Westbrook, J. | bioRxiv Science

bioRxiv2019

The Chinese chestnut genome: a reference for species restoration

Forest tree species are increasingly subject to severe mortalities from exotic pests, diseases, and invasive organisms, accelerated by climate change. Forest health issues are threatening multiple species and ecosystem sustainability globally. While sources of resistance may be available in related species, or among surviving trees, introgression of resistance genes into threatened tree species in reasonable time frames requires genome-wide breeding tools. Asian species of chestnut (Castanea spp.) are being employed as donors of disease resistance genes to restore native chestnut species in North America and Europe. To aid in the restoration of threatened chestnut species, we present the assembly of a reference genome with chromosome-scale sequences for Chinese chestnut (C. mollissima), the disease-resistance donor for American chestnut restoration. We also demonstrate the value of the genome as a platform for research and species restoration, including new insights into the evolution of blight resistance in Asian chestnut species, the locations in the genome of ecologically important signatures of selection differentiating American chestnut from Chinese chestnut, the identification of candidate genes for disease resistance, and preliminary comparisons of genome organization with related species.

genomics↗

bioRxiv2017

Contemporary evolution of a Lepidopteran species, Heliothis virescens, in response to modern agricultural practices

Adaptation to human-induced environmental change has the potential to profoundly influence the genomic architecture of affected species. This is particularly true in agricultural ecosystems, where anthropogenic selection pressure is strong. Heliothis virescens feeds on cotton in its larval stages and US populations have been declining since the widespread planting of transgenic cotton, which endogenously express proteins derived Bacillus thuringiensis (Bt). No physiological adaptation to Bt toxin has been found in the field, so adaptation to this altered environment could involve: 1) shifts in host plant selection mechanisms to avoid cotton, 2) changes in detoxification mechanisms required for cotton-feeding versus feeding on other host plants, or 3) loss of resistance to previously used management practices including insecticides. Here we begin to address the question of whether such changes occurred in H. virescens populations between the years 1997 and 2012. As part of our study, we produced an H. virescens genome assembly and used this in concert with a ddRAD-seq enabled genome scan to identify loci with significant allele frequency changes over the 15 year period after Bt crops became widespread in the agricultural landscape. Confirmation that a known genetic change at a previously described H. virescens target of selection was detectable in our genome scan increased our confidence in this methodology. We quantified the strength of selection required to elicit the observed allele frequency changes at loci under selection. Potential contributions of genes near the loci under selection to adaptive phenotypes in the H. virescens cotton system are discussed.

evolutionary biology↗