Messenger RNA Exchange between Scions and Rootstocks in Grafted Grapevines

Grafting has been widely practiced for centuries in the propagation and production of many vegetable and fruit species. However, the underlying molecular and genetic mechanisms for how the graft partners interact with each other to produce a successful graft remain largely unknown. Using diagnostic SNPs derived from high throughput genome sequencing, we characterized the patterns of genome-wide mRNA exchanges across graft junctions in grafted grapevines grown in the in vitro and field conditions. More than three thousand genes transporting mRNAs across graft junctions were identified in this study. These genes were involved in diverse biological processes and many of those which were involved in basic cellular, biosynthetic, catabolic, and metabolic activities, as well as responses to stress and signal transduction, were highly enriched. Field-grown mature grafts had much fewer genes transmitting mRNAs than the in vitro young grafts. These mobile mRNAs could move directionally or bi-directionally between scions and rootstocks. The mRNA transmission rates of these genes were generally low, with 65% or more having transmission rates lower than 0.01. Furthermore, genotypes, graft combinations and growth environments had impact on the directions of mRNA movement as well as the numbers and species of mRNAs being exchanged. Moreover, we found evidence for the presences of both passive and selective mechanisms underlying long distance mRNA trafficking in grafted grapevines.