Abstract
Stomatal movement driven by ion transport in guard cells regulates carbon dioxide uptake and transpirational water loss of plants upon environmental constraints. Anion channels/transporters have received particular attention due to their key roles in stomatal regulation. We report that AtALMT12, which is a homologue of the aluminum-activated malate transporter in wheat roots, is strongly expressed in guard cells of Arabidopsis thaliana. The loss-of-function mutations in AtALMT12 impairs the stomatal closure induced by abscisic acid, calcium or dark-treatments, but does not abolish typical rapid- and slow-type anion currents, major characteristics in anion flux for stomatal closure in our measurements, although Meyer et al. have reported that AtALMT12 is rapid-type anion channel. AtALMT12 facilitates inorganic anions in Xenopus oocytes. Therefore, we conclude that AtALMT12 is an anion transporter essential for stomatal closure. Furthermore, these findings indicate that the ALMT-family proteins comprise a diverse function as anion transporters.
