Signaling peptide involved in the regulation of nodulation (PubMed:20348212). Moves from root to shoot to function with the receptor kinase SUNN, in a signaling pathway that plays roles during cellular differentiation, both at the onset of nodulation, and later during nodule meristem development and subsequent homeostasis (PubMed:20348212). Interacts with SUNN signaling to control nodule numbers (PubMed:22168914). SUNN is involved in the autoregulation of nodulation (AON), a long distance systemic signaling from root to shoot and back again, which allows legumes to limit the number of root nodules formed based on available nitrogen and previous rhizobial colonization (Probable). Expressed in young nodules throughout the central tissue (PubMed:20348212). Expressed in the apical region of elongated nodules, corresponding to the meristematic and early infection zones (PubMed:20348212). Induced in roots during nodulation triggered by low nitrogen and infection with Sinorhizobium meliloti. The O-glycosylation (arabinosylation) of the hydroxyproline Pro-76 enhances binding affinity of the CLE12p peptide for its receptor. Overexpression of CL12 in roots almost abolishes nodule formation when inoculated with Sinorhizobium species (PubMed:28592666). Roots of plants silencing CLE12 and CLE13 exhibit increased number of nodules after infection with Sinorhizobium meliloti (PubMed:22168914). Belongs to the CLV3/ESR signal peptide family.