Genetically engineered resistance in tobacco against South African strainsof tobacco necrosis and cucumber mosaic viruses

The coat protein (CP) genes of local isolates of tobacco necrosis (TNV) and cucumber mosaic virus (CMV) were sequenced. The TNV-F5P gene was similar t o TNV-A and the CMV-Wem gene showed the greatest similarity to subgroup II CP genes. The TNV gene was cloned in the sense and antisense orientation, a nd the CMV gene in the sense orientation, into plant expression vectors. A C-terminally truncated TNV CP gene was also cloned in the sense orientation . Nicotianum tabacum was transformed with the various constructs and resist ance to TNV was achieved in plants expressing both the full-length CP and t he antisense RNA. Protection was lower in plants expressing the truncated C P gene. Protection against CMV was also achieved in transgenic plants expre ssing the CP gene and appeared to be due to a combination of inhibition of viral replication and movement. Some plants expressing both the TNV and CMV CP genes were protected against infection by both viruses.