Arabidopsis plasma membrane protein crucial for Ca2+ influx and touch sensing in roots

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 Ca2+-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 Mcal) that correlates Ca2+ influx with mechanosensing in Arabidopsis thaliana. MCA1 cDNA was cloned by the functional complementation of lethality of a yeast midl mutant lacking a putative Ca2+-permeable SA channel component. Mcal was localized to the yeast plasma membrane as an integral membrane protein and mediated Ca2+ influx. Mcal also increased [Ca2+](cyt) upon plasma membrane distortion in Arabidopsis. The growth of MCAl-overexpressing plants was impaired in a high-calcium but not a low-calcium medium. The primary roots of mcal-null plants failed to penetrate a harder agar medium from a softer one. These observations demonstrate that Mcall plays a crucial role in a Ca2+-permeable SA channel system that leads to mechanosensing in Arabidopsis. We anticipate our findings to be a starting pointfor a deeper understanding of the molecular mechanisms of mechanotransduction in plants.