Plant Pathogens Trick Guard Cells into Opening the Gates

The stomata of plants regulate gas exchange and water transpiration in response to changing environmental conditions. New work reveals that stomata also have an important role in host defense. In this issue of Cell, Melotto et al. (2006) show that stomata close upon detection of potential microbial pathogens to prevent the infection of the leaf interior. Moreover, pathogenic bacteria have evolved strategies to suppress the closure of stomata.