MULTI-FLORET SPIKELET 2, a MYB Transcription Factor, Determines Spikelet Meristem Fate and Floral Organ Identity in Rice

Abstract

An understanding of flower and panicle development is crucial for improving yield and quality in majority of grass crops. In this study, we used mapping-based cloning to identify <i>MULTI</i>-<i>FLORET SPIKELET2</i> (<i>MFS2</i>), which encodes a MYB transcription factor and regulates flower and spikelet development in rice (<i>Oryza sativa</i>). In the <i>mfs2</i> mutant, specification of palea identity was severely disturbed and showed degradation or transformation into a lemma-like organ, and the number of all floral organs was increased to varying degrees. Due to the increase in the number of floral organs and development of extra transformed palea/marginal region of the palea-like organs, some <i>mfs2</i> spikelets had a tendency to produce two florets. These defects implied that the <i>mfs2</i> mutation caused abnormal specification of palea identity and partial loss of spikelet determination. We confirm that <i>MFS2</i> is a transcriptional repressor that shows strong repression activity by means of two typical ethylene-responsive element binding factor-associated amphiphilic motifs, one of which locates at the C terminus and is capable of interaction with three rice TOPLESS and TOPLESS-related proteins. The results indicate that <i>MFS2</i> acts as a repressor that regulates floral organ identities and spikelet meristem determinacy in rice by forming a repression complex with rice TOPLESS and TOPLESS-related proteins.