title: Methylation of a phosphatase specifies dephosphorylation and degradation of activated brassinosteroid receptors.
abstract: 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.
authors.affiliation: Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA. gwu3@wisc.edu
authors.forename: Guang
authors.initials: G
authors.lastname: Wu
authors.forename: Xiuling
authors.initials: X
authors.lastname: Wang
authors.forename: Xianbin
authors.initials: X
authors.lastname: Li
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Marisa S
authors.initials: MS
authors.lastname: Otegui
authors.forename: Joanne
authors.initials: J
authors.lastname: Chory
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D006868:Hydrolysis; D008745:Methylation; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011497:Protein O-Methyltransferase / Q000737:chemistry / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction
chemical_list: D011987:Receptors, Steroid; D011497:Protein O-Methyltransferase; D054648:Protein Phosphatase 2