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 that N. glutinosa is resistant to W260, but responds with local chlorotic lesions rather than necrotic lesions. In contrast, N. clevelandii responds to W260 with systemic cell death. The reactions of the progenitors of N. edwardsonii 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 can indeed be uncoupled. First, we showed that the non-necrotic resistance response of N. glutinosa could be converted to HR when these plants were crossed with N. clevelandii. Second, we found that cell death and resistance segregated independently in the F2 population of a cross between N. edwardsonii and N. clevelandii. We concluded that the resistance of N. edwardsonii to W260 infection was conditioned by a gene derived from N. glutinosa, whereas cell death was conditioned by a gene derived from N. clevelandii. An analysis of pathogenesis-related (PR) protein expression in response to W260 infection revealed that elicitation of PR proteins was associated with resistance rather than with the onset of cell death.