Study of VIPER and TATE in kinetoplastids and the evolution of tyrosine recombinase retrotransposons

Background: Kinetoplastids are a flagellated group of protists, including some parasites, such as Trypanosoma and Leishmania species, that can cause diseases in humans and other animals. The genomes of these species enclose a fraction of retrotransposons including VIPER and TATE, two poorly studied transposable elements that encode a tyrosine recombinase (YR) and were previously classified as DIRS elements. This study investigated the distribution and evolution of VIPER and TATE in kinetoplastids to understand the relationships of these elements with other retrotransposons.

Results: We observed that VIPER and TATE have a discontinuous distribution among Trypanosomatidae, with several events of loss and degeneration occurring during a vertical transfer evolution. We were able to identify the terminal repeats of these elements for the first time, and we showed that these elements are potentially active in some species, including T. cruzi copies of VIPER. We found that VIPER and TATE are strictly related elements, which were named in this study as VIPER-like. The reverse transcriptase (RT) tree presented a low resolution, and the origin and relationships among YR groups remain uncertain. Conversely, for RH, VIPER-like grouped with Hepadnavirus, whereas for YR, VIPER-like sequences constituted two different clades that are closely allied to Crypton. Distinct topologies among RT, RH and YR trees suggest ancient rearrangements/exchanges in domains and a modular pattern of evolution with putative independent origins for each ORF.

Conclusions: Due to the presence of both elements in Bodo saltans, a nontrypanosomatid species, we suggested that VIPER and TATE have survived and remained active for more than 400 million years or were reactivated during the evolution of the host species. We did not find clear evidence of independent origins of VIPER-like from the other YR retroelements, supporting the maintenance of the DIRS group of retrotransposons. Nevertheless, according to phylogenetic findings and sequence structure obtained by this study and other works, we proposed separating DIRS elements into four subgroups: DIRS-like, PAT-like, Ngaro-like, and VIPER-like.