May be involved in modulation of pathogen defense and leaf cell death. Activity seems to be regulated by Ca(2+)-dependent calmodulin binding and seems not to require heterotrimeric G proteins (By similarity). Controls pollen tube reception in the female gametophyte synergids. In synergids of unfertilized mature female gametophytes, present in a punctate pattern of endomembranes throughout the cytoplasm. Become polarly localized to the basal half of the synergids, to the filiform apparatus, upon pollen tube arrival at the micropyle. This relocalization upon fertilization requires FER. Restricted to pollen, synergids, pistils and immature anthers. Also detected in seedlings, leaves, stems and inflorescens. The C-terminus contains a calmodulin-binding domain, which binds calmodulin in a calcium-dependent fashion. Impaired pollen tube reception in the female gametophyte synergids; the pollen tube fails to arrest and continues to grow inside the female gametophyte. Belongs to the MLO family.