CRE RECOMBINASE-MEDIATED SITE-SPECIFIC RECOMBINATION BETWEEN PLANT CHROMOSOMES

We report the use of the bacteriophage P1 Cre-lox system for generatin g conservative site-specific recombination between tobacco chromosomes . Two constructs, one containing a promoterless hygromycin-resistance gene preceded by a lex site (lox-hpt) and the other containing a cauli flower mosaic virus 35S promoter linked to a fox sequence and the cre coding region (35S-lox-cre), were introduced separately into tobacco p lants. Crosses between plants harboring either construct produced plan ts with the two constructs situated on different chromosomes. Plants w ith recombination events were identified by selecting for hygromycin r esistance, a phenotype expressed upon recombination. Molecular analysi s showed that these recombination events occurred specifically at the lox sites and resulted in the reciprocal exchange of flanking host DNA . Progenies of these plants showed 67-100% cotransmission of the new t ransgenes, 35S-lox-hpt and lox-cre, consistent with the preferential c osegregation of translocated chromosomes. These results illustrate tha t site-specific recombination systems can be useful tools for the larg e-scale manipulation of eukaryotic chromosomes in vivo.