated antagonistically by jasmonate/ethylene and salicylic acid signaling pathways in rice roots

Plant roots play important roles not only in the absorption of water and nutrients, but also in stress tolerance. Previously, we identified RSOsPR10 as a root-specific pathogenesis-related (PR) protein induced by drought and salt treatments in rice. Transcripts and proteins of RSOsPR10 were strongly induced by jasmonate (JA) and the ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid (ACC), while salicylic acid (SA) almost completely suppressed these inductions. Immunohistochemical analyses showed that RSOsPR10 strongly accumulated in cortex cells surrounding the vascular system of roots, and this accumulation was also suppressed when SA was applied simultaneously with stress or hormone treatments. In the JA-deficient mutant hebiba, RSOsPR10 expression was up-regulated by NaCl, wounding, drought and exogenous application of JA. This suggested the involvement of a signal transduction pathway that integrates JA and ET signals in plant defense responses. Expression of OsERF1, a transcription factor in the JA/ET pathway, was induced earlier than that of RSOsPR10 after salt, JA and ACC treatments. Simultaneous SA treatment strongly inhibited the induction of RSOsPR10 expression and, to a lesser extent, induction of OsERF1 expression. These results suggest that JA/ET and SA pathways function in the stress-responsive induction of RSOsPR10, and that OsERF1 may be one of the transcriptional factors in the JA/ET pathway.

Transcriptional regulation of the rice arginine decarboxylase (Adc1) and S-adenosylmethionine decarboxylase (Samdc) genes by methyl jasmonate

We investigated the effect of methyl jasmonate (MeJa) treatment on the expression of two genes in the rice polyamine biosynthesis pathway and on the polyamine content in wild type plants and transgenic rice plants expressing a Datura stramonium (Ds) Adc cDNA, the latter accumulating up to three-fold the normal level of putrescine. Exogenous MeJa transiently inhibited the expression of OsAdc1, OsSamdc and Spermidine synthase (OsSpds) genes in the polyamine biosynthesis pathway, probably through transcriptional repression. There was also a similar negative impact on the DsAdc transgene in transgenic plants, even though a constitutive promoter was used to drive transgene expression. The free putrescine content was reduced significantly in the leaves of both wild type and transgenic plants in response to MeJa, although the magnitude of the effect was greater in wild type plants. We discuss our findings with respect to the previously proposed threshold model of polyamine metabolism in plants subjected to abiotic stress.

Sugarcane DIRIGENT and O-methyltransferase promoters confer stem-regulated gene expression in diverse monocots

Transcription profiling analysis identified Saccharum hybrid DIRIGENT (SHDIR16) and Omicron-Methyltransferase (SHOMT), putative defense and fiber biosynthesis-related genes that are highly expressed in the stem of sugarcane, a major sucrose accumulator and biomass producer. Promoters (Pro) of these genes were isolated and fused to the beta-glucuronidase (GUS) reporter gene. Transient and stable transgene expression analyses showed that both Pro( DIR16 ):GUS and Pro( OMT ):GUS retain the expression characteristics of their respective endogenous genes in sugarcane and function in orthologous monocot species, including rice, maize and sorghum. Furthermore, both promoters conferred stem-regulated expression, which was further enhanced in the stem and induced in the leaf and root by salicylic acid, jasmonic acid and methyl jasmonate, key regulators of biotic and abiotic stresses. Pro( DIR16 ) and Pro( OMT ) will enable functional gene analysis in monocots, and will facilitate engineering monocots for improved carbon metabolism, enhanced stress tolerance and bioenergy production.

The NAC transcription factor RIM1 of rice is a new regulator of jasmonate signaling

Jasmonates (JAs) are lipid-derived regulators that play crucial roles in both host immunity and development. We recently identified the NAC transcription factor RIM1 as a host factor involved in multiplication of rice dwarf virus (RDV). Here, we report that RIM1 functions as a transcriptional regulator of JA signaling and is degraded in response to JA treatment via a 26S proteasome-dependent pathway. Plants carrying rim1 mutations show a phenotype of root growth inhibition. The expression profiles of the mutants were significantly correlated with those of JA-treated wild-type plants without accumulation of endogenous JA, indicating that RIM1 functions as a component of JA signaling. The expression of genes encoding JA biosynthetic enzymes (lipoxygenase (LOX), allene oxide synthase 2 (AOS2) and OPDA reductase 7 (OPR7)) was up-regulated in the rim1 mutants under normal conditions, and a rapid and massive accumulation of endogenous JA was detected in the mutants after wounding. These results suggest that RIM1 may represent a new molecular link in jasmonate signaling, and may thereby provide new insights into the well-established coronatine-insensitive 1 (COI1)-Jasmonate ZIM-domain (JAZ) JA signaling pathway.

Direct induced resistance in Oryza sativa to Spodoptera frugiperda

Rice, Oryza sativa, is the most important staple food for a significant portion of the world's population. Despite the importance of rice, however, induced resistance to insects has not been thoroughly studied in rice; in fact, to our knowledge, direct induced resistance after injury by chewing insects has not been shown in rice. We conducted a series of experiments designed to characterize direct induced resistance in rice after feeding by larvae of the fall armyworm (Spodoptera frugiperda J. E. Smith) and application of jasmonic acid. Weight gains and relative growth rates of fall armyworm larvae were lower when fed leaves from plants previously damaged by armyworms than when fed leaves from undamaged plants. This response was stronger at a systemic spatial scale; that is, the induced resistance was stronger in newly emerged leaves not present at the time plants were damaged than in damaged leaves themselves. Armyworm growth rates were also reduced on foliage from plants treated with jasmonic acid, a hormone known to mediate plant responses to wounding. The response to injury by armyworm larvae and to exogenous jasmonic acid was stronger in transgenic rice plants in which levels of salicylic acid (a signaling molecule that inhibits jasmonic acid) were suppressed. These results show the existence of a direct induced resistance response in rice and suggest that this response to injury by a chewing insect may be mediated by jasmonic acid.