The Sweet Potato May be Naturally 'Genetically Modified' by Agrobacterium

There is a lot of controversy surrounding genetic modification. But what if genetic modification occurred naturally? That seems to be what happened with the sweet potato. Scientists have found that sweet potatoes naturally contain genes from the bacterium Agrobacterium.

The scientists actually discovered the foreign DNA sequences of Agrobacterium while searching the genome of sweet potato for viral diseases. This prompted them to study the sequences in a bit more detail to see exactly how the foreign DNA wound up there in the first place.

The scientists found the sequences in each of the 291 tested sweet potato cultivars, and even in some wild species. This meant that the sequences are not due to contamination, but are instead part of the sweet potato genome. Not only that, but the DNA sequences are active in sweet potato, which means that they provide some sort of positive characteristic.

So what does this mean? It shows that horizontal gene transfer probably occurred in sweet potatoes at some point in the past. Horizontal gene transfer occurs when there is an exchange of genes between different species, which is in contrast to normal gene transfer from parents to progeny.

With that said, this isn't the first time that researchers have found bacterial, fungal or viral DNA in the genome of plants or animals. Genome analyses in recent years have shown that horizontal gene transfer may be more common than anyone suspected.

What's interesting is that this is a naturally occurring incident of genetic modification. The mechanisms that Agrobacterium use to incorporate its own T-DNA in the genetic material of plants forms the basis of GMO technology.

"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 researchers, in a news release. "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."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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