Transcription factor acting as a regulator of arbuscular mycorrhiza (AM)-related genes (e.g. STR) (PubMed:26511916). Required for the morphogenesis of arbuscules upon symbiosis with AM fungi (e.g. Glomus versiforme) (PubMed:26511916). Also involved in restricting mycorrhizal colonization of the root meristem (By similarity). Interacts with RAM1 (PubMed:26511916). Interacts with NSP2 (By similarity). Accumulates in roots, in a RAM1-dependent manner, during colonization by arbuscular mycorrhizal fungi (e.g. Glomus versiforme) (PubMed:26511916). Triggered by RAM1 (PubMed:26511916). Reduced intraradical colonization by arbuscular mycorrhiza (AM)-fungi (e.g. Glomus versiforme) upon symbiosis in roots. Belongs to the GRAS family.