BACKGROUND: Multicellular organisms rely on the transmission of information between cells to coordinate various biological processes during growth and development. Plants, like animals, utilize small peptide ligands as signaling molecules to transmit information between cells. These polypeptides typically act as extracellular messengers that are perceived by membrane-bound receptors, which then transduce the signal into the recipient cell to modify downstream gene transcription. The CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) proteins represent one of the largest and best understood families of small polypeptides in plants. Members of the CLE family play critical roles in mediating cell fate decisions during plant development, particularly within the unique meristem structures that contain stem cell reservoirs acting as sources of cells for continuous organ formation.

OBJECTIVE: Here we review the roles of CLE family members in regulating the activity of the shoot apical meristems that generate the aerial parts of the plants, and of the vascular meristems that produce the sugar- and water-conducting tissues.

METHODS: A systematic literature search was performed using the Google Scholar and PubMed search engines. The keywords “CLE”, “CLV3”, “TDIF”, “meristem”, and “plant stem cells” were used as search terms. The 95 retrieved articles, dating from 1992, were organized by topic and their key findings incorporated into the text.

RESULTS: We summarize our current understanding of how the CLE peptide CLV3 orchestrates the activity of shoot apical meristems, describing its expression, processing and movement, as well as its intracellular signal transduction pathways, key target genes and downstream gene regulatory networks. We also discuss the roles of CLE peptide signaling in the vascular meristems to promote procambial cell proliferation and suppress xylem differentiation.

CONCLUSIONS: Signaling pathways mediated by CLE peptides are critical for stem cell maintenance and differentiation in shoot apical and vascular meristems in plants, exposing CLE genes as potential targets for increasing yield and biomass production. While large numbers of CLE genes are being discovered in plants, only a few have been functionally characterized. We anticipate that future research will continue to elucidate the roles of the CLE family in plant development, and their potential impacts on agriculture and commerce.