Atypical R2R3-MYB transcription factor FOUR LIPS is a pleiotropic regulator of plant development: from stomatal development to crop architecture

Jie Le, Huichao Liu
Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China

FOUR LIPS (FLP), encoding an atypical R2R3 MYB transcription factor also named MYB124 in Arabidopsis, was first identified in a screen for mutants with defects in stomatal development at decades ago. FLP and its paralog MYB88 function redundantly in regulating the terminal transition of stomatal development, limiting the frequency of guard mother cell division and promoting guard cell differentiation. OsFLP is the only homolog of FLP/MYB88 in the rice genome. OsFLP is required for the correct orientation of guard mother cell division and the responses to stresses. In this study, we demonstrate that OsFLP, as a direct target of OsBZR1, mediates BR signals to lignin deposition during leaf angle formation by directly regulating the transcription of OsPAL4 and OsPAL6. Intriguingly, OsFLP feedback regulated the transcription of OsGSK1 and the phosphorylation status of OsBZR1. In addition, A-to-T substitution within OsFLP R3 helix-turn-helix domain, an equivalent mutation in Osflp-1 mutant plants, affected the binding ability and transcriptional activity of OsFLP. Our results reveal that OsFLP integrates with OsGSK1 and OsBZR1 in BR signaling to maintain an appropriate leaf angle by modulating the lignin deposition in mechanical tissues of the lamina joint.