Virus Resistance -
Several approaches have been used to engineer plants for virus resistance, which are as follows:
(1) coat protein gene,
(2) cDNA of satellite RNA,
(3) defective viral genome,
(4) antisense RNA approach, and
(5) ribozyme­ mediated protection.

Of these strategies, use of coat protein gene has been the most successful. Transgenic plants having virus coat protein gene linked to a strong promoter have been produced m many crop plants, tobacco, tomato, alfalfa, sugarbeet, potato, etc.

The effectiveness of coat protein (CP) gene in conferring virus resistance can be affected by both the amount of coat protein produced in transgenic plants and by the concentration of virus inoculum.
Most likely the resistance generated by CP is due to the blocking of the process of uncoating of virus particles, which is necessary for viral genome replication as well as expression. However, other effects seem to be involved in producing coat protein mediated virus resistance; one such mechanism appears to be the prevention or delay of systemic spread of the viruses.

But at least in some cases, the resistance mechanism does not involve the coat protein itself since CP genes even in antisense orientation produce resistance to the virus.