OsTT2, an R2R3-MYB transcription factor, is involved in regulating anthocyanin biosynthesis and grain yield in rice

Black rice contains substantial levels of anthocyanins, a class of bioactive compounds recognized for their health-promoting properties that constitute an important determinant of nutritional and functional quality. In this study, we cloned rice TRANSPARENT TESTA 2 (OsTT2), a regulatory gene for anthocyanin biosynthesis that is located on chromosome 3 with a 331 bp segmental duplication in its promoter region. OsTT2 encodes an R2R3-MYB transcription factor that localizes to the nucleus. Interestingly, OsTT2 significantly influences plant height, panicle length, total grain number per plant, grain length, and grain width. Although no significant differences were detected in the number of panicles per plant or 1000-grain weight, the presence of a functional OsTT2 gene substantially increases overall rice yield. We found that OsTT2 binds to the promoter region of OsMED15a, which activates the OsMED15a-OsNAC024 pathway, thereby modulating grain length and width. Our findings provide new resources and novel approaches for the genetic improvement of rice anthocyanin biosynthesis, quality, and yield.