Kinase activity and calmodulin binding are essential for growth signaling by the phytosulfokine receptor PSKR1. (5th March 2014)

• Record Type: Journal Article
• Authors: Hartmann, Jens; Fischer, Cornelia; Dietrich, Petra; Sauter, Margret
• Is Part Of: Plant journal. Volume 78:Number 2(2014:Apr.)
• Page Start: 192
• Page End: 202
• Publication Date: 2014-03-05
• Subjects: Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.12460
• Languages: English
• ISSNs: 0960-7412

Abstract

<abstract abstract-type="main" id="tpj12460-abs-0001"> <title>Summary</title> <p>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<sup>2+</sup> sensors and evaluated the contribution of these activities to growth control <italic>in planta</italic>. 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 <italic>pskr</italic> 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 <italic>pskr</italic> null background resulted in growth inhibition that was similar to that of the kinase‐inactive receptor. We conclude that PSK signaling requires Ca<sup>2+</sup>/CaM binding and kinase activity of PSKR1 <italic>in planta</italic>. We further propose that the inactivated kinase interferes with other growth‐promoting signaling pathway(s).</p> </abstract>