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 (PubMed:19220794). Also induced transiently in roots epidermal cells (including root hair cells in nodule vicinity) during symbiosis with Rhizobia bacteria (e.g. Mesorhizobium loti), but not observed in nodules (PubMed:19220794). Rapidly induced in roots during development of arbuscular mycorrhiza (AM) upon colonization by AM fungus (e.g. Glomeromycota intraradices) (PubMed:19220794, PubMed:15980262). Up-regulated transiently during root nodule symbiosis with Mesorhizobium loti (PubMed:19220794, PubMed:15980262). Belongs to the peptidase S8 family.