ALTERED RESPONSE TO VIRAL-INFECTION BY TOBACCO PLANTS PERTURBED IN UBIQUITIN SYSTEM

Tobacco plants can be perturbed in their ubiquitin system by expressio n of a ubiquitin variant with a lys to arg change at position 48. Plan ts expressing this ubiquitin variant have a tendency to form necrotic lesions resembling those occurring as defense reactions against some p athogens. Using the interaction between tobacco and tobacco mosaic vir us (TMV), it was investigated whether the ubiquitin variant influences plant responses to pathogen infection. Expression of the ubiquitin va riant leads to changes in the response of both resistant and susceptib le 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 vari ant induce PR-1 mRNA in response to virus, whereas controls do not exp ress PR-1 under these conditions.