Functional characterization of the Arabidopsis AtMID1B gene encoding a putative Ca²⁺-permeable, stretch-activated channel

Abstract

In the last JSPP meeting, we have shown that the Arabidopsis AtMID1A gene product has a Ca²⁺-permeable, stretch-activated channel activity. The data have suggested that AtMid1A acts as a sensor of mechanical stimuli and participates in generating a Ca²⁺ signal. We discovered AtMID1B, the homolog of AtMID1A in the Arabidopsis genome. Both had 73% amino acid identity and a similar hydropathy profile. Therefore, AtMid1B is expected to have a function similar to AtMid1A. Growth of the atmid1a/b double mutant delayed for 1-2 days under usual conditions. In addition, the atmid1a/b double mutant exhibited a severe growth defect when grown on media containing high concentrations of Mg²⁺, but this phenotype was alleviated by supplementing CaCl₂ to the media. Mg²⁺ is known to be a natural blocker for Ca²⁺ channels. Therefore, our findings suggest that the loss of AtMID1A and AtMID1B decreased Ca²⁺ influx and thereby caused Ca²⁺ deficiency in Arabidopsis plants.