Abscisic acid (ABA) plays a crucial role to integrate plant response to abiotic stress (particularly drought and salinity) into the regulation of plant growth and development. An increase in ABA levels and the subsequent plant response to the hormone are key components of the adaptive mechanism to resist/avoid those forms of abiotic stress. Accordingly, the characterization of ABA signaling offers a high biotechnological potential to improve plant tolerance to drought and salinity. 
            Because of its essential function in plant stress physiology, elucidating the abscisic acid (ABA) signalling pathway holds enormous promise for application in agriculture. Key details of the pathway have been elucidated recently, such as the discovery of the 14-member PYR/PYL/RCAR family of ABA-receptors (Park et al., 2009; Ma et al., 2009; Santiago et al., 2009a). Control of ABA signalling by PYR/PYL/RCAR ABA-receptors involves direct ABA-dependent inhibition of clade A phosphatases type-2C (PP2Cs), for instance ABI1, HAB1, PP2CA, which are key negative regulators of the pathway (Saez et al., 2006; Rubio et al., 2009). Inhibition of PP2Cs leads to activation of sucrose non-fermenting 1-related subfamily 2 (SnRK2) kinases, which regulate stomatal aperture and transcriptional response to ABA. Thus, a core signalling network for ABA has emerged from these findings (Fujii et al., 2009; Cutler et al., 2010).            

        Crystallographic models are available for three receptors, PYR1, PYL1 and PYL2, and two receptor-ABA-phosphatase complexes, PYL1-ABA-ABI1 and PYL2-ABA-HAB1, which permits a detailed understanding at the very first step in the ABA signaling cascade (Miyazono et al., 2009; Melcher et al., 2009; Santiago et al., 2009b; Nishimura et al., 2009; Yin et al., 2009). Thus, crystallographic data reveal key details on the mode of interaction between the receptor, the hormone and the protein phosphatase as well as the mechanism of activation of the ABA signalling pathway in plants. This information will be used in the structure-assisted identification of synthetic molecules able to act as agonists of ABA receptors and activate ABA signalling in plants. These molecules could have the potential to improve the yield of crop plants under drought stress or any other properties modulated by the ABA pathway in crop or ornamental plants. Additionally, we will physiologically characterize the Arabidopsis family of PYR/PYL receptors in order to identify the most relevant targets for agonist screening or transgenic approaches, i.e. those receptors that regulate ABA response in vegetative tissues. To this end, we will obtain a detailed gene expression pattern of PYR/PYL receptors and their sub-cellular localization, we will generate and analyze ABA-response in genetic backgrounds with combined (quadruple, quintuple, sextuple) inactivation of pyr/pyl loci and finally, we will identify new regulatory proteins of PYR/PYL receptors through proteomic approaches based on TAP technology.