Mitogen-activated protein kinase kinase; part of the MST11-MST7-PMK1 MAP kinase (MAPK) cascade that is essential for appressorium formation, penetration and invasive growth (PubMed:15749760, PubMed:21283781, PubMed:23454094, PubMed:27059015). The MST11-MST7-PMK1 MAP kinase cascade transduces signals from the cell surface sensors MDB2 and SHO1 that recognize various surface signals such as surface hydrophobicity, cutin monomers, and rice leaf waxes (PubMed:21283781). MST7 acts as the upstream MAPKK that directly phosphorylates MAP kinase PMK1 (PubMed:15749760). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer (PubMed:27059015). Interacts with the adapter protein MST50 (PubMed:15749760). Interacts with TRX2 (PubMed:27059015). Produces much less aerial hyphae and conidia and shows weakened cell walls and higher sensitivity to cell wall-degrading enzymes (PubMed:15749760). Impairs the formation of appressoria and the ability to infect rice plants (PubMed:15749760, PubMed:23454094). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.