Abstract
Virus-resistant transgenic plants have been created primarily through the expression of viral sequences. It has been hypothesized that recombination between the viral transgene mRNA and the RNA of an infecting virus could generate novel viruses. As mRNA/viral RNA recombination can occur in virus-resistant transgenic plants, the key to testing this risk hypothesis is to compare the populations of recombinant viruses generated in transgenic and non-transgenic plants. This has been done with two cucumoviral systems, involving either two strains of cucumber mosaic virus (CMV), or CMV and the related tomato aspermy virus (TAV). Although the distribution of the sites of recombination in the CMV/CMV and TAV/CMV systems was quite different, equivalent populations of recombinant viruses were observed in both cases. These results constitute the first comparison of the populations of recombinants in transgenic and non-transgenic plants, and suggest that there is little risk of emergence of recombinant viruses in these plants, other than those that could emerge in non-transgenic plants.
Highlights
The first virus-resistant transgenic plants were reported two decades ago (Abel et al, 1986) and, since the early 1990s, various concerns have been expressed regarding the potential impact of such plants, those expressing viral genes (Tepfer, 2002)
As has been reviewed previously (Tepfer, 2002), mRNA/viral RNA recombination has been clearly shown to occur in transgenic plants expressing sequences from several viruses when they are inoculated with viruses that bear deletions in the sequence expressed from the transgene, but there is no clear evidence that this phenomenon constitutes a risk of virus emergence
As mRNA/viral RNA recombination can occur in transgenic plants, the critical question is whether this can be the source of recombinants different from those that would be
Summary
The first virus-resistant transgenic plants were reported two decades ago (Abel et al, 1986) and, since the early 1990s, various concerns have been expressed regarding the potential impact of such plants, those expressing viral genes (Tepfer, 2002). 0008-3339 G 2008 SGM Printed in Great Britain produced in non-transgenic plants infected with more than one virus, a situation that occurs frequently in the field Attempts to answer this question should be based on a comparative study of the populations of recombinants that occur under conditions of the lowest possible selection pressure in favour of the recombinants (Tepfer, 2002). This requires development of highly sensitive RT-PCR techniques for amplifying recombinant viral RNAs that occur as a very minor component of the total viral RNA population This has been shown to be possible with two cucumoviruses, cucumber mosaic virus (CMV) and tomato aspermy virus (TAV) (Aaziz & Tepfer, 1999; de Wispelaere et al, 2005), but was not possible with three other virus groups (Dietrich et al, 2007; Koenig & Buttner, 2004; Meier & Truve, 2006). We have developed the cucumovirus recombination system further
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