Search Results (107)

Rice blast is one of the main diseases of rice, causing severe economic losses to agricultural production; thus, the search for blast resistance is a top priority for rice breeding. When challenged by the blast causal fungus Magnaporthe oryzae the expression level of OsMAPKKK69 gene in rice cultivar Nipponbar was found to increase significantly. Such an induction was also found in a different genetic material, cultivar Shufanggaonuo, indicating that OsMAPKKK69 plays an important role in blast disease response. However, the function of OsMAPKKK69 remains unclear. In this study, wild type ZH11 was selected as the background material to investigate the expression and functions of OsMAPKKK69 in rice disease resistance by constructing knockout mutants. The results showed that OsMAPKKK69 is mainly expressed in four-week-old shoots and localized in cell membrane, cytoplasm, and nucleus. The two allelic knockout mutants, osmapkkk69-1 and osmapkkk69-2, were more resistant to M. oryzae and bacterial blight Xanthomonas oryzae pv. Oryzae (Xoo). Further agronomic trait analysis revealed that the osmapkkk69-1 and osmapkkk69-2 mutants had reduced plant height, smaller grain size, a significant increase in tillering number, but also a significant increase in yield per plant. Our results show that OsMAPKKK69 is involved in the immune response of rice by negatively regulating the resistance to rice blast and blight diseases, and in regulating important agronomic traits. This study lays a foundation for revealing the molecular mechanism of OsMAPKKK69 in the immune response to rice diseases and provides novel genetic resources for rice breeding. Full article

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major threat to global rice productivity. Although hybrid rice breeding has significantly enhanced yields, persistent genetic vulnerabilities within restorer lines continue to compromise BB resistance. This study addresses this challenge by implementing functional marker-assisted selection (FMAS) to pyramid two broad-spectrum resistance (R) genes, Xa21 and Xa23, into the elite, yet BB-susceptible, restorer line K608R. To enable precise Xa23 genotyping, we developed a novel three-primer functional marker (FM) system (IB23/CB23/IR23). This system complements the established U1/I2 markers used for Xa21. This recombination-independent FMAS platform facilitates simultaneous, high-precision tracking of both homozygous and heterozygous alleles, thereby effectively circumventing the linkage drag limitations typical of conventional markers. Through six generations of marker-assisted backcrossing followed by intercrossing, we generated K608R2123 pyramided lines harboring both R genes in homozygous states, achieving a recurrent parent genome recovery rate of 96.93%, as determined by single nucleotide polymorphism (SNP) chip analysis. The pyramided lines exhibited enhanced resistance against six virulent Xoo pathogenic races while retaining parental yield performance across key agronomic traits. Our FMAS strategy overcomes the historical trade-off between broad-spectrum resistance and the preservation of elite phenotypes, with the developed lines exhibiting resistance coverage complementary to that of both introgressed R genes. This integrated approach provides breeders with a reliable molecular tool to accelerate the development of high-yielding, disease-resistant varieties, demonstrating significant potential for practical deployment in rice improvement programs. The K608R2123 germplasm represents a dual-purpose resource suitable for both commercial hybrid seed production and marker-assisted breeding programs, and it confers synergistic resistance against diverse Xoo races, thereby providing a pivotal breeding resource for sustainable BB control in epidemic regions. Full article

