Sequential Transphosphorylation of the BRI1/BAK1 Receptor Kinase Complex Impacts Early Events in Brassinosteroid Signaling

Xiaofeng Wang, Uma Kota, Kai He, Kevin Blackburn, Jia Li, Michael B. Goshe, Steven C. Huber, Steven D. Clouse

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)220-235
Number of pages16
JournalDevelopmental cell
Volume15
Issue number2
DOIs
StatePublished - Aug 12 2008

Keywords

  • SIGNALING

ASJC Scopus subject areas

  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Developmental Biology
  • Cell Biology

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