Most plants are resistant to most viruses. There are few compatible interactions between viruses and host plants. The N gene appears to sense the presence of virus by binding to the TMV replicase protein. During the HR the cells containing virus die, resulting in a small necrotic lesion in the leaf. The HR prevents spread of the virus throughout the plant and contains the virus.
Plants infected with one virus often show decreased susceptibility for other viruses.
The molecular basis is unclear, but could involve 'coat protein mediated resistance', or 'systemic aquired resistance'. Unfortunately, cross-protection as a viral control strategy is difficult to apply in the field. While some viruses tend to prevent the infection of a host plant with another virus, the opposite is true for other pairs of viruses. Recently, evidence has been presented that TEV is capable of overriding a powerful anti-viral defense mechanism of the host plant, termed 'gene silencing'. Other viruses may be taking advantage of the ability of TEV to overcome this host defense mechanism.