Jacalin-related lectins play crucial roles in plant adaptation to abiotic and biotic stresses. The rice genome encodes four putative jacalin-related lectin kinase genes (OsJacLKs), but their functions toward environmental stresses remain largely uncharacterized. This study demonstrates that a putative jacalin-related lectin kinase, OsJacLK1, conferred resistance to the rice blast fungus Magnaporthe oryzae rather than salt stress. OsJacLK1 protein exhibited agglutination activities and affinity toward chitin, fungal cell wall, and mannose. OsJacLK1 was transcriptionally activated by stress-related phytohormones salicylic acid (SA), methyl jasmonate (MeJA), abscisic acid (ABA), and indoleacetic acid (IAA), as well as salinity, chitin, and M. oryzae inoculation, suggesting its involvement in broad stress-responsive signaling pathways. Overexpression of OsJacLK1 in rice led to reduced susceptibility to rice blast disease, whereas loss-of-function osjaclk1 lines showed no significant phenotypic difference from wild-type plants upon infection. Enhanced resistance in OsJacLK1-overexpressing lines was associated with a stronger reactive oxygen species (ROS) burst and elevated hydrogen peroxide accumulation, accompanied by the up-regulation of defense-related genes (OsRac1, OsSGT1, OsMAPK6, OsPAL1, OsNAC4, OsPBZ1, OsAOS2, and OsJAZ8). Collectively, our findings establish that OsJacLK1 acts as a positive regulator of rice immunity against M. oryzae, modulating the cellular redox state, highlighting its potential as a candidate for genetic improvement of disease resistance in rice.

Rice (Oryza sativa L.) production is severely threatened by rice blast disease caused by the hemibiotrophic fungus Magnaporthe oryzae. Chemical fungicides, although effective, cause environmental pollution, disrupt soil microbiomes, and select for resistant pathogen populations, creating an urgent need for sustainable alternatives. In this study, we isolated Kitasatospora hibisci strain 21007 from mangrove soil and evaluated its biocontrol potential through integrated phenotypic and transcriptomic analyses. The cell-free culture filtrate (CFCF) extract showed potent antifungal activity, inhibiting M. oryzae mycelial growth and suppressing conidial germination as well as appressorium formation in a concentration-dependent manner via antibiosis. Fermentation optimization identified Gauze’s Synthetic Medium No. 1 as optimal for metabolite production. Both inoculation of M. oryzae spores with 21007 CFCF extract and pre-treatment of rice seedlings with 21007 CFCF significantly reduced disease severity under greenhouse conditions. Transcriptomic analysis revealed extensive reprogramming of gene expression in leaves of rice seedlings cultured with 21007 CFCF extract. KEGG pathway enrichment analysis indicated activation of the plant–pathogen interaction and MAPK signaling pathways in rice seedlings cultured with 5% and 10% CFCF extract, suggesting that 21007 CFCF induces host defense signaling. These results support the potential of K. hibisci 21007 as a candidate for sustainable biocontrol of rice blast disease and establish a foundation for future metabolomic and genomic investigations.