Exogenous Application of ENOD40 and CEP1 Peptides Boosts Symbiotic Signaling Gene Expression and Productivity in Common Bean

Small signaling peptides play crucial roles in the regulation of legume–rhizobia symbiosis, yet their potential as exogenous biostimulants remains largely unexplored. In this study, we evaluated the effects of foliar application of the synthetic peptides ENOD40 and CEP1 on common bean (Phaseolus vulgaris) under both greenhouse and field conditions. Using a factorial design, we examined gene expression patterns, nodulation parameters, and yield-related traits in response to peptide treatments alone or in combination with Rhizobium. Results showed that ENOD40 and CEP1 significantly enhanced the transcription of key symbiotic signaling genes (PvENOD40, PvSYMRK, PvCCaMK, PvCYCLOPS, PvVAPYRIN) and modulated defense-related genes (PvAOS, PvICS), with the strongest effects observed at concentrations of 10⁻⁷ M and 10⁻⁸ M. In greenhouse assays, peptide-treated plants exhibited increased root and shoot biomass, nodule number, and seed yield. Field trials confirmed these responses, with CEP1 10⁻⁷ M + Rhizobium treatment achieving the highest grain yield (3322 kg ha⁻¹). Our findings provide the first evidence that ENOD40 and CEP1 peptides can function as foliar-applied biostimulants to enhance nodulation efficiency and improve yield in legumes. This approach offers a promising and sustainable strategy to reduce chemical nitrogen inputs and support biological nitrogen fixation in agricultural systems.