Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2007
Publication Date: 12/29/2007
Citation: Zagrai, I., Capote, N., Ravelonandro, M., Cambra, M., Zagrai, L., Scorza, R. 2007. Silencing mechansim of C5 transgenic plums is stable under challenge inoculation with heterologous viruses. Journal of Plant Pathology. 90:41-46. Interpretive Summary: RNA silencing is a natural plant protective mechanism against virus infections. It is also a mechanism that is induced in transgenic plants when the natural levels of RNA silencing are not effective enough to ward off virus invasion. One reason for the lack of effectiveness is that viruses have evolved mechanisms to shut down the plant's RNA silencing. We have developed a genetically engineered (GE) plum that has very high levels of RNA silencing against Plum pox virus (PPV), one of the most serious diseases of plum and other stone fruits. In order to determine if other viruses could shut down the silencing in this GE plum ('HoneySweet' or C5) and render it susceptible to PPV, we inoculated 'HoneySweet' with some common stone fruit viruses and also PPV to see if the other viruses would make 'HoneySweet' susceptible to PPV. In three years of greenhouse and field tests in two locations (Spain and Romania), the PPV resistance of 'HoneySweet' remained high and stable even in the presence of three other common stone fruit viruses.
Technical Abstract: Transgenic C5 'HoneySweet' is a clone of Prunus domestica L. transformed with the Plum pox virus coat protein gene (PPV-CP). This transgenic plum displays post-transcriptional gene silencing (PTGS) which makes it highly resistant to PPV infection. To test the effect of heterologous viruses on the efficacy and stability of PTGS against PPV, transgenic C5 trees were graft-inoculated with different combinations of Prunus necrotic ringspot virus (PNRSV), Apple chlorotic leaf spot (ACLSV), Prune dwarf virus (PDV) and PPV-D strain. The potential for suppression of the silencing mechanism mediated by these viruses was evaluated. Challenge experiments were performed in Romanian and Spanish experimental fields comprising two different environments, continental and Mediterranean, respectively. Tests were also preformed in a greenhouse. Virus infections were evaluated by visual monitoring of symptom development and by serological and molecular diagnosis. Across all trials, the engineered resistance to PPV in C5 transgenic plums was stable and was not suppressed by the presence of the assayed heterologous viruses over a three-year experimental period.