A novel Ca²⁺-binding protein PCaP2 acts as a signal transducer from Ca²⁺ signaling to the phosphatidylinositol phosphate signaling and is involved in root hair formation

Abstract

We recently found novel plasma membrane associated calcium-binding proteins in Arabidopsis thaliana. One of these proteins, AtPCaP2 was predominantly expressed in root hairs and pollen tubes and interacted with Ca²⁺, phosphatidylinositol phosphates (PIPs) and calmodulin (CaM) (Kato et al. Plant Cell Physiol. 2010). However, its physiological function is unknown.
Here, we investigated the domain in PCaP2 for interaction with PIPs, CaM and Ca²⁺ by using recombinant proteins. The mutant PCaP2 lacking the N-terminal domain with 23 residues bound neither PIPs or CaM and the recombinant peptide of N-terminal domain bound these ligands. Then we prepared transgenic lines, which expressed PCaP2 mutants lacking the N-terminal domain under the control of the root hair specific promoter. Plant lines expressing mutant PCaP2 lacking N-terminal gave swollen root hairs. From the results we propose that PCaP2 acts as a signal transducer of the PIPs signaling mediated by Ca²⁺ signaling and is involved in formation and growth of root hairs.