Abstract
To investigate the mechanism of mechanosensing in plants, we have isolated MCA1 and MCA2 genes encoding Ca2+-permeable mechanosensitive channel candidates from Arabidopsis thaliana (Nakagawa et al. , PNAS 104:3639-3644, 2007). MCA1 and MCA2 have 73 % identity in amino acid sequence and can complement a low Ca2+ influx activity of the yeast mid1 mutant, although sequence similarity between MCA1/MCA2 and Mid1 is low. We have reported previously that MCA1 is localized in the plasma membrane in Arabidopsis and yeast. MCA1 and MCA2 have an EF-hand-like motif. Here, we performed further molecular characterization of MCA1/MCA2 using yeast. We found that the EF hand-like motif possessed a weak Ca2+ binding activity, as revealed by 45Ca2+ overlay assays. A fraction of MCA2 proteins expressed from a multicopy plasmid in yeast was found to be localized to the plasma membrane. In addition, we confirmed that MCA1 and MCA2 each formed a tetramer with disulfide bonding.