G1 Interacts with OsMADS1 to Regulate the Development of the Sterile Lemma in Rice

Flower development, as the basis for plant seed development, is principally conserved in angiosperms. At present, a number of genes regulating flower organ differentiation have been identified, and an ABCDE model has also been proposed. In contrast, the mechanism that regulates the development of the sterile lemma remains unclear. In this study, we identified and characterized a rice floral organ mutant, M15, in which the sterile lemma transformed into a lemma-like organ. Positional cloning combined with a complementary experiment demonstrated that the mutant phenotype was restored by LONG STERILE LEMMA1/(G1). G1 was expressed constitutively in various tissues, with the highest expression levels detected in the sterile lemma and young panicle. G1 is a nucleus-localized protein and functions as a homomer. Biochemical assays showed that G1 physically interacted with OsMADS1 both in vitro and in vivo. Interestingly, the expression of G1 in M15 decreased, while the expression level of OsMADS1 increased compared with the wild type. We demonstrate that G1 plays a key role in sterile lemma development through cooperating with OsMADS1. The above results have implications for further research on the molecular mechanisms underlying flower development and may have potential applications in crop improvement strategies.