Bits of bacterial DNA naturally lurk inside sweet potatoes

Sweet potatoes farmed worldwide picked up a bit of genetic engineering — without human help.

Samples collected from 291 cultivated sweet potatoes carry at least one stretch of DNA from Agrobacterium, says plant molecular biologist Godelieve Gheysen of Ghent University in Belgium. The Agrobacterium genus includes the main bacterial species that makes intentionally transgenic plants possible. It allows geneticists to hitch desired genes to a bacterial delivery service and patch them into a plant’s normal DNA.

None of the bacterial DNA fragments found in sweet potatoes match DNA used to create today’s genetically modified crops. The fragments come from some extinct or not yet discovered relative in the same genus, Gheysen and colleagues report April 20 in Proceedings of the National Academy of Sciences. One stretch of bacterial DNA in particular shows up in cultivated sweet potato samples from Peru, the United States, Japan, Australia, Nigeria and many other places. Such breadth suggests that the bacterial DNA wormed its way into sweet potatoes long before people could create GMO foods.

The find “shows that crossing species boundaries is nothing unnatural,” Gheysen says.

Geneticists have yet to recover the widespread stretch of bacterial DNA from wild relatives of the cultivated sweet potatoes. So the add-on may have contributed to whatever traits made farmers favor these lineages of sweet potato instead of wildlings, Gheysen speculates. The DNA bits are active, but figuring out their function will take more work.