Heat shock-regulated site-specific excision of extraneous DNA in transgenic plants

We have developed a heat shock-inducible, site-specific DNA excision system in transgenic plants mediated by the Cre/ loxP DNA recombination system. The heat shock-inducible promoter, HSP81-1, tightly controlled the expression of the Cre recombinase. Upon induction by heat shock, extraneous sequences (the selectable marker, the undesirable bar gene, NLS, Cre, and HSP flanked by two loxP sites) were excised from the tobacco genome, leading to activation of the downstream GUS reporter gene. Genetic and molecular analyses indicate that the system is tightly controlled, showing high-efficiency inducible DNA excision in 17 transgenic lines. This system provides a highly reliable method for the removal of sequences that have fulfilled their duties in the generation of transgenic plants, thus creating transgenic plants free from useless exogenous DNA.