Plants can sense and respond to mechanical stimuli, like animals. An early mechanism of mechanosensing and response is speculated to be governed by as-yet-unidentified sensory complexes containing a Ca 2؉ -permeable, stretch-activated (SA) channel. However, the components or regulators of such complexes are poorly understood at the molecular level in plants. Here, we report the molecular identification of a plasma membrane protein (designated Mca1) that correlates Ca 2؉ influx with mechanosensing in Arabidopsis thaliana. MCA1 cDNA was cloned by the functional complementation of lethality of a yeast mid1 mutant lacking a putative Ca 2؉ -permeable SA channel component. Mca1 was localized to the yeast plasma membrane as an integral membrane protein and mediated Ca 2؉ influx. Mca1 also increased [Ca 2؉ ]cyt upon plasma membrane distortion in Arabidopsis. The growth of MCA1-overexpressing plants was impaired in a high-calcium but not a low-calcium medium. The primary roots of mca1-null plants failed to penetrate a harder agar medium from a softer one. These observations demonstrate that Mca1 plays a crucial role in a Ca 2؉ -permeable SA channel system that leads to mechanosensing in Arabidopsis. We anticipate our findings to be a starting point for a deeper understanding of the molecular mechanisms of mechanotransduction in plants.calcium ͉ calcium channel ͉ calcium uptake ͉ mechanosensing

By establishing a unique screening method, we have isolated yeast mutants that die only after differentiating into cells with a mating projection, and some of them are also defective in Ca2+ signaling. The mutants were classified into five complementation groups, one of which we studied extensively. This mutation defines a new gene, designated MIDI, which encodes an N-glycosylated, integral plasma membrane protein with 548 amino acid residues. The mid)-) mutant has low Ca21 uptake activity, loses viability after receiving mating pheromones, and escapes death when incubated with high concentrations of CaCl2. The MID) gene is nonessential for vegetative growth. The efficiency of mating between AL4Ta mid)-) and MATa mid)-) cells is low. These results demonstrate that MID) is required for Ca2+ influx and mating.