Latz A, Mehlmer N, Zapf S, Mueller TD, Wurzinger B, Pfister B, Csaszar E, Hedrich R, Teige M, Becker D

14-3-3 proteins play an important role in the regulation of many cellular processes. The Arabidopsis vacuolar two pore K+ channel 1 (TPK1) interacts with the 14-3-3 protein GRF6 (GF14-λ). Upon phosphorylation of the putative binding motif in the N-terminus of TPK1, GRF6 binds to TPK1 and activates the potassium channel. ...

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In order to gain a deeper understanding of this 14-3-3 mediated signal transduction, we set out to identify the respective kinases, which regulate the phosphorylation status of the 14-3-3 binding motif in TPK1. Here we report that the calcium dependent protein kinases (CDPKs) can phosphorylate and thereby activate the 14-3-3 binding motif in TPK1. Focusing on the stress-activated kinase CPK3 we visualised direct and specific interaction of TPK1 with the kinase at the tonoplast in vivo. In line with its proposed role in K(+) homeostasis, TPK1 phosphorylation was found to be induced by salt stress in planta, and both, cpk3 and tpk1 mutants displayed salt sensitive phenotypes. Molecular modelling of the TPK1-CPK3 interaction domain provided mechanistic insights into TPK1 stress regulated phosphorylation responses and pinpointed two arginine residues in the N-terminal 14-3-3 binding motif in TPK1 critical for kinase interaction. Taken together our studies provide evidence for an essential role of the vacuolar potassium channel TPK1 in salt stress adaptation as a target of calcium regulated stress signalling pathways involving Ca2+, Ca2+-dependent kinases and 14 3-3 proteins.

Date: Dec. 19, 2012

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