Chemical-regulated, site-specific DNA excision in transgenic plants

We have developed a chemical-inducible, site-specific DNA excision system i n transgenic Arabidopsis plants mediated by the Cre/loxP DNA recombination system. Expression of the Cre recombinase was tightly controlled by an estr ogen receptor-based fusion transactivator XVE. Upon induction by beta -estr adiol, sequences encoding the selectable marker, Cre, and XVE sandwiched by two loxP sites were excised from the Arabidopsis genome, leading to activa tion of the downstream GFP (green fluorescent protein) reporter gene. Genet ic and molecular analyses indicated that the system is tightly controlled, showing high-efficiency inducible DNA excision in all 19 transgenic events tested with either single or multiple T-DNA insertions. The system provides a highly reliable method to generate marker-free transgenic plants after t ransformation through either organogenesis or somatic embryogenesis.