Mitogen-activated kinase kinase kinase (MAPKKK), part of the cell wall integrity (CWI) signaling pathway composed by three protein kinases bck1, mkk2 and mpkA and responsible for the maintaining of cell-wall integrity balance (PubMed:19715768). The CWI pathway regulates also the oxidative stress response, as well as the production of some secondary metabolites including pyomelanin (PubMed:19715768). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Leads to the formation of thicker hyphae, which appear less elongated and form more branched hyphae (PubMed:19715768). Results in increased sensitivity to cell wall integrity inhibitors such as glucanex, SDS, congo red and calcofluor white (PubMed:19715768). Impairs phosphorylation of the MAPK mpkA (PubMed:19715768). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.