RESUMEN
To gain insight into the cellular functions of the mid1-complementing activity (MCA) family proteins, encoding putative Ca²âº-permeable mechanosensitive channels, we isolated two MCA homologs of tobacco (Nicotiana tabacum) BY-2 cells, named NtMCA1 and NtMCA2. NtMCA1 and NtMCA2 partially complemented the lethality and Ca²âº uptake defects of yeast mutants lacking mechanosensitive Ca²âº channel components. Furthermore, in yeast cells overexpressing NtMCA1 and NtMCA2, the hypo-osmotic shock-induced Ca²âº influx was enhanced. Overexpression of NtMCA1 or NtMCA2 in BY-2 cells enhanced Ca²âº uptake, and significantly alleviated growth inhibition under Ca²âº limitation. NtMCA1-overexpressing BY-2 cells showed higher sensitivity to hypo-osmotic shock than control cells, and induced the expression of the touch-inducible gene, NtERF4. We found that both NtMCA1-GFP and NtMCA2-GFP were localized at the plasma membrane and its interface with the cell wall, Hechtian strands, and at the cell plate and perinuclear vesicles of dividing cells. NtMCA2 transcript levels fluctuated during the cell cycle and were highest at the G1 phase. These results suggest that NtMCA1 and NtMCA2 play roles in Ca²âº-dependent cell proliferation and mechanical stress-induced gene expression in BY-2 cells, by regulating the Ca²âº influx through the plasma membrane.