ObRc regulates seed dormancy through abscisic acid and proanthocyanidin biosynthesis pathway in African rice

Seed dormancy is crucial for plant reproduction, ensuring that germination occurs under favorable environmental conditions. In rice, moderate seed dormancy reduces the risk of pre-harvest sprouting, thereby minimizing yield losses and preserving seed quality. In this study, we cloned the seed dormancy gene ObRc from African wild rice (Oryza barthii) accession W1411. ObRc encodes a basic helix-loop-helix transcription factor. In African cultivated rice (Oryza glaberrima), a 2-bp insertion in the ObRc coding region introduces a premature stop codon, resulting in a loss-of-function allele. We demonstrate that ObRc regulates seed dormancy by modulating zeaxanthin biosynthesis (an abscisic acid [ABA] precursor), thereby influencing endogenous ABA levels. Additionally, ObRc influences seed coat pigmentation by regulating the expression of multiple genes in anthocyanidin biosynthesis, ultimately impacting both seed coat color and permeability. The functional ObRc allele is preserved in the vast majority of African cultivated rice accessions, likely because it confers moderate dormancy, which enhances environmental adaptation in West African climates and contributes to the preservation of seed nutritional value. Elucidating the molecular mechanism of ObRc provides valuable insights for improving PHS resistance and enhancing the nutritional value of rice through breeding.