Natural variation in GNP3 determines grain number and grain yield in rice.

Grain number per panicle critically determines rice yield. Although many underlying genes have been reported, yet the molecular mechanisms linking ethylene to panicle development remain unclear. Here, we identify GRAIN NUMBER PER PANICLE 3 (GNP3) as a regulator of GNP through genome-wide association study (GWAS) combined with map-based cloning. GNP3 encodes a MITOGEN-ACTIVATED PROTEIN KINASE KINASE KINASE 22 (OsMKKK22) that phosphorylates S-adenosyl-L-methionine synthetase 1 (SAMS1), triggering its degradation to suppress ethylene biosynthesis. Ethylene overaccumulation in gnp3-1 mutants reduces grain number, while GNP3 overexpression enhances panicle branching and grain yield by lowering ethylene levels. We demonstrate that a natural haplotype GNP3(Hap-T)prevalent in indica subspecies strengthens GNP3-SAMS1 interaction, accelerating SAMS1 degradation and improving grain number. Furthermore, overexpressing GNP3 increases grain yield by approximately 20% in field plot conditions. Our findings unveil a MAPK-ethylene regulatory module and highlight GNP3(Hap-T) as a valuable genetic resource for breeding high-yield rice.