Required for arbuscular mycorrhiza (AM) development during AM symbiosis with AM fungi (e.g. Glomeromycota intraradices). Accumulates in the intercellular spaces and the periarbuscular space (PAS) during arbuscular mycorrhizal (AM) symbiosis. Accumulates in root cells that are adjacent to intra-radical fungal hyphae or in cells that harbor them during arbuscular mycorrhizal (AM) symbiosis, especially in epidermal and cortical cells. Rapidly induced in roots during development of arbuscular mycorrhiza (AM) upon colonization by AM fungus (e.g. Glomeromycota intraradices). Decreased fungal colonization and impaired arbuscular mycorrhiza (AM) development during AM symbiosis with AM fungi (e.g. Glomeromycota intraradices). Belongs to the peptidase S8 family.