Functional Analysis of NtMCA1 and NtMCA2 Involved in Ca²⁺ Uptake in Tobacco BY-2 Cells

Abstract

Ca²⁺-permeable mechanosensitive channels are supposed to be involved in mechano-sensing in plants, but their molecular nature is basically unknown. Two candidates for such channels in Arabidopsis, designated as Mca1 and Mca2, have been recently reported. Here, we identified two MCA orthologues in tobacco BY-2 cells, named NtMCA1 and NtMCA2. The NtMca1/2-GFP fusion proteins appeared to be localized in the plasma membrane and were not observed in the vacuolar membrane. NtMCA1/2 complemented the lethal phenotype of the yeast mid1 mutant defective in a putative Ca²⁺-permeable mechanosensitive channel component, suggesting that both proteins have an activity to mediate Ca²⁺ uptake in yeast. Inhibition of growth of BY-2 cells under Ca²⁺ deficiency was significantly alleviated by overexpression of either NtMCA1 or NtMCA2. We will report ⁴⁵Ca²⁺ uptake characteristics of the overexpressors and discuss about possible roles of NtMca1/2 as well as their physiological relevance.