Gene acquisition by giant transposons primes eukaryotes for rapid evolution via horizontal gene transfer.

Horizontal gene transfer (HGT) disseminates genetic information between species and is a powerful mechanism of adaptation. Yet, we know little about its underlying drivers in eukaryotes. Giant transposons have been implicated as agents of fungal HGT, providing an unprecedented opportunity to reveal the evolutionary parameters behind this process. Here, we characterize the gene cluster, which contributes to formaldehyde resistance, and use it to demonstrate how mobile element evolution shapes fungal adaptation. We found that clusters have been acquired by various distantly related , which each exhibit multiple instances of horizontal transfer across fungal species (at least nine events, including between different taxonomic orders). Many clusters have subsequently integrated into their host's genome, illustrating how shape the evolutionary trajectory of fungal hosts beyond any single transfer. Our results demonstrate the key role play in mediating rapid and repeated adaptation via HGT, elevating the importance of mobile element evolution in eukaryotic biology.