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 b een used to engineer resistance to many viruses. This paper reviews PDR app roaches 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 mecha nism that controls gene expression in eukaryotic cells and provides natural protection against virus infections. Viruses,in turn, can suppress the PTG S with some of their proteins, such as the helper component-proteinase prot ein of PVY. Expression of PVY proteins in transgenic plants entails a risk for heterologous encapsidation or synergism with viruses that infect the PV Y-resistant transgenic plant. These risks are avoided using RNA-mediated re sistance, but a risk still exists for recombination between the transgene t ranscript and the RNA genome of the infecting virus, which may create a vir us with altered properties. The harmful consequences can be limited to some extent by removing functional motifs from the viral sequence used as a tra nsgene.