Grafting “Away” the Concerns on Genetically Engineered Plants?

Grafting is a well-established agricultural practice, and it now has implications for the commercialization of transgenic plants for non-transgenic products. In our recent studies, we transformed a hairpin RNA (hpRNA) vector to a major sweet cherry rootstock cv. Gisela 6 in order to silence Prunus necrotic ringspot virus (PNRSV), which is a major pollen-disseminated Ilarvirus. All transgenic rootstocks showed accumulation of hpRNA-derived small interfering RNAs (siRNAs) and high resistance to the PNRSV. Subsequently, we performed grafting studies to investigate whether PNRSV-resistant transgenic rootstocks developed through siRNA-mediated gene silencing can enhance virus resistance of non-transgenic scions. We found transported (rootstock-to-scion) siRNAs in a non-transgenic scion of sweet cherry grafted on a transgenic rootstock. More importantly, inoculation of non-transgenic scions with PNRSV revealed that the transferred siRNAs enhanced PNRSV resistance in the scions grafted on the transgenic rootstocks. Low amounts of transferred hpRNA siRNAs in scions, compared to those detected in PNRSV-infected but symptomless cherry plants using non-transgenic rootstocks, implied little concern of these siRNAs for food safety. These findings provide the basis for ‘using transgenic rootstocks to produce non-transgenic products of scions in rootstock-scion grafted plants’, while minimizing concerns about food and environmental safety.