The distribution and characteristic of two transposable elements in the genome of Cydia pomonella granulovirus and codling moth

Baculoviruses are capable to acquire insect host transposable elements (TEs) in their genomes and are hypothesized as possible vectors of insect transposons between Lepidopteran species. Here, we investigated the host origin of two TEs, namely the Tc1/mariner-like element TCp3.2 and a 0.7 kbp insertion sequence (IS07), found in the genome of different isolates of Cydia pomonella granulovirus (CpGV), a member of the Betabaculovirus genus. The sequences of both TEs were searched for in the full genome sequence database of codling moth (CM, Cydia pomonella L.). A total of eleven TCp3.2 TE copies and 76 copies of the IS07 fragments were identified in the CM genome. These TEs were distributed over the 22 autosomes and the Z chromosome (chr1) of CM, except chr6, chr12, chr16, chr23, chr27 and the W chromosome (chr29). TCp3.2 copies with two transposase genes in opposite direction, representing a novel feature, were identified on chr10 and chr18. The TCp3.2 transposase was characterized by DD41D motif of classic Tc1/mariner transposons, consisting of DNA-binding domain, catalytic domain and nuclear localization signal (NLS). Transcription analyses of uninfected and CpGV-infected CM larvae suggested a doubling of the TCp3.2 transposase transcription rate in virus infected larvae. Furthermore, IS07 insertion into the CpGV genome apparently added new transcription initiation sites to the viral genome. The global analysis of the distribution of two TEs in the genome of CM addressed the influx of mobile TEs from CM to CpGV, a genetic process that contributes to the population diversity of baculoviruses.