Molecular Genetics of Stomatal Development in Arabidopsis

The intensity of gas exchange between the plant and the atmosphere, and therefore the balance between photosynthesis and transpiration that set plant performance, is influenced by numbers and spatial patterns of stomata, microscopic pores in the otherwise impermeable aerial epidermis delimited by two guard cells that act as highly regulated dynamic valves. Molecular and genetic control of stomatal development has been intensively studied in Arabidopsis and found to be basically conserved across the plant phylogeny. Stomata form during early stages of organ development from scattered protodermal cells that found stomatal cell lineages, through stereotyped cell division and differentiation processes that produce stomata but also most pavement cells. Three master transcription factors consecutively drive the birth and amplification of stomatal precursors—meristemoids—through asymmetric cell divisions (SPEECHLESS), meristemoid commitment to stomatal fate and its symmetric division (MUTE), and the differentiation of the twin cell products into the guard cells that constitute a stoma (FAMA). A wealth of negative regulators ensure that stomata are never in contact and modulate their numbers and spatial patterns. This work is an updated review of the molecular and cellular mechanisms that underlie stomatal lineage development in Arabidopsis and presents a summary of the interplay of this genetic program with hormones and external factors to establish functional stomatal patterns that optimize plant performance under different environments.