BBX21, an Arabidopsis B-box protein, directly activates HY5 and is targeted by COP1 for 26S proteasome-mediated degradation.
BBX21 (also known as SALT TOLERANCE HOMOLOG 2), a B-box (BBX)-containing protein, has been previously identified as a positive regulator of light signaling; however, the precise role of BBX21 in regulating seedling photomorphogenesis remains largely unclear. In this study, we report that CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) interacts with BBX21 in vivo and is able to ubiquitinate BBX21 in vitro. Thus, BBX21 is targeted for 26S proteasome-mediated degradation in dark-grown Arabidopsis seedlings in a COP1-dependent manner. Moreover, we show that BBX21 binds to the T/G-box in the ELONGATED HYPOCOTYL 5 (HY5) promoter and directly activates HY5 expression in the light. Transgenic seedlings overexpressing BBX21 exhibit dramatically shortened hypocotyls in the light, and this phenotype is dependent on a functional HY5. Taken together, our data suggest a molecular base underlying BBX21-mediated seedling photomorphogenesis, indicating that BBX21 is a pivotal component involved in the COP1-HY5 regulatory hub.
['Xu|Dongqing|D|', 'Jiang|Yan|Y|', 'Li|Jigang|J|', 'Lin|Fang|F|', 'Holm|Magnus|M|', 'Deng|Xing Wang|XW|']
D017360:Arabidopsis D029681:Arabidopsis Proteins D050976:Basic-Leucine Zipper Transcription Factors D015870:Gene Expression D018506:Gene Expression Regulation, Plant D008027:Light D009687:Nuclear Proteins D030821:Plants, Genetically Modified D046988:Proteasome Endopeptidase Complex D014157:Transcription Factors D044767:Ubiquitin-Protein Ligases D054875:Ubiquitination
BBX21 Arabidopsis HY5 COP1 photomorphogenesis