Abstract
The leucine-rich-repeat receptor serine/threonine kinase, BRI1, is a cell-surface receptor for brassinosteroids (BRs), the steroid hormones of plants, yet its activation mechanism is unknown. Here, we report a unique autoregulatory mechanism of BRI1 activation. Removal of BRI1's C terminus leads to a hypersensitive receptor, indicated by suppression of dwarfism of BR-deficient and BR-perception mutants and by enhanced BR signaling as a result of elevated phosphorylation of BRI1. Several sites in the C-terminal region can be phosphorylated in vitro, and transgenic Arabidopsis expressing BRI1 mutated at these sites demonstrates an essential role of phosphorylation in BRI1 activation. BRI1 is a ligand-independent homo-oligomer, as evidenced by the transphosphorylation of BRI1 kinase in vitro, the dominant-negative effect of a kinase-inactive BRI1 in transgenic Arabidopsis, and coimmunoprecipitation experiments. Our results support a BRI1-activation model that involves inhibition of kinase activity by its C-terminal domain, which is relieved upon ligand binding to the extracellular domain.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Amino Acid Sequence
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Arabidopsis / genetics
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Arabidopsis / metabolism*
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Arabidopsis Proteins / chemistry
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Arabidopsis Proteins / metabolism*
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Blotting, Western / methods
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Cell Membrane / metabolism
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Dose-Response Relationship, Drug
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Enzyme Inhibitors / pharmacology
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Gene Expression Regulation, Plant / drug effects
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Gene Expression Regulation, Plant / physiology
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Green Fluorescent Proteins / metabolism
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Homeostasis / physiology*
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Immunoprecipitation / methods
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In Vitro Techniques
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Models, Biological
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Mutagenesis / physiology
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Mutation
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Oligopeptides
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Peptide Mapping / methods
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Peptides / metabolism
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Phenotype
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Phosphorylation
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Plant Growth Regulators / physiology*
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Plants, Genetically Modified
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Protein Kinases / chemistry
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Protein Kinases / metabolism*
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Protein Structure, Tertiary
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Sequence Homology, Amino Acid
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Steroids, Heterocyclic / chemistry
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Steroids, Heterocyclic / metabolism*
Substances
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Arabidopsis Proteins
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Enzyme Inhibitors
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Oligopeptides
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Peptides
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Plant Growth Regulators
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Steroids, Heterocyclic
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Green Fluorescent Proteins
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FLAG peptide
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Protein Kinases
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BRI1 protein, Arabidopsis