RSP Gene Encodes a MED Subunit 33a, Which Is Involved in the Regulation of PCD and Immune Responses

Rice lesion mimic mutants (LMMs) spontaneously form lesion-like symptoms without pathogen infection and are vital for studying plant immune and defense responses. Here, we identified an EMS-mutagenized Nipponbare-derived LMM, russet spots leaf (rsp), exhibiting leaf russet spots and deteriorated agronomic traits with significantly reduced grain yield. These abnormal phenotypes correlate with impaired photosynthetic efficiency, aberrant programmed cell death (PCD) and excessive reactive oxygen species (ROS) accumulation. Moreover, rsp shows enhanced resistance to bacterial blight and rice stripe virus, driven by altered defense-related genes and metabolites. Map-based cloning localized RSP (encoding MED subunit 33a), where a single nucleotide substitution causes its inactivation. This mutation alters plant responses to abiotic stresses and exogenous hormones, likely via disrupting its conserved domain mediating multiple biological processes. Our findings confirm RSP as a pivotal regulator of immune responses and grain yield, laying a theoretical foundation for breeding high-yield, high-quality and disease-resistant rice cultivars.