Uncoupling resistance from cell death in the hypersensitive response of Nicotiana species to Cauliflower mosaic virus infection

Cauliflower mosaic virus strain W260 elicits a hypersensitive response (HR) in leaves of Nicotiana edwardsonii, an interspecific hybrid derived from a cross between N, glutinosa and N, clevelandii. Interestingly, we found tha t N. glutinosa is resistant to W260, but responds with local chlorotic lesi ons rather than necrotic lesions. In contrast, N. clevelandii responds to W 260 with systemic cell death. The reactions of the progenitors of N. edward sonii to W260 infection indicated that each contributed a factor toward the development of HR. In this study, we present two lines of evidence to show that the resistance and cell death that comprise the HR elicited by W260 c an indeed be uncoupled. First, we showed that the non-necrotic resistance r esponse of N. glutinosa could be converted to HR when these plants were cro ssed with N, clevelandii. Second, we found that cell death and resistance s egregated independently in the Fz population of a cross between N. edwardso nii and N. clevelandii. We concluded that the resistance of N. edwardsonii to W260 infection was conditioned by a gene derived from N, glutinosa, wher eas cell death was conditioned by a gene derived from N. clevelandii, An an alysis of pathogenesis-related (PR) protein expression in response to W260 infection revealed that elicitation of PR proteins was associated with resi stance rather than with the onset of cell death.