During arbuscular mycorrhizal symbiosis, colonization of the root is modulated in response to the physiological status of the plant, with regulation occurring locally and systemically. Here, we identify differentially expressed genes encoding CLAVATA3/ESR-related (CLE) peptides that negatively regulate colonization levels by modulating root strigolactone content. CLE function requires a receptor-like kinase, SUNN; thus, a CLE-SUNN-strigolactone feedback loop is one avenue through which the plant modulates colonization levels.