Evaluation of the hrpN gene for increasing resistance to fire blight in transgenic apple

M.26 apple rootstock was transformed with different hrpN gene constructs to evaluate their potential for increasing resistance to fire blight. One approach was to attempt to induce a resistance reaction in transgenic apple by low-level expression of harpin from the nos promoter. A second approach was to engineer programmed cell death by high-level expression of harpin from a pathogen-inducible promoter. Since the cell wail is thought to be the site of harpin and host-cell interaction, constructs for both approaches were made with and without a signal peptide sequence (SS) to direct harpin to the intercellular space. For the first approach, two plasmid binary vectors containing hrpN gene constructs, pBINPLUS: :Pnos-hrpN-Tnos and pBINPLUS: :Pnos-antihrpN-Tnos (antisense version), were transferred to M.26 explants using Agrobacterium tumefaciens. Regenerants were obtained on media containing kanamycin (100 mg/1) and transformation was confirmed by NPTII ELISA and PCR analysis for the presence of the hrpN gene. Expression of harpin was demonstrated by western analysis. For the second approach, the pathogenesis-related protein gene promoter (gst-1, formerly prp1-1)) of potato is being evaluated in apple for its ability to be specifically induced by apple pathogens, including Erwinia amylovora.