Kinase activity and calmodulin binding are essential for growth signaling by the phytosulfokine receptor PSKR1.
The cell growth-promoting peptide phytosulfokine (PSK) is perceived by leucine-rich repeat (LRR) receptor kinases. To elucidate PSK receptor function we analyzed PSKR1 kinase activity and binding to Ca(2+) sensors and evaluated the contribution of these activities to growth control in planta. Ectopically expressed PSKR1 was capable of auto- and transphosphorylation. Replacement of a conserved lysine within the ATP-binding region by a glutamate resulted in the inhibition of auto- and transphosphorylation kinase activities. Expression of the kinase-inactive PSKR1(K762E) receptor in the pskr null background did not restore root or shoot growth. Instead, the mutant phenotype was enhanced suggesting that the inactive receptor protein exerts growth-inhibitory activity. Bioinformatic analysis predicted a putative calmodulin (CaM)-binding site within PSKR1 kinase subdomain VIa. Bimolecular fluorescence complementation analysis demonstrated that PSKR1 binds to all isoforms of CaM, more weakly to the CaM-like protein CML8 but apparently not to CML9. Mutation of a conserved tryptophan (W831S) within the predicted CaM-binding site strongly reduced CaM binding. Expression of PSKR1(W831S) in the pskr null background resulted in growth inhibition that was similar to that of the kinase-inactive receptor. We conclude that PSK signaling requires Ca(2+) /CaM binding and kinase activity of PSKR1 in planta. We further propose that the inactivated kinase interferes with other growth-promoting signaling pathway(s).
Entwicklungsbiologie und Physiologie der Pflanzen, Universität Kiel, Am Botanischen Garten 5, Kiel, 24118, Germany.
Jens
J
Hartmann
Cornelia
C
Fischer
Petra
P
Dietrich
Margret
M
Sauter
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D001665:Binding Sites; D002147:Calmodulin / Q000378:metabolism*; D019295:Computational Biology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D020539:Sequence Analysis, Protein; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D002147:Calmodulin; C515018:PSKR1 protein, Arabidopsis; D011956:Receptors, Cell Surface
Arabidopsis thaliana; LRR receptor kinase; calcium; calmodulin; kinase activity; phytosulfokine; root growth