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Two putative BIN2 substrates are nuclear components of brassinosteroid signaling
Jun Zhao1, Peng Peng, Robert J Schmitz
1Department of Molecular and Cell Biology, University of Michigan, Ann Arbor 48109-1048, USA.
Plant Physiology
|November 13, 2002
Summary
Glycogen synthase kinase 3 (GSK3)-like kinase BIN2 negatively regulates brassinosteroid (BR) signaling by phosphorylating BES1 and BZR1. These nuclear proteins are key components of BR signaling, with BIN2 controlling their activity through phosphorylation.
Area of Science:
- Plant molecular biology
- Cell signaling
- Biochemistry
Background:
- Glycogen synthase kinase 3 (GSK3) is a conserved kinase regulating cellular processes via protein phosphorylation.
- In Arabidopsis, BIN2, a GSK3-like kinase, acts as a negative regulator of brassinosteroid (BR) signaling.
- BR signaling involves the receptor kinase BRI1, which is proposed to inactivate BIN2.
Purpose of the Study:
- To identify downstream targets of BIN2 in BR signaling.
- To elucidate the mechanism by which BIN2 regulates BR signaling components.
- To characterize the roles of BES1 and BZR1 in BR signaling.
Main Methods:
- Yeast two-hybrid screening to identify BIN2 interacting proteins.
- In vitro kinase assays to assess BIN2 phosphorylation of substrates.
- Genetic analysis of Arabidopsis mutants (bes1, bzr1, bin2, bri1).
- Confocal microscopy for protein localization studies.
Main Results:
- BES1 and BZR1 were identified as direct substrates of BIN2, interacting with it in yeast.
- BIN2 phosphorylates BES1 and BZR1 in vitro via a novel mechanism.
- Mutations in BES1/BZR1 can suppress bri1 mutations, indicating their role in BR signaling.
- BES1 and BZR1 proteins are localized to the nucleus.
Conclusions:
- BES1 and BZR1 are nuclear components of the BR signaling pathway.
- BIN2 negatively regulates BES1/BZR1 activity through phosphorylation.
- This phosphorylation-dependent mechanism is crucial for BR signal transduction in plants.