Transposable element dynamics among asymbiotic and ectomycorrhizal Amanita fungi

Transposable elements (TEs) are ubiquitous inhabitants of eukaryotic genomes and their proliferation and dispersal shape genome architectures and diversity. Nevertheless, TE dynamics are often explored for one species at a time, and are rarely considered in ecological contexts. Recent work with plant pathogens sug-gests a link between symbiosis and TE abundance. The genomes of pathogenic fungi appear to house an increased abundance of TEs, and TEs are frequently associated with the genes involved in symbiosis. To investigate if this pattern is general, and relevant to mutualistic plant-fungal symbioses, we sequenced the genomes of related asymbiotic (AS) and ectomycorrhizal (ECM) Amanita fungi. Using methods developed to interrogate both assembled and unassembled se-quence, we characterized and quantified TEs across three AS and three ECM species, including the AS outgroup Volvariella volvacea. The ECM genomes are characterized by abundant numbers of TEs, an especially prominent feature of unassembled sequencing libraries. Increased TE activity in ECM species is also supported by phylogenetic analysis of the three most abundant TE superfam