OsWRKY10 extensively activates multiple rice diterpenoid phytoalexin biosynthesis to enhance rice blast resistance

Plant secondary metabolites against biotic stresses for sustainable crop protection

Sustainable agriculture practices are indispensable for achieving a hunger-free world, especially as the global population continues to expand. Biotic stresses, such as pathogens, insects, and pests, severely threaten global food security and crop productivity. Traditional chemical pesticides, while effective, can lead to environmental degradation and increase pest resistance over time. Plant-derived natural products such as secondary metabolites like alkaloids, terpenoids, phenolics, and phytoalexins offer promising alternatives due to their ability to enhance plant immunity and inhibit pest activity. Recent advances in molecular biology and biotechnology have improved our understanding of how these natural compounds function at the cellular level, activating specific plant defense through complex biochemical pathways regulated by various transcription factors (TFs) such as MYB, WRKY, bHLH, bZIP, NAC, and AP2/ERF. Advancements in multi-omics approaches, including genomics, transcriptomics, proteomics, and metabolomics, have significantly improved the understanding of the regulatory networks that govern PSM synthesis. These integrative approaches have led to the discovery of novel insights into plant responses to biotic stresses, identifying key regulatory genes and pathways involved in plant defense. Advanced technologies like CRISPR/Cas9-mediated gene editing allow precise manipulation of PSM pathways, further enhancing plant resistance. Understanding the complex interaction between PSMs, TFs, and biotic stress responses not only advances our knowledge of plant biology but also provides feasible strategies for developing crops with improved resistance to pests and diseases, contributing to sustainable agriculture and food security. This review emphasizes the crucial role of PSMs, their biosynthetic pathways, the regulatory influence of TFs, and their potential applications in enhancing plant defense and sustainability. It also highlights the astounding potential of multi-omics approaches to discover gene functions and the metabolic engineering of genes associated with secondary metabolite biosynthesis. Taken together, this review provides new insights into research opportunities for enhancing biotic stress tolerance in crops through utilizing plant secondary metabolites.

The WRKY Family Transcription Factor GmWRKY72 Represses Glyceollin Phytoalexin Biosynthesis in Soybean

Phytoalexins are plant defense metabolites that are biosynthesized transiently in response to pathogens. Despite that their biosynthesis is highly restricted in plant tissues, the transcription factors that negatively regulate phytoalexin biosynthesis remain largely unknown. Glyceollins are isoflavonoid-derived phytoalexins that have critical roles in protecting soybean crops from the oomycete pathogen Phytophthora sojae. To identify regulators of glyceollin biosynthesis, we used a transcriptomics approach to search for transcription factors that are co-expressed with glyceollin biosynthesis in soybean and stilbene synthase phytoalexin genes in grapevine. We identified and functionally characterized the WRKY family protein GmWRKY72, which is one of four WRKY72-type transcription factors of soybean. Overexpressing and RNA interference silencing of GmWRKY72 in the soybean hairy root system decreased and increased expression of glyceollin biosynthetic genes and metabolites, respectively, in response to wall glucan elicitor from P. sojae. A translational fusion with green fluorescent protein demonstrated that GFP-GmWRKY72 localizes mainly to the nucleus of soybean cells. The GmWRKY72 protein directly interacts with several glyceollin biosynthetic gene promoters and the glyceollin transcription factor proteins GmNAC42-1 and GmMYB29A1 in yeast hybrid systems. The results show that GmWRKY72 is a negative regulator of glyceollin biosynthesis that may repress biosynthetic gene expression by interacting with transcription factor proteins and the DNA of glyceollin biosynthetic genes.

Transcriptomic and metabolomic reveal OsCOI2 as the jasmonate-receptor master switch in rice root

Jasmonate is an essential phytohormone involved in plant development and stress responses. Its perception occurs through the CORONATINE INSENSITIVE (COI) nuclear receptor allowing to target the Jasmonate-ZIM domain (JAZ) repressors for degradation by the 26S proteasome. Consequently, repressed transcription factors are released and expression of jasmonate responsive genes is induced. In rice, three OsCOI genes have been identified, OsCOI1a and the closely related OsCOI1b homolog, and OsCOI2. While the roles of OsCOI1a and OsCOI1b in plant defense and leaf senescence are well-established, the significance of OsCOI2 in plant development and jasmonate signaling has only emerged recently. To unravel the role of OsCOI2 in regulating jasmonate signaling, we examined the transcriptomic and metabolomic responses of jasmonate-treated rice lines mutated in both the OsCOI1a and OsCOI1b genes or OsCOI2. RNA-seq data highlight OsCOI2 as the primary driver of the extensive transcriptional reprogramming observed after a jasmonate challenge in rice roots. A series of transcription factors exhibiting an OsCOI2-dependent expression were identified, including those involved in root development or stress responses. OsCOI2-dependent expression was also observed for genes involved in specific processes or pathways such as cell-growth and secondary metabolite biosynthesis (phenylpropanoids and diterpene phytoalexins). Although functional redundancy exists between OsCOI1a/b and OsCOI2 in regulating some genes, oscoi2 plants generally exhibit a weaker response compared to oscoi1ab plants. Metabolic data revealed a shift from the primary metabolism to the secondary metabolism primarily governed by OsCOI2. Additionally, differential accumulation of oryzalexins was also observed in oscoi1ab and oscoi2 lines. These findings underscore the pivotal role of OsCOI2 in jasmonate signaling and suggest its involvement in the control of the growth-defense trade-off in rice.

