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dc.contributor.authorSollars, Elizabeth
dc.identifier.citationSollars, E. 2017. The genome and epigenome of the European ash tree (Fraxinus excelsior). Queen Mary University of Londonen_US
dc.description.abstractEuropean ash trees (Fraxinus excelsior ) are under threat from the fungal pathogen Hy- menoscyphus fraxineus causing ash dieback disease (ADB). Previous research has shown heritable variation in ADB susceptibility in natural ash populations. Prior to this project, very little genetic data were available for ash, thus hampering efforts to identify markers associated with susceptibility. In this thesis, I have presented nuclear and organellar assemblies of the 880 Mbp F. excelsior genome, with a combined N50 scaffold size of over 100 kbp. Using Ks distributions for six plant species, I found evidence for two whole genome duplication (WGD) events in the history of the ash lineage, one potentially shared with olive (Ks 0.4), and one potentially with other members of the Lamiales order (Ks 0.7). Using a further 38 genome sequences from trees originating throughout Europe, I found little evidence of any population structure throughout the European range of F.excelsior, but nd a substantial decrease in effective population size, both in the distant (from 10 mya) and recent past. Linkage disequilibrium is low at small distances between loci, with an r2 of 0.15 at a few hundred bp, but decays slowly from this point. From whole genome DNA methylation data of twenty F. excelsior and F. mandshurica trees, I identi ed 665 Differ- entially Methylated Regions (DMRs) between those with high and low ADB susceptibility. Of genes putatively duplicated in historical WGD events, an average of 25.9% were differen- tially methylated in at least one cytosine context, possibly indicative of unequal silencing. Finally, I found some variability in methylation patterns among clonal replicates (Pearson's correlation coefficient 0.960), but this was less than the variability found between different genotypes ( 0.955). The results from this project and the genome sequence especially, will be valuable to researchers aiming to breed or select ash trees with low susceptibility to ADB.en_US
dc.description.sponsorshipEU FP7-PEOPLE project `INTERCROSSING', ID:289974. Sequencing of the reference tree was funded by NERC emergency grant NE/K01112X/1.en_US
dc.publisherQueen Mary University of Londonen_US
dc.rightsThe copyright of this thesis rests with the author and no quotation from it or information derived from it may be published without the prior written consent of the author
dc.subjectBiological and Chemical Sciencesen_US
dc.subjectEuropean ash treeen_US
dc.subjectash dieback diseaseen_US
dc.titleThe genome and epigenome of the European ash tree (Fraxinus excelsior)en_US

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