Highly heterogeneous Ty3/Gypsy-like retrotransposon sequences in the genome of cassava (Manihot esculenta Crantz)
The use of PCR has enabled the survey of transposable elements in many plants; thereby making the study of their diversity and applications possible in species where the full genome sequence data are not yet available. In the present study, we used PCR primers anchored on the conserved domain of reverse transcriptase and endonuclease to amplify the Ty3/Gypsy-like polyprotein fragment from the genome of cassava (Manihot esculenta Crantz). The PCR product was cloned and sequenced. Sequence analysis of individual clones clearly identified the conserved domain of the polyprotein enzymes and showed the cassava Ty3/Gypsy-like retrotransposon, Megyp (for Manihot esculenta gypsy-like), sequences to be highly heterogeneous. Some Megyps clustered with other plants’ Ty3/Gypsy-like retrotransposons, while some clustered with Gypsy of Drosophila melanogaster and Ty3-2 of Saccharomyces cerevisiae in the comparative multiple sequence analysis. This suggests that the later belong to the retrovirus lineage of this group of elements. Southern analysis showed that, the Megyps and analogues were highly repeated within the genomes of cassava cultivars.
Key words: Cassava, transposable-elements, retrotransposons, retroviruses, Manihot esculenta, Ty3/Gypsy.