Completely dephosphorylates 'Ser-2', and partially 'Ser-5' and 'Ser-7' of the heptad repeats YSPTSPS in the C-terminal domain (CTD) of the largest RNA polymerase II subunit (RPB1) (PubMed:25464831). Involved in defense response (PubMed:25464831). Acts as negative regulator of immune gene expression and immunity to pathogen infections (PubMed:25464831). Preferentially dephosphorylates 'Ser-2' of RNA polymerase II CTD (PubMed:25464831). This counterregulates the MAP kinase (MAPK) or cyclin-dependent kinase C (CDKC)-mediated phosphorylation of CTD in response to pathogens and upon perception of microbe-associated molecular patterns (MAMPs) (PubMed:25464831). MAPKs phosphorylate and activate CDKCs, which are CTD kinases that positively regulate plant innate immunity (PubMed:25464831). Acts as negative regulator of stress gene transcription involved in abscisic acid (ABA) mediated signaling pathway and cold resistance (PubMed:12149434, PubMed:16905668). Acts as post-transcriptional gene silencing (PTGS) suppressor (PubMed:31076735). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds Mg(2+), Co(2+) or Mn(2+). Interacts with RAP74. By NaCl. The BRCT domain is required for interaction with RAP74. Grows more slowly and flower earlier than wild-type plants. ABA hyperactivation of stress-inducible genes.