Is Required for Formation of the Stigma and Style in Rice.

The stigma is the entry point for sexual reproduction in plants, but the mechanisms underlying stigma development are largely unknown. Here, we disrupted putative auxin biosynthetic and signaling genes to evaluate their roles in rice () development. Disruption of the rice () gene completely eliminated the development of stigmas, and overexpression of led to overproliferation of stigmas, suggesting that is a key determinant for stigma development. Interestingly, mutants did not display defects in flower initiation, nor did they develop any pin-like inflorescences, a characteristic phenotype observed in mutants in Arabidopsis () and maize (). We constructed double mutants of and its closest homolog, , yet the double mutants still did not develop any pin-like inflorescences, indicating that either is compensated by additional homologous genes or has different functions in rice compared with in other organisms. We then knocked out one of the () genes, which cause the formation of pin-like inflorescences in Arabidopsis when compromised, in the background. The double mutants developed pin-like inflorescences, which were phenotypically similar to mutants in Arabidopsis and maize, demonstrating that the roles of in inflorescence development are likely masked by redundant partners. This work identified a key determinant for stigma development in rice and revealed a complex picture of the gene in rice development. Furthermore, the stigma-less mutants are potentially useful in producing hybrid rice.