Cre-lox site-specific recombination between Arabidopsis and tobacco chromosomes

To create hybrid chromosomes, we tested the Cre-lox system to mediate recombination between Arabidopsis thaliana and Nicotiana tabacum chromosomes. Protoplasts of the two plants were fused to allow site-specific recombination to join a promoter from tobacco to a hygromycin resistance coding-region from Arabidopsis. The expected recombination junction was detected in hygromycin-resistant calli. Analysis of one hybrid suspension cell line revealed the presence of markers corresponding to the north arm of Arabidopsis chromosome III, but not markers from other chromosome arms. However, these markers were not detected in regenerated plants. With a second hybrid cell line we obtained a single hygromycin-resistant progeny from approximately 18 000 self-fertilized seeds of one regenerated plant. Molecular analysis of this hybrid indicated that a small portion of the north arm of Arabidopsis chromosome V is present in the tobacco genome. However, neither the recombination junction nor Arabidopsis DNA was detected in tissue from the plant grown without selection or in the subsequent generation. Thus interspecies transfer of a chromosome arm between plant cells is possible, but maintenance of the hybrid chromosome in a plant is unlikely. The feasibility of site-specific recombination between genomes of different species offers new possibilities for engineering hybrid chromosomes that may be maintained in cell culture.