Altered response to viral infection by tobacco plants perturbed in ubiquitin system.

Tobacco plants can be perturbed in their ubiquitin system by expression of a ubiquitin variant with a lys to arg change at position 48. Plants expressing this ubiquitin variant have a tendency to form necrotic lesions resembling those occurring as defense reactions against some pathogens. Using the interaction between tobacco and tobacco mosaic virus (TMV), it was investigated whether the ubiquitin variant influences plant responses to pathogen infection. Expression of the ubiquitin variant leads to changes in the response of both resistant and susceptible tobacco varieties. Resistant plants form fewer, but darker lesions. In sensitive plants, TMV replication is inhibited, but not completely abolished. Moreover, susceptible plants expressing the ubiquitin variant induce PR-1 mRNA in response to virus, whereas controls do not express PR-1 under these conditions.