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Rhizoctonia solani AG‐1 IA causes a necrotrophic rice disease and is a serious threat to rice production. To date, only a few effectors have been characterized in AG‐1 IA. We previously identified RsIA_CtaG/Cox11 and showed that infiltration of the recombinant protein into rice leaves caused disease‐like symptoms. In the present study, we further characterized the functionality of RsIA_CtaG/Cox11. RsIA_CtaG/Cox11 is an alternative transcript of cytochrome c oxidase copper chaperone Cox11 that starts from the second AUG codon, but contains a functional secretion signal peptide. RNA interference with RsIA_CtaG/Cox11 reduced the pathogenicity of AG‐1 IA towards rice and Nicotiana benthamiana without affecting its fitness or mycelial morphology. Transient expression of the RsIA_CtaG/Cox11‐GFP fusion protein demonstrated the localization of RsIA_CtaG/Cox11 to mitochondria. Agro‐infiltration of RsIA_CtaG/Cox11 into N. benthamiana leaves inhibited cell death by BAX and INF1. In contrast to rice, agro‐infiltration of RsIA_CtaG/Cox11 did not induce cell death in N. benthamiana. However, cell death was observed when it was coinfiltrated with Os_CoxVIIa, which encodes a subunit of cytochrome c oxidase. Os_CoxVIIa appeared to interact with RsIA_CtaG/Cox11. The cell death triggered by coexpression of RsIA_CtaG/Cox11 and Os_CoxVIIa is independent of the leucine‐rich repeat receptor kinases BAK1/SOBIR1 and enhanced the susceptibility of N. benthamiana to AG‐1 IA. Two of the three evolutionarily conserved cysteine residues at positions 25 and 126 of RsIA_CtaG/Cox11 were essential for its immunosuppressive activity, but not for cell death induction. This report suggests that RsIA_CtaG/Cox11 appears to have a dual role in immunosuppression and cell death induction during pathogenesis. RsIA_CtaG/Cox11, a secreted form of Cox11 in Rhizoctonia solani AG‐1 IA, exerts immunosuppressive effects against HR‐inducing factors and induces cell death with rice CoxVIIa in Nicotiana benthamiana leaves.

The necrotrophic fungal pathogen Rhizoctonia solani anastomosis group 3 (AG3‐TB) is a major cause of global tobacco crop yield losses. Secreted proteins produced by filamentous fungi, as important virulence factors, play a core role in the interaction between plants and pathogens. In this study, we identified a secretory protein, RsDN3377, which localised to the intercellular space and induced cell death in Nicotiana benthamiana. Heterologous expression in Escherichia coli coupled with matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry analysis confirmed RsDN3377 possessed deacetylase activity. In addition, RsDN3377 was an essential pathogenicity factor for mycelial development by double‐stranded RNA‐mediated gene silencing. Through yeast two‐hybrid and bimolecular fluorescence complementation assays, we demonstrated that RsDN3377 interacted with the calcium‐binding protein NtCML19. In addition, transgenic Yunyan 87 overexpressing NtCML19 exhibited enhanced resistance to R. solani AG3‐TB infection. Microscale thermophoresis analysis verified the calcium‐binding activity of NtCML19. These lines of evidence indicate that the deacetylase RsDN3377 is secreted by R. solani AG3‐TB, and this protein, critical for promoting fungal mycelial development and pathogenicity, was disrupted by its resistance‐related interaction with NtCML19. The deacetylase RsDN3377 is recognised by the calcium‐binding protein NtCML19, which enhances host resistance against Rhizoctonia solani infection by inducing cell death and reactive oxygen species (ROS) accumulation.

Summary Rice sheath blight (RSB) is an economically significant disease affecting rice yield worldwide. Genetic resistance to RSB is associated with multiple minor genes, with each providing a minor phenotypic effect, but the underlying dominant resistance genes remain unknown. A genome‐wide association study (GWAS) of 259 diverse rice varieties, with genotypes based on a single nucleotide polymorphism (SNP) and haplotype, was conducted to assess their sheath blight reactions at three developmental stages (seedlings, tillering and booting). A total of 653 genes were correlated with sheath blight resistance, of which the disease resistance protein RPM1 (OsRSR1) and protein kinase domain‐containing protein (OsRLCK5) were validated by overexpression and knockdown assays. We further found that the coiled‐coil (CC) domain of OsRSR1 (OsRSR1‐CC) and full‐length OsRLCK5 interacted with serine hydroxymethyltransferase 1 (OsSHM1) and glutaredoxin (OsGRX20), respectively. It was found that OsSHM1, which has a role in the reactive oxygen species (ROS) burst, and OsGRX20 enhanced the antioxidation ability of plants. A regulation model of the new RSB resistance though the glutathione (GSH)‐ascorbic acid (AsA) antioxidant system was therefore revealed. These results enhance our understanding of RSB resistance mechanisms and provide better gene resources for the breeding of disease resistance in rice.

