<i>PINOID</i> Is Required for Formation of the Stigma and Style in Rice

Abstract

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 (<i>Oryza sativa</i>) development. Disruption of the rice <i>PINOID</i> (<i>OsPID</i>) gene completely eliminated the development of stigmas, and overexpression of <i>OsPID</i> led to overproliferation of stigmas, suggesting that <i>OsPID</i> is a key determinant for stigma development. Interestingly, <i>ospid</i> mutants did not display defects in flower initiation, nor did they develop any pin-like inflorescences, a characteristic phenotype observed in <i>pid</i> mutants in Arabidopsis (<i>Arabidopsis thaliana</i>) and maize (<i>Zea mays</i>). We constructed double mutants of <i>OsPID</i> and its closest homolog, <i>OsPIDb</i>, yet the double mutants still did not develop any pin-like inflorescences, indicating that either <i>ospid</i> is compensated by additional homologous genes or <i>OsPID</i> has different functions in rice compared with <i>PID</i> in other organisms. We then knocked out one of the <i>NAKED PINS IN YUC MUTANTS</i> (<i>NPY</i>) genes, which cause the formation of pin-like inflorescences in Arabidopsis when compromised, in the <i>ospid</i> background. The <i>ospid osnpy2</i> double mutants developed pin-like inflorescences, which were phenotypically similar to <i>pid</i> mutants in Arabidopsis and maize, demonstrating that the roles of <i>OsPID</i> 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 <i>PID</i> gene in rice development. Furthermore, the stigma-less <i>ospid</i> mutants are potentially useful in producing hybrid rice.