Molecular characterization of Arabidopsis Ca²⁺-permeable mechanosensitive channel candidates expressed in yeast

Abstract

We have identified MCA1 and MCA2 genes encoding Ca²⁺-permeable mechanosensitive channel candidates from Arabidopsis thaliana. MCA1 and MCA2 are highly homologous in amino acid sequence and involved in Ca²⁺ uptake. Although there are homologs of MCA1 and MCA2 in various plants, their functions are unknown. We reported previously that MCA1 and MCA2 are localized in the yeast plasma membrane. Here, we performed further molecular characterization of MCA1 and MCA2 using yeast. To investigate relationships between the structure and function in Ca²⁺ uptake, we made a series of truncation mutants lacking the N-terminal or C-terminal region of MCA1 and MCA2 and a D/E to A substitution mutant of an EF hand-like motif and introduced these mutants to yeast cells. Ca²⁺ uptake assays indicated that functional mechanism of MCA1 or MCA2 is different. We also demonstrate that MCA2 is localized in the Arabidopsis plasma membrane and that it is an integral plasma membrane protein in yeast cells.