Going ho for sweet potatoes

Going ho = the Ultimate move where players propel themselves horizontally through the air like a superhero in an attempt to catch a disc. Because it’s catchier than “horizontal gene transfer.” Photo: Yves Verrière, Le Progrès

Unless you’re a cat, bedbug or other unfortunate critter, moving genes is a pretty pleasant affair involving a couple of parents and resulting in offspring. This is called vertical gene transfer. (Ooh, talk science to me baby …)

But what if you want to transfer genes horizontally? 

“Going ho” is pretty exciting when an athlete does it in a game of Ultimate. When we’re talking going ho with genes between species that would never otherwise get it on, people freak out.

Enter GMOs, or specifically, transgenic GMOs. These are the ones that involve putting genes from one organism into another, unrelated organism. Like putting strawberry genes into fish – or was it putting fish genes into tomatoes? Or tomato genes into fish? Genetic engineering and PhotoShop often get mixed up on the interwebs…

Some actual examples of GMO crops are corn, canola, and soybeans. These crops have had genes from bacteria added to them. For example, to give crops built-in pest resistance, developers inserted genes from Bacillus thuringiensis (Bt), a soil bacterium that naturally controls insects. Organic farmers apply Bt preparations on their crops and many municipalities use Bt to control pests such as mosquito larvae in standing water. By putting the Bt genes directly into the crops, farmers don’t need to spray their crops as often (sometimes not at all). Also, beneficial and benign insects don’t get hit as collateral damage from spraying. If the bug doesn’t eat the crop, the crop doesn’t harm the bug.

Eww. Bacteria genes in my food? That just ain’t natural.

Well, it turns out, Momma Nature does this sort of thing all the time. One critter that does it a lot is a soil microbe called Agrobacterium tumefaciens. It has basically figured out how to have sex with plants. By “going ho,” it inserts its own genes into the plant’s cells. Why? Well, the genes cause the plants to grow galls. While these lumps aren’t especially great for the plants, they’re great habitat for Agrobacterium.

Researchers got to thinking: what if we swap in some other genes instead, for things that we want–like insect or herbicide resistance? It took a while for them to figure out how to do this, but they got it to work. The first GMO crops made this way came out in the 1990s. Farmers continue to adopt them at record rates because of their great in-field advantages such as lower production costs and ease of use.

Consumers, on the other hand, were not particularly enthusiastic, especially when their doubts were fanned by dire warnings of advocacy groups. Researchers playing god, unnatural selection – that sort of thing. It’s been an extremely successful tack: there’s a multimillion-dollar enterprise devoted to providing a “non-GMO” seal for food producer to assure their products are untainted by genetic engineering. Organic production standards and labels assure consumers likewise.

But there’s a problem with the “unnatural” standard. When researchers got better tools to study genes, they started poking around in a lot of genomes to see what they could find. When they looked at sweet potatoes, lo and behold, there were some Agrobacterium genes in all cultivated varieties they looked at, as well as some wild relatives. The speculation is that Agrobacterium infected an ancestral sweet potato and instead of creating a gall, it caused the plant to grow bigger tubers (there is a set of Agrobacterium genes that is only found in cultivated varieties). It was a “gall gone right” as far as early humans were concerned and they started cultivating these natural GMO sweet potatoes by preference. 

It turns out going ho – that is, swapping genes through horizonal transfer – isn’t really that unusual. Once they started looking, researchers found that Agrobacterium really has been getting around. It’s genes have been found in more than 35 species of plants across nearly two dozen genera. 
It seems Momma Nature hasn’t been respecting species boundaries. Then again, she didn’t create the boundaries; we did. 

People always strive to identify patterns, create categories and assign things to their proper boxes. Nearly 300 years ago, Carl Linnaeus, a Swedish botanist, zoologist and physician came up with the system of “boxes” we use today – kingdom, phylum, class, order, family, genus, species. Like mates with like, producing similar offspring. Step too far out of the box and you got things like sterile hybrids, underlining the importance of the rules.
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As researchers learned more about genomics and could track on a genetic level what living things were getting up to in private, they found a more complicated picture. Like mates with like, yes, but players such as Agrobacterium and various viruses also get in the game from the sidelines all the time.

​Could it be that creating GMOs via horizontal gene transfer – whether it be natural or human-made –  isn’t that unusual after all? Maybe “going ho” is just part of the natural order of things.

*Note: “Going ho” only applies to one kind of GMO: transgenics. There are other kinds, created by using different techniques to change an organism’s genome without adding anything. Depending on the definition – and this varies by jurisdiction – GMOs can include products of gene silencing such as the Arctic Apple or more recently CRISPR gene editing and older techniques such as mutagenesis.
There are currently about 10 transgenic GMO food crops available, including papaya, eggplant and one food animal, salmon). Bananas and cowpea are in development and being adopted in some countries.