Overexpression of RCN1 and RCN2, rice Terminal Flower 1/Centroradialis homologs, confers delay of phase transition and altered panicle morphology in rice

TERMINAL FLOWER 1 (TFL1)/CENTRORADIALIS (CEN)-like genes play important roles in determining plant architecture, mainly by controlling the timing of phase transition. To investigate the possibility of similar mechanisms operating in the control of inflorescence architecture in rice, we analysed the functions of RCN1 and RCN2, rice TFL1/CEN homologs. Constitutive overexpression of RCN1 or RCN2 in Arabidopsis caused a late-flowering and highly branching phenotype, indicating that they possess conserved biochemical functions as TFL1. In 35S::RCN1 and 35S::RCN2 transgenic rice plants, the delay of transition to the reproductive phase was observed. The transgenic rice plants exhibited a more branched, denser panicle morphology. Detailed observation of the panicle structure revealed that the phase change from the branch shoot to the floral meristem state was also delayed, leading to the generation of higher-order panicle branches. These results suggest rice has a pathway that can respond to the overexpressed TFL1/CEN-like functions, and the molecular mechanisms controlling the phase transition of meristems are conserved between grass and dicot species, at least to some extent.