title: Darkness and gulliver2/phyB mutation decrease the abundance of phosphorylated BZR1 to activate brassinosteroid signaling in Arabidopsis.
abstract: Light is essential for plant survival; as such, plants flexibly adjust their growth and development to best harvest light energy. Brassinosteroids (BRs), plant growth-promoting steroid hormones, are essential for this plasticity of development. However, the precise mechanisms underlying BR-mediated growth under different light conditions remain largely unknown. Here, we show that darkness increases the activity of the BR-specific transcription factor, BZR1, by decreasing the phosphorylated (inactive) form of BZR1 in a proteasome-dependent manner. We observed that COP1, a dark-activated ubiquitin ligase, captures and degrades the inactive form of BZR1. In support of this, BZR1 is abundant in the cop1-4 mutant. The removal of phosphorylated BZR1 in darkness increases the ratio of dephosphorylated to phosphorylated forms of BZR1, thus increasing the chance of active homodimers forming between dephosphorylated BZR1 proteins. Furthermore, a transcriptome analysis revealed the identity of genes that are likely to contribute to the differential growth of hypocotyls in light conditions. Transgenic misexpression of three genes under the 35S promoter in light conditions resulted in elongated petioles and hypocotyls. Our results suggest that light conditions directly control BR signaling by modulating BZR1 stability, and consequently by establishing light-dependent patterns of hypocotyl growth in Arabidopsis.
authors.affiliation: School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Korea.
authors.forename: Bokyung
authors.initials: B
authors.lastname: Kim
authors.forename: Yu Jeong
authors.initials: YJ
authors.lastname: Jeong
authors.forename: Claudia
authors.initials: C
authors.lastname: Corvalán
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Seoae
authors.initials: S
authors.lastname: Cho
authors.forename: Taesung
authors.initials: T
authors.lastname: Park
authors.forename: Sunghwa
authors.initials: S
authors.lastname: Choe
mesh_terms: D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D060406:Brassinosteroids / Q000378:metabolism*; D004268:DNA-Binding Proteins; D003624:Darkness; D019281:Dimerization; D018506:Gene Expression Regulation, Plant; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D051939:Phytochrome B / Q000235:genetics; D063245:Plant Development; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases
chemical_list: D029681:Arabidopsis Proteins; C454444:BZR1 protein, Arabidopsis; D060406:Brassinosteroids; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C497952:PHYB protein, Arabidopsis; D051939:Phytochrome B; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases
keywords: Arabidopsis thaliana; brassinazole; brassinosteroids; hypocotyl elongation; photomorphogenesis; proteasome