The basic leucine zipper (bZIP) transcription factors are involved in a wide range of physiological processes in plants, including hormone signaling, stress responses, and growth and development regulation. They play a key role in abscisic acid (ABA)-mediated immune regulation. However, the immune-related function of OsbZIP76 in rice remains poorly understood. In this study, we generated OsbZIP76 knockout (KO) lines using CRISPR/Cas9-mediated genome editing and examined their phenotypic responses to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) and the fungal pathogen Magnaporthe oryzae. The KO lines showed increased susceptibility to both pathogens compared to wild-type (WT) plants. Furthermore, qRT-PCR analysis revealed that, upon pathogen infection, the expression of pathogenesis-related genes such as PR1a, PR5, and NPR1 was significantly suppressed in the KO lines. ABA treatment experiments showed that KO lines were hypersensitive to exogenous ABA, indicating a role for OsbZIP76 in ABA perception and signaling. Notably, the expression of the OsbZIP76 gene itself was strongly induced by both ABA treatment and pathogen infection, supporting its role as a positive regulator in ABA-associated immune signaling. Overall, this study demonstrates that OsbZIP76 functions as an important immune regulator by integrating defense gene expression with ABA signaling, providing new insights into the molecular crosstalk between hormonal signaling and pathogen defense mechanisms. Full article

Background: Xanthomonas oryzae pv. oryzae (Xoo) causes rice leaf blight (BLB) and poses a major threat to global rice production. In rice production, tetramycin agents provide good control of rice leaf blight, while the standardization of the reference genes of Xoo under tetramycin stress has not been reported. The aim of this study was to identify the most stable reference genes for quantitative PCR analysis of Xoo under tetramycin stress. Methods: Six candidate reference genes, gyrB (RNA polymerase β gene), GADPH (glyceraldehyde-3-phosphate dehydrogenase gene), recA (recombinase A gene), gyrA (citrate synthase encoding gene), dnaK (molecular chaperone protein gene), and 16S rRNA (16S ribosomal RNA gene) were selected and their expression stability was assessed under tetramycin stress conditions using real-time quantitative PCR (qRT-PCR). GeNorm, NormFinder, BestKeeper and RefFinder were used to assess the expression stability, the relative expression values of the eight genes involved QS (Quorum sensing) pathway under tetramycin stress were used to validate by the rpf (regulation of pathogenic factors) gene family. Results: 16S rRNA expression was most stable under tetracycline stress, whereas GADPH was the least. The rpf gene family showed a highly stable expression level, confirming the reliability of 16S r RNA as a reference gene in the study of Xoo under tetramycin stress. Conclusions: 16S rRNA was identified as the best reference gene for Xoo gene expression analysis under tetramycin stress. It provides a reliable support for the molecular research on the control strategy of rice BLB. Full article

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae (Xoo), poses a serious threat to rice cultivation. This study presents the green synthesis of zinc oxide nanoparticles (ZnO NPs) using an aqueous leaf extract of the medicinal plant Centella asiatica (L.) Urban and evaluates their potential as dual-function nanopesticides. The synthesized CA-ZnO NPs exhibited high crystallinity, a hexagonal to quasi-spherical morphology, and nanoscale dimensions (~22.5 nm), as confirmed by UV–Vis spectroscopy, XRD, FTIR, SEM, TEM, and SAED analyses. These nanoparticles demonstrated potent antibacterial activity against a highly virulent, field-derived Thai Xoo strain, with a minimum inhibitory concentration (MIC) of 8 µg/mL. Mechanistic investigations revealed substantial membrane disruption, intracellular nanoparticle penetration, and elevated reactive oxygen species (ROS) generation in treated cells. Cytotoxicity testing using human dermal fibroblasts (HDFs) revealed excellent biocompatibility, with no statistically significant reduction in cell viability at concentrations up to 500 µg/mL. In contrast, viability markedly declined at 1000 µg/mL. These findings underscore the selective antibacterial efficacy and minimal mammalian cytotoxicity of CA-ZnO NPs. Overall, CA-ZnO NPs offer a promising green nanopesticide platform that integrates potent antibacterial activity with biocompatibility, supporting future applications in sustainable crop protection and biomedical nanotechnology. Full article

