Intrachromosomal recombination between attP regions as a tool to remove selectable marker genes from tobacco transgenes.

Recombinant genes conferring resistance to antibiotics or herbicides are widely used as selectable markers in plant transformation. Once transgenic material has been selected, the marker gene is dispensable. We report a novel strategy to remove undesirable parts of a transgene after integration into the tobacco genome. This approach is based on the transfer of a vector containing a NPTII gene flanked by two 352 bp attachment P (attP) regions of bacteriophage lambda, and the identification of somatic tissue with deletion events following intrachromosomal recombination between the attP regions. This system was used to delete a 5.9 kb region from a recombinant vector that had been inserted into two different genomic regions. As the attP system does not require the expression of helper proteins to induce deletion events, or a genetic segregation step to remove recombinase genes, it should provide a useful tool to remove undesirable transgene regions, especially in vegetatively propagated species.