Trans-grafting revolution: From molecular regulation mechanisms to biotech applications

Grafting is a routine method widely used for the vegetative propagation of fruit trees and several vegetable crops. The selection of a compatible rootstock is essential, as it strongly influences scion growth, development, and resilience to biotic and abiotic stresses. It has been proven that messenger RNAs (mRNAs), small RNAs (sRNAs), proteins, and peptides move through the phloem and cross the graft interface, enabling direct communication between rootstock and scion. In particular, sRNAs and regulatory peptides have emerged as key mediators of stress resistance by modulating gene expression and activating systemic defence responses. In this review, we summarise genetic engineering approaches used to express target molecules, including CRISPR-Cas9-associated sequences, specifically in the rootstock, and we examine their effects following translocation to the scion. Engineered rootstocks have been shown to act as sources of mobile molecules that are transported to the scion, enhancing its tolerance to pathogens, pests, and environmental stresses without modifying the scion genome. Understanding the transport mechanisms and functional roles of these molecules represents a promising avenue for developing crops with reduced susceptibility to a wide range of biotic and abiotic stresses through advanced grafting technologies. Furthermore, this approach expands the potential of grafting as a biotechnological tool and represents a promising frontier also from a regulatory perspective.