Horizontal gene transfer of the Pytheas sequence from Cuscuta to Orobanche via a host-mediated pathway

Horizontal Gene Transfer (HGT) is a phenomenon of DNA transfer between organisms that does not involve a parent-offspring relationship. HGT is believed to play an important role in all groups of organisms, including plants, and especially in parasites. Here we describe a chain of transfers from Cuscuta (Convolvulaceae) to Orobanche rigens (Orobanchaceae)—both parasitic plants—via a host belonging to tribe Genisteae (Fabaceae). During its “journey” between genomes, the transferred sequence, which we named Pytheas , was altered by deletions, additions of new segments from the current genome, substitutions, and rearrangements. This is the first robustly documented case of a multi-step transfer pathway—involving one IGT and two HGTs—connecting three plant species. Specifically, this system involves a host plant mediated gene flow between two distinct parasites without involvement of transposable elements, the cox1 intron, or other vectors. This case also demonstrates how host-parasite interactions can facilitate the spread of genetic material between evolutionarily distant lineages.