title: The Brassinosteroid-Activated BRI1 Receptor Kinase Is Switched off by Dephosphorylation Mediated by Cytoplasm-Localized PP2A B' Subunits.
abstract: Brassinosteroid (BR) binding activates the receptor kinase BRI1 by inducing heterodimerization with its co-receptor kinase BAK1; however, the mechanisms that reversibly inactivate BRI1 remain unclear. Here we show that cytoplasm-localized protein phosphatase 2A (PP2A) B' regulatory subunits interact with BRI1 to mediate its dephosphorylation and inactivation. Loss-of-function and overexpression experiments showed that a group of PP2A B' regulatory subunits, represented by B'η, negatively regulate BR signaling by decreasing BRI1 phosphorylation. BR increases the expression levels of these B' subunits, and B'η interacts preferentially with phosphorylated BRI1, suggesting that the dynamics of BR signaling are modulated by the PP2A-mediated feedback inactivation of BRI1. Compared with PP2A B'α and B'β, which promote BR responses by dephosphorylating the downstream transcription factor BZR1, the BRI1-inactivating B' subunits showed similar binding to BRI1 and BZR1 but distinct subcellular localization. Alteration of the nuclear/cytoplasmic localization of the B' subunits revealed that cytoplasmic PP2A dephosphorylates BRI1 and inhibits the BR response, whereas nuclear PP2A dephosphorylates BZR1 and activates the BR response. Our findings not only identify the PP2A regulatory B subunits that mediate the binding and dephosphorylation of BRI1, but also demonstrate that the subcellular localization of PP2A specifies its substrate selection and distinct effects on BR signaling.
authors.affiliation: Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China.
authors.forename: Ruiju
authors.initials: R
authors.lastname: Wang
authors.affiliation: Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Liu
authors.affiliation: Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China.
authors.forename: Min
authors.initials: M
authors.lastname: Yuan
authors.affiliation: Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Oses-Prieto
authors.affiliation: Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China.
authors.forename: Xingbo
authors.initials: X
authors.lastname: Cai
authors.affiliation: Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA.
authors.forename: Alma L
authors.initials: AL
authors.lastname: Burlingame
authors.affiliation: Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA.
authors.forename: Zhi-Yong
authors.initials: ZY
authors.lastname: Wang
authors.affiliation: Hebei Collaboration Innovation Center for Cell Signaling, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Key Laboratory of Molecular and Cellular Biology of Ministry of Education, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China; Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang, Hebei 050024, China. Electronic address: tangwq@mail.hebtu.edu.cn.
authors.forename: Wenqiang
authors.initials: W
authors.lastname: Tang
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D007527:Isoenzymes; D011494:Protein Kinases; D054648:Protein Phosphatase 2; C448985:At4g18710 protein, Arabidopsis; C108270:BRI1 protein, Arabidopsis; C489810:type 2A protein serine-threonine phosphatase 55 kDa B, Arabidopsis
keywords: BRI1 dephophorylation; Brassinosteroid; PP2A; receptor inactivation; signal transduction