Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
Sci Signal. 2011 May 10;4(172):ra29. doi: 10.1126/scisignal.2001258.
Internalization of cell surface receptors, followed by either recycling back to the plasma membrane or degradation, is crucial for receptor homeostasis and signaling. The plant brassinosteroid (BR) receptor, BRASSINOSTEROID INSENSITIVE 1 (BRI1), undergoes constitutive cycling between the plasma membrane and the internal membranes. We show that protein phosphatase 2A (PP2A) dephosphorylated BRI1 and that Arabidopsis thaliana rcn1, a mutant for a PP2A subunit, caused an increase in BRI1 abundance and BR signaling. We report the identification, in A. thaliana, of a suppressor of bri1, sbi1, which caused selective accumulation of BR-activated BRI1, but not the BR co-receptor BAK1 (BRI1-ASSOCIATED KINASE 1), in the membranous compartment. SBI1 mRNA was induced by BRs, and SBI1 encodes a leucine carboxylmethyltransferase (LCMT) that methylated PP2A and controlled its membrane-associated subcellular localization. We propose that BRs increase production of SBI1, which methylates PP2A, thus facilitating its association with activated BRI1. This leads to receptor dephosphorylation and degradation, and thus to the termination of BR signaling.
细胞表面受体的内化，随后要么循环回到质膜，要么降解，对于受体的稳态和信号转导至关重要。植物油菜素甾体（BR）受体 BRASSINOSTEROID INSENSITIVE 1（BRI1）在质膜和内膜之间持续循环。我们表明蛋白磷酸酶 2A（PP2A）去磷酸化 BRI1，并且拟南芥 rcn1，一个 PP2A 亚基的突变体，导致 BRI1 丰度增加和 BR 信号转导增加。我们报告了在拟南芥中鉴定出 bri1 的一个抑制物 sbi1，它导致 BR 激活的 BRI1选择性积累，但 BR 共受体 BAK1（BRI1-ASSOCIATED KINASE 1）不在膜区室中积累。SBI1 mRNA 被 BR 诱导，并且 SBI1 编码一种亮氨酸羧甲基转移酶（LCMT），它甲基化 PP2A 并控制其与质膜相关的亚细胞定位。我们提出 BR 增加 SBI1 的产生，SBI1 甲基化 PP2A，从而促进其与激活的 BRI1 结合。这导致受体去磷酸化和降解，从而终止 BR 信号转导。
