Involved symbiotic signaling. Required for root infection by symbiotic rhizobia, infection thread (IT) formation, and nodule development (PubMed:9790580). Required for symbiosome formation (i.e. the release of the bacteria from the ITs) and subsequent symbiosome development (PubMed:21787150). Involved in arbuscular mycorrhizal (AM) symbiosis (PubMed:12634913, PubMed:12634914). No visible phenotype under normal growth conditions, but roots of mutant plants are impaired in the interaction with rhizobia, specifically in infection thread (IT) formation in symbiotic roots. Belongs to the CYCLOPS family.