FLP-mediated recombination for use in hybrid plant production

We have studied the feasibility in Arabidopsis of using a site-specific rec ombination system FLP/FRT, from the 2 mu m plasmid of yeast, for making pla nt hybrids. Initially, Arabidopsis plants expressing the FLP site-specific recombinase were crossed with plants transformed with a vector containing k anamycin-resistance gene (npt) flanked by FRT sites, which also served to s eparate the CaMV35S promoter from a promoterless gusA. Hybrid progeny were tested for excision of the npt gene and the positioning of 35S promoter pro ximal to gusA. GUS activity was observed in the progeny of all crosses, but not in the progeny derived from the self-pollinated homozygous parents. We then induced male sterility in Arabidopsis plants using the antisense expr ession of a pollen- and tapetum-specific gene, bcp1, flanked by FRT sites. Upon cross-pollination of flowers on the same male-sterile plants with poll en from FLP-containing plants, viable seeds were produced and the progeny h ybrid plants developed normally. Molecular analyses revealed that the antis ense expression cassette of bcp1 had been excised in these plants. These re sults show for the first time that a site-specific recombinase can be used to restore fertility in male-sterile plants, providing an alternative metho d for the production of hybrid seeds and plants.