Bacterial leaf blight (BLB) is a destructive disease caused by Xanthomonas oryzae pv. oryzae (Xoo). It has been proven that BLB adversely influences the growth and production of rice, resulting in substantial losses in yield. Nanoparticle–antimicrobial compounds possess excellent physicochemical properties, which have generated groundbreaking applications in protecting rice against BLB attacks. However, there is less research focused on the interaction between nanoparticles and the microbiome of BLB rice leaves, particularly the structure and function of endophytic bacteria, which are essential to plant health and pathogenesis. Therefore, the study explored how Cu-Ag nanoparticles influenced the endophytic bacteria’s composition and functions in healthy and BLB rice leaves. The data demonstrated that the relative abundance of beneficial bacteria, Burkholderiales, Micrococcales, and Rhizobiales, increased after the introduction of Cu-Ag nanoparticles on the leaves of BLB rice. The examination of PAL activity demonstrated that nanoparticles limited the spread of Xoo in rice leaves. Furthermore, endophytic community functional prediction demonstrated that nanoparticles may regulate the physiological process associated with potential stress resistance and growth-promoting function in the endophytic communities. This investigation may enhance the understanding of interactions between nanoparticles and the composition of rice endophytic microbiome, which can contribute to the exploration and application of nanomaterials in crop pathogen management. Full article

Rice bacterial blight (BB) and bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), respectively, are among the most devastating bacterial diseases threatening global rice production. The interactions between rice and Xanthomonas oryzae are complex and dynamic, involving recognition, attack, defense, and adaptation mechanisms enacted by both the rice host and the pathogens. This review summarizes recent advances in understanding rice–Xanthomonas oryzae interactions, focusing on infection models, pathogenic mechanisms, and immune responses elicited by Xanthomonas oryzae. Special attention is devoted to the roles of transcription activator-like effectors (TALEs) and non-TALE effectors in pathogenicity, the functions of resistance (R) genes in defense, and the interconnected molecular networks of interactions derived from multi-omics approaches. Understanding these interactions is essential for developing effective disease-resistance strategies and creating elite disease-resistant rice varieties. Full article

Xanthomonas oryzae pv. oryzae (Xoo) is a biotrophic bacterial pathogen, which causes devastating bacterial blight disease worldwide. In this study, we thoroughly investigated the antimicrobial effect of the plant-derived extract chelerythrine against Xanthomonas oryzae pv. oryzae (Xoo) and elucidated its mechanism. Chelerythrine is a quaternary ammonium alkaloid with a 2,3,7,8-tetrasubstituted phenanthridine structure, extracted from plants, such as the whole plant of Chelidonium majus, and the roots, stems, and leaves of Macleaya cordata. We found that chelerythrine significantly inhibited the growth of Xoo at a concentration of 1.25 μg/mL. Further experiments revealed that chelerythrine interfered with the division and reproduction of the bacterium, leading to its filamentous growth. Additionally, it increased the permeability of Xoo cell membranes and effectively decreased the pathogenicity of Xoo, including the inhibition of extracellular polysaccharide production, cellulase secretion, and biofilm formation. Chelerythrine induced the accumulation of reactive oxygen species in the bacterium, triggering oxidative stress. The result showed that chelerythrine inhibited the formation of the Z-ring of Xoo, interfered with the synthesis of pyrimidine and purine nucleotides, inhibited DNA damage repair, and inhibited the formation of peptidoglycan and lipid-like A, thus interfering with cell membrane permeability, inhibiting carbohydrate metabolism and phosphorylation of sugars, reducing pathogenicity, and ultimately inhibiting bacterial growth and leading to the destruction or lysis of bacterial cells. Altogether, our results suggest that the antimicrobial effect of chelerythrine on Xoo exhibits multi-target properties. Additionally, its effective inhibitory concentration is low. These findings provide a crucial theoretical basis and guidance for the development of novel and efficient plant-derived antimicrobial compounds. Full article

