The Role of OsYUCCA2 in Auxin Synthesis and Promotion of Rice Growth and Development

YUCCA (YUC) proteins are essential for auxin production and play critical roles in plant growth and development. Many of the fourteen rice OsYUCs identified to date have been characterized, but the functions and expression patterns of OsYUC2 remain unclear. In this study, transgenic rice seedlings (Oryza sativa L. ‘Nipponbare’) overexpressing GUS-tagged OsYUC2 under the control of the ubiquitin promoter or the native OsYUC2 promoter were used to investigate OsYUC2 expression and function. OsYUC2 distribution was restricted to rapidly dividing cells in callus, vegetative, and reproductive tissues. OsYUC2 overexpression promoted plant growth, leading to proliferation of embryonic, adventitious, and lateral roots, and increases in shoot height and grain weight. OsYUC2 localization correlated with auxin localization, and auxin content analysis showed that IAA levels were higher in OsYUC2 transgenic rice than in the wild-type. Furthermore, exogenous addition of 3-indolebutyric acid (IBA, an analogue of IAA) in wild-type plants produced growth phenotypes similar to those of OsYUC2 transgenic rice seedlings. Our results indicate that OsYUC2 has distinct expression patterns and regulates major growth and developmental processes in rice.