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Title: RESPONSE OF TRANSGENIC 'ROYAL GALA' APPLE (MALUS X DOMESTICA BORKH.) SHOOTS, CARRYING A MODIFIED MB39 GENE, TO ERWINIA AMYLOVORA

Author
item LIU, QINGZHONG - VISITING SCIENTIST
item INGERSOLL, JOHN - VISITING SCIENTIST
item OWENS, LOWELL - ARS RETIRED COLLABORATOR
item Salih, Sarbagh
item MENG, RENGONG - USDA/ARS/HCRL CORVALLIS
item Hammerschlag, Freddi

Submitted to: Plant Cell Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2001
Publication Date: 7/20/2001
Citation: Liu, Q., Ingersoll, J., Owens, L., Salih, S.S., Meng, R., Hammerschlag, F.A. 2001. Response of transgenic 'royal gala' apple (malus x domestica borkh). shoots, carrying a modified mb39 gene, to erwinia amylovora. Plant Cell Reports. 20:306-312

Interpretive Summary: Fire blight, caused by the bacterium Erwinia amylovora, is a serious and difficult to control disease of many important apple cultivars, and economic losses in commercial orchards can be significant, and sometimes devastating. Improvement of apple via conventional breeding is a slow, lengthy process and although gene transfer techniques make it possible to overcome this problem by the direct transfer of useful genes (e.g. for disease resistance) into commercially important cultivars, very few transgenic apple trees have been produced. Recently, genes for several bactericidal proteins were successfully transferred to apple cultivar Galaxy and several resulting transgenic lines expressed increased disease resistance. In this study, we report on the introduction of the gene for the bactericidal peptide cecropin into 'Royal Gala'apple (highly susceptible to fire blight) and then treatment of two of the transgenic lines with a chromosome doubling agent. Several transgenic lines expressed increased levels of resistance to fire blight and doubling the chromosome numbers of these lines increased resistance even further. This research should be of use to scientists interested in using gene transfer techniques to introduce genes for disease resistance into apple and other species susceptible to bacterial diseases.

Technical Abstract: Transgenic 'Royal Gala' apple (Malus x domestica Borkh.) shoots were obtained by Agrobacterium-mediated gene transfer using a plasmid vector pGV with T-DNA encoding a modified cecropin gene (MB39) joined to a secretory coding sequence from barley alpha-amylase and placed under the control of a wound-inducible promoter osmotin from tobacco. The integration of the cecropin MB39 gene into apple was confirmed by Southern blot analysis. The transformation efficiency was 1.5 % when internodes from etiolated shoots were used as explants and 2% when leaf explants were used. Both non-transgenic and transgenic tetraploid plants were produced by treatment of leaf explants with colchicine at 25 mg/liter. Polyploidy was confirmed by flow cytometry. Three of the diploid transgenics were significantly more resistant to Erwinia amylovora than the non-transformed 'Royal Gala' control, and in one case, a tetraploid transgenic line was significantly more resistant than the diploid shoot it was derived from.