This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In a study published in the journal Nature Communications, researchers from the Royal Botanic Gardens, Kew, Forest Research and collaborating organizations present the first-ever European ash (Fraxinus excelsior) pangenome, using high-quality DNA to aid research into natural ash dieback resistance. Using the pangenome, constructed from a group of 50 trees of diverse origins, the scientists analyzed a genomic dataset from more than 1,000 trees to identify genes associated with resistance.
They found 211 genes with possible links to ash dieback resistance, 16 of which were dispensable, meaning they were present in only some individual trees and not across the board. Unlike genes found in every individual of a species, dispensable genes are not always essential. They may, however, confer traits advantageous in certain contexts, like disease resistance or better drought tolerance, potentially allowing populations to adapt more quickly to changing circumstances.
A traditional genome assembly approach captures information from only a single individual—only a pangenome allows dispensable genes to be identified. In total, the researchers identified more than 3,400 genes as dispensable across the trees sampled. Although they represent only 9% of all genes, these may play a critical role in determining differences between individuals.
Unlocking these data could enable researchers to more accurately predict which trees are likely to be genetically shielded against ash dieback disease, caused by the fungus Hymenoscyphus fraxineus, and could help breed resistant populations by identifying the most promising trees from their genetic code alone. Ash dieback is a major concern for the UK and has decimated British treescapes since first being detected in 2012, killing millions of trees. Only a tiny proportion of trees—as low as 0.5%—remain healthy after long-term disease exposure.
Pangenomes provide a more comprehensive way of studying susceptibility to pathogens, compared with using a single genome, as they capture the dispensable DNA sequences carried by some trees but not others. In fact, the pangenome constructed in this study was 22% larger than a high-quality genome from a single ash individual when accounting for dispensable genetic sequences. Daniel Wood, Kew research fellow and first author, says, "If each ash genome is the same movie, these findings highlight how many director's cuts, extended editions, deleted scenes and alternate endings nevertheless exist in wild populations—perhaps most of the runtime is the same, but the variable bits can potentially make the difference between a box-office smash and a flop.
"Using the total catalog of genetic sequences, represented in the pangenome, we identified genes potentially associated with resistance to ash dieback. However, this resource can be applied to identify the genetic basis of other traits of interest, such as environmental resilience, or resistance to other threats such as the emerald ash borer beetle." Dr. Laura Kelly, research leader at Kew and senior author, says, "The pangenome provides a powerful new tool in the continued fight against ash dieback, and in the response to the ever-growing threat from the emerald ash borer as its invasion advances across Europe." Among the 50 sampled trees was a young ash specimen grown at Kew Gardens in London, as well as trees sampled from a Forest Research trial site outside Norwich.
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