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Grow your own designer genes

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POSTED: May 25, 2011 11:06 a.m.

As a species, we humans have become increasingly creative in manipulating the plants we grow for food and fiber.
In previous columns, I described how American plant breeders successfully exploited a gene from a single corn plant to dramatically reduce production costs and increase yields in North America, but learned a hard lesson about the importance of maintaining diversity in the genetic heritage of our crop plants.
This was an example of using genetic variables within the gene pool of a single species of crop plant – corn.
The next logical step would be seeing if beneficial genes could be transferred between different species. This would provide a much more diverse set of genes to engineer a plant to do more than it originally was designed to do – like mating a British Merlin engine to the American P-51 to turn a low-level reconnaissance plane into the dominant air superiority fighter of World War II.
One of the models used to understand gene transfer between species was a bacterial disease called crown gall. Crown gall is a disease that occurs on 643 species representing 331 genera and 93 families of flowering plants. That is a really broad array of plants for one bacteria species to attack.
From tomatoes to oak trees, crown gall hits them all, from big and woody plants to small and herbaceous ones. Crown gall is caused by the bacterium Agrobacterium tumefaciens. I’m going to call it AT for short.
When AT infected a plant, the plant started to produce many abnormally small cells and a small number of very large cells. This reaction bore a striking resemblance to growth associated with cancer tumors.
The plant continued to produce this cancer-like growth even when the AT died out and no longer was alive in the gall. This piqued the interest of cancer researchers, who wanted to understand how this permanent change in cancer-like growth in plants was turned on and if it could be turned off.
Maybe AT was a good model for studying cancer. Cancer-research money started funding research into crown gall.
Soon, the secrets of AT were being revealed. It turned out that after AT infected a plant, it injected a section of its DNA into the host plant cells. This foreign DNA hijacked the host plant’s mitochondria and caused the plant cells to create ring-shaped nitrogen compounds that the AT could use but the plant could not. The AT bacterium had a free ride. It had made a permanent change in the mitochondrial DNA of the host plant.
Even if the AT died out, the mitochondria of the host plant had their marching orders and would continue to produce ring nitrogen indefinitely. Exactly how the plant does this still is under active investigation. From it, we learned to start looking at viruses as possible causes for cancer.
The other 800-pound gorilla in the room was the fact that here was a lowly bacterium essentially injecting a new gene or genes into plants, not from just another species, genus or even family, but from another freaking kingdom.
Moving genes from a bacterium to a tree is quite a jump. It turns out that moving around genes from kingdom to kingdom of life forms not only is natural, it is downright common. This puts quite a new face on what our expectations for genetic engineering should be.
I always have perceived an attitude from opponents to so-called genetically engineered crop plants that this manipulation of genes and inserting bacterial genes into crop plants was unnatural at best and a downright Frankenstein-like affront to nature and nature’s God at worst. Nope. It happens all the time. We call it crown gall.
Our species is so smart that we still are learning from this lowly bacterium. Folks who believe we humans have come up with something truly novel in nature just are not informed on how many ways nature works and how amazing the world around us is.
Whatever we think is new already has been tried and perfected by nature long before the inspiration hit us. Why is it OK for nature to insert genes from a soil bacterium into hundreds of plant species, but it is horrible when we humans do the exact same thing?
Apparently, it is OK for us to backcross to get genes assembled into a new plant variety like the wind or a honeybee does, but it is not OK to do it the way a bacterium does.
The transfer of genes from bacteria to flowering plants is a well-trodden path by nature, so to suggest that this type of plant breeding is unnatural is irrational nonsense. Opponents try to separate out kingdom-to-kingdom gene shifts by calling it “genetic engineering.”
Would someone please tell me what food or fiber crop humans have not genetically engineered or genetically modified through plant selection? Every crop plant has been genetically engineered, whether tomato, pine or cotton. The argument appears to be about technique – or is it the mistaken belief that there is some kind of natural firewall against gene transfer between species?
This is neither the first time nor the last that opponents to human progress have built elaborate and contorted opposition on an absent foundation. Even with this advance, we agriculturists still use the genetic material we find laying around on the planet.
We have not created a new gene. We have not created a new life form. We have not even pushed the envelope beyond what nature already does, but we are learning from nature how to migrate genes from species to species.
Next time: the upside of genetically modified crops.

Gardner is the extension agent for Bryan County and can be reached at dgardner@uga.edu.

 

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