Rice OsRDR1 and OsSGS3b enhance defense against viral, bacterial, and fungal infections

RNA-dependent RNA polymerase 1 (RDR1) and Suppressor of Gene Silencing 3 (SGS3) are central components of RNA silencing in plants. Here, we investigated the rice homologs of the genes OsRDR1 and OsSGS3b to determine their roles in defense against viral, bacterial, and fungal pathogens in rice. Tos17 retrotransposon insertion rice mutant lines were used to generate single mutant lines (Osrdr1 and Ossgs3b), and a double mutant line (Osrdr1/Ossgs3b) was created through crossing. In addition, overexpressed (oe) lines of OsRDR1 and OsSGS3b were developed (OsRDR1oe and OsSGS3boe). These lines were inoculated with Cucumovirus cucumber mosaic virus (CMV), Bymovirus rice necrosis mosaic virus (RNMV), Xanthomonas oryzae pv. Oryzae (XO) and Magnaporthe oryzae (MO), respectively. Among all lines tested, the double mutant showed the highest susceptibility to all pathogens, while single mutants were more susceptible than the wild type. Microarray analysis of the mutant lines revealed downregulation of defense-related and signaling pathway genes. Together, these findings demonstrate that OsRDR1 and OsSGS3b positively regulate broad-spectrum disease resistance in rice, highlighting the contribution of RNA silencing not only to antiviral defense but also to antibacterial and antifungal immunity.