Calcium/calmodulin inhibition of the Arabidopsis BRASSINOSTEROID-INSENSITIVE 1 receptor kinase provides a possible link between calcium and brassinosteroid signalling.
The receptor kinase BRI1 (BRASSINOSTEROID-INSENSITIVE 1) is a key component in BR (brassinosteroid) perception and signal transduction, and has a broad impact on plant growth and development. In the present study, we demonstrate that Arabidopsis CaM (calmodulin) binds to the recombinant cytoplasmic domain of BRI1 in a Ca2+-dependent manner in vitro. In silico analysis predicted binding to Helix E of the BRI1 kinase subdomain VIa and a synthetic peptide based on this sequence interacted with Ca2+/CaM. Co-expression of CaM with the cytoplasmic domain of BRI1 in Escherichia coli strongly reduced autophosphorylation of BRI1, in particular on tyrosine residues, and also reduced the BRI1-mediated transphosphorylation of E. coli proteins on tyrosine, threonine and presumably serine residues. Several isoforms of CaM and CMLs (CaM-like proteins) were more effective (AtCaM6, AtCaM7 and AtCML8, where At is Arabidopsis thaliana) than others (AtCaM2, AtCaM4 and AtCML11) when co-expressed with BRI1 in E. coli. These results establish a novel assay for recombinant BRI1 transphosphorylation activity and collectively uncover a possible new link between Ca2+ and BR signalling.
Department of Plant Biology, University of Illinois, Urbana, IL 61801, USA.
Man-Ho
MH
Oh
Hyoung Seok
HS
Kim
Xia
X
Wu
Steven D
SD
Clouse
Raymond E
RE
Zielinski
Steven C
SC
Huber
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002147:Calmodulin; D020033:Protein Isoforms; D011494:Protein Kinases; C108270:BRI1 protein, Arabidopsis; D002118:Calcium