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 that act to control CO2 uptake and water loss. By integrating information derived from endogenous signals with cues from the surrounding environment, the guard cells, which surround the pore, 'set' the stomatal aperture to suit the prevailing conditions. Much research has concentrated on understanding the rapid intracellular changes that result in immediate changes to the 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 abscisic acid (ABA), increased CO2, decreased relative air humidity and darkness each access a unique gene network made up of clusters (or modules) of common cellular processes. However, within these networks some gene clusters are shared amongst all four stimuli. All stimuli modulate the expression of members of the PYR/PYL/RCAR family of ABA receptors. However, they 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 in breeding crops with improved water and nutrient efficiency.