Plasticity in stomatal development: what role does MAPK signaling play?

Stomata are specialized pores found on the epidermal surface of many aerial tissues of plants, where they function to regulate the exchange of gases such as carbon dioxide and water vapor between the plant and its environment. This makes stomatal complexes essential for the survival of the plant; a complete loss of stomata is lethal. On a global level, stomatal regulation of gas exchange makes stomata critical regulators of carbon and water cycles, while on an organismal level, stomatal development is flexible in that the ultimate distribution of stomata can be controlled by environmental stimuli. (1) While several environmental factors capable of influencing stomatal development have been identified, the molecular mechanisms mediating this flexibility have remained elusive. Recent studies suggest that this plasticity involves an expanding collection of mitogen activated protein kinase (MAPK) signaling components and putative upstream extracellular ligands. (2,3) Furthermore, it appears that stomatal development and distribution may not be the result of a simple "on/off" switch regulating lineage entry. Rather, stomatal precursors in Arabidopsis can be influenced at multiple points in the well-characterized stomatal development pathway by modulation of a core MAPK signaling module. (3.)