A TMV-Cg mutant with a truncated coat protein induces cell death resembling the hypersensitive response in Arabidopsis

Tobacco mosaic virus (TMV)-Cg is able to propagate and multiply systemically to high levels in Arabidopsis thaliana ecotype Col-0. In this study, we obtained a Cg mutant, Cgk1, which expresses a coat protein with a truncated carboxyl terminus. Interestingly, Cgk1 induced necrosis that resembled the hypersensitive response and caused more pronounced disease symptoms than wild type Cg in Arabidopsis Col-0 plants. A reactive oxidative burst occurred prior to this necrosis. We found that expression of the pathogenesis-related gene PR-1 was induced by Cgk1 infection, and also by infection with wild type Cg, but only in npr1-2 mutant plants, not in NahG transgenic plants. These results suggested that PR-1 expression is dependent on the salicylic acid signaling pathway, but is independent of NPR1.