Genetic Engineering of Plants for Protection Against Virus Diseases

Summary

The practice of protecting plants against severe virus disease by cross-protection has been in use in agriculture for more than 15 years but the molecular mechanism(s) that lead to cross-protection have not been characterized. Tobacco and tomato plants have been produced with some of the characteristics of cross-protection against tobacco mosaic virus (TMV) and alfalfa mosaic virus (AlMV). Transgenic plants were generated that express the coat protein-coding sequence of TMV or AlMV. Plants expressing the TMV or AlMV coat protein were protected against TMV or AlMV infection, respectively, due to an 80–90% reduction in the numbers of sites at which infection is established on the inoculated leaves. Many of the inoculated plants escaped infection; others became infected but expressed a delay in the development of disease similar to the delay in plants that are cross-protected in the classical sense. Protection was also expressed in protoplasts isolated from transgenic plants. In these experiments TMV RNA or TMV was introduced into isolated protoplasts by electroporation. Expression of the TMV (U1 strain) coat protein-coding sequence in transgenic plants protected against a variety of tomato mosaic virus strains (L-TMV, ToMV-1, ToMV-2, ToMV-2a) as well as against the U1 strain and a severe, yellow strain of TMV. Protection against the C_c strain of TMV (sunn hemp mosaic virus) was less dramatic than against other TMV strains. The results suggest that this approach may be used for controlling virus infections when other types of disease resistance genes are not available.