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Kinase activity and calmodulin binding are essential for growth signaling by the phytosulfokine receptor PSKR 1
Author(s) -
Hartmann Jens,
Fischer Cornelia,
Dietrich Petra,
Sauter Margret
Publication year - 2014
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12460
Subject(s) - biology , kinase , calmodulin , complementation , signal transduction , microbiology and biotechnology , biochemistry , protein kinase a , protein fragment complementation assay , mutant , enzyme , gene
Summary The cell growth‐promoting peptide phytosulfokine ( PSK ) is perceived by leucine‐rich repeat ( LRR ) receptor kinases. To elucidate PSK receptor function we analyzed PSKR 1 kinase activity and binding to Ca 2+ sensors and evaluated the contribution of these activities to growth control in planta . Ectopically expressed PSKR 1 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 PSKR 1(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 PSKR 1 kinase subdomain VI a. Bimolecular fluorescence complementation analysis demonstrated that PSKR 1 binds to all isoforms of CaM, more weakly to the CaM‐like protein CML 8 but apparently not to CML 9. Mutation of a conserved tryptophan (W831S) within the predicted CaM‐binding site strongly reduced CaM binding. Expression of PSKR 1(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 PSKR 1 in planta . We further propose that the inactivated kinase interferes with other growth‐promoting signaling pathway(s).