The role of Arabidopsis ABA receptors from the PYR/PYL/RCAR family in stomatal acclimation and closure signal integration

Stomata are microscopic pores found on the surfaces of leaves which act to control CO2 uptake and water loss. By integrating information derived from endogenous signals with cues from the surrounding environment the guard cells, that surround the pore, ‘set’ stomatal aperture to suit the prevailing conditions. Much research has concentrated on understanding the rapid intracellular changes that result in immediate changes to stomatal aperture. In this study we look instead at how stomata acclimate to longer timescale variations in their environment. We show that the closure-inducing signals ABA, increased CO2, decreased relative air humidity (RH), and darkness each access a unique gene network made up of clusters (or modules) of common cellular processes. However, within these some gene clusters are shared among all four stimuli. All stimuli modulate the expression of members of the PYR/PYL/RCAR family of ABA receptors, however these are modulated differentially in a stimulus-specific manner. Of the six members of the PYR/PYL/RCAR family expressed in guard cells, PYL2 is sufficient for guard cell ABA-induced responses. Whereas, in the responses to CO2 PYL4 and PYL5 are essential. Overall our work shows the importance of ABA as a central regulator and integrator of long-term changes in stomatal behaviour, including sensitivity, elicited by external signals. Understanding this architecture may aid breeding of crops with improved water and nutrient efficiency.