Structural variability of Tvv1 grapevine retrotransposons can be caused by illegitimate recombination

Structural variability of Tvv1, a grapevine retrotransposon Ty1 copia-like family, was investigated within the grape genome and the canonical sequence of Tvv1 determined. Then, two remarkable elements, Tvv1-Δ3001 and Tvv1-Δ3640, which had suffered large deletions 3,001 bp and 3,460 bp in length of their coding sequences were compared to the canonical copy. In both deleted elements, the deletion breakpoint was characterized by a stretch 13 bp-long in Tvv1-Δ3001 and 11 bp-long in Tvv1-Δ3640 found duplicated in the canonical copy at each bound of the deleted regions. Tvv1-Δ3001 and Tvv1-Δ3460 were both shown to be unique copies fixed at a single locus in the grapevine genome. Their presence was very variable in a set of 58 varieties and wild vines. These elements have most likely been dispersed through natural intermixing after their initial insertion whose chronology was estimated. The model that we propose to explain the structure of Tvv1-Δ3001 and Tvv1-Δ3640, implies illegitimate recombination involving template switching between two RNA molecules co-packaged in the VLP prior to the integration of the deleted daughter copy into the host genome.