Effectors and environment modulating rice blast disease: from understanding to effective control

Rice blast is a highly destructive crop disease that requires the interplay of three essential factors: the virulent blast fungus, the susceptible rice plant, and favorable environmental conditions. Although previous studies have focused mainly on the pathogen and rice, recent research has shed light on the molecular mechanisms by which the blast fungus and environmental conditions regulate host resistance and contribute to blast disease outbreaks. This review summarizes significant achievements in understanding the sophisticated modulation of blast resistance by Magnaporthe oryzae effectors and the dual regulatory mechanisms by which environmental conditions influence rice resistance and virulence of the blast fungus. Furthermore, it emphasizes potential strategies for developing blast-resistant rice varieties to effectively control blast disease.

Enhancing Crop Resilience: Insights from Labdane-Related Diterpenoid Phytoalexin Research in Rice (Oryza sativa L.)

Rice (Oryza sativa L.), as one of the most significant food crops worldwide, holds paramount importance for global food security. Throughout its extensive evolutionary journey, rice has evolved a diverse array of defense mechanisms to fend off pest and disease infestations. Notably, labdane-related diterpenoid phytoalexins play a crucial role in aiding rice in its response to both biotic and abiotic stresses. This article provides a comprehensive review of the research advancements pertaining to the chemical structures, biological activities, and biosynthetic pathways, as well as the molecular regulatory mechanisms, underlying labdane-related diterpenoid phytoalexins discovered in rice. This insight into the molecular regulation of labdane-related diterpenoid phytoalexin biosynthesis offers valuable perspectives for future research aimed at improving crop resilience and productivity.

OsWRKY70 Plays Opposite Roles in Blast Resistance and Cold Stress Tolerance in Rice

The transcription factor WRKYs play pivotal roles in the adapting to adverse environments in plants. Prior research has demonstrated the involvement of OsWRKY70 in resistance against herbivores and its response to abiotic stress. Here, we reported the functional analysis of OsWRKY70 in immunity against fungal diseases and cold tolerance. The results revealed that OsWRKY70 was induced by various Magnaporthe oryzae strains. Knock out mutants of OsWRKY70, which were generated by the CRISPR/Cas9 system, exhibited enhanced resistance to M. oryzae. This was consistent with fortifying the reactive oxygen species (ROS) burst after inoculation in the mutants, elevated transcript levels of defense-responsive genes (OsPR1b, OsPBZ1, OsPOX8.1 and OsPOX22.3) and the observation of the sluggish growth of invasive hyphae under fluorescence microscope. RNA sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) validations demonstrated that differentially expressed genes were related to plant-pathogen interactions, hormone transduction and MAPK cascades. Notably, OsbHLH6, a key component of the JA signaling pathway, was down-regulated in the mutants compared to wild type plants. Further investigation confirmed that OsWRKY70 bound to the promoter of OsbHLH6 by semi-in vivo chromatin immunoprecipitation (ChIP). Additionally, the loss-function of OsWRKY70 impaired cold tolerance in rice. The enhanced susceptibility in the mutants characterized by excessive ROS production, elevated ion leakage rate and increased malondialdehyde content, as well as decreased activity of catalase (CAT) and peroxidase (POD) under low temperature stress was, which might be attributed to down-regulation of cold-responsive genes (OsLti6b and OsICE1). In conclusion, our findings indicate that OsWRKY70 negatively contributes to blast resistance but positively regulates cold tolerance in rice, providing a strategy for crop breeding with tolerance to stress.

Genome-Wide Identification and Expression Analysis of ent-kaurene synthase-like Gene Family Associated with Abiotic Stress in Rice

Rice (Oryza sativa) is one of the most important crops for humans. The homologs of ent-kaurene synthase (KS) in rice, which are responsible for the biosynthesis of gibberellins and various phytoalexins, are identified by their distinct biochemical functions. However, the KS-Like (KSL) family's potential functions related to hormone and abiotic stress in rice remain uncertain. Here, we identified the KSL family of 19 species by domain analysis and grouped 97 KSL family proteins into three categories. Collinearity analysis of KSLs among Poaceae indicated that the KSL gene may independently evolve and OsKSL1 and OsKSL4 likely play a significant role in the evolutionary process. Tissue expression analysis showed that two-thirds of OsKSLs were expressed in various tissues, whereas OsKSL3 and OsKSL5 were specifically expressed in the root and OsKSL4 in the leaf. Based on the fact that OsKSL2 participates in the biosynthesis of gibberellins and promoter analysis, we detected the gene expression profiles of OsKSLs under hormone treatments (GA, PAC, and ABA) and abiotic stresses (darkness and submergence). The qRT-PCR results demonstrated that OsKSL1, OsKSL3, and OsKSL4 responded to all of the treatments, meaning that these three genes can be candidate genes for abiotic stress. Our results provide new insights into the function of the KSL family in rice growth and resistance to abiotic stress.

SmRAV1, an AP2 and B3 Transcription Factor, Positively Regulates Eggplant's Response to Salt Stress

Salt stress is a lethal abiotic stress threatening global food security on a consistent basis. In this study, we identified an AP2 and B3 domain-containing transcription factor (TF) named SmRAV1, and its expression levels were significantly up-regulated by NaCl, abscisic acid (ABA), and hydrogen peroxide (H2O2) treatment. High expression of SmRAV1 was observed in the roots and sepal of mature plants. The transient expression assay in Nicotiana benthamiana leaves revealed that SmRAV1 was localized in the nucleus. Silencing of SmRAV1 via virus-induced gene silencing (VIGS) decreased the tolerance of eggplant to salt stress. Significant down-regulation of salt stress marker genes, including SmGSTU10 and SmNCED1, was observed. Additionally, increased H2O2 content and decreased catalase (CAT) enzyme activity were recorded in the SmRAV1-silenced plants compared to the TRV:00 plants. Our findings elucidate the functions of SmRAV1 and provide opportunities for generating salt-tolerant lines of eggplant.