Evolutionary diversification and repeated gene capture by telomeric retrotransposons across the Drosophila genus
Authors: Jae Hak Son 1; Mia Levin 2; Christopher Ellison 1
Affiliations: 1) Department of Genetics, Human Genetics Institute of New Jersey, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States of America; 2) Department of Biology and Epigenetics Institute, University of Pennsylvania, Philadelphia, United States of America
Keywords: a. genome evolution; m. Telomeres
Transposable elements (TEs) are mobile genetic elements that must replicate faster than their host to avoid extinction. TEs often evolve antagonistically with their host in a classic evolutionary arms race scenario. On the other hand, the co-evolution between TEs and the host genome can be mutualistic, where TEs are co-opted to benefit their host. Telomere-specialized non-LTR retrotransposons in Drosophila have traditionally been known for their mutualistic relationship with their host. These elements have replaced the role of telomerase, which is absent across the Drosophila genus, and replicate specifically to chromosome ends to protect them from erosion. However, more recent work has identified rapid evolution in many telomere binding proteins, which is more consistent with antagonistic evolution rather than a mutualism. Furthermore, we recently found that the D. melanogaster TART-A telomere-specialized transposon has captured a portion of the piRNA pathway gene, nxf2, which allows it to target nxf2 for suppression, again consistent with antagonistic evolution. Here we have examined the evolutionary diversification of telomere-specialized retrotransposons across the Drosophila genus using publicly available long-read genome assemblies from 106 Drosophila species genomes. We identify 9 major telomeric retrotransposon clades from the gag gene and 7 major clades from the pol gene, including the previously described HTT clade from melanogaster group and the TR2 clade found in the ananassae and montium groups. We find that host gene capture among these telomere-specialized TEs is relatively common and propose that this phenomenon may serve as an important source of host gene regulation in the Drosophila germline.