Solution NMR studies of the plant peptide hormone CEP inform function

•C-terminally Encoded Peptides (CEP) are found in vascular plants and RKN only.•RKN encodes a 12 member family of CEP mimics.•NMR demonstrated defined tertiary structure of CEP.•Posttranslational modifications influence CEP structure and flexibility. The C-terminally Encoded Peptide (CEP) family of regulatory peptides controls root development in vascular plants. Here, we present the first NMR structures of CEP. We show that root-knot nematode (RKN: Meloidogyne spp.) also encodes CEP, presumably to mimic plant CEP as part of their stereotypic, parasitic interaction with vascular plants. Molecular dynamics simulations of plant- and nematode-encoded CEP displaying known posttranslational modifications (PTM) provided insight into the structural effects of PTM and the conformational plasticity and rigidity of CEP. Potential mechanisms of action are discussed with respect to the structure and sampling of conformational space.