Plant Genomes May Incorporate Agrobacterium Chromosomal DNA

Thirty years ago scientists found that the pathogenic soil bacterium Agrobacterium tumefaciens is capable of interkingdom genetic transfer. The crown gall-causing bacterium can integrate transfer DNA (T-DNA) on the tumor-inducing (Ti) plasmid into the genomes of most crops. Since this discovery, Agrobacterium-mediated DNA transfer has been exploited to introduce transgenes into plants and to transform other organisms such as yeast, fungi and even human cells.

It has been well documented that part of the Ti plasmid outside the T-DNA borders may be integrated into plant genomes. In a paper published by Nature Biotechnology, Bekir Ulker and colleagues from the Max Planck Institute for Plant Breeding Research and Bielefeld University in Germany report that large (up to 18 kb) gene-bearing fragments of Agrobacterium chromosomal DNA (AchrDNA) can also be integrated into Arabidopsis genomic DNA during transformation.

The researchers analyzed databases that contain Arabidopsis–flanking sequence tags (sequences found on both sides of T-DNA insertion sites). They found that one in every 250 transgenic plants (0.4 percent) may carry AchrDNA fragments. The discovery highlights the need for more research to understand the mechanisms of horizontal gene flow through bacteria in the evolution of higher organisms. It also indicates the need for increased vigilance in testing for undesired bacterial DNA in transgenic plants.

Subscribers can download the article at http://dx.doi.org/10.1038/nbt.1491 Non subscribers can read the abstract at http://www.nature.com/nbt/journal/v26/n9/abs/nbt.1491.html.