Comparison of the hypersensitive response induced by the tomato Cf-4 and Cf-9 genes in Nicotiana spp.

We have previously shown that tomato Cf-9 induces an Avr9-dependent hyperse nsitive response (HR) in Nicotiana tabacum and potato. We show here that Cf -4 also induces an Avr4-dependent HR in two tobacco species (N. tabacum and N. benthamiana). The HR induced by Cf-4 and Cf-9 was compared in stable to bacco transgenics by a seedling lethal assay and resistance to recombinant Potato virus X expressing Avp4 or Avr9. We also compared HR induction with Agrobacterium-mediated transient expression. The Cf-4/Avr4 combination indu ced a more rapid KR than Cf-9/Avr9. Sensitive assays for Cf-9 and Cf-4 func tion should prove useful for structure/function analyses of these resistanc e proteins in tobacco.