RNA-Mediated Gene Silencing Signals Are Not Graft Transmissible from the Rootstock to the Scion in Greenhouse-Grown Apple Plants Malus sp.

Abstract

RNA silencing describes the sequence specific degradation of RNA targets. Silencing is a non-cell autonomous event that is graft transmissible in different plant species. The present study is the first report on systemic acquired dsRNA-mediated gene silencing of transgenic and endogenous gene sequences in a woody plant like apple. Transgenic apple plants overexpressing a hairpin gene construct of the gusA reporter gene were produced. These plants were used as rootstocks and grafted with scions of the gusA overexpressing transgenic apple clone T355. After grafting, we observed a reduction of the gusA gene expression in T355 scions in vitro, but not in T355 scions grown in the greenhouse. Similar results were obtained after silencing of the endogenous Mdans gene in apple that is responsible for anthocyanin biosynthesis. Subsequently, we performed grafting experiments with Mdans silenced rootstocks and red leaf scions of TNR31-35 in order to evaluate graft transmitted silencing of the endogenous Mdans. The results obtained suggested a graft transmission of silencing signals in in vitro shoots. In contrast, no graft transmission of dsRNA-mediated gene silencing signals was detectable in greenhouse-grown plants and in plants grown in an insect protection tent.

The knock‐down of the expression of MdMLO19 reduces susceptibility to powdery mildew (Podosphaera leucotricha) in apple (Malus domestica)

“…() and Flachowsky et al . (). However, both these studies were carried out on apple cultivars different from ‘Gala’ using different plasmids from those used in this work.…”

Literature review of baseline information to support the risk assessment of RNAi‐based GM plants

“…It was shown that by RNA-mediated gene silencing signals are not graft transmissible from the rootstock to the scion in greenhouse-grown apple plants Malus sp. (Flachowsky et al, 2012). Further research is needed to reveal the molecular mechanisms and biological role(s) of the root-to-shoot (rootstockscion) transmission of RNA silencing.…”

Generation of Transgenic Rootstock Plum ((Prunus pumila L. × P. salicina Lindl.) × (P. cerasifera Ehrh.)) Using Hairpin-RNA Construct for Resistance to the Plum pox virus

“…For example, the transfer of transgene-derived siRNAs from the transgenic cherry rootstocks to the non-transgenic scions in grafted trees was effective in inducing resistance to the Prunus necrotic ringspot virus [16]. In apples, however, the transmission of siRNAs from transgenic rootstock to non-transgenic scion was not observed [17]. Such contradictory data indicates that direct trials of rootstock-to-scion delivery are required to confirm the efficacy of the transgrafting technology for individual species.…”