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.
State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, School of Advanced Agriculture Sciences and School of Life Sciences, Peking University, Beijing 100871, China;
Dongqing
D
Xu
State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, School of Advanced Agriculture Sciences and School of Life Sciences, Peking University, Beijing 100871, China;
Yan
Y
Jiang
State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China;
Jigang
J
Li
State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, School of Advanced Agriculture Sciences and School of Life Sciences, Peking University, Beijing 100871, China;
Fang
F
Lin
Department of Biological and Environmental Sciences, Gothenburg University, SE-405 30 Gothenburg, Sweden.
Magnus
M
Holm
State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, School of Advanced Agriculture Sciences and School of Life Sciences, Peking University, Beijing 100871, China; deng@pku.edu.cn.
Xing Wang
XW
Deng
D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism*; D015870:Gene Expression / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant; D008027:Light; D009687:Nuclear Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
D029681:Arabidopsis Proteins; C556245:BBX21 protein, Arabidopsis; D050976:Basic-Leucine Zipper Transcription Factors; C109254:HY5 protein, Arabidopsis; D009687:Nuclear Proteins; D014157:Transcription Factors; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
Arabidopsis; BBX21; COP1; HY5; photomorphogenesis