title: Multiple mechanism-mediated retention of a defective brassinosteroid receptor in the endoplasmic reticulum of Arabidopsis.
abstract: Endoplasmic reticulum-mediated quality control (ERQC) is a well-studied process in yeast and mammals that retains and disposes misfolded/unassembled polypeptides. By contrast, how plants exert quality control over their secretory proteins is less clear. Here, we report that a mutated brassinosteroid receptor, bri1-5, that carries a Cys69Tyr mutation, is retained in the ER by an overvigilant ERQC system involving three different retention mechanisms. We demonstrate that bri1-5 interacts with two ER chaperones, calnexin and binding protein (BiP), and is degraded by a proteasome-independent endoplasmic reticulum-associated degradation (ERAD). Mutations in components of the calnexin/calreticulin cycle had little effect on the fidelity of the Arabidopsis thaliana ERQC for bri1-5 retention. By contrast, overexpression of bri1-5, treatment with an ERAD inhibitor, RNA interference-mediated BiP silencing, or simultaneous mutations of Cys-69 and its partner Cys-62 can mitigate this quality control, resulting in significant suppression of the bri1-5 phenotype. Thus, bri1-5 is an excellent model protein to investigate plant ERQC/ERAD in a model organism.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, An Arbor, Michigan 48109-1048, USA.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Hong
authors.forename: Hua
authors.initials: H
authors.lastname: Jin
authors.forename: Tzvi
authors.initials: T
authors.lastname: Tzfira
authors.forename: Jianming
authors.initials: J
authors.lastname: Li
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D037281:Calnexin / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D011485:Protein Binding
chemical_list: D029681:Arabidopsis Proteins; D037281:Calnexin