The biology of grafting and its applications in studying information exchange between plants

Grafting techniques have been used for centuries for trait improvement in agriculture and horticulture. In recent years, technical progress with the grafting of species previously thought to be recalcitrant to the formation of a graft union, and the discovery of new types of information exchange between grafted plants, have stirred renewed interest in the use of grafting as a research tool. In this Review, we describe our current understanding of the molecular and cellular processes involved in the establishment of successful grafts between plants of the same genotype (homografts) or different genotypes (heterografts). We also highlight recent progress with the elucidation of the mechanisms underlying the exchange of macromolecules (small RNAs, messenger RNAs and proteins) across graft junctions as well as the transfer of cell organelles and its role in horizontal gene and genome transfer. Finally, we discuss novel applications of grafting, including new opportunities for transgene-free genetic engineering, and the relevance of grafting in plant evolution.