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 (sms2) mutant was identified, and MutMap resequencing analysis results showed that a 2 bp insertion in the second exon of the LOC_Os02g01590 gene resulted in a grain length and width lower than those of the wild-type Teqing (TQ). We found that SMS2 encoded vacuolar acid invertase, a novel allele of OsINV3, which regulates grain size. GO and KEGG enrichment analyses showed that SMS2 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 SMS2 reduced sucrose, fructose, and starch contents, thus regulating grain size. A haplotype analysis showed that Hap2 of SMS2 had a longer grain and was widely present in indica rice varieties. Our results provide a new theoretical basis for the molecular and physiological mechanisms by which SMS2 regulates grain size.

The DA1-like gene family plays a crucial role in regulating seed and organ size in plants. The DA1 gene family has been identified in several species but has not yet been reported in sweet potatoes. In this study, nine, eleven, and seven DA1s were identified in cultivated sweet potato (Ipomoea batatas, 2n = 6x = 90) and its two diploid wild relatives, I. trifida (2n = 2x = 30) and I. triloba (2n = 2x = 30), respectively. The DA1 genes were classified into three subgroups based on their phylogenetic relationships with Arabidopsis thaliana and Oryza sativa (rice). Their protein physiological properties, chromosomal localization, phylogenetic relationships, gene structure, promoter cis-elements, and expression patterns were systematically analyzed. The qRT-PCR results showed that the expression levels of four genes, IbDA1-1, IbDA1-3, IbDA1-6, and IbDA1-7, were higher in the sweet potato leaves than in the roots, fiber roots, and stems. In our study, we provide a comprehensive comparison and further the knowledge of DA1-like genes in sweet potatoes, and provide a theoretical basis for functional studies.