Simplifying transgene locus structure through Cre-lox recombination.

Transgene silencing is often associated with multicopy integrations, which occur frequently during plant transformation. Transgene expression can be restored in a number of multicopy loci by converting them to single copy. This chapter describes a plant transformation protocol based on use of the Cre-lox system, which allows conversion of a multicopy transgene locus into single copy. The strategy is based on designing a transformation vector with lox sites, developing transgenic lines, and introducing Cre activity to initiate Cre-lox recombination, which leads to the simplification of a multicopy locus to a single- or low-copy state. This method is compatible with both gene gun and Agrobacterium-mediated gene delivery and should be particularly useful for crops that are difficult to transform.