Mitogen-activated protein kinase kinase kinase; part of cell wall integrity (CWI) signaling pathway composed of pkcA, the bck1-mkk2-mpka MAPK cascade and the downstream rlmA transcription regulator (PubMed:19715768). The CWI signaling pathway regulates cell wall integrity and pyomelanin formation (PubMed:19715768). CWI controls also oxidative stress response, gliotoxin production, iron adaptation and asexual development (PubMed:21883519, PubMed:32005734). Finally, CWI is constitutively required for A.fumigatus to cope with the temperature increase found in the mammalian lung environment, during infection (PubMed:33010083). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Results in severe sensitivity against cell wall-disturbing compounds congo red or calcofluor white, and drastic alterations of the fungal morphology (PubMed:19715768). Impairs phosphorylation of mpkA (PubMed:19715768). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.