Sequential transphosphorylation of the BRI1/BAK1 receptor kinase complex impacts early events in brassinosteroid signaling.
Brassinosteroids (BRs) regulate plant development through a signal transduction pathway involving the BRI1 and BAK1 transmembrane receptor kinases. The detailed molecular mechanisms of phosphorylation, kinase activation, and oligomerization of the BRI1/BAK1 complex in response to BRs are uncertain. We demonstrate that BR-dependent activation of BRI1 precedes association with BAK1 in ... planta, and that BRI1 positively regulates BAK1 phosphorylation levels in vivo. BRI1 transphosphorylates BAK1 in vitro on specific kinase-domain residues critical for BAK1 function. BAK1 also transphosphorylates BRI1, thereby quantitatively increasing BRI1 kinase activity toward a specific substrate. We propose a sequential transphosphorylation model in which BRI1 controls signaling specificity by direct BR binding followed by substrate phosphorylation. The coreceptor BAK1 is then activated by BRI1-dependent transphosphorylation and subsequently enhances signaling output through reciprocal BRI1 transphosphorylation. This model suggests both conservation and distinct differences between the molecular mechanisms regulating phosphorylation-dependent kinase activation in plant and animal receptor kinases.
Mesh Terms:
Amino Acid Sequence, Arabidopsis, Arabidopsis Proteins, Cholestanols, Chromatography, Liquid, Flagellin, Mass Spectrometry, Models, Biological, Molecular Sequence Data, Mutation, Phosphorylation, Protein Kinases, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Signal Transduction, Steroids, Heterocyclic, Substrate Specificity
Amino Acid Sequence, Arabidopsis, Arabidopsis Proteins, Cholestanols, Chromatography, Liquid, Flagellin, Mass Spectrometry, Models, Biological, Molecular Sequence Data, Mutation, Phosphorylation, Protein Kinases, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Signal Transduction, Steroids, Heterocyclic, Substrate Specificity
Dev. Cell
Date: Aug. 01, 2008
PubMed ID: 18694562
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