Sweet potato naturally 'genetically modified'

Sweet potatoes all over the world contain 'foreign' DNA sequences, according to a new study which concludes that the popular food can be seen as naturally 'genetically modified'.
Researchers from Ghent University in Belgium and the International Potato Center (CIP) in Peru found that sweet potatoes naturally contain genes from the bacterium Agrobacterium.
The researchers discovered the foreign DNA sequences of Agrobacterium while searching the genome of sweet potato for viral diseases.
The sequences appeared to be present in each of the 291 tested sweet potato cultivars and even in some wild related species. Different research methods confirmed the same conclusion: the specific sequences are not due to contamination, but they are part of the sweet potato genome.

The genes in the foreign DNA sequences were also shown to be active in sweet potato, which can indicate that they provide a positive characteristic which was selected for by the farmers during domestication.
It is not the first time that researchers find bacterial, fungal or viral DNA in the genome of plants or animals. High throughput genome analyses in recent years has found more and more examples of possible "horizontal gene transfers."

In a horizontal gene transfer there is exchange of genes between different species - in contrast to normal gene transfer from parents to progeny which occurs within one species.

Finding similar sequences is not a full proof that they are the result of horizontal gene transfer, but in the case of sweet potato there are strong indications that this has happened, researchers said.
Agrobacterium is specialised to transfer a part of its own DNA, the so-called T-DNA, to plants. And it is this T-DNA that has been found in sweet potato.
The mechanism that Agrobacterium uses to incorporate its own T-DNA in the genetic material of plants forms the basis of the genetically modified organism (GMO) technology.
While Agrobacterium traditionally introduces its T-DNA only in a few plant cells, biotechnologist have succeeded to regenerate plants from these cells.

The finding of T-DNAs in sweet potato shows that this extra step has also occurred in nature thousands of years ago.
"The natural presence of Agrobacterium T-DNA in sweet potato and its stable inheritance during evolution is a beautiful example of the possibility of DNA exchange across species barriers," said Lieve Gheysen, one of the study researchers.
"It demonstrates that genetic modification also happens in nature. In comparison to "natural" GMOs, that are beyond our control, human-made GMOs have the advantage that we know exactly which characteristic we add to the plant," Gheysen said.