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. Regulated by RAM1 during arbuscular mycorrhiza (AM) formation after inoculation with Rhizophagus irregularis. Belongs to the peptidase S8 family.