Characterization of non-LTR retrotransposable TRAS elements in the aphids Acyrthosiphon pisum and Myzus persicae (Aphididae, Hemiptera).

A non-LTR TRAS retrotransposon (identified as TRASAp1) has been amplified in the pea aphid Acyrthosiphon pisum and its presence has been assessed also in the peach potato aphid Myzus persicae. This TRAS element possesses 2 overlapping ORFs (a gag-ORF1 and a pol-ORF2 containing the reverse transcriptase and the endonuclease domains) that show a similarity ranging from 40% to 48% to proteins coded by other TRAS elements identified in insects (including the beetle Tribolium castaneum and the moth Bombyx mori). The study of the TRAS chromosomal insertion sites, performed by standard fluorescent in situ hybridization (FISH) and fiber FISH, showed that TRAS elements were located in a subtelomeric position, just before the telomeric (TTAGG) n repeats. In both the aphid species, TRAS elements were present at all termini of autosomes, but the 2 X chromosome telomeres show a clear-cut structural difference. Indeed, cromomycin A3 staining, together with FISH using a TRAS probe, revealed that TRAS signals only occur at the telomere opposite to the NOR-bearing one. Lastly, the analysis of the distribution of TRAS retrotransposons in a M. persicae strain possessing spontaneous fragmentations of the X chromosomes assessed that TRAS elements were not involved in the healing of de novo telomeres.