Abstract
Cold shock triggers an immediate rise in the cytosolic free calcium concentration ([Ca(2+)](cyt)) in Arabidopsis thaliana and this cold-induced elevation of [Ca(2+)](cyt) is inhibited by lanthanum or EGTA. It is suggested that intracellular calcium mainly contributes to the cold-induced [Ca(2+)](cyt) response by entering into the cytosol. Two calcium-permeable mechanosensitive channels, MCA1 and MCA2 (mid1-complementing activity), have been identified in Arabidopsis. Here, we demonstrate that MCA1 and MCA2 are involved in a cold-induced increase in [Ca(2+)](cyt). The cold-induced [Ca(2+)](cyt) increase in mca1 and mca2 mutants was markedly lower than that in wild types. The mca1 mca2 double mutant exhibited chilling and freezing sensitivity, compared to wild-type plants. Expression of At5g61820, At3g51660, and At4g15490, which are not regulated by the CBF/DREB1s transcription factor, was down-regulated in mca1 mca2. These results suggest that MCA1 and MCA2 are involved in the cold-induced elevation of [Ca(2+)](cyt), cold tolerance, and CBF/DREB1-independent cold signaling.