Graduate student University of Texas at Austin Austin, Texas
Body of Abstract: The shade avoidance response allows plants to better access sunlight to compete against surrounding plants. In Arabidopsis, PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) as a major regulator can be dephosphorylated under shade conditions and accumulates into the nucleus to promote auxin biosynthetic and signaling genes (YUCCA8 and IAA19) expression to promote stem elongation. However, how PIF7 is dephosphorylated under shade conditions and which phosphatases are involved in this process are not well understood. By yeast two-hybrid screen, we identified two regulatory subunits in the protein phosphatase 2A (PP2A) family (B''α and B''β) that interact with PIF7. Furthermore, we demonstrate that these two B subunits directly interact with PIF7 in pull-down and co-immunoprecipitation assays. The pp2ab''αβ double mutant in Arabidopsis shows short hypocotyl length in shade light conditions compared with that of the wild type. The hypocotyl lengths of the overexpression of B subunits were significantly longer than that of wild type in shade light conditions. Genetic evidence shows that PIF7 is epistatic to B''α and B''β subunits in regulating hypocotyl elongation under shade light conditions. In the future, it will be interesting to test if PP2A can directly dephosphorylate PIF7 in vitro and how PP2A regulates PIF7 phosphorylation status in vivo. Overall, our study will disclose an essential function of PP2A-PIF7 to modulate shade avoidance response in Arabidopsis.