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Mol Cell. 2017 Jun 1;66(5):648-657.e4. doi: 10.1016/j.molcel.2017.05.012.

The F-box Protein KIB1 Mediates Brassinosteroid-Induced Inactivation and Degradation of GSK3-like Kinases in Arabidopsis.

Author information

1
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA.
2
Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; Institute of Horticulture, Shanxi Academy of Agriculture Sciences, Taiyuan 030031, China.
3
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA; Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
4
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA; Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 61186, South Korea.
5
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA.
6
Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA. Electronic address: zywang24@stanford.edu.

Abstract

The glycogen synthase kinase-3 (GSK3) family kinases are central cellular regulators highly conserved in all eukaryotes. In Arabidopsis, the GSK3-like kinase BIN2 phosphorylates a range of proteins to control broad developmental processes, and BIN2 is degraded through unknown mechanism upon receptor kinase-mediated brassinosteroid (BR) signaling. Here we identify KIB1 as an F-box E3 ubiquitin ligase that promotes the degradation of BIN2 while blocking its substrate access. Loss-of-function mutations of KIB1 and its homologs abolished BR-induced BIN2 degradation and caused severe BR-insensitive phenotypes. KIB1 directly interacted with BIN2 in a BR-dependent manner and promoted BIN2 ubiquitination in vitro. Expression of an F-box-truncated KIB1 caused BIN2 accumulation but dephosphorylation of its substrate BZR1 and activation of BR responses because KIB1 blocked BIN2 binding to BZR1. Our study demonstrates that KIB1 plays an essential role in BR signaling by inhibiting BIN2 through dual mechanisms of blocking substrate access and promoting degradation.

KEYWORDS:

Arabidopsis; BIN2; E3 ubiquitin ligase; F-box protein; GSK3; GSK3 degradation; brassinosteroid; proteasome; steroid hormone; ubiquitination

PMID:
28575660
PMCID:
PMC5935450
DOI:
10.1016/j.molcel.2017.05.012
[Indexed for MEDLINE]
Free PMC Article

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