Calcium/calmodulin inhibition of the Arabidopsis BRASSINOSTEROID-INSENSITIVE 1 receptor kinase provides a possible link between calcium and brassinosteroid signalling

Abstract

<jats:p>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.</jats:p>

Teaching an Old Hormone New Tricks: Cytosolic Ca2+ Elevation Involvement in Plant Brassinosteroid Signal Transduction Cascades

“…The exciting work of Oh et al (2012) also demonstrated that coexpression of CaM with the cytosolic kinase domain of BRI1 in a heterologous system (E. coli) resulted in an impairment of BRI1 autophosphorylation and transphosphorylation (in this case, of E. coli proteins). This work raises the intriguing possibility that elevation of cytosolic Ca 2+ might act, through Ca…”

“…However, a recent report has demonstrated a physical and functional interaction between BRI1 and the Ca 2+ -binding protein CaM. Oh et al (2012) have shown that Arabidopsis CaM7 displays Ca…”

“…In this manner, microdomains may exist where the localized concentration of a cytosolic messenger molecule (such as cyclic nucleotide) is elevated in proximity to the channel that is activated by the molecule. When the recent work of Oh et al (2012) is considered along with the results presented here, the notion of a multienzyme microdomain could provide an explanation for how BRI1, the Ca 2+ -conducting CNGC, and CaM act in concert to initiate a finely regulated signal. It is germane to note that in animal cells, CNGCs as well as enzymes that activate the channels and receptors are envisioned to operate as multimolecular complexes existing as membrane "signalosomes" (Trudeau and Zagotta, 2003;Wang and Malbon, 2011;Bankston et al, 2012;Ostrom et al, 2012).…”

Recent Advances in Calcium/Calmodulin-Mediated Signaling with an Emphasis on Plant-Microbe Interactions

“…-mediated signals could regulate a broad range of physiological activities related to plant growth, development, and responses to environmental stimuli (Zhang et al, 2002;Vanoosthuyse et al, 2003;Charpenteau et al, 2004;Hua et al, 2004;Liu et al, 2008;Kim et al, 2009a;Yang et al, 2010;Oh et al, 2012). Among all these CaM-regulated kinases, CCaMK has been widely studied because of its role in symbioses, developmental processes, and stress responses.…”

“…Some RLKs from plants contain only a kinase domain and thus are named receptor-like cytoplasmic kinases. Some receptor-like cytoplasmic kinases, such as CRCK1 and homologs (Yang et al, 2004), and RLKs, such as SRK, CaM-binding receptor-like kinase, AtCaMRLK, AtCRLK1, and BRI1, are CaM-binding proteins (Vanoosthuyse et al, 2003;Charpenteau et al, 2004;Kim et al, 2009a;DeFalco et al, 2010b;Yang et al, 2010;Oh et al, 2012). Last but not least, some of the mitogen-activated protein kinases (MAPKs), specifically members of Moon et al (2005) subgroup D of MAPK in Arabidopsis and rice (Oryza sativa), were reported to be regulated by Ca 2+ /CaM (Ding et al, 2009;Takahashi et al, 2011).…”