An overview of irritans-mariner transposons in two Mayetiola species (Diptera: Cecidomyiidae)

Mariner-like elements (MLEs) are widespread Class II transposable elements in insects that are subdivided into several subfamilies. In the current study, we carried out in silico analysis and in vitro experiments to identify MLEs belonging to the irritans subfamily in two cecidomyiid flies, Mayetiola destructor and M. hordei. In silico investigation of M. destructor genome allowed the identification of 25 irritans-like elements, which were mostly defective due to several mutations. These defective forms might be the remnants of active elements that ancestrally invaded the host genome. Structural analyses, including signature motifs and transposase-encoding ORFs, revealed structural heterogeneity and the presence of two full length copies. Five consensuses, reflecting the probable evolutionary groups of these elements, were constructed, based on a similarity matrix. The first consensus (Maymarcons1) belonged to Himar1-like elements reported in other insects, while the remaining four (Maymarcons2 to 5) seemed to be more specific to Cecidomyiidae. Moreover, the presence of elements belonging to the Maymarcons4 group was ascertained by PCR amplification, in both Mayetiola species, and was further identified in the Transcriptome Shotgun Assembly (TSA) of the orange fly, Sitodiplosis mosellana (Cecidomyiidae), suggesting the existence of irritans elements within the Cecidomyiidae, which were derived from an ancestral species by vertical transmission during speciation. On the other hand, consensuses that are specific to M. destructor could be derived from a more recent invasion. This study suggests that both M. destructor and M. hordei genomes have been invaded by irritans elements many times with at least two different evolutionary histories.