CEP-CEPR1 Signalling in Cereal Crops: Integrating Nitrogen Demand, Root System Architecture, and Drought Resilience

Cereal crops collectively account for more than half of global human caloric intake, yet the molecular mechanisms governing their root systems under water and nitrogen limitation remain poorly understood relative to their agronomic importance. The C-terminally encoded peptide (CEP) family has emerged, primarily from work in Arabidopsis thaliana and Medicago truncatula, as a class of post-translationally modified peptide hormones that coordinate nitrogen demand signalling through a root-to-shoot-to-root relay involving CEPR1 leucine-rich repeat receptor-like kinases and phloem-mobile CEPD glutaredoxins, regulate lateral root gravitropic set-point angle through integrated auxin and cytokinin pathway interactions, and contribute to abiotic stress responses through stabilisation of AUX/IAA transcriptional repressors under osmotic stress. This review synthesises CEP biology with the specific architectural and agronomic characteristics of cereal root systems, explicitly distinguishing between findings established in model dicots, evidence for receptor-ligand conservation in cereals, and mechanisms that remain untested in crops. CEPR1 orthologues in barley, maize, and rice restore wild-type phenotypes in Arabidopsis complementation assays, and CRISPR-Cas9 knockout of CEPR1 in barley confirms effects on seminal root angle, though an associated fecundity defect highlights translational complexity. Proposed connections between CEP signalling and ABA pathways remain hypothetical. In wheat, TaCEP15 modulates primary root length and drought tolerance through a receptor pathway mechanistically distinct from the canonical CEP-CEPR1-CEPD nitrogen relay, indicating functional diversification within the CEP family. Five tractable research priorities are identified, and CRISPR-based approaches, synthetic peptide application, and marker-assisted selection are discussed as near-term strategies for cereal crop improvement under drought and nitrogen-limited conditions.