Component of an exocyst subcomplex specifically required for periarbuscular membrane (PAM) biogenesis during arbuscular mycorrhizal (AM) symbiosis with AM fungi (e.g. Glomus versiforme), especially critical during the early branching phase of arbuscule development; probably involved in STR and STR2 delivery into the PAM. Subunit of the exocyst complex that mediates vesicle tethering during exocytosis (Probable). Interacts with VPY at the periarbuscular membrane (PAM) around the arbuscule hyphal tips (PubMed:26234213). During arbuscule branching, restricted to zones adjacent to the periarbuscular membrane (PAM) around the arbuscule hyphal tips. Present at low levels in non-mycorrhizal root tips. During arbuscular mycorrhizal (AM) symbiosis with (AM) fungi (e.g. Glomus versiforme), accumulates strongly in cortical cells containing arbuscules. Accumulates in roots, in a RAM1-dependent manner, during colonization by arbuscular mycorrhizal fungi (e.g. Glomus versiforme) (PubMed:26511916, PubMed:26234213). Triggered by RAM1 (PubMed:26511916). Induced during root nodule symbiosis with rhizobium bacteria (e.g. Sinorhizobium meliloti) (PubMed:26234213). Abnormal arbuscule development (reduced arbuscule branching and aberrant hyphal branches frequently distorted in shape) during arbuscular mycorrhizal (AM) symbiosis with AM fungi (e.g. Glomus versiforme) characterized by reduced STR and STR2 incorporation into the periarbuscular membrane (PAM) (PubMed:26234213). Normal root nodules development during symbiosis with rhizobium bacteria (e.g. Sinorhizobium meliloti) (PubMed:26234213). Belongs to the EXO70 family. Truncated N-terminus.