Multiple massive domestication and recent amplification of Kolobok superfamily transposons in the clawed frog Xenopus

DNA transposons are generally destroyed by mutations and have short lifespans in hosts, as they are neutral or harmful to the host and therefore not conserved by natural selection. The clawed frog harbors many DNA transposons and certain families, such as T2-MITE, have extremely long lives. These have ancient origins, but have shown recent transposition activity. In addition, certain transposase genes may have been "domesticated" by and conserved over long time periods by natural selection. The aim of this study was to elucidate the evolutionary interactions between the host and the long-lived DNA transposon family it contains. Here, we investigated the molecular evolution of the DNA transposon superfamily. is thought to contribute to T2-MITE transposition. In the diploid western clawed frog and the allotetraploid African clawed frog , we searched for transposase genes homologous to those in the superfamily. To determine the amplification and domestication of these genes, we used molecular phylogenetics and analyses of copy numbers, conserved motifs, orthologous gene synteny, and coding sequence divergence between the orthologs of and , or between those of two distant lineages. Among 38 and 24 prospective transposase genes, 10 or more in and 14 or more in were apparently domesticated. These genes may have undergone multiple independent domestications from before the divergence of and In contrast, certain other transposases may have retained catalytic activity required for transposition and could therefore have been recently amplified. Multiple domestication of certain transposases and prolonged conservation of the catalytic activity in others suggest that superfamily transposons were involved in complex, mutually beneficial relationships with their hosts. Some transposases may serve to activate long-lived T2-MITE subfamilies.