MKK3-MPK7 module acts as a positive regulator of PR1 gene expression. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by threonine and tyrosine phosphorylation (By similarity). Activated in response to hydrogen peroxide. Activation is triggered by MAPKKK17 and MAPKKK18 in a MKK3-dependent manner (PubMed:25720833). Interacts with MKK3. The TXY motif contains the threonine and tyrosine residues whose phosphorylation activates the MAP kinases. Dually phosphorylated on Thr-191 and Tyr-193, which activates the enzyme. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. MAP kinase subfamily.