Background: Rice bacterial leaf blight, caused by the Gram-negative bacterium Xanthomonas oryzae pv. Oryzae (Xoo), significantly impacts rice production. To address this disease, research efforts have focused on discovering and utilizing novel disease-resistant genes and examining their functional mechanisms. Methods and Results: In this study, a variety of bacterial strains were utilized. CX28-3, AX-11, JC12-2, and X10 were isolated from the high-altitude japonica rice-growing region on the Yunnan Plateau. Additionally, PXO61, PXO86, PXO99, and PXO339, sourced from the International Rice Research Institute (IRRI), were included in the analysis. To evaluate the resistance characteristics of Haonuoyang, artificial leaf cutting and inoculation methods were applied. Results indicated that Haonuoyang exhibited broad-spectrum resistance. Additionally, to explore the genetic mechanisms of resistance, the TFAIII-type transcription factor OsZFPH was cloned from Haonuoyang using PCR amplification. The subcellular localization method identified the precise location of the OsZFPH gene within the cell. The expression of OsZFPH was induced by Xoo stress. The overexpression of OsZFPH resulted in increased activities of enzymes, including SOD, CAT, and POD, while silencing the gene led to reduced enzyme activities. Furthermore, the hormones SA (salicylic acid), JA (jasmonic acid), and GA (gibberellin) were shown to positively regulate the gene expression. Protein interactions with OsZFPH were verified through a yeast two-hybrid system and BiFC technology. Hap5, which aligned with the sequence of Haonuoyang, was found to belong to a haplotype consisting of Jingang 30, 40 resequenced rice varieties, 18 Oryza rufipogon, and 29 Oryza granulata. Conclusions: The findings of this study emphasize the vital role of OsZFPH in rice resistance to bacterial leaf blight. The identification of broad-spectrum resistance in Haonuoyang and the understanding of OsZFPH gene functions provide valuable insights for the future development of rice varieties with improved resistance to this destructive disease. Full article

Polyhydroxyalkanoates (PHAs), synthesized by Xanthomonas to endure adverse conditions, are primarily regulated by the critical genes phaC and phaZ. Poly-3-hydroxybutyrate (PHB), a common polyhydroxyalkanoate (PHA), has been implicated in metabolism, pathogenicity, and various physiological processes in Xanthomonas oryzae pv. oryzae (Xoo). In this study, we investigated the effects of HN-2 using n-butanol extract (HN-2 n-butanol extract) derived from Bacillus velezensis on Xoo. The results showed that HN-2 n-butanol extract could induce PHB accumulation in Xoo, potentially via surfactin. Moreover, examination of drug resistance, pathogenicity, and morphological characteristics of Xoo revealed PHB played a significant role in the drug resistance, pathogenicity, membrane integrity, and growth rate of Xoo strains following the deletion of phaZ and phaC. The ∆phaZ strain was the most significant, with a growth rate reduced to 58.19% of the PXO99^A at 36 h and an inhibition zone 57.46% larger than that of PXO99^A by HN-2 n-butanol extract. Transmission electron microscopy further revealed blank spots in Xoo after treatment, with the fewest spots observed in ∆phaZ, indicating its impaired ability to repair and maintain membrane integrity. These findings offer valuable insights that could serve as a foundation for elucidating the mechanisms of drug resistance and future research on preventing Xoo-induced diseases. Full article

Rice is exposed to attacks by the three most destructive pathogens, Magnaporthe oryzae (M. oryzae), Xanthomonas oryzae pv. oryzae (Xoo), and Rhizoctonia solani (R. solani), which cause substantial yield losses and severely threaten food security. To cope with pathogenic infections, rice has evolved diverse molecular mechanisms to respond to a wide range of pathogens. Among these strategies, plant microRNAs (miRNAs), endogenous single-stranded short non-coding RNA molecules, have emerged as promising candidates in coordinating plant–pathogen interactions. MiRNAs can modulate target gene expression at the post-transcriptional level through mRNA cleavage and/or translational inhibition. In rare instances, they also influence gene expression at the transcriptional level through DNA methylation. In recent years, substantial advancements have been achieved in the investigation of microRNA-mediated molecular mechanisms in rice immunity. Therefore, we attempt to summarize the current advances of immune signaling mechanisms in rice–pathogen interactions that are regulated by osa-miRNAs, including their functions and molecular mechanisms. We also focus on recent findings concerning the role of osa-miRNAs that respond to M. oryzae, Xoo, and R. solani, respectively. These insights enhance our understanding of how the mechanisms of osa-miRNAs mediate rice immunity and may facilitate the development of improved strategies for breeding pathogen-resistant rice varieties. Full article

