, a Novel Allele of , Regulates Grain Size in Rice.

Grain size has an important effect on rice yield. Although several key genes that regulate seed size have been reported in rice, their molecular mechanisms remain unclear. In this study, a rice small grain size 2 () mutant was identified, and MutMap resequencing analysis results showed that a 2 bp insertion in the second exon of the gene resulted in a grain length and width lower than those of the wild-type Teqing (TQ). We found that encoded vacuolar acid invertase, a novel allele of , which regulates grain size. GO and KEGG enrichment analyses showed that was involved in endoplasmic reticulum protein synthesis, cysteine and methionine metabolism, and propionic acid metabolism, thereby regulating grain size. An analysis of sugar content in young panicles showed that reduced sucrose, fructose, and starch contents, thus regulating grain size. A haplotype analysis showed that Hap2 of had a longer grain and was widely present in rice varieties. Our results provide a new theoretical basis for the molecular and physiological mechanisms by which regulates grain size.