An “Acceptable” GMO?

Soybean Field

For many opponents of genetically modified foods, the idea of fiddling with an organism’s genome doesn’t quite sit well in their stomachs. The type of genetic tweaking that renders soybean plants resistant to the herbicide Roundup strikes some not only as unnatural but something that borders on playing God. Similarly, another common objection to genetic engineering is that the transfer of genetic material/DNA genes violates a so-called “species barrier.” Such is the case for Bt corn, which harbors the bacterial gene for Bt toxin, a compound that is poisonous to insect pests. This argument, however, disregards the fact that Nature ignores this barrier all the time. In the wild, DNA is often transferred between species through processes collectively known as horizontal gene transfer. So, not even Nature plays by antiGMO rules.

But what if an already existing gene variant with a desired trait from one organism is genetically engineered into another organism of the same species? Would this make GMOs a little bit more palatable to their detractors?

Soy is one of the most important crops grown in the US and it is nearly ubiquitous in the market. It’s in our food, drinks, biodiesel fuel, even cosmetics. If you rummage through my mom’s kitchen you’ll find soy sauce in the pantry, tofu in the fridge, and edamame in the freezer. Back in the day, she used to keep soybeans on hand for when she’d press her own soy milk.

Soybean cyst nematode and egg SEM

“Low-temperature scanning electron micrograph of soybean cyst nematode and its egg. Magnified 1,000 times.”

Latte drinkers, vegetarians, and us Asians aren’t the only ones who love soy, however. Lurking underground are parasitic worms known as soybean cyst nematodes, which find the roots of the soybean plant irresistible. These agricultural pests invade the roots of the soy plant where they do a bit of their own agriculturing. These nematodes can create a steady supply of food for themselves by making the root cells that they feed on divide. Whereas males leave the comforts of their “root homes” in order to find mates, females remain there where they continue to feed and swell in size until eventually their bodies burst through the root. Once mated and having laid her eggs, the female dies and her cuticle hardens to form characteristic the cysts on the roots of the soybean plant. The damage to soy crops is damages to the tune of $500 million to $1 billion annually in the US alone.

Segment of soybean root infected with soybean cyst nematode. Signs of infection are brown-white females or cysts with egg masses that are attached to root surfaces.

“Segment of soybean root infected with soybean cyst nematode. Signs of infection are brown-white females or cysts with egg masses that are attached to root surfaces.”

Soybean plants aren’t entirely defenseless, however, as there are soybean plant strains, such as the Forrest cultivar, that are resistant to nematode attack. In this cultivar, the feeding cells that the nematodes “cultivate” in the roots of the soybean plant die off and the worms starve before they can reproduce. (Conversely, there are also soybean cyst nematodes that are resistant to resistant soybean plants. It wouldn’t be Nature without the wrinkles, now would it?)

While exactly how the feeding cells in the Forrest cultivar degenerate in response to soybean cyst nematode is unknown, a team of scientists led by Shiming Liu (Southern Illinois University) and Pramod Kandoth (University of Missouri) has recently identified mutations in the serine hydroxymethyltransferase (SHMT) gene that are responsible for nematode resistance. Serine hydroxymethyltransferase is an enzyme involved in the shuttling of one-carbon units between molecules–folate in particular–until the carbon is ultimately freed up for the cell to use in important processes such as DNA and protein synthesis. For instance, one of the important functions of serine hydroxymethyltransferase is to convert serine into glycine, both of which are amino acids found in proteins.

One of the reactions that serine hydroxymethyl transferase catalyzes is the conversion of the amino acid serine to glycine.

One of the reactions that serine hydroxymethyl transferase catalyzes is the conversion of the amino acid serine to glycine.

Since the mutations cause changes near the active site of the SHMT protein, or the “business end” where the shuttling of carbons occurs, it’s possible that the mutations affect the activity of the SHMT protein. To test this model, Liu and Kandoth compared the ability of the normal and mutant forms of SHMT to make glycine by expressing these genes in an E. coli bacteria strain that can’t make its own glycine.  This particular strain of bacteria dies when glycine is removed from its diet, but was able to survive when Liu and Kandoth expressed the normal form of SHMT in this bacteria. This indicated that expressing the normal SHMT protein restored the bacteria’s ability to make glycine. However, the bacteria didn’t survive as well when the mutant form of SHMT protein was expressed which suggested to the scientists that the mutant protein was less efficient in making glycine.

More importantly, soybean plants that were susceptible to SCN infection became resistant when Liu and Kandoth transferred the mutated Forrest SHMT gene in the susceptible plants. This demonstrated that the mutated Forrest SHMT was responsible for soybean cyst nematode resistance. The scientists speculate that the decreased activity of the mutated SHMT in the feeding cells found in the soybean plant root reduces either their “nutritiousness” or their ability to divide. As a result the nematodes that infect the Forrest cultivar starve to death.

So, this brings me back to my original question of what, if anything, would constitute an “acceptable” GMO to opponents of genetic engineering? Would detracters object to a scenario where an already existing mutation* that confers resistance to an agricultural pest is engineered into other soybean plants. Directly transferring the existent Forrest SHMT variant would be more efficient over traditional methods of breeding, since only the Forrest SHMT gene would be introduced into another soybean plant without carrying over any unwanted traits or genes. There are, after all, many different cultivars of soybean plants used for different applications that may benefit from nematode resistance.

*I’ll avoid saying “naturally-occurring” since the Forrest cultivar was developed by a USDA breeding program.

