PATHOGEN-DERIVED RESISTANCE TO PLANT-VIRUSES

Transformation of plants with portions of viral genomes frequently gives rise to lines of plants that are resistant to the virus from which the sequence was derived. This phenomenon has been termed ''pathogen-derived resistance.'' The nature of the resistance obtained is variable and can be either protein- or RNA-mediated. RNA-mediated resistance often protects against very high levels of inoculum but is highly specific; protein-mediated resistance generally offers lower level but broader spectrum resistance. The mechanism of protein-mediated resistance is probably specific to the protein concerned, while RNA-mediated resistance appears to operate by a mechanism similar to that of cosuppression. The type of resistance obtained is governed, at least in part, by the way the transgene is inserted into the plant chromosomes.