title: Inhibition of the Arabidopsis bHLH transcription factor by monomerization through abscisic acid-induced phosphorylation.
abstract: We have demonstrated that the Arabidopsis basic helix-loop-helix (bHLH) transcription factor, ABA-responsive kinase substrate 1 (AKS1; also known as FLOWERING BHLH 3, FBH3), enhances K(+) channel expression in guard cells leading to stomatal opening. The expression is suppressed by ABA-induced phosphorylation of AKS1. Here we show that the phosphorylation results in the monomerization of AKS1 multimers and inhibits AKS1 binding to DNA. AKS1 forms homo-multimers which dissociate following phosphorylation. Replacement of a critical amino acid in the bHLH domain inhibited multimer formation and decreased the binding of AKS1 to DNA. The monomerization was elicited via phosphorylation at three serine residues, which is mediated by SNF1-related protein kinase 2.6 (SnRK2.6), in the vicinity of bHLH domain. Furthermore, ABA induced the phosphorylation-dependent release of AKS1 from DNA, thereby suppressing transcriptional activity in vivo. Our results document a mechanism that inhibits gene expression by phosphorylation of a bHLH transcription factor.
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka, 812-8581, Japan.|Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, 464-8602, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, 464-8602, Japan.|Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, 464-8602, Japan.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Kinoshita
authors.affiliation: Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Maidashi, Fukuoka, 812-8582, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsumoto
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka, 812-8581, Japan. kenrcb@kyushu-u.org.
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Shimazaki
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D018744:DNA, Plant / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D010766:Phosphorylation; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D000072417:Protein Domains; D055503:Protein Multimerization
chemical_list: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D018744:DNA, Plant; C000623268:FBH3 protein, Arabidopsis
keywords: Arabidopsis thaliana; abscisic acid; gene expression; protein phosphorylation; transcription factor