Abstract
Agrobacterium tumefaciens transfers part of its tumour-inducing (Ti) plasmid, the transferred or T-DNA, to plants during tumourigenesis. This represents the only example of naturally occurring trans-kingdom transfer of genetic material. Here we report that A.tumefaciens can transfer its T-DNA not only to plant cells, but also to another eukaryote, namely the yeast Saccharomyces cerevisiae. The Ti plasmid virulence (vir) genes that mediate T-DNA transfer to plants were found to be essential for transfer to yeast as well. Transgenic S.cerevisiae strains were analysed for their T-DNA content. Results showed that T-DNA circles were formed in yeast with precise fusions between the left and right borders. Such T-DNA circles were stably maintained by the yeast if the replicator from the yeast 2 mu plasmid was present in the T-DNA. Integration of T-DNA in the S.cerevisiae genome was found to occur via homologous recombination. This contrasts with integration in the plant genome, where T-DNA integrates preferentially via illegitimate recombination. Our results thus suggest that the process of T-DNA integration is predominantly determined by host factors.