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

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Abstract
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 Mca1) that correlates Ca2+influx with mechanosensing inArabidopsis thaliana.MCA1cDNA was cloned by the functional complementation of lethality of a yeastmid1mutant lacking a putative Ca2+-permeable SA channel component. Mca1 was localized to the yeast plasma membrane as an integral membrane protein and mediated Ca2+influx. Mca1 also increased [Ca2+]cytupon plasma membrane distortion inArabidopsis. The growth ofMCA1-overexpressing plants was impaired in a high-calcium but not a low-calcium medium. The primary roots ofmca1-null plants failed to penetrate a harder agar medium from a softer one. These observations demonstrate that Mca1 plays a crucial role in a Ca2+-permeable SA channel system that leads to mechanosensing inArabidopsis. We anticipate our findings to be a starting point for a deeper understanding of the molecular mechanisms of mechanotransduction in plants.