Proteomic profiling of defense/resistant genes induced during the tripartite interaction of Oryza sativa, Rhizoctonia solani AG1-1A, and Bacillus subtilis against rice sheath blight

Rice is affected by many diseases, among which sheath blight incited by Rhizoctonia solani causes substantial loss to the crop worldwide. The present investigation aims to assess the efficacy of Bacillus subtilis strain EBPBS4 against rice sheath blight and to delineate the mechanism of resistance through a proteomic approach. Eighty endophytic Bacillus isolates were screened for the antagonistic activity against rice sheath blight disease. Among them, Bacillus subtilis isolate EBPBS4, displayed highest antagonistic activity, possessed 13 antimicrobial peptide genes viz., iturin A, iturin D, iturin C, surfactin, bacilysin, fengycin, ericin, mycosubtilin, subtilosin, mersacidin, and plant growth promoting genes. Sequential application of the endospore-based liquid formulation of Bacillus subtilis, EBPBS4 as seed treatment + seedling dip + soil application + foliar spray reduced sheath blight severity significantly when compared to control under in vivo. Unraveling the molecular mechanism of resistance through 2D-PAGE-MALDI-TOF Mass spectrometry (MS) analysis revealed a total of 15 defense/resistant proteins viz., beta-1,3-glucanase, ascorbate peroxidases, PAL, chitinase, putative disease resistance protein RGA1, NBS-LRR L type lectin-domain containing receptor kinase, serine threonine protein kinase, and HSP20-like chaperone domain containing protein which are found to be differentially regulated when there is a tripartite interaction of host, pathogen and biocontrol agent. Thus endospore-based bioformulation of B. subtilis EBPBS4 was found to induce the expression of defense/resistance genes in plants and thus can be commercially exploited for the management of sheath blight of rice.