Isolation and functional characterization of an Arabidopsis cDNA encoding a putative Ca²⁺-permeable stretch-activated channel

Abstract

Stretch-activated (SA) channels are thought to be a candidate for sensors of mechanical stimuli. We isolated an Arabidopsis cDNA by functional complementation of yeast mutant defective in the MID1 gene encoding a putative Ca²⁺-permeable SA channel component. To investigate functions of the cDNA (named AtMID1A), we made transgenic plants overexpressing AtMID1A. The transgenic plants showed a dwarf phenotype. Increases in Ca²⁺ concentration in medium aggravated this phenotype, whereas decreases in Ca²⁺ concentration alleviated it. Hypotonic shock increased cytosolic free Ca²⁺ concentration ([Ca²⁺] _cyt) higher in the transgenic plants than in control plants, as monitored with aequorin. The [Ca²⁺]_cyt increase was inhibited by cation channel blockers and a Ca²⁺ chelator. Additionally, trinitrophenol, which presumably expands the outer lipid layer of the plasma membrane, also increased [Ca²⁺]_cyt higher in the transgenic plants than in control plants. These data suggest that the AtMID1A product is a Ca²⁺-permeable SA channel.