Analysis of phosphorylation of the BRI1/BAK1 complex in arabidopsis reveals amino acid residues critical for receptor formation and activation of BR signaling.
The plasma membrane-localized BRASSINOSTEROID-INSENSITIVE1 (BRI1) and BRI1-ASSOCIATED KINASE1 (BAK1) are a well-known receptor pair involved in brassinosteroids (BR) signaling in Arabidposis. The formation of a receptor complex in response to BRs and the subsequent activation of cytoplasmic domain kinase activity share mechanistic characteristics with animal receptor kinases. Here, we demonstrate that BRI1 and BAK1 are BR-dependently phosphorylated, and that phosphorylated forms of the two proteins persist for different lengths of time. Mutations of either protein abolished phosphorylation of the counterpart protein, implying transphosphorylation of the receptor kinases. To investigate the specific amino acids critical for formation of the receptor complex and activation of BAK1 kinase activity, we expressed several versions of BAK1 in yeast and plants. L32E and L46E substitutions resulted in a loss of binding of BAK1 to BRI1, and threonine T455 was essential for the kinase activity of BAK1 in yeast. Transgenic bri1 mutant plants overexpressing BAK1(L46E) displayed reduced apical dominance and seed development. In addition, transgenic wild type plants overexpressing BAK1(T455A) lost the phosphorylation activity normally exhibited in response to BL, leading to semi-dwarfism. These results suggest that BAK1 is a critical component regulating the duration of BR efficacy, even though it cannot directly bind BRs in plants.
Yun
Hye Sup
HS
Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea.
Bae
Young Hee
YH
Lee
Yun Ji
YJ
Chang
Soo Chul
SC
Kim
Seong-Ki
SK
Li
Jianming
J
Nam
Kyoung Hee
KH
D016960:Agrobacterium tumefaciens / Q000254:growth & development / Q000378:metabolism; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060406:Brassinosteroids; D002462:Cell Membrane / Q000378:metabolism; D002777:Cholestanols / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D010937:Plant Growth Regulators / Q000494:pharmacology*; D030821:Plants, Genetically Modified; D010957:Plasmids; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction; D013260:Steroids, Heterocyclic / Q000494:pharmacology*
D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D010937:Plant Growth Regulators; D013260:Steroids, Heterocyclic; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; C108270:BRI1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; C023623:brassinolide