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 mycorrhizal roots upon colonization by the arbuscular mycorrhiza (AM) fungus Glomus versiforme. Belongs to the peptidase S8 family.