Xanthomonas oryzae pv. oryzae (Xoo) is the causative agent of rice bacterial blight (RBB), resulting in substantial harvest losses and posing a challenge to maintaining a stable global supply. In this study, Xoo strains isolated from Shaoxing, Quzhou, and Taizhou, where RBB occurred most frequently in Zhejiang Province in 2019, were selected as the subjects of research. Three isolated pathogenic bacteria of ZXooS (from Shaoxing), ZXooQ (from Quzhou), and ZXooT (from Taizhou) were all identified as novel Xoo strains. These novel strains demonstrate greater virulence compared to Zhe173, the previous epidemic Xoo strain from Zhejiang Province. Subsequent genomic sequencing and analysis revealed that there existed significant differences in the genome sequence, especially in effector genes corresponding to some known rice resistance (R) genes between the novel strains and Zhe173. The sequence alignment of avirulent genes (effector genes) indicated that nucleic and amino acid sequences of AvrXa5, AvrXa7, AvrXa10, and AvrXa23 in the novel strains varied prominently from those in Zhe173. Interestingly, it seemed that only the genome of ZXooQ might contain the AvrXa3 gene. In addition, the phylogenetic analysis of 61 Xoo strains revealed that the novel strains were situated in a distinct evolutionary clade separate from Zhe173. These results here suggest that the emergence of novel Xoo strains may lead to resistance loss of some R genes used in commercial rice varieties, potentially serving as one of the factors leading to RBB resurgence in Zhejiang Province, China. Full article

Rice (Oryza sativa) produces phenolamides and diterpenoids as major phytoalexins. Although the biosynthetic pathways of phenolamides and diterpenoids in plants have been revealed, knowledge of their accumulation regulatory mechanisms remains limited, and, in particular, no co-regulatory factor has been identified to date. Here, using a combined co-expression and evolutionary analysis, we identified the basic helix–loop–helix (bHLH) transcription factor OsbHLH5 as a positive bifunctional regulator of phenolamide and diterpenoid biosynthesis in rice. Metabolomic analysis revealed that OsbHLH5 significantly increased the content of phenolamides (such as feruloyl tryptamine (Fer-Trm) and p-coumaroyl tyramine (Cou-Tyr)) and diterpenoid phytoalexins (such as momilactones A, momilactones B) in the overexpression lines, while their content was reduced in the OsbHLH5 knockout lines. Gene expression and dual-luciferase assays revealed that OsbHLH5 activates phenolamide biosynthetic genes (including putrescine hydroxycinnamoyltransferase 3 (OsPHT3), tyramine hydroxycinnamoyltransferases 1/2 (OsTHT1/2), and tryptamine benzoyltransferase 2 (OsTBT2)) as well as diterpenoid biosynthetic genes (including copalyl diphosphate synthase 4 (OsCPS4) and kaurene synthase-like 4/7/10/11 (OsKSL4/7/10/11)). Furthermore, we have demonstrated that OsbHLH5 is induced by jasmonic acid (JA), while pathogen inoculation assays indicated that the overexpression of OsbHLH5 in transgenic rice plants leads to enhanced resistance to Xanthomonas oryzae pv. oryzae (Xoo). Overall, we have identified a positive regulator of phenolamide and diterpenoid biosynthesis and have demonstrated that biotic stress induces phytoalexin accumulation partly in an OsbHLH5-dependent manner, providing new insights into the metabolic interactions involved in pathogen response and offering valuable gene resources for the development, through genetic improvement, of new rice varieties that are resistant to diseases. Full article

