Resistance to Viral Disease through Expression of Viral Genetic Material from the Plant Genome

Summary

It has been predicted that expression of viral sequences in transformed plants may result in resistance to viral infection. This paper describes and evaluates examples in which this prediction has been tested. When the viral sequence used was based on the satellite RNA of cucumber mosaic virus (CMV) the approach was successful and the transformed tobacco plants did not show the typical CMV symptoms in the systemically infected leaves. This attenuation was not necessarily a result of an inhibitory influence of satellite RNA on viral RNA replication and so is thought to involve a direct interference between satellite RNA and the symptom-inducing capability of the virus. Other viral sequences have also been expressed in transformed plants in attempts to produce virus-resistant or tolerant plants. The degree of success has varied. In experiments in which different regions of the tobacco rattle virus (TRV) genome were expressed as antisense RNA in tobacco, the transformed plants did not show resistance to infection by TRV, possibly because the encapsidated viral RNA is not accessible to the antisense RNA molecules. Expression of viral coat protein in transformed plants did produce resistance to virus infection, but the resultant protection had different properties from the resistance produced by expression of satellite RNA sequences.