Inhibitor of protein-phosphatase 1 (PP1). Binds to and inhibits PP1 activity (PubMed:21222654, PubMed:26943172). Acts as negative regulator of abscisic acid (ABA) signaling. Enhances the inhibition of SRK2E/SNRK2.6 by TOPP1. May promote the interaction between TOPP1 and the ABA receptor PYL11 (PubMed:26943172). Interacts with protein phosphatase 1 (PubMed:21222654). Interacts with TOPP1, SRK2D/SNRK2.2, SRK2I/SNRK2.3, SRK2E/SNRK2.6, SRK2C/SNRK2.8 and PYL11 (PubMed:26943172). Predominantly localizes in the nucleus. A number of isoform are produced. According to EST sequences. Expressed in roots, cotyledons, leaves, flowers and siliques. Phosphorylated in vivo. No visible phenotype under normal growth conditions, but mutant seedlings exhibit hypersensitivity to abscisic acid (ABA) or salt treatments.