Natural variation in OsMYB305 downregulating cytokinin-mediated inhibition of leaf senescence contributes to regional adaptation in rice.

Accumulating evidence has identified transcription factors (TFs) as key regulators of the onset and progression of leaf senescence. However, the regulatory role of the rice myeloblastosis (MYB) TF OsMYB305 in this process remains largely unknown. CRISPR/Cas9-mediated osmyb305 knockout mutants were used to examine senescence phenotypes. Protein-DNA interactions were analyzed using in vivo and in vitro binding assays and predicted using AlphaFold. Natural variations in OsMYB305 were investigated using the International Rice Genebank Collection Information System database. osmyb305 mutants exhibited delayed leaf senescence under both natural and dark-induced senescence conditions. OsMYB305 TF downregulated adenosine phosphate-isopentenyltransferase 8 (OsIPT8) and upregulated cytokinin oxidase/dehydrogenase 2 (OsCKX2) by directly binding to their promoters, thereby modulating cytokinin homeostasis during leaf senescence. Natural single-nucleotide polymorphisms (SNPs) in OsMYB305 were associated with phenotypic variation in leaf senescence among 3000 rice accessions, and a SNP in the cis-element of OsIPT8 promoter disrupted OsMYB305 binding affinity. These results identify OsMYB305 as a key transcriptional activator inducing leaf senescence and suggest that natural allelic variation in OsMYB305 contributes to regional adaptation in rice cultivation.