Inducible excision of selectable marker gene from transgenic plants by the Cre/lox site-specific recombination system

In a plant transformation process, it is necessary to use marker genes that allow the selection of regenerated transgenic plants. However, selectable marker genes are generally superfluous once an intact transgenic plant has been established. Furthermore, they may cause regulatory difficulties for approving transgenic crop release and commercialization. We constructed a binary expression vector with the Cre/lox system with a view to eliminating a marker gene from transgenic plants conveniently. In the vector, recombinase gene cre under the control of heat shock promoter and selectable marker gene nptII under the control of CaMV35S promoter were placed between two loxP sites in direct orientation, while the gene of interest was inserted outside of the loxP sites. By using this vector, both cre and nptII genes were eliminated from most of the regenerated plants of primary transformed tobacco through heat shock treatment, while the gene of interest was retained and stably inherited. This autoexcision strategy, mediated by the Cre/lox system and subjected to heat shock treatment to eliminate a selectable marker gene, is easy to adopt and provides a promising approach to generate marker-free transgenic plants.