In the Erwinia amylovora genome, the hrp gene cluster containing the dspA/E/EB/F operon plays a crucial role in mediating the pathogenicity and the hypersensitive response (HR) in the host plant. The role of the dspA/E gene derived from E. amylovora was investigated by monitoring the expression of the beta-glucuronidase (GUS) reporter system in transgenic Arabidopsis thaliana cv. Pri-Gus seedlings. A mutant Delta dspA/E strain of E. amylovora was generated to contain a deletion of the dspA/E gene for the purpose of this study. Two-week-old seedlings of GUS transgenic Arabidopsis were vacuum-infiltrated with the wild-type and the mutant (Delta dspA/E) E. amylovora strains. The Arabidopsis seedlings were fixed and stained for GUS activity after 3-5 days following infiltration. The appearance of dense spots with blue staining on the Arabidopsis leaves indicated the typical characteristic of GUS activity. This observation indicated that the wild-type E. amylovora strain had induced a successful and efficient infection on the A. thaliana Pri-Gus leaves. In contrast, there was no visible GUS expression on leaf tissues which were inoculated with the Delta dspA/E mutant E. amylovora strain. These results indicate that the dspA/E gene is required by the bacterial cells to induce HR in non-host plants.