Red Light Triggers Lesion Formation in the sdr7-6 Mutant of Rice.

Lesion mimic mutants are ideal materials for investigating programmed cell death in plants. The rice mutant sdr7-6 exhibits a light-dependent lesion mimic phenotype, but the specific light conditions that trigger necrosis and the underlying molecular mechanisms remain unclear. In this study, we characterized the light-dependent necrotic phenotype of sdr7-6 under red, blue, and far-red light. We found that lesion formation was exclusively triggered by red light and occurred independently of light intensity or photoperiod. Knockout of phyB markedly alleviated lesion development, confirming the role of phyB-mediated red-light signaling in this process. Physiological analyses revealed a significant reduction in photosynthetic capacity in sdr7-6, primarily due to disrupted chloroplast ultrastructure. Consistent with these findings, transcriptome profiling indicated strong downregulation of genes associated with chloroplast function, photosynthesis, and light responses. Together, these results demonstrate that SDR7-6 functions as a previously unrecognized downstream component of phyB-mediated red-light signaling and is involved in red-light-dependent lesion formation in rice, which is tightly associated with compromised chloroplast integrity and function. This work provides new insights into the molecular mechanisms underlying red-light perception and its regulation of lesion formation in rice.