The marker removal system (schemes in Figures 1 & 2) fits easily in existing Agrobacterium -mediated transformation protocols.
After positive selection of transgenic tissue or plants, chemical induction of Recombinase R activity will result in elimination of DNA-sequences that are flanked by intact recombination sites (Rs). The Recombinase R protein is inactivated by the presence of the Ligand Binding Domain (LBD) of the glucocorticoid receptor. Activation of the Recombinase R protein activity is achieved by an overnight incubation of plant tissue in a 10 µM dexamethasone solution. Subsequent (negative) selection on 5-FC should prevent development of plant tissue still containing the cod A-gene, thereby preventing the occurrence of chimeras due to incomplete DNA excision.