DSD1/ZmICEb regulates stomatal development and drought tolerance in maize.

Maize (Zea mays L.) growth and yield are severely limited by drought stress worldwide. Stomata play crucial roles in transpiration and gas exchange and are thus essential for improving plant water-use efficiency (WUE) to help plants deal with the threat of drought. In this study, we characterized the maize dsd1 (decreased stomatal density 1) mutant, which showed defects in stomatal development, including guard mother cell differentiation, subsidiary cell formation and guard cell maturation. DSD1 encodes the basic helix-loop-helix transcription factor INDUCER OF CBF EXPRESSION b (ZmICEb) and is a homolog of ICE1 in Arabidopsis (Arabidopsis thaliana). DSD1/ZmICEb is expressed in stomatal file cells throughout stomatal development and plays a conserved role in stomatal development across maize and Arabidopsis. Mutations in DSD1/ZmICEb dramatically improved drought tolerance and WUE in maize and reduced yield losses under drought conditions. Therefore, DSD1/ZmICEb represents a promising candidate target gene for the genetic improvement of drought tolerance in maize by manipulating stomatal density.