PP2A Dephosphorylates Phytochrome-Interacting Factor 3 to Modulate Photomorphogenesis in Arabidopsis

Abstract

The phytochrome (phy) family of sensory photoreceptors modulates developmental programs in response to ambient light. phys control gene expression in part by directly interacting with the bHLH class of transcription factors, phytochrome-interacting factors (PIFs), and inducing their rapid phosphorylation and degradation. Several kinases have been shown to phosphorylate PIFs and promote their degradation. However, the phosphatases that dephosphorylate PIFs are less investigated. Here we describe the identification of four regulatory subunits of Arabidopsis protein phosphatase 2A (PP2A) family (B’α, B’β, B’’α and B’’β) that interacted with PIF3 in yeast-two-hybrid, in vitro and in vivo assays. The pp2ab’’αβ and b’’αβ/b’αβ displayed short hypocotyls, while the overexpression of the B subunits induced longer hypocotyls compared to wild type under red light. The light-induced degradation of PIF3 was faster in b’’αβ/b’αβ quadruple mutant compared to wild type. Consistently, immunoprecipitated PP2A A and B subunits directly dephosphorylated PIF3-MYC in vitro. RNA-seq analyses showed that B’’α and B’’β alter global gene expression in response to red light. PIFs (PIF1, PIF3, PIF4 and PIF5) are epistatic to these four B subunits in regulating hypocotyl elongation under red light. Collectively, these data show an essential function of PP2A in dephosphorylating PIF3 to modulate photomorphogenesis in Arabidopsis.