Rice is one of the most important staple crops worldwide. However, the bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) poses a major threat to the production of rice. In this study, we isolated and identified the strain Pseudomonas aeruginosa SF416, which exhibited significant antagonistic activity against Xoo, from a soil sample collected in a winter wheat field in Shannanzhalang County, Tibet, China. The bacterial solution (BS) and cell-free supernatant (CFS) of SF416 had significant prevention effects for the bacterial blight of rice, with an efficacy of 45.1% and 34.18%, respectively, while they exhibited a slightly lower therapeutic efficiency of 31.64% and 25.09%. The genomic analysis showed that P. aeruginosa SF416 contains genes involved in cell motility, colonization, cold and hot shock proteins, antibiotic resistance, and plant growth promotion. SF416 also harbors two sets of phenazine-1-carboxylic acid (PCA) synthesis gene clusters, phz1 (phzA1-G1) and phz2 (phzA2-G2), and other phenozine product-synthesis--related genes phzS, phzM, and phzH, as well as genes in the SF416 genome that share high similarity with the ones in the genomes of P. aeruginosa M18, suggesting that the two sets of PCA synthesis gene clusters are responsible for the antagonistic effect of SF416 against Xoo. A comparative antiSMASH analysis revealed that P. aeruginosa SF416 contains 17 gene clusters related to secondary metabolite synthesis, 7 of which, encoding for pyochelin, azetidomonamide A/B, L-2-amino-4-methoxy-trans-3-butenoic acid, hydrogen cyanide, pyocyanine, pseudopaline, and bicyclomycin, are conserved in strains of P. aeruginosa. Moreover, SF416 can produce protease and siderophores and display a broad-spectrum antagonistic activity against various major plant pathogenic bacteria and fungi. The results suggest that P. aeruginosa SF416 could be a potential candidate agent for the bacterial blight of rice. Full article

Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is a major threat to rice production and food security. Exploring new resistance genes and developing varieties with broad-spectrum and high resistance has been a key focus in rice disease resistance research. In a preliminary study, rice cultivar Fan3, exhibiting high resistance to PXO99^A and susceptibility to AH28, was developed by enhancing the resistance of Yuehesimiao (YHSM) to BB. This study performed a transcriptome analysis on the leaves of Fan3 and YHSM following inoculation with Xoo strains AH28 and PXO99^A. The analysis revealed significant differential expression of 14,084 genes. Among the transcription factor (TF) families identified, bHLH, WRKY, and ERF were prominent, with notable differences in the expression of OsWRKY62, OsWRKY76, and OsbHLH6 across samples. Over 100 genes were directly linked to disease resistance, including nearly 30 NBS–LRR family genes. Additionally, 11 SWEET family protein genes, over 750 protein kinase genes, 63 peroxidase genes, and eight phenylalanine aminolysase genes were detected. Gene ontology (GO) analysis showed significant enrichment in pathways related to defense response to bacteria and oxidative stress response. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that differentially expressed genes (DEGs) were enriched in phenylpropanoid biosynthesis and diterpenoid biosynthesis pathways. Gene expression results from qRT-PCR were consistent with those from RNA-Seq, underscoring the reliability of the findings. Candidate genes identified in this study that may be resistant to BB, such as NBS–LRR family genes LOC_Os11g11960 and LOC_Os11g12350, SWEET family genes LOC_Os01g50460 and LOC_Os01g12130, and protein kinase-expressing genes LOC_Os01g66860 and LOC_Os02g57700, will provide a theoretical basis for further experiments. These results suggest that the immune response of rice to the two strains may be more concentrated in the early stage, and there are more up-regulated genes in the immune response of the high-resistant to PXO99A and medium-resistant to AH28, respectively, compared with the highly susceptible rice. This study offers a foundation for further research on resistance genes and the molecular mechanisms in Fan3 and YHSM. Full article