The evolutionary genomics of infectious phytopathogen emergence

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Infectious pathogens impose a substantial burden on the global agricultural industry and result in major food deficits in developing nations. Much of this burden is inflicted by emerging pathogens that have recently evolved to cause disease on important crops. However, we know surprisingly little about the evolutionary mechanisms that enable pathogens to emerge and cause outbreaks. The long-term goal of the Dillon Lab is to understand how novel infectious diseases emerge through diversification of critical disease-causing genes (virulence factors) so that we can better protect vulnerable crops from devastating pathogens. In pursuit of this goal, we are leveraging the plant pathogen Xanthomonas to address the following three objectives: 1.Characterize the distribution and diversification of critical virulence factors. We will analyze more than a thousand genomes to identify virulence factors displaying evolutionary signatures associated with the host-pathogen arms race. We are particularly interested in effector genes that are found in multiple species and are thus capable of generating cross-species resistance barriers. 2.Functionally assess the role of virulence factor diversification in the fate of host-pathogen interactions. We will test whether candidate virulence factors elicit plant immunity and combine the results with our comparative genomic analysis to develop quantitative models of host specificity. 3.Dissect the evolutionary pathways through which novel infectious diseases emerge. We will experimentally evolve three different X. campestris strains on a model host and characterize the phenotypic and genetic basis of disease emergence through time. We will also identify evolutionary tradeoffs associated with disease emergence on alternative hosts, which will reveal vulnerabilities that are a consequence of host specific adaptation. Our research will capture how virulence factors are disseminated across distantly related pathogens, pinpoint cross-species resistance factors that determine the fate of host-pathogen interactions, and produce the first direct insight into the evolutionary pathways that yield the emergence of new plant diseases. We will also provide a rich new source of host resistance targets and develop genome-enabled pathogen diagnostics for use in the field. This work will directly benefit Canadians by contributing these resources to ongoing breeding and surveillance programs, ultimately reducing the burden of pathogens on Canadian farmers and the downstream costs for Canadian consumers. In the next five years, I will also provide advanced multidisciplinary training for more than 25 HQP at all levels (B.Sc., M.Sc., Ph.D., PDF) to fill critical roles in academia, industry, and government. As our changing climate continues to create conditions conducive to pathogen success, we will help build robust disease-control strategies that help shift the balance of host-pathogen interactions in favour of our vulnerable crops.