Genome-wide characterization of LTR retrotransposons in the non-model deep-sea annelid Lamellibrachia luymesi.

backgroundLong Terminal Repeat retrotransposons (LTR retrotransposons) are mobile genetic elements composed of a few genes between terminal repeats and, in some cases, can comprise over half of a genome's content. Available data on LTR retrotransposons have facilitated comparative studies and provided insight on genome evolution. However, data are biased to model systems and marine organisms, including annelids, have been underrepresented in transposable elements studies. Here, we focus on genome of Lamellibrachia luymesi, a vestimentiferan tubeworm from deep-sea hydrocarbon seeps, to gain knowledge of LTR retrotransposons in a deep-sea annelid.

resultsWe characterized LTR retrotransposons present in the genome of L. luymesi using bioinformatic approaches and found that intact LTR retrotransposons makes up about 0.1% of L. luymesi genome. Previous characterization of the genome has shown that this tubeworm hosts several known LTR-retrotransposons. Here we describe and classify LTR retrotransposons in L. luymesi as within the Gypsy, Copia and Bel-pao superfamilies. Although, many elements fell within already recognized families (e.g., Mag, CSRN1), others formed clades distinct from previously recognized families within these superfamilies. However, approximately 19% (41) of recovered elements could not be classified. Gypsy elements were the most abundant while only 2 Copia and 2 Bel-pao elements were present. In addition, analysis of insertion times indicated that several LTR-retrotransposons were recently transposed into the genome of L. luymesi, these elements had identical LTR's raising possibility of recent or ongoing retrotransposon activity.

conclusionsOur analysis contributes to knowledge on diversity of LTR-retrotransposons in marine settings and also serves as an important step to assist our understanding of the potential role of retroelements in marine organisms. We find that many LTR retrotransposons, which have been inserted in the last few million years, are similar to those found in terrestrial model species. However, several new groups of LTR retrotransposons were discovered suggesting that the representation of LTR retrotransposons may be different in marine settings. Further study would improve understanding of the diversity of retrotransposons across animal groups and environments.