A genome-wide analysis of parasitic fitness in the Dutch elm disease fungus Ophiostoma novo-ulmi

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More than one billion elms have been killed by two successive pandemics of Dutch elm disease (DED) since the early 20th century. The highly aggressive fungus Ophiostoma novo-ulmi is responsible for the current DED pandemic and has had a dramatic impact on populations of Ulmus americana, the most widespread native elm species in North America. Understanding the genetic basis of the host-pathogen interaction leading to DED is basic to developing control methods involving manipulation of the pathogen or its host. The general objective of the proposed research is to identify, characterize and manipulate genes that contribute to overall parasitic fitness in O. novo-ulmi. More specifically, we are targeting genes involved in pathogenicity, as well as genes that control the transition between the two growth forms (yeast and mycelium) observed in the DED fungi when they develop in their host. The proposed research takes advantage of the expertise and resources we have developed over the years in the analysis of O. novo-ulmi. These include 1) maintenance of an extensive collection of field isolates of DED fungi from around the world; 2) recovery of O. novo-ulmi mutants with altered fitness; 3) inoculation procedures under controlled environmental conditions for identifying mutants with reduced virulence; 4) methods for monitoring gene expression in DED fungi under different experimental conditions; and 5) access to the full genome sequence of O. novo-ulmi. We will use the latest genomic techniques (including Next Generation Sequencing) in an extensive search for genes that contribute making O. novo-ulmi such a successful pathogen. The significance of the proposed work is that once genes that contribute to parasitic fitness of O. novo-ulmi are identified and characterized, it becomes possible to propose and develop new ways to interrupt the life cycle of the pathogen, in order to protect the remaining elm populations in North America.