Inter- and Intramolecular Recombinations in the Cucumber Mosaic Virus Genome Related to Adaptation to Alstroemeria

One possible environmental risk related to the utilization of virus-resistant transgenic plants expressing viral sequences is the emergence of new viruses generated by recombination between the viral transgene mRNA and the RNA of an infecting virus. This hypothesis has been tested recently for cucumber mosaic virus (CMV) by comparing the recombinant populations in transgenic and non-transgenic plants under conditions of minimal selection pressure in favour of the recombinants. Equivalent populations were observed in transgenic and non-transgenic plants but, in both, there was a strongly dominant hotspot recombinant which was shown recently to be nonviable alone in planta, suggesting that its predominance could be reduced by applying an increased selection pressure in favour of viable recombinants. Partially disabled I17F-CMV mutants were created by engineering 6 nt deletions in five sites in the RNA3 39-non-coding region (39-NCR). One mutant was used to inoculate transgenic tobacco plants expressing the coat protein and 39-NCR of R-CMV. A total of 22 different recombinant types were identified, of which 12 were, as expected, between the transgene mRNA and the mutated I17F-CMV RNA3, while 10 resulted from recombination between the mutated RNA3 and I17F-CMV RNA1. Twenty recombinants were of the aberrant type, while two, including the dominant one detected previously under conditions of minimal selection pressure, were homologous recombinants. All recombinants detected were very similar to ones observed in nature, suggesting that the deployment of transgenic lines similar to the one studied here would not lead to the emergence of new viruses.

Section: Mechanism Of Recombination That Produces Aberrant Cucumovirasupporting

confidence: 71%

Section: Discussion Effects Of 6 Nt Deletions In I17f-cmv Rna3mentioning

confidence: 99%

Analysis of recombination between viral RNAs and transgene mRNA under conditions of high selection pressure in favour of recombinants

Morroni

Thompson

Tepfer

2009

“…In addition, more than one-third of the R-CMV/P-TAV recombinants were of an aberrant type, resulting in a 160-180 nt duplication in the 39 NCR (de Wispelaere et al, 2005). As similar recombinants have also been observed in certain natural CMV and TAV isolates (Chen et al, 2002;Moreno et al, 1997), it is surprising that this type of recombinant was not detected in the present study, but this may be due to the instability in tobacco plants of I17F-CMV/R-CMV recombinants of this type (Pierrugues et al, 2007).…”

Section: Discussionmentioning

confidence: 74%

Evaluation of potential risks associated with recombination in transgenic plants expressing viral sequences

Turturo

Friscina

Gaubert

et al. 2008

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.

“…Focusing on the family Bromoviridae, reports include recombination events in members of the genera Cucumovirus (Férnandez-Cuartero et al, 1994;Fraile et al, 1997;Roossinck et al, 1999;Chen et al, 2002;Bonnet et al, 2005) and Bromovirus (Bujarski & Kaesberg 1986;Allison et al, 1990), as well as between viruses belonging to different genera (de Wispelaere et al, 2005). Phylogenetic trees for proteins were obtained using the PHYML program implemented in PROTTEST that builds the best tree under the best molecular evolutionary model.…”

Section: Introductionmentioning

confidence: 99%

The promiscuous evolutionary history of the family Bromoviridae

Codoñer

Elena

2008

Recombination and segment reassortment are important contributors to the standing genetic variation of RNA viruses and are often involved in the genesis of new, emerging viruses. This study explored the role played by these two processes in the evolutionary radiation of the plant virus family Bromoviridae. The evolutionary history of this family has been explored previously using standard molecular phylogenetic methods, but incongruences have been found among the trees inferred from different gene sequences. This would not be surprising if RNA exchange was a common event, as it is well known that recombination and reassortment of genomes are poorly described by standard phylogenetic methods. In an attempt to reconcile these discrepancies, this study first explored the extent of segment reassortment and found that it was common at the origin of the bromoviruses and cucumoviruses and at least at the origin of alfalfa mosaic virus, American plum line pattern virus and citrus leaf rugose virus. Secondly, recombination analyses were performed on each of the three genomic RNAs and it was found that recombination was very common in members of the genera Bromovirus, Cucumovirus and Ilarvirus. Several cases of recombination involving species from different genera were also identified. Finally, a phylogenetic network was constructed reflecting these genetic exchanges. The network confirmed the taxonomic status of the different genera within the family, despite the phylogenetic noise introduced by genetic exchange. INTRODUCTIONRecombination and segment reassortment are important mechanisms for the genesis of new genetic variability in RNA virus populations. Proportionally, the amount of genetic variability produced after a single recombination event is larger than that produced by single point mutations. Although the importance of recombination was underappreciated in early studies of virus genome evolution, it is now recognized as a widespread phenomenon among positive-strand RNA viruses in animals (Grassly & Holmes, 1997;Holmes et al., 1999;Wilson et al., 1988) and plants (Nagy & Bujarski, 1993;Revers et al., 1996;Aranda et al., 1997;Olsthoorn et al., 2002;Bousalem et al., 2003;Cheng & Nagy, 2003;Moreno et al., 2004;Tan et al., 2004;Bonnet et al., 2005;Urbanowicz et al., 2005;Chare & Holmes, 2006;Weng et al., 2007), as well as in retroviruses such as human immunodeficiency virus type 1 Prljic et al., 2004;Althaus & Bonhoeffer, 2005;Galetto & Negroni, 2005), although it is a rare or even non-existent phenomenon among negativestrand viruses (Chare et al., 2003). There are several mechanisms by which RNA recombination may take place, the most common of which is homologous recombination (Lai, 1992). During this process, the donor replaces a highly homologous region in the acceptor, with the recombinant retaining exactly the same genomic organization of the parental RNA molecules. Therefore, the term homologous refers not only to the presence of sequence homology between both parental RNAs but also the necessity of homologous...