Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/1999
Publication Date: N/A
Interpretive Summary: One of the myriad ways plants defend themselves from fungal and bacterial pathogens is by generating hydrogen peroxide. This defense is often inadequate making it necessary to supplement with chemical sprays to protect crops from toxic fungal and bacterial pathogens. Recent studies have shown that the lethality of hydrogen peroxide increases 30-fold in the presence of chloroperoxidase, a bacterial gene product. In our current research we genetically engineered tobacco to test this hypothesis. Transgenic tobacco expressing a bacterial chloroperoxidase gene showed improved level of resistance to several fungal and bacterial pathogens including Aspergillus flavus, the fungus that produces aflatoxin. Using the tobacco model system, we have clearly demonstrated the utility of this novel gene in boosting plant defense against phytopathogens. Built-in defense mechanisms in crop plants will require less spraying and will save farmers significant production costs. Additionally, less dependence on chemical sprays will reduce environmental and ecological concerns. The research will also benefit biotechnology scientists and plant breeders involved in genetic modification of important crops for improved disease resistance and food and feed safety.
Technical Abstract: Transgenic tobacco plants producing chloroperoxidase, encoded by a novel gene from Pseudomonas pyrrocinia, were obtained by Agrobacterium-mediated transformation. Successful transformation was shown by PCR, Southern, Northern and Western blot analyses. The halogenating activity of the enzyme was demonstrated in transgenic tobacco leaf extracts. Leaf extracts from transformed tobacco inhibited the growth of germinating conidia of Aspergillus flavus, Fusarium moniliforme and Verticillium dahliae. The transformed tobacco plants showed greater levels of disease resistance in planta, against a fungal pathogen, Colletotrichum destructivum and a bacterial phytopathogen, Pseudomonas syringae pv. tabaci. Chloroperoxidase appeared to confer increased disease resistance by catalyzing the conversion of hydrogen peroxide to more lethal antimicrobial hypohalites and peracetic acid.