The hrp pilus and extracellular proteins of erwinia amylovora

Erwinia amylovora is the causal agent of fire blight on apple and pear trees. It elicits a hypersensitive response (HR) on nonhost plant species, such as tobacco. The long-term goal of this project is to produce fire-blight-resistant apple plants expressing antibody genes that target key extracellular pathogenicity proteins of E. amylovora. Toward this goal, we are characterizing pathogenicity-associated extracellular proteins and macromolecular structures of E. amylovora. We found that E. amylovora secreted six major extracellular proteins in hrp-inducing broth culture. The extracellular appearance of at least three of these was hrp dependent. One of the secreted proteins had an apparent molecular weight (MW) of 6.5 kDa, which is consistent with the predicted MW of HrpA of E. amylovora. Another hrp-dependent secreted protein had a molecular weight of 198 kDa, which is consistent with the expected MW of the extracellular disease-specific protein DspE of E. amylovora. The third protein had a MW of 48 kDa and reacted with a harpin antibody. Polyclonal antibodies against HrpA and DspE have been produced in mice and the scFv (single chain fragment variable) antibody genes have been isolated from immunized mice. Finally, we found that E. amylovora produced a pilus structure on hip-inducing agar medium. This pilus structure was not produced when E. amylovora was grown on the hip-repressing Luria-Bertani medium.

Duke Scholars

Author Sheng-Yang He Biology