CHARACTERIZATION OF ACQUIRED-RESISTANCE IN LESION-MIMIC TRANSGENIC POTATO EXPRESSING BACTERIOOPSIN

The lesion-mimic mutants of certain plants display necrotic lesions re sembling those of the hypersensitive response and activate local and s ystemic defense responses in the absence of pathogens, We have enginee red a lesion-mimic phenotype in transgenic Russet Burbank potato plant s through constitutive expression of a bacterio-opsin (bO) proton pump derived from Halobacterium halobium, Transgenic potato plants exhibit ing a lesion-mimic phenotype had increased levels of salicylic acid an d overexpressed several pathogenesis-related messenger RNAs, all hallm arks of systemic acquired resistance (SAR), The lesion-mimic plants al so displayed enhanced resistance to the US1 isolate (A1 mating type) o f a fungal pathogen, Phytophthora infestans, a causal agent of late bl ight disease, In contrast, little resistance was observed against the US8 isolate (A2 mating type) of this pathogen, Furthermore, a majority of the transgenic plants displaying the lesion-mimic phenotype had in creased susceptibility to potato virus X. The tubers of these plants w ere not resistant to the bacterial pathogen Erwinia carotovora, These results indicate that expression of bO can result in the activation of defense responses in transgenic potato plants and show for the first time that bO expression can confer resistance to a pathogenic fungus, However, our results also demonstrate that like SAR, this ''engineered '' resistance is likely to be limited to certain pathogens and particu lar cultivars.