Mediates the dephosphorylation of 'Ser-2' of the heptad repeats YSPTSPS in the C-terminal domain of the largest RNA polymerase II subunit (RPB1). This promotes the activity of RNA polymerase II. Regulates positively abscisic acid (ABA) and drought responses, including the regulation of specific genes expression. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Expressed in roots, seedlings, hypocotyls, cotyledons, leaves, siliques and flowers. In the vegetative stage, first detected in the seed coat upon germination and in the hypocotyl of young seedlings. In seedlings, expressed in roots (mostly in primary roots), hypocotyl, rosette leaves and cotyledons. In rosette leaves, observed in the vascular tissue of major veins, guard cells and trichomes. During the reproductive stage, expressed in flower buds, stems, stamens, carpels and funiculi of siliques. Induced transiently by abscisic acid (ABA), salt (NaCl), cold and drought. Weak abscisic acid (ABA) hyposensitivity during the early stages of seedling development. Slighty decreased drought stress tolerance. The predicted split genes At3g19595 and At3g19600 have been merged into a single gene: At3g19600. The predicted split genes At3g19595 and At3g19600 have been merged into a single gene: At3g19600.