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GMO ‘foreign gene’ fears? Breeders incorporating unknown DNA into food crops for centuries

When transgenic plants (the so-called GMO plants) hit the market in 1996, conventional wisdom at the time was that these new plants differed fundamentally from the older, more traditional plants in that the GMO plants contained a gene not found in the present-day plants on the market.

This difference is the reason for the testing required to “deregulate” a transgenic plant before marketing and is one of the stated causes behind the anti-GMO crusade.  Recent findings, however, show unequivocally that this distinction, in fact, does not exist.

Until recently, it was thought that plant breeding programs selected the superior forms (termed alleles in genetic parlance) of existing genes. Breeders selected for the form or allele of the gene that, for example, encoded a more efficient protein, expressed the gene at a higher (or lower) level, etc.  Selection by the breeder was not at the gene level but rather at a level easily observed by the breeder. This could be greater yield, enhanced disease or insect resistance, sweeter fruit, larger berry, earlier maturity, etc. Then it was thought that all members of a particular plant family (corn, soybean, wheat, blue berry, orange, etc.) contained the same genes; they simply differed in the forms of those genes existing in a particular family.

It turns out that this is all wrong.

The remarkable advances in the way DNA is sequenced have made the sequencing of all the genes in a particular organism (termed the genome) extremely cheap. Thousands of genomes from different organisms have been decrypted and comparative genomics is a thriving field of scientific endeavor. Investigators have also sequenced different members of a particular family and unexpectedly found that the two different members of the family did NOT contain the same genes.  Some genes were found in some members of the family but not in others. This phenomenon of plus/minus genes is particularly rampant in plants.

An exceptionally striking case of this was published recently in the journal Plant Cell. Of 8681 corn genes studied at the DNA level by this group, only a small fraction, 16.4 percent, were found in all 503 lines examined. The vast majority of these genes (83.6 percent) were found in some BUT NOT ALL lines. Corn is not an exception since similar cases of plus/minus genes have been found with other important food crops. Hence, new non-GMO or conventional varieties of food crops appearing on the market this year likely contain genes that were not in those same crops the year before.  Also, the new ones likely lack genes that were present the year before.

Where do these genes come from? There are several sources. First, most food plants underwent a duplication of most if not all their genomes during their course of evolution. This duplication then allowed some relaxation from Darwinian selection such that the one gene copy was free to diverge in sequence and take on a new function.

Second, some transposable elements – pieces of DNA that naturally move around in the genome and insert at random  into the genome– actually pick up pieces of old genes and put these pieces together to make brand new genes. This is not a rare event.  For example in corn a particular transposable element termed a Helitron has synthesized (estimated conservatively) ~11,000 new coding regions. Since the total number of genes in corn is around 40,000 the number of coding regions coming from Helitrons is quite significant.

Note that these newly evolved chimeric genes–arising naturally from transposable elements — bear striking similarities to chimeric genes synthesized by scientists and inserted into plant genomes. The major difference is that the chimeric genes arising in nature via transposable elements occur unsuspectingly.  We don’t know when they arise or where, we don’t know what the final product is.  We don’t spend millions of dollars monitoring them for safety and hence we don’t know whether they might encode an allergenic protein or otherwise be dangerous. But because eating our typical food plants has a long history of being safe we don’t worry about it.

To summarize, the new methods to rapidly, accurately and cheaply decipher genomes have uncovered hitherto unimaginable variation in the genetic material of all organisms, including the ones we eat. Hence, labelling plants and their derived foods GMO and non-GMO is clearly a distinction without a difference.

L. Curtis Hannah is a University of Florida Research Foundation professor in the Horticultural Sciences Department focusing on molecular biology and plant genetics. [email protected]

21 thoughts on “GMO ‘foreign gene’ fears? Breeders incorporating unknown DNA into food crops for centuries”

  1. All these data clearly show that a given plant line contains a subset of the gene pool available to the plant species, i.e. the various lines of this species. But we have to remember that the gene pool of a plant species is distinct to the gene pool of another species. Thus, when we introduce into a plant species the Bt gene of a bacterial gene we add a foreign gene to the gene pool. This Bt gene we classify as a transgene to distinguish it from the introduction of a gene that belongs
    to the gene pool of a given plant. In this case we refer to the introduced gene as a cisgene. As we cannot easily predict how a transgene influences an existing gene pool, it makes sense to have a closer look. In the case of a cisgene introduced into gene pool of a specific plant we do not alter the existing gene pool of this species. Therefore, in this case we just alter the gene pool of the cisgenic plant in way that could occur by natural breeding and we may be more relaxed.

      • exactly. I don’t think it is irrational to ask the question whether intoducing a gene not known to be found within the gene pool of a given species somehow violates a an unknown, currently unfathomable law of nature that simultaneously intoduces chaotic problems. If this gene did not show up in that species over evolutionary time, then perhaps there is a good reason for that.

        A fair question yes, but this article undermines that there is an orderliness and exclusiveness to a specific set of genes, and that things are more chaotic within species, than a species constrained genetic limitation that an intuitive naturalistic assumption of species barrier predicts. Again, not an invalid concern, but each new discovery such as that discussed in this article seems to weaken rather than confirm or reinforce some inviolate species barrier theory.

        in fact, I believe that the underlying new knowledge talked about in the artile is just one more in a growing list of revalations converging toward a conclusion that the process if genetic engineering is no more chatic or disruptive than other methods of human intervention in changing the genetic endowmwnt of crops, and perhaps no more disruptive than nature itself. That doesn’t settle the debate, however. Even if safe, that does not automatically mean each and every application is ge is necessarily wise. That is an external issue of how the genetic manipulation is used in real life, does the innovation actually improve the world. But that is an issue outside the scope of this article and is a case-by-case evaluation.

  2. “As we cannot easily predict how a transgene influences an existing gene pool, it makes sense to have a closer look”

    Fine but what tests not already done would you like to see added to the evaluation process of GE crops and why?

  3. “But we have to remember that the gene pool of a plant species is distinct to the gene pool of another species.”

    And yet, there is a lot of similarity of genes in different species of the grass family, a concept known as synteny. Using this idea, genes for disease resistance or metabolic functions can be predicted in one species based on its presence in another species.

  4. I often wonder if one did an exhaustive analysis of the tomato genome, how many genes would be found that were introgressed from South American ‘weeds’ by Charlie Rick and other breeders. Not that there’s anything wrong with that!!

  5. Mixing genes in the same Phylum makes sense genetically and evolutionarilly. The question arise about cross Phyla transgenic varieties and the associated massive damage to the helix when you force this type of integrated “trans-gene” that evolutionarrily could NEVER occur.

      • OK. Nice source. I guess your the go to guy on GMO safety Larry just like your buddy Clarence Thomas. Who by the way represented Monsanto before becoming a Supreme Court Shill for Monsanto.

        • Do you expect me to reply to each irrelevant post you make? Does anyone with experience in making GMOs make them unreliable? Would you rather have someone who has no experience (read: no credibility) be handing out information?

        • So, your assertion that integrating a trans-gene that evolutionarily could not occur causes massive damage to the helix is proven by Clarence Thomas was at one time a representative for Monsanto? Well now that settles it right there.
          Here’s another one, “Q. What’s the difference between and orange? A. A banana is [ ] this color. I think this somehow proves that fracking is wrong.

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