The virus has more secrets to reveal

Committing suicide in order to survive: How do viruses cause plants to do this?

The way a plant reacts to a viral infection depends on both the genetic information in the plant cell and on the virus's RNA.
Mundry and his work groups focussed on the latter factor in the 1980s and chose the tobacco mosaic virus as a model organism.

Mundry's discovery of 1958 had already been based on the observation that the virus strain he had chosen caused different symptoms in the plant after mutating than it did before. Instead of spreading throughout the plant with almost no visible outward signs, the infection caused by the mutations was restricted to individual cells of the leaves that had been rubbed with the virus. Although the affected areas died (local necroses), the source of infection was consequently contained. This is referred to as a hypersensitive reaction by the leaf tissue. It makes the plant resistant to the virus.

This led to another question: What forces the plant to react hypersensitively after the virus has mutated?
Mundry's work groups came to the conclusion that it was caused by the changed signal properties of the protein that the virus normally transports into neighbouring cells.

This result remained controversial. Other research groups considered a mutation of the envelope protein to be the trigger for the hypersensitive reaction. The debate has yet to be resolved. However, attempts have been made to use both components to generate resistance.

Further information for experts: Stuttgart's contributions to understanding the hypersensitive reaction