Together with STR2, required for arbuscule development in arbuscular mycorrhizal (AM) symbiosis. Heterodimerizes with STR2; the resulting transporter is located in the peri-arbuscular membrane. Located in the peri-arbuscular membrane of arbuscular mycorrhiza (AM). Regulated by RAM1 during arbuscular mycorrhiza (AM) formation after inoculation with Rhizophagus irregularis. Belongs to the ABC transporter superfamily. ABCG family. Stunted arbuscule (STR) subfamily.