Sheath blight disease of rice caused by the fungal pathogen R. solani AG1‐IA remains a big threat to rice production worldwide. A limited genetic variation in rice for tolerance to this pathogen and little success in understanding how it defeats host defence are major reasons behind it. In this study, we attempted to decode the virulence spectrum of R. solani AG1‐IA in rice using time‐course transcriptome analysis and functional genomics tools. Several stage‐specific and commonly expressed genes were identified. Notably, the shikimate pathway emerged as an important pathway and was implicated in the virulence of R. solani AG1‐IA. Inhibition of the shikimate pathway by glyphosate, a known inhibitor of 5‐enolpyruvylshikimate‐3‐phosphate (EPSP) synthase, reduced the vegetative growth of R. solani AG1‐IA and several other phytopathogens. Our results were complemented by in vitro inhibition studies of RsEPSP synthase using a recombinantly expressed protein. Comparative sequence analysis of RsEPSP synthase with plants and known major phytopathogens revealed a distinct region in RsEPSP synthase. Using Nicothaiana benthamiana as a model system and stable rice transgenic lines, we demonstrated that targeting this distinct region through host‐induced gene silencing (HIGS) compromises the growth and virulence of R. solani AG1‐IA. The study lays a foundation for a deeper understanding of the identified virulence genes and establishes the shikimate pathway as a central target to control phytopathogens.

Streptomyces strain KX852460 having antifungal activity against Rhizoctonia solani AG-3 KX852461 that is the causal agent of target spot disease in tobacco leaf. The aim of the study was to determine the antifungal activity of Streptomyces strain KX852460 extract against R. solani AG-3 and to identify bioactive antifungal compounds produced by strain KX852460. Crude substance was produced by submerged fermentation process from Streptomyces strain KX852460. Various solvent was used to extract the culture filtrate. Among all, ethyl acetate extracted supernatant showed great potency against R. solani AG-3 KX852461. The active fractions were purified by silica gel column chromatography having 52 mm zone of inhibition against R. solani AG-3 KX852461. The purified fractions were identified by gas chromatography–mass spectrometry technique. Twenty-seven compounds were identified and most of the compounds were the derivatives of aromatic compounds. Eicosane (C 20 H 42 ) and dibutyl phthalate (C 16 H 22 O 4 ) were found antifungal compounds in this study. While morphinan, 7,8-didehydro-4,5-epoxy-17-methyl-3,6-bis[(trimethylsilyl)oxy]-, (5.Alpha. 6.Alpha)—(C 23 H 35 NO 3 Si 2 ), cyclononasiloxane, octadecamethyl—(C 18 H 54 O 9 Si 9 ) and benzoic acid, 2,5-bis(trimethylsiloxy) (C 16 H 30 O 4 Si 3 ) were the major compounds with highest peak number. These results suggested that Streptomyces strain KX852460 had good general antifungal activity and might have potential biocontrol antagonist against R. solani AG-3 KX852461 to cure the target spot in tobacco leaf.

Rice sheath blight, caused by , is one of the most devastating diseases for stable rice production in most rice-growing regions of the world. Currently, studies of the molecular mechanism of rice sheath blight resistance are scarce. Here, we used an RNA-seq approach to analyze the gene expression changes induced by the AG1 IA strain of in rice at 12, 24, 36, 48, and 72 h. By comparing the transcriptomes of TeQing (a moderately resistant cultivar) and Lemont (a susceptible cultivar) leaves, variable transcriptional responses under control and infection conditions were revealed. From these data, 4,802 differentially expressed genes (DEGs) were identified. Gene ontology and pathway enrichment analyses suggested that most DEGs and related metabolic pathways in both rice genotypes were common and spanned most biological activities after AG1 IA inoculation. The main difference between the resistant and susceptible plants was a difference in the timing of the response to AG1 IA infection. Photosynthesis, photorespiration, and jasmonic acid and phenylpropanoid metabolism play important roles in disease resistance, and the relative response of disease resistance-related pathways in TeQing leaves was more rapid than that of Lemont leaves at 12 h. Here, the transcription data include the most comprehensive list of genes and pathway candidates induced by AG1 IA that is available for rice and will serve as a resource for future studies into the molecular mechanisms of the responses of rice to AG1 IA.

Sakuranetin (1) is a rice flavanone-type phytoalexin. We have already reported that the metabolites from the detoxification of 1 by Pyricularia oryzae are naringenin (2) and sternbin. In this study, we investigated whether the rice sheath blight fungus Rhizoctonia solani, another major rice pathogen, can detoxify 1. The extract of R. solani suspension culture containing 1 was analyzed by LC-MS to identify the metabolites of 1. Three putative metabolites of 1 were detected in the extract from the R. solani suspension culture 12 h after the addition of 1, and they were identified as 2, sakuranetin-4′-O-β-d-xylopyranoside (3), and naringenin-7-O-β-d-xylopyranoside (4) by NMR, LC-MS/MS, and GC-MS analyses. The accumulation of 2, 3, and 4 reached their maximum levels 9–12 h after the addition of 1, whereas the content of 1 decreased to almost zero within 9 h. The antifungal activities of 3 and 4 against R. solani were negligible, and 2 showed weaker antifungal activity than 1. We concluded that 2, 3, and 4 are metabolites from the detoxification of 1 by R. solani. Xylosylation is a rare and efficient detoxification method for phytoalexins.

