TCl4.7: A Novel Lepidopteran Transposon Found in Cydia pomonella Granulosis Virus

Abstract

After the co-infection of larvae of the lepidopteran Cryptophlebia leucotreta with the two baculoviruses C. leucotreta granulosis virus and Cydia pomonella granulosis virus (ClGV and CpGV, respectively), three CpGV mutants and one ClGV mutant carrying insertions of 0.9 to 4.7 kb have been isolated. By cloning, sequencing, and hybridization analysis, one of these insertions was identified as a transposon-like element derived from the C. leucotreta genome. This element, called TCl4.7, was found in the genome of CpGV which naturally replicates in C. pomonella. Sequence analysis suggested that TCl4.7 is 4726 bp in size, flanked by imperfect inverted terminal repeats of 29 bp, and integrated into the target dinucleotide TA. TCl47 encompasses an open reading frame sharing homologies to transposase genes of the Tc1-related transposable elements found in Caenorhabditis and in Drosophila species. The open reading frame might represent a pseudogene since it is missing an ATG start codon. The integration site of TCl4.7 is located in a non-protein-coding region of the CpGV genome at m.u. 9.5. In bioassays the TCl4.7-carrying virus and all the other mutants except for one showed LC 50 values similar to those of CpGV and ClGV. This is the first report of the horizontal escape of a transposable element during the in vivo infection of lepidopteran larvae by granulosis viruses.