Signaling peptide involved in the regulation of root colonization by arbuscular mycorrhizal (AM) fungi (PubMed:31477892). Moves from root to shoot to function with the receptor kinase SUNN, in a signaling pathway that repress strigolactone biosynthetic genes and strigolactone content in the roots, and consequently reduces the promotion of further colonization by AM fungi (PubMed:31477892). Expressed in root vasculature. Induced in roots by treatment with inorganic phosphate. The O-glycosylation (arabinosylation) of the hydroxyproline Pro-70 enhances binding affinity of the CLE33p peptide for its receptor. Roots of plants overexpressing CLE33 exhibit normal growth, but reduced levels of colonization by arbuscular mycorrhizal (AM) fungi. Belongs to the CLV3/ESR signal peptide family.