Autoregulation and homodimerization are involved in the activation of the plant steroid receptor BRI1

Dev Cell. 2005 Jun;8(6):855-65. doi: 10.1016/j.devcel.2005.05.001.


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

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / metabolism*
  • Blotting, Western / methods
  • Cell Membrane / metabolism
  • Dose-Response Relationship, Drug
  • Enzyme Inhibitors / pharmacology
  • Gene Expression Regulation, Plant / drug effects
  • Gene Expression Regulation, Plant / physiology
  • Green Fluorescent Proteins / metabolism
  • Homeostasis / physiology*
  • Immunoprecipitation / methods
  • In Vitro Techniques
  • Models, Biological
  • Mutagenesis / physiology
  • Mutation
  • Oligopeptides
  • Peptide Mapping / methods
  • Peptides / metabolism
  • Phenotype
  • Phosphorylation
  • Plant Growth Regulators / physiology*
  • Plants, Genetically Modified
  • Protein Kinases / chemistry
  • Protein Kinases / metabolism*
  • Protein Structure, Tertiary
  • Sequence Homology, Amino Acid
  • Steroids, Heterocyclic / chemistry
  • Steroids, Heterocyclic / metabolism*


  • Arabidopsis Proteins
  • Enzyme Inhibitors
  • Oligopeptides
  • Peptides
  • Plant Growth Regulators
  • Steroids, Heterocyclic
  • Green Fluorescent Proteins
  • FLAG peptide
  • Protein Kinases
  • BRI1 protein, Arabidopsis