Protein-tyrosine-phosphatase that dephosphorylates and probably inhibits MPK6 in non-oxidative stress conditions. In association with MKP1, represses salicylic acid (SA) and camalexin biosynthesis, thus modulating defense response. May also repress MPK3. Dephosphorylates and inactivates MPK4 in vitro. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Inhibited by hydrogen peroxide. Interacts with MPK6 (PubMed:19789277). Interacts with KIN10 (PubMed:27029354). A number of isoforms are produced. According to EST sequences. Expressed in roots, stems and flowers, and at low levels in leaves. By salt treatment. Down-regulated by cold. Phosphorylated by KIN10. No visible phenotype under normal growth conditions.