The Brassinosteroid-Activated BRI1 Receptor Kinase Is Switched off by Dephosphorylation Mediated by Cytoplasm-Localized PP2A B' Subunits.
The Brassinosteroid-Activated BRI1 Receptor Kinase Is Switched off by Dephosphorylation Mediated by Cytoplasm-Localized PP2A B' Subunits.
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DOI：
10.1016/j.molp.2015.10.007
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发表时间：
2016-01
期刊：
影响因子：
27.5
通讯作者：
Ruiju Wang;Mengmeng Liu;Min Yuan;J. Oses-Prieto;X. Cai;Ying Sun;A. Burlingame;Zhi-Yong Wang
中科院分区：
文献类型：
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作者：
Ruiju Wang;Mengmeng Liu;Min Yuan;J. Oses-Prieto;X. Cai;Ying Sun;A. Burlingame;Zhi-Yong Wang
β-胆固醇（BR）结合通过诱导与其辅助受体激酶BAK 1的异源二聚化来激活受体激酶BRI 1;然而，可逆地使BRI 1活化的机制仍不清楚。在这里，我们表明，细胞质定位的蛋白磷酸酶2A（PP 2A）B′调节亚基与BRI 1相互作用，介导其去磷酸化和失活。功能丧失和过表达实验表明，一组PP 2A B′调节亚基，以B′η为代表，通过降低BRI 1磷酸化来负调节BR信号传导。BR增加了这些B′亚基的表达水平，并且B′η优先与磷酸化的BRI 1相互作用，表明BR信号传导的动力学受到PP 2A介导的BRI 1反馈失活的调节。与PP 2A B′α和B′β通过去磷酸化下游转录因子BZR 1来促进BR反应相比，BRI 1失活B′亚基与BRI 1和BZR 1的结合相似，但亚细胞定位不同。B′亚基的核/胞质定位的改变揭示了胞质PP 2A使BRI 1去磷酸化并抑制BR反应，而核PP 2A使BZR 1去磷酸化并激活BR反应。我们的研究结果不仅确定了PP 2A调节B亚基介导的结合和去磷酸化的BRI 1，但也表明，亚细胞定位的PP 2A指定其底物选择和BR信号的不同影响。
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.