Host defense peptides and mechanisms of broad-spectrum disease resistance in plants.

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Pathogenic fungi, oomycetes, and bacteria are the leading cause of plant diseases, contributing to more than one-third of total crop losses throughout the world. Development of plants with durable, broad-spectrum disease resistance is one of the greatest challenges in continuing to meet current and future world food needs. The goal of this research program is to conduct fundamental studies of the properties of natural host defense peptides (HDPs) in potatoes, and their primary roles in the protection of plants against pathogenic microorganisms. These peptides, also called cationic antimicrobial peptides, represent a diverse family of small, membrane-active molecules that are found in many evolutionarily distant organisms, ranging from primitive invertebrates to plants and humans, and are thought to be part of the innate defense system against pathogen invasion. The most important and unique feature of HDPs, which gives them a well-defined advantage over other defensive molecules, is that they target the fundamental design differences between microbial membranes and the membranes of plants and animals. Therefore, the emergence of resistant strains of the pathogens is less probable compared to that of other compounds. The novelty of this research includes the development of broad-spectrum disease resistance in potato using natural plant defense peptides (HDPs), testing hypothesis of HDPs as immunomodulators in plant innate immune response, simultaneous expression of different HDP-coding genes in one plant (gene pyramiding), induced and organ-specific expression of HDPs, and exploring the suitability of potato tubers as low cost, safe, and effective platform for the production of therapeutic HDPs. The research will elucidate the molecular mechanism(s) of HDP-mediated disease resistance in plants, including the mode of action of HDPs and their structural motifs essential for antimicrobial activity, their intracellular localization and transport within the host plant, and will clarify other, unknown roles of HDPs in plant functions that result in improved plant productivity and higher yield. The immediate impact of this proposed research program to Canada is that the resulting potato genotypes can be used as a source of valuable defense genes (germplasm) in conventional potato breeding programs. Other benefits include higher yields, reduced post-harvest losses, and improved food safety due to lower level of fungal toxin contaminants. In addition, this approach may be useful to improve disease resistance in other crops. Finally, HQP involved in this unique research program will be exposed to a variety of experimental learning opportunities, essential for their future careers in academia, government, and industry.