Reference
Liu, S., Kandoth, P., Warren, S., Yeckel, G., Heinz, R., Alden, J., Yang, C., Jamai, A., El-Mellouki, T., Juvale, P., Hill, J., Baum, T., Cianzio, S., Whitham, S., Korkin, D., Mitchum, M., & Meksem, K. (2012). A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens Nature, 492 (7428), 256-260 DOI: 10.1038/nature11651

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12 responses to “An “Acceptable” GMO?

  1. I think a big issue for lay people that don’t really understand GMOs is that anything that nature doesn’t do itself is scary. I would imagine that anti-GMO sentiment would reply that just because something exists in nature, doesn’t mean that it should be artificially (i.e. by people) put into another organism. I don’t think it’s the degree of fiddling that bothers anti-GMO people, it’s simply the fiddling with genes period. The word “engineered” freaks people out. What occurs in nature is often out of our control, so people seem more comfortable with that. Also, human history doesn’t have a great track record of taking care of nature when we butt in (e.g. pollution, deforestation, species extinction, etc.). Additionally, foresight is a huge issue. People can cause change much more quickly than nature in many situations. That sudden change has effects that people may or may not foresee. A good example would be Thalidomide in the ’50’s or the introduction of a non-native species into a new environment like the snakehead fish in America. Those aren’t GMO examples, but they are examples where foresight was a problem.

    One way to try and bridge that gap could be to show people that just because something is “natural” doesn’t mean that it’s automatically good. Nature is apparently random, so natural selection is the only thing that really keeps order. GMO’s at least have some kind of plan for the benefit of humanity. For example, a mutation that occurs naturally could weaken a species. I can’t think of any specific example (maybe sickle cell anemia?), but I’m not a scientist. If nature can cause problems to arise, then perhaps GMOs in a controlled capacity (I know that’s a vague concept) could also provide benefits.

  2. “just because something is “natural” doesn’t mean that it’s automatically good.”

    This is commonly referred to as the naturalistic fallacy. And yes I do see the distinction. I was just illustrating that in this case you could arrive at nematode resistance either by traditional crossing and breeding methods (which I would argue is a form of genetic fiddling) or genetic engineering.

  3. Hello.

    Thank you for this post.

    As a very vocal opponent of currently-commercialized-agricultural- GMO-crops, I would not be concerned about the public health impacts of this kind of genetic modification; just as I am not concerned about marker assisted selection of flood resistant rice. http://www.scidev.net/en/news/india-takes-to-new-flood-tolerant-rice.html

    My opposition is to a barrage of lies about the “precision” of Agrobacterium and ballistics techniques in crops such as this: http://www.cera-gmc.org/?action=gm_crop_database&mode=ShowProd&data=NK603

    given stunningly unconvincing, deficient and unscientific safety studies http://cera-gmc.org/docs/articles/09-215-016.pdf

    • Thank you for bringing my attention to marker assisted selection in the context of plant and crop breeding. With respect to your statement, “given stunningly unconvincing, deficient and unscientific safety studies,” are you arriving at your conclusion regarding the safety of GMOs based on that study or are you presenting it as being representative of GMO safety studies in general?

  4. I wish that it would be acceptable. But sadly there are similar examples that have shown nothing is acceptable to the party of “no”.

    For example, that blight resistant potato that’s being protested in Europe is made with a gene from a wild potato relative. However, breeding that would be arduous or impossible. Yet it could save massive amounts of chemical spraying. But anti-GMO groups have a zero-tolerance policy.

    And sometimes people will try to tell you that marker-assisted selection (MAS) is the solution to everything, when it’s not. It’s a great tool when you have the right plants and genes. But it’s not the right tool for everything. Some plants you just can’t modify that way. Bananas are another example of where that’s not possible.

    • Do you know if the anti-GMO groups are aware of the fact that the gene is from a close relative?

      Interesting how this Guardian article describes transgenic as “sinister.”

      For Mullins, a vital aspect of the project is that the potato gets its protective gene from a closely related plant, not a distant plant genus or even an animal. This makes it, in genetic parlance, “cisgenic” instead of the more sinister “transgenic”.

      • Oh yes, I know what it is scientifically. I also know opposition groups have been told this. But see this:

        http://www.bbc.co.uk/news/science-environment-19000190

        “It’s only a two-hectare trial, but that’s like saying you’re only a little bit pregnant, there are no grey areas with GM.”

        No gray areas.

        I can give you a half dozen articles that I’m sure activists read. They were quoted. And it doesn’t matter at all. They see any modification as a “camel nose under the tent” and have to be reactionary about it.

  5. Hi Mary.

    Thanks for your response.

    I an not a member of the party of No. I think of myself as someone who advocates evaluating each and every case as a stand-alone, on its own merits- on a case by case basis
    –guided by well established and fundamental scientific principles.

    Cheers,

    Ena

    (please do pass on my apologies to Karl. It would mean a lot to me, cause I behaved like a total a$$-o I am sorry :( !

  6. Pingback: Weekly Science Picks - Australian Science·

  7. Pingback: Blight-Resistant Potato: an “Acceptable” GMO? | Amasian Science·

  8. It is very romantic idea to live a natural way of life but all kinds of diseases, aging and finally the death are also natural processes which the proponents of natural living should readily accepted and should take medicines to fight disease and prolong life expectancy which has led to the human population explosion on the planet earth at the cost of other species. Now if we reject use of technology to enhance food productivity then it is hypocrisy that will further increase the pressure on other species on the planet. Advocates of natural living should also reject the five star culture including heavy reliance on fossil fuels and chemical poisoning of the planet, like the ancient Indian sages living an austere life who practiced what they preached. In contrast, today’s naturalists only preach to others but their own life style is hardly natural.

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