The GSK3-like kinase BIN2 phosphorylates and destabilizes BZR1, a positive regulator of the brassinosteroid signaling pathway in Arabidopsis.
Brassinosteroids (BRs) are a class of steroid hormones essential for normal growth and development in plants. BR signaling involves the cell-surface receptor BRI1, the glycogen synthase kinase-3-like kinase BIN2 as a negative regulator, and nuclear proteins BZR1 and BZR2/BES1 as positive regulators. The interactions among these components remain unclear. Here we report that BRs induce dephosphorylation and accumulation of BZR1 protein. Experiments using a proteasome inhibitor, MG132, suggest that phosphorylation of BZR1 increases its degradation by the proteasome machinery. BIN2 directly interacts with BZR1 in yeast two-hybrid assays, phosphorylates BZR1 in vitro, and negatively regulates BZR1 protein accumulation in vivo. These results strongly suggest that BIN2 phosphorylates BZR1 and targets it for degradation and that BR signaling causes BZR1 dephosphorylation and accumulation by inhibiting BIN2 activity.
He
Jun-Xian
JX
Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA.
Gendron
Joshua M
JM
Yang
Yanli
Y
Li
Jianming
J
Wang
Zhi-Yong
ZY
D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D018506:Gene Expression Regulation, Plant; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D010840:Phytosterols / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics*
D029681:Arabidopsis Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004268:DNA-Binding Proteins; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D009687:Nuclear Proteins; D010840:Phytosterols; D011494:Protein Kinases; C454444:BZR1 protein, Arabidopsis; C448985:At4g18710 protein, Arabidopsis