UC Riverside

Chapter 1

Abscisic acid (ABA) is a phytohormone that plays important roles in plant development and environmental stress response. When bound to a family of star-related lipid-transfer (START) proteins, clade A subfamily of type II C protein phosphatases (PP2Cs) are negatively regulated leading to ABA response. It was only recently that the mechanism involved in ABA perception was identified. This was due in part to the success of bypassing this redundancy with the use of forward chemical genetics in Arabidopsis thaliana. Many biological findings utilizing forward chemical genetics have been limited to A. thaliana. Although a general insight has been gained from these studies, A. thaliana cannot fully address development and physiological phenomena in monocots. Here we describe a screening system in Panicum virgatum (Switchgrass) which we developed and used for a forward chemical genetics screen in search of an ABA agonist exclusive to monocots. Although a bonafide agonist was not isolated, our findings do illustrate the potential biological studies our screening system can be extended towards.

Chapter 2

Clade A subfamily of type II C protein phosphatases (PP2C) is negatively regulated by a family of star-related lipid-transfer (START) proteins called PYR/PYLs (pyrabactin resistance1/PYR1-like). In vivo, these proteins are activated when bound to Abscisic acid. This interaction stabilizes its conformation, leading to ABA signaling. Previous work done by Mosquna, et al.2011 were able to use that mimicked the agonist-bound conformation leading to the activations of signaling in vivo. Multiple yeast two-hybrid screens were performed to construct PYL2 receptors that inhibited PP2Cs in the absence of ABA. Here we compare the efficiencies of the constitutive active PYL2 receptors under drought stress in comparison to wildtype. Receptors were tested using the drought inducible promoter Rd29A. Our results reveal that conditional activation of constitutively active PYL2 is sufficient to elicit drought stress tolerance.