Rhizoctonia solani AG1 IA is a harmful necrotrophic fungus responsible for various crop diseases, including maize and rice sheath blight, which can lead to significant production losses. However, the pathogenic mechanisms and the roles of effectors in this pathogen remain poorly understood. In this study, we identified a glycoside hydrolase 16 family gene, RsEG146, from R. solani that was upregulated during its infection of Zea mays leaves. When transiently expressed through agroinfiltration, RsEG146 induced cell death in the leaves of tobacco (Nicotiana tabacum ‘Samsun’). The predicted signal peptide of RsEG146 was essential for its cell death‐inducing activity, while the conserved enzymic active site was not required. The chitin‐binding domain was critical for the cell death‐inducing activity of RsEG146, with Gly47 identified as the key residue. Substitution of Gly47 with aspartate, glutamate, or proline significantly impaired the cell death‐inducing activity of RsEG146. Additionally, transient and heterogeneous expression of RsEG146 enhanced the pathogenicity of Botrytis cinerea on tobacco, and silencing this gene through spray‐induced gene silencing (SIGS) reduced the severity of the disease in maize, indicating that RsEG146 functions as an effector. Furthermore, RsEG146 triggered a plant immune response in tobacco. This study demonstrates that RsEG146 is a potential effector and plays a crucial role in the interactions between R. solani AG1 IA and its host. We identified a glycoside hydrolase 16 family member RsEG146 from Rhizoctonia solani AG1 IA that acts as an effector by inducing Nicotiana tabacum cell death via its chitin‐binding domain.

Background Plant pathogenic isolates of Rhizoctonia solani anastomosis group 1-intraspecific group IA (AG1-IA) infect a wide range of crops causing diseases such as rice sheath blight (ShB). ShB has become a serious disease in rice production worldwide. Additional genome sequences of the rice-infecting R. solani isolates from different geographical regions will facilitate the identification of important pathogenicity-related genes in the fungus. Results Rice-infecting R. solani isolates B2 (USA), ADB (India), WGL (India), and YN-7 (China) were selected for whole-genome sequencing. Single-Molecule Real-Time (SMRT) and Illumina sequencing were used for de novo sequencing of the B2 genome. The genomes of the other three isolates were then sequenced with Illumina technology and assembled using the B2 genome as a reference. The four genomes ranged from 38.9 to 45.0 Mbp in size, contained 9715 to 11,505 protein-coding genes, and shared 5812 conserved orthogroups. The proportion of transposable elements (TEs) and average length of TE sequences in the B2 genome was nearly 3 times and 2 times greater, respectively, than those of ADB, WGL and YN-7. Although 818 to 888 putative secreted proteins were identified in the four isolates, only 30% of them were predicted to be small secreted proteins, which is a smaller proportion than what is usually found in the genomes of cereal necrotrophic fungi. Despite a lack of putative secondary metabolite biosynthesis gene clusters, the rice-infecting R. solani genomes were predicted to contain the most carbohydrate-active enzyme (CAZyme) genes among all 27 fungal genomes used in the comparative analysis. Specifically, extensive enrichment of pectin/homogalacturonan modification genes were found in all four rice-infecting R. solani genomes. Conclusion Four R. solani genomes were sequenced, annotated, and compared to other fungal genomes to identify distinctive genomic features that may contribute to the pathogenicity of rice-infecting R. solani . Our analyses provided evidence that genomic conservation of R. solani genomes among neighboring AGs was more diversified than among AG1-IA isolates and the presence of numerous predicted pectin modification genes in the rice-infecting R. solani genomes that may contribute to the wide host range and virulence of this necrotrophic fungal pathogen.

Rhizoctonia solani virus717 (RhsV717) was isolated from the Rhizoctonia solani (R. solani) AG-2 strain Rhs717. This study isolated a virus designated as Rhizoctonia solani partitivirus BS-5 (RsPV-BS5) from the R. solani AG-3 strain BS-5, the causal agent of tobacco target spot disease. The virus was identified as a strain of RhsV717. Transmission electron microscopy (TEM) images showed that RsPV-BS5 had virus particles with a diameter of approximately 40 nm. Importantly, it can be horizontally transmitted through hyphal anastomosis and vertically transmitted via sexual basidiospores. Furthermore, this study demonstrated that RsPV-BS5 infection significantly impedes mycelial growth and induces hypovirulence in tobacco leaves. Thus, RsPV-BS5 presents a promising avenue for biocontrolling tobacco target spot disease. Transcriptome analysis unveiled differential expression of four genes related to cell wall-degrading enzymes between two isogenic strains, 06-2-15V and 06-2-15. These findings shed light on the molecular mechanism through which RsPV-BS5 reduces host pathogenicity.