Isolation and characterization of seventy-nine full-length <Emphasis Type="Italic">mariner</Emphasis>-like transposase genes in the Bambusoideae subfamily

Mariner-like elements (MLEs) are the most diverse and widespread transposable elements, with members of the MLE superfamily found in fungi, plants, ciliates and animals. In a previous study, we characterized 82 MLE transposase gene fragments (average length 383 bp) in 44 bamboo species, indicating that MLEs are widespread, abundant and diverse in the Bambusoideae subfamily. In this study, we isolated 79 full-length MLE transposase genes from 63 bamboo species representing 38 genera in six subtribes mainly found in China. The transposases were highly conserved, mostly uniform in length and contained intact DNA-binding motifs and DD39D catalytic domains with few notable frameshift, indel and nonsense mutations. This suggested the MLEs are probably still mobile, not yet affected by vertical inactivation. A phylogenetic tree of the Bambusoideae subfamily established using ribosomal DNA internal transcribed spacer sequences was incongruent with a second tree based on the MLE transposase genes. This evidence, together with the presence of near-identical MLEs in distantly related species and diverse MLEs in closely related species, indicates that MLEs have evolved in a distinct manner, probably independently of speciation events in the subfamily. The evolution and diversity of MLE transposase genes in the Bambusoideae subfamily is discussed.