Speedy grass stomata : emerging molecular and evolutionary features

Stomata in most land plants are formed by a pair of guard cells, controlling the water loss and the carbon dioxide uptake. The development, patterning, and density of stomata are fundamental traits for stomatal function, contributing to plant growth and productivity (Pillitteri and Torii, 2012). The stomata of most plant species consist of two kidney-shaped guard cells, while stomata of grass species are formed by two dumbbell-shaped guard cells flanked by two subsidiary cells (Figure 1A). The four-celled stomatal complex in grasses may facilitate a fast response to environmental cues for efficient photosynthesis and water use, possibly through the rapid transport of ions and osmolytes between guard cells and subsidiary cells (see Jezek and Blatt, 2017; Chen et al., 2017 and references therein). Given that many grasses are agronomically important species as staple food, feed, and biofuel sources, it is vital to understand the molecular mechanisms of grass stomata development and patterning, and of membrane transport in guard cells and subsidiary cells, which govern the opening and closure of stomatal pores.