Formation of two florets within a single spikelet in the rice tongari-boushi1 mutant.

Communication between the meristem and lateral organs plays important roles in plant development. The TONGARI-BOUSHI1 (TOB1) gene that encodes a YABBY transcription factor is involved in the regulation of meristem maintenance and fate determination of the meristem in rice spikelets. TOB1 is likely to act non-cell autonomously on the meristem, because as this gene is expressed in the lateral organ primordia but not in the meristem. Mutation in of the TOB1 gene results in pleiotropic phenotypes in the spikelet, such as abnormal morphology, formation of the two florets and premature termination of the meristem. Among these phenotypes, the formation of the two florets within a single spikelet is very unique, because one -floret per spikelet is a characteristics of the spikelet of the Oryza genus and is strictly regulated. Here, we describes the phenotype of the two-floret type spikelets and discuss the formation of this type of the spikelet in relation to the regulation of the meristem.