Pathogen derived resistance to Potato virus Y: mechanisms and risks

Since the concept of pathogen derived resistance (PDR) was proposed in 1985, genetic transformation of plants to express virus-derived sequences has been used to engineer resistance to many viruses. This paper reviews PDR approaches to Potato virus Y (PVY, type member of the genus Potyvirus). PDR to viruses operates often through RNA-mediated resistance mechanisms that do not require protein expression. Studies on the RNA-mediated resistance have led to the discovery of posttranscriptional gene silencing (PTGS), a mechanism that controls gene expression in eukaryotic cells and provides natural protection against virus infections. Viruses, in turn, can suppress the PTGS with some of their proteins, such as the helper component-proteinase protein of PVY. Expression of PVY proteins in transgenic plants entails a risk for heterologous encapsidation or synergism with viruses that infect the PVY-resistant transgenic plant. These risks are avoided using RNA-mediated resistance, but a risk still exists for recombination between the transgene transcript and the RNA genome of the infecting virus, which may create a virus with altered properties. The harmful consequences can be limited to some extent by removing functional motifs from the viral sequence used as a transgene.