Seems to be involved in modulation of pathogen defense and leaf cell death. Down-regulates broad spectrum resistance to powdery mildew fungus and its defense suppression activity is enhanced by Ca(2+)-dependent calmodulin binding. Signaling seems not to require heterotrimeric G proteins. By fungal infection and abiotic stress. The C-terminus contains a calmodulin-binding domain, which binds calmodulin in a calcium-dependent fashion. Mutations in the MLO gene confer broad spectrum resistance to the powdery mildew fungus and a enhanced susceptibility to fungal pathogens Magnaporthe grisea and Bipolaris sorokiniana. Belongs to the MLO family.