Primer design in this study.

Grain shape is a critical factor that directly influences rice yield and quality, however, the molecular mechanisms underlying the regulation of grain shape development remains elusive. In this study, we characterized an oval-shaped grain mutant, osg, from the rice radiation mutagenesis mutant library via 60Co-γ ray irradiation. Compared to ZH11, the osg mutant exhibited decreased grain length and thousand-grain weight but increased grain width and thickness, while displaying significantly reduced plant height, tiller number, pollen viability, and seed setting rate. Map-based cloning revealed that OsSRS3, a known regulator of rice grain size and fertility, was identified as the candidate gene for OSG. The loss-of-function mutant in OsSRS3 exhibit abnormal phenotypes similar to that in osg. Comparative transcriptome sequencing of young panicles from ZH11 and osg showed that up-regulated genes were predominantly enriched in pathways related to plant hormone signal transduction and MAPK signaling, whereas down-regulated genes were mostly associated with starch and sucrose metabolism. Further analysis of differentially expressed genes (DEGs) within the pathways revealed that multiple DEGs in osg, such as OsJAZ11, OsUgp1 and OsUgp2, have been functionally characterized, and their mutant phenotypes align with those observed in osg. These findings provide a crucial foundation for elucidating the molecular mechanisms by which the SRS3 gene regulates grain size and fertility in rice.