Exploring effectors in Puccinia striiformis f. sp. tritici and identifying new sources of host resistance

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Crop pathogens jeopardize global food production and Puccinia striiformis f. sp. tritici (Pst), the cause of stripe/yellow rust, is one of the most devastating wheat pathogens in Canada and worldwide. Fungal urediniospores are reproduced asexually on wheat via repeated cycles of infections and in conducive environments can cause disease epidemic; this polycyclic disease cycle can produce zillions of urediniospores on a single susceptible wheat plant and the number of spores in a single crop field can be unimaginable. In such scenarios, even the lowest rate of random mutation coupled with host selection pressure can give rise to new variants/races in the population. Physiologic races or virulence phenotypes of Pst are characterized on wheat genotypes carrying known stripe rust resistance genes (Yr genes) and through our past research we have characterized >35 Pst races in western Canada. The wheat-Pst pathosystem follows the classical gene-for-gene relationship; to successfully infect wheat and overcome deployed Yr genes, Pst uses a cocktail of weapons and the most important of those is 'effectors' or 'Avr genes' which are then perceived by immune receptors in wheat to confer resistance. Identification and characterization of Pst effectors, which results in virulence on wheat Yr genes, is one of the two long-term goals of my research program. We have extensively characterized Pst population from western Canada for virulence phenotypes and genetic lineages (using molecular markers and whole-genome sequencing) and have generated enormous genomic resources. For rust management, identification of Avr effectors is half the battle, the other half of the battle is to strengthen wheat immune system. Identification of stripe rust resistance in wheat & wheat relatives, genetic characterization (mapping, fine-mapping, cloning, functional characterization) and utilization of the resistance by generating pre-breeding germ plasm for wheat breeders is the other major goal of my research program. To this end, we have identified several accessions (cultivated, wild, and landraces) of wheat with resistance and have cloned two novel Yr genes (unpublished) from wild wheat panel. The short-term objectives are to utilize available genomic resources, generate more genomic data on Canadian and selected Pst races from other countries to identify Avr genes corresponding to our cloned Yr genes and clone novel Yr genes from wild wheat and Watkins landraces using cutting-edge gene cloning technology named AgRenSeq. Understanding effector biology and cloning of new Yr genes in wheat will enable us breed for better resistance in wheat varieties for farmers (in Canada and globally) because the project will deliver knowledge about the 'weapons' used by Pst and evolutionary potential of the pathogen. The project will train students (in a diverse lab group) to prepare them to become confident scientists & build their own research programs in academia or become leaders in industry.