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Title: Ectopic expression of the Dahlia merckii defensin peptide DmAMP1 improves resistance against Phytophthora palmivora by reducing pathogen vigor

Author
item ZHU, YUN - HI AG RESEARCH CENTER
item AGBAYANI, RICELLE - HI AG RESEARCH CENTER
item Moore, Paul

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2006
Publication Date: 6/20/2007
Citation: Zhu, Y.J., Agbayani, R., Moore, P.H. 2007. Ectopic expression of the Dahlia merckii defensin peptide DmAMP1 improves resistance against Phytophthora palmivora by reducing pathogen vigor. Planta 226:87-97.

Interpretive Summary: The gene responsible for resistance of Dahlia to a range of pathogens has been cloned and transferred into numerous other plant species to increase their resistance to diseases to which they were originally susceptible, however, the mechanism by which resistance is achieved is unknown. Collaborative research between scientists of the Hawaii Agriculture Research Center and ARS studied the mechanism of action of the cloned Dahlia defensin gene by using it to increase resistance of papaya to phytophthora, a pathogen responsible for crown rots or collar rots of many woody and herbaceous plants including papaya, citrus, avocado, stone fruits, walnut, apple, peppers, and soybean. Papaya lines transformed with the Dahlia definsin gene showed increased resistance to phytophthora infections that was associated with a newly synthesized peptide that inhibited the development of phytophthora hyphae as they were growing in inoculated leaves and when leaf protein extracts from the transformed plants was added to media for growing phytophthora artificially in the laboratory. Hints that the Dahlia defensin affects phytophthora's plasmamembrane will suggest ways to increase plant resistance to this pathogen and the transformed papaya lines will be advanced to field trials for performance in fruit production and may prove beneficial to the papaya fruit industry.

Technical Abstract: Defensins are cysteine-rich antimicrobial peptides that are widely distributed among plants, insects, and mammals. As potent defenders in protecting plants from pathogenic fungal attack, plant defensins are presumed to play an important role in the innate immunity of plants and are expected to find broad ranged applications in the production of transgenic crops. The defensin gene DmAMP1, cloned from Dahlia merckii (Osborn et al., 1995), has been introduced as a transgene into a range of species to increase host resistance to pathogens to which they were originally susceptible (Terras et al., 1995; Wang et al., 1999; Gao et al., 2000). However, the mechanism of interaction of the DmAMP1 peptide with Phytophthora spp, one of the more important causal agents of plant diseases in worldwide, has not been clearly characterized in planta. In this study, we expressed DmAMP1 in papaya (Carica papaya L.), a plant highly susceptible to a root, stem, and fruit rot disease caused by Phytophthora palmivora, to study the interaction of the DmAMP1 defensin with P. palmivora. Our results demonstrate that expressing the DmAMP1 gene in papaya plants increased resistance against P. palmivora and that this increased resistance is associated with reduced hyphae growth of P. palmivora at the infection sites.