Grafting as a Clean Agronomic Technology for Cadmium Risk Reduction in Contaminated Farmlands: miRNA-Mediated Mechanisms and Food Safety Implications in Eggplant ( Solanum melongena ) Production

Soil cadmium (Cd) pollution has emerged as one of the key environmental issues threatening the safety of agricultural products worldwide, yet clean and low-cost intervention strategies that reduce Cd accumulation in edible crops without disrupting agricultural production remain scarce. Grafting onto tolerant rootstocks represents an emerging clean agronomic technology that achieves in situ Cd risk reduction within a single growing season. However, the molecular mechanisms by which rootstocks regulate scion phenotypes remain poorly understood. MicroRNAs (miRNAs) act as critical long-distance signals in plants, yet their roles in rootstock-mediated growth promotion and Cd reduction remain largely unclear. In this study, we used Solanum torvum as rootstock and purple eggplant ( Solanum melongena ) as scion to investigate growth, fruit quality, Cd accumulation, and miRNA-mediated regulatory mechanisms. Grafting significantly increased plant height (by 18%), stem diameter (by 12%), and yield without obvious effects on fruit quality. Under Cd stress, the Cd content in grafted eggplant fruits was reduced by 76%, whereas leaf potassium (K), calcium (Ca), and magnesium (Mg) contents were elevated by 21%, 17%, and 10%, respectively. High-throughput sequencing and quantitative real-time polymerase chain reaction identified five key differentially expressed miRNAs, including miR164a and miR166b, four of which were related to Cd stress. Gene Ontology (GO) enrichment analyzes that their target genes were mainly involved in hormone signal transduction and ion transport. Further validation suggested that grafting improved growth and reduced Cd accumulation by regulating genes of the NAC , SPL , and HD-ZIP III families. These results suggested that suitable rootstocks can enhance crop productivity and reduce toxic metal accumulation in edible parts through miRNA-mediated regulation.