Mitogen-activated protein kinase 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:23454094). 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). MST11 acts as the upstream MAPKKK that directly phosphorylates MAPKK MST7 (Probable). MST11 but not MST7 may also be involved in the OSM1 MAPK pathway in response to osmotic stresses (PubMed:15749760). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with the adapter protein MST50. The N-terminal sterile alpha motif (SAM) domain, but not the Ras-associating (RA) domain, is essential for the function. 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 kinase subfamily.