Structure and evolution of DNA transposons of the <i>L31</i> superfamily of bivalves

Abstract

DNA transposons of the IS630/Tc1/mariner (ITm) are widespread representatives of DNA transposons that make a significant contribution to the evolution of eukaryotic genomes. With the start of large-scale application of next generation sequencing (NGS) technologies and the emergence of many new whole genome sequences of organisms in nucleotide collections, ITm elements have been identified in most taxa of the eukaryotic tree of life. Despite the rather detailed study of the diversity of ITm representatives, elements are still found that contribute to the expansion and revision of the classification of this group of DNA transposons. This paper presents for the first time a detailed analysis of the L31 elements of bivalves, which resulted in a description of the structure, diversity, distribution, and phylogenetic position among the ITm elements. It was found that L31 transposons are an independent superfamily in the ITm group, which has an ancient origin. Within the L31 clade, rather high diversity was observed: five phylogenetic clusters were identified. At the moment, the presence of L31 transposons in molluscs has been revealed only in bivalves in the subclass Autobranchia, with a predominance in diversity and quantity in the infraclass Pteriomorphia. It has also been shown that the protein encoded by the second open reading frame (ORF2) is an integral structural component of almost all full-length L31 elements. The data obtained contribute to a better understanding of the evolution of representatives of ITm transposons. Further study of L31 transposons in other taxa (cnidaria), as well as the study of the function of the second ORF protein, will provide an opportunity to better understand the evolution of DNA transposons, the mechanisms of horizontal transfer, and the contribution to eukaryotic biodiversity.