A positive feedback loop of BBX11-BBX21-HY5 promotes photomorphogenic development in Arabidopsis

Light is an utmost important environmental factor affecting many aspects of plant development. In this study, we report that B-box protein 11 (BBX11) acts as a positive regulator of red light signaling. Loss of BBX11 function mutant seedlings display significantly elongated hypocotyls in both red light and long days, whereas overexpression of BBX11 cause markedly shortened hypocotyls in various light conditions. BBX11 binds to the HY5 promoter to activate its transcription, while both BBX21 and HY5 associate with promoter region of BBX11 and positively regulate its expression. Taken together, our study reveals that a positive feedback regulation consisting of BBX11, BBX21 and HY5 in promoting photomorphogenesis, and thus provides a transcriptional regulatory mechanism in maintaining normal development in response to light in plants.