StARK · Deciphering Signaling Networks Regulating Stomatal Movement during Plant Rehydration

In terrestrial plants, small openings on the leaf surface, called stomata, allow CO2 to diffuse in for photosynthesis but also lead to water loss. Each pore is flanked by a pair of guard cells (GC). Regulation of stomatal aperture is key for optimization of plant water usage and productivity. During drought, the plant hormone abscisic acid (ABA) induces stomatal closure to minimize water loss. Instead, starch breakdown in GC enables rapid stomatal opening in response to light. ABA regulates enzymes involved in starch degradation under osmotic stress, suggesting crosstalk between ABA signaling and starch metabolism. Soil rewatering after a period of water withdrawal rapidly induces stomatal opening in Arabidopsis leaves. Remarkably, I found that it also increases the cytosolic concentration of calcium ions (hereafter referred to as calcium). Calcium is a key second messenger in all organisms. Since ABA- and light-induced stomatal movement depend on cytosolic calcium dynamics, I hypothesize this calcium concentration increase contributes to stomatal regulation under fluctuating water conditions. I designed the StARK (Starch and ABA in Rehydration Kinetics) project, which will: 1) investigate the role of cytosolic calcium concentration increase upon soil rehydration, 2) determine the impact of ABA catabolism and GC starch degradation on stomatal movement under fluctuating water conditions, and 3) uncover crosstalk between these pathways. Arabidopsis plants expressing fluorescence biosensors and knockout mutants in ABA catabolism and GC starch degradation enzymes will be used. StARK will advance our understanding of how plants optimize water usage. This knowledge will contribute to the development of crops with enhanced water use efficiency and productivity.