Journal Article

An Arabidopsis Hydrophilic Ca<sup>2+</sup>-Binding Protein with a PEVK-Rich Domain, PCaP2, is Associated with the Plasma Membrane and Interacts with Calmodulin and Phosphatidylinositol Phosphates

Mariko Kato, Nahoko Nagasaki-Takeuchi, Yuki Ide and Masayoshi Maeshima

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 3, pages 366-379
Published in print March 2010 | ISSN: 0032-0781
Published online January 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq003
An Arabidopsis Hydrophilic Ca2+-Binding Protein with a PEVK-Rich Domain, PCaP2, is Associated with the Plasma Membrane and Interacts with Calmodulin and Phosphatidylinositol Phosphates

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We found a new hydrophilic protein in Arabidopsis thaliana. Real-time PCR demonstrated that the protein was expressed in roots. Histochemical analysis of promoter–β-glucuronidase fusions demonstrated its extensive expression in root hairs. The protein is rich in proline, glutamate, valine and lysine residues (PEVK-rich domain), and bound Ca2+ even in the presence of Mg2+ and K+ when examined by the 45Ca overlay assay. Treatment of seedlings with K+, Mn2+, Zn2+, Na+, ABA and gibberellic acid, and cold and drought stresses enhanced the transcription. Expression of the protein linked to green fluorescent protein in A. thaliana showed its plasma membrane localization and cell-specific expression in the epidermal cells including root hairs and the elongating pollen tubes. Therefore, we named the protein PCaP2 (plasma membrane-associated Ca2+-binding protein-2). The substitution of glycine at position 2 with alanine resulted in cytoplasmic localization of PCaP2. These results and the N-terminal characteristic motif suggest that PCaP2 is N-myristoylated at Gly2. We examined the capacity for binding to phosphatidylinositol phosphates (PtdInsPs), and found that PCaP2 interacts strongly with PtdIns(3,5)P2, PtdIns(4,5)P2 and PtdIns(3,4,5)P3, and weakly with PtdIns(3,4)P2. Furthermore, calmodulin was associated with PCaP2 in a Ca2+-dependent manner, and its association weakened the interaction of PCaP2 with PtdInsPs. These results indicate that PCaP2 is involved in intracellular signaling through interaction with PtdInsPs and calmodulin in growing root hairs. PCaP2 was previously reported as microtubule-associated protein-18. We discuss the physiological roles of PCaP2 in relation to microtubules in cells.

Keywords: Calcium-binding protein; Calmodulin-binding protein; N-myristoylation; Phosphatidylinositol phosphate; Plasma membrane; Root hair

Journal Article.  7680 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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