The aerial epidermis of terrestrial plants is covered by a bioplastic cuticle largely impermeable to gases such as water vapor or CO2. This protects the plant from excessive water loss and thence desiccation, but also impedes taking up CO2 and thence photosynthesis. Regulated gas exchange between the plant and the atmosphere takes place through special structures called stomata. These are microscopic valves made by two guard cells that delimit a stomatal pore. Shape changes in guard cells open or close the pore, allowing a precise adjustment of gas fluxes and regulating photosynthesis and also transpiration –and therefore cooling of the plant. Stomata operate within relatively narrow margins set for their optimal function and are rarely wide open. For this reason, their abundance and also their distribution patterns are essential for determining the maximum area available for gas exchange, thus impinging on plant survival and reproduction.
The formation of stomata in Arabidopsis is accompanied by a series of stereotyped cell divisions where many of the resulting cells become pavement cells. At the end of this process the majority of all pavement cells in a leaf derive from these stomata lineages and are developmentally related to the stomata. So, studying stomata formation is also studying epidermal development. Among the many proteins know to regulate this developmental process are three related transcription factors of the basic-Helix-loop-Helix (bHLH) superfamily, SPEECHLESS (SPCH), MUTE and FAMA, which consecutively drive cell division and differentiation events from stomatal lineage initiation to stoma formation. We are interested in the genetic and molecular control of these cell division and fate acquisition processes, using as a model Arabidopsis thaliana, and combining direct and reverse genetics with transcriptomics and cell and developmental biology, exploiting induced mutants, transgenic lines and natural genetic variants in the three stomatal bHLHs. In collaboration with other groups, we also study the physiological differences of alleles of these stomatal genes that determine different stomatal numbers.
As stomatal abundance is crucial for crop productivity and performance, particularly in the Climate Change scenario, we are translating our research to crops like tomato and grapevine, finding functional orthologues of Arabidopsis stomatal genes and studying the anatomical and physiological consequences of mutations in these genes. In collaboration with breeding experts we plan to introduce useful variants in breeding programs aimed at obtaining better water use efficiency under drought conditions (low-stomata varieties), or sustained productivity at high temperatures under irrigation (high-stomata varieties).