Highly similar piggyBac elements in Bactrocera that share a common lineage with elements in noctuid moths

Abstract

The piggyBac IFP2 transposable element, originally discovered in a Trichoplusia ni cell line, also exists as nearly identical elements in other noctuid lepidopterans, and in several species of the tephritid genus Bactrocera. To further define the distribution of piggyBacs in Bactrocera, and compare their relationship to sequences found in Lepidoptera, a survey by PCR amplification was performed in a range of Bactrocera species. Highly similar piggyBac sequences were found in all B. dorsalis complex species tested, as well as in species in the B. zonata and B. frauenfeldi complexes. All nucleotide sequences had > 94% identity to corresponding sequences in the T. ni IFP2 element, and > 88% identity among the sequences. Conserved primers did not amplify any distantly related sequences that have been found by computational searches in a wider range of insect and non-insect species. Notably, 55 nucleotide substitutions relative to IFP2 were common to all the Bactrocera sequences, 44 of which exist in piggyBacs previously sequenced from moths, with 17 resulting in amino acid substitutions. These piggyBac elements, that apparently traversed orders by horizontal transfer, probably arose from a lineage separate from IFP2 and the other known elements in T. ni. Implications for the presence of nearly identical piggyBacs, in widely distributed insects, to the applied use of piggyBac vectors are discussed.