A Novel Transcription Factor CDI6 Regulates Stomatal CO₂ Response

Abstract

CO₂ is an environmental signal that regulates stomatal movements. High CO₂ concentrations reduce stomatal aperture, whereas low concentrations lead to stomatal opening. However, molecular mechanisms underlying stomatal CO₂ sensing and the downstream signaling pathway are largely unknown. To identify genes that function in CO₂ responses in guard cells, we previously isolated Arabidopsis CO₂ insensitive mutants that were roughly categorized into two-types according to their phenotypes; (1) impaired in stomatal opening under low CO₂ concentrations (2) impaired in stomatal closing under high CO₂ concentrations. Among these, we especially focused on a novel type mutant cdi6 (carbon dioxide insensitive 6) that impaired in both CO₂ responses. The CDI6 is a plant transcription factor, and is localized specifically to the nucleus of guard cells. We examined transcriptional profiles in guard cell protoplasts using Arabidopsis DNA microarray. From the results, the expression of several genes that were involved in stomatal function or development was changed in cdi6 mutant. These results suggest that CDI6 has an important role in regulation of guard cell gene expression.