The Genome of Fraxinus excelsior (European ash)

Fraxinus excelsior (European Ash) is widespread throughout Europe and is of great ecological and economic value. It is currently threatened by the fungal pathogen Hymenoscyphus fraxineus, the causative agent of ash dieback disease, which has been found in almost every European country within the tree’s range. Natural genetic variation within ash populations yields a small percentage of low-susceptibility individuals, which could provide a basis for the selective breeding of disease resistance.

The British Ash Tree Genome Project has provided a reference F. excelsior genome sequence (N50 of 98 kbp) of a low heterozygosity British ash tree produced by self-pollination. We have identified approximately 40k genes from an integrated RNA-seq and ab initio prediction analysis, and find high levels of shared gene content with tomato (Solanum lycopersicum), as well as the other woody angiosperms grape (Vitis vinifera) and poplar (Populus trichocarpa).

We have also resequenced 37 trees representing various locations in Europe to study the genetic diversity of F. excelsior. In total, we identify over 13 million polymorphic positions within the genome. By comparing the variation of resistant and susceptible trees, we aim to find candidate resistance variants that we can study further in the next stages of the project.

Much of our data and analysis results are hosted on our project website, ashgenome.org. These will provide a foundational resource not only for researchers studying ash dieback, but also resistance to the Emerald Ash Borer, currently devastating Fraxinus populations in North America, as well as the study of other tree species.