Evolution of meristem zonation by CLE gene duplication in land plants

CLE peptides control stem-cell activity in meristems. Recent studies in Marchantia and Arabidopsis support the idea that an ancestral function of CLE peptides was to promote stem cells. After gene duplication in angiosperms, a subset of CLE peptides became stem-cell suppressors. In angiosperms, a negative feedback pathway involving CLAVATA3 (CLV3) peptide and WUSCHEL transcription factor maintains the stem-cell population in the shoot apical meristem and is central for continued shoot growth and organogenesis. An intriguing question is how this cell-signalling system was established during the evolution of land plants. On the basis of two recent studies on CLV3/ESR-related (CLE) genes, this paper proposes a model for the evolution of meristem zonation. The model suggests that a stem-cell-limiting CLV3 pathway is derived from stem-cell-promoting CLE pathways conserved in land pants by gene duplication in the angiosperm lineage. The model can be examined in the future by genomic and developmental studies on diverse plant species.