Serine/threonine-protein phosphatase that possesses phosphatase activity toward para-nitrophenyl phosphate (pNPP) in vitro (PubMed:21222654). Acts as positive regulator in the gibberellin (GA) signaling pathway to regulate plant growth and development. Promotes the GA-induced and proteasomal-dependent degradation of the DELLA proteins RGA and GAI by directly binding and dephosphorylating these proteins (PubMed:25010794). Involved in the regulation of phytochrome B (phyB) signaling pathway that controls photomorphogenesis. Promotes the proteasomal-dependent degradation of PIF5 factor by directly binding and dephosphorylating this protein (PubMed:26704640). Involved in the regulation of pavement cell (PC) interdigitation by modulating the auxin efflux carrier PIN1 polarity and endocytic trafficking. Regulates PIN1 polar targeting through direct binding and dephosphorylation. Acts antagonistically with PID in regulating PC development (PubMed:25560878). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 manganese ions per subunit. Phosphatase activity is strongly reduced by the protein phosphatase inhibitor 2 (I-2). Interacts with the DELLA proteins RGA and GAI (PubMed:25010794). Interacts with PIF3 and PIF5 (PubMed:26704640). Interacts with the auxin efflux carrier PIN1 (PubMed:25560878). Localizes predominantly to the nucleus. Expressed in the vasculature of roots and cotyledons, tips of leaves, guard cells, bases of trichomes, pistils and stamen filaments. Dwarf phenotype and decreased fertility. Belongs to the PPP phosphatase family. PP-1 subfamily.