Could Transgenic Plants Expressing Virus-Derived Sequences Create New Routes for Virus Evolution?

Virus resistance is a major objective in the development of genetically engineered crops. The biotechnological strategies developed to control plant viruses can be classified into three major categories based on the type of nucleic acid sequence used [1]. The first category makes use of sequences derived from the viral genomes; a concept known as pathogen-derived resistance (PDR). The second involves plant-derived genes; and the third is non-viral, non-plant derived sequences, such as antibodies directed against the specific virus. So far, the only solutions implemented in commercial agriculture have exploited the first strategy, PDR, and consist of fourteen events regarding seven plant species and eight viruses [2]. Shortly after the publication of the first scientific reports on transgenic plant resistant to virus, there were concerns regarding the potential impacts that these plants could have on the environment and in particular regarding the risk that, under particular conditions, they could lead to the generation of new viruses and thus new diseases. In this context, heteroencapsidation, synergism and recombination, all well-known phenomena naturally occurring in nature when plants are simultaneously infected with more than one virus, were reanalyzed under a new perspective.