FLP recombinase-mediated site-specific recombination in rice

The feasibility of using the FLP/FRT site-specific recombination system in rice for genome engineering was evaluated. Transgenic rice plants expressing the FLP recombinase were crossed with plants harbouring the kanamycin resistance gene (neomycin phosphotransferase II, nptII) flanked by FRT sites, which also served to separate the corn ubiquitin promoter from a promoterless gusA. Hybrid progeny were tested for excision of the nptII gene and the positioning of the ubiquitin promoter proximal to gusA. While the hybrid progeny from various crosses exhibited beta-glucuronidase (GUS) expression, the progeny of selfed parental rice plants did not show detectable GUS activity. Despite the variable GUS expression and incomplete recombination displayed in hybrids from some crosses, uniform GUS staining and complete recombination were observed in hybrids from other crosses. The recombined locus was shown to be stably inherited by the progeny. These data demonstrate the operation of FLP recombinase in catalysing excisional DNA recombination in rice, and confirm that the FLP/FRT recombination system functions effectively in the cereal crop rice. Transgenic rice lines expressing active FLP recombinase generated in this study provide foundational stock material, thus facilitating the future application and development of the FLP/FRT system in rice genetic improvement.