Role of Protein Phosphatase1 Regulatory Subunit3 in Mediating the Abscisic Acid Response.

Protein phosphatase1 (PP1) plays important roles in eukaryotes, including in plant hormone responses, and functions as a holoenzyme that consists of catalytic and regulatory subunits. Animal genomes encode ∼200 PP1-interacting proteins; by contrast, only a few have been reported in plants. In this study, PP1 Regulatory Subunit3 (PP1R3), a protein that interacts with PP1 in Arabidopsis (), was characterized by mass spectrometry. was widely expressed in various plant tissues and PP1R3 colocalized with Type One Protein Phosphatases (TOPPs) in the nucleus and cytoplasm. The mutants were hypersensitive to abscisic acid (ABA), similar to the dominant-negative mutant or the loss-of-function multiple mutants , , , , and (). About two-thirds of differentially expressed genes in showed the same gene expression changes as in In response to ABA, the phenotypes of and were consistent with those of , while showed an additive effect of the and (mutation in []) single mutants. Moreover, could partially recover the ABA response-related phenotype, gene expression, and plant morphology of PP1R3 inhibited TOPP enzyme activity and facilitated the nuclear localization of TOPP4. By contrast, ABA treatment increased the amounts of TOPP1 and TOPP4 in the cytoplasm. Importantly, nuclear localization of TOPP4 partially restored the ABA-hypersensitive phenotype of Overall, our results suggest that the PP1R3:TOPP holoenzyme functions in parallel with ABI1 in the nucleus to regulate ABA signaling.