(and a few other topics - note that I posted some of these thoughts over in the General Discussion forum, but perhaps this forum would be more appropriate)
Without considering any specific examples, basic evolutionary theory confirms that ‘superweeds’ are unlikely to be a threat of any significance (scientifically speaking, it would be incorrect to suggest that they posed absolutely zero threat, but close). Supposedly, a ‘superweed’ is one that is now expressing genes that confers resistance against pesticides – however, under normal circumstances expression of these genes in NOT advantageous to the recipient organism. On a most basic level, if a gene is to be expressed, first RNA has to be made from the DNA template, then the RNA must be transcribed into a protein. This process requires energy and slows down the growth of a plant and after a few generations in the ‘real world’ (i.e., not in a cultivated field), the progeny of the want-to-be ‘superweed’ in question could not compete with the growth rates of unaltered natural weeds and would go extinct (natural selection at work).
An exception is that when a gene that confers pesticide resistance is expressed in some plants (presumably the crop being grown) all non-genetically altered plants (the natural weeds) will be killed by the application of pesticide. Thus, the genetically altered plant, in the farmer’s field, will be the only plant left and can grow unimpeded (albeit more slowly than if never modified in the first place). In this case, if transfer of the pesticide resistant gene to a weed has occurred, the ‘superweed’ would now also be able to grow in the farmers field, and perhaps at near the periphery where residual pesticide occurs. Outside the field (and beyond the reaches of residual pesticide), any superweeds expressing the pesticide-resistant gene will grow more slowly and be out-competed by their wild-type compatriots.
At this point is worth focusing a bit more on the differences between what occurs INSIDE the field and the LARGER environment. INSIDE the field, it is quite likely that the pesticide will soon (2 years? 5 years?) become ineffective for growing the crop in question (because the weeds IN the field are no longer killed). Of course, if the very same pesticide (eg. Round-up) is used over millions of contiguous acres, the pesticide-resistant weeds could become quite wide-spread (but that's more a reflection on really stupid agricultural practices than on the underlying technology). In same ways Round-Up may be considered to be like Penicillin – the original form of penicillin is rarely used any more because extensive OVER use in the past has allowed resistant microbes to widely flourish. A much more sensible approach would be to have dozens of control agents, the use of each would be carefully restricted in space and time to prevent the development of resistance ‘superweeds’.
Notwithstanding the above-mentioned developments, the pesticide-resistant gene will not spread throughout the entire biome for natural-selection reasons mentioned above, but will instead be restrained to locations of pesticide use simply because the natural weeds have a growth advantage because they’re not foolishly wasting energy to produce a protein they don’t need. A basic understanding of evolutionary principles shows that the fear of genes that have been introduced into GM crops spreading like wildfire throughout the biome is completely unfounded. After all, these genes already exist in nature (and most of them have for hundreds of millions of years) and they have remained carefully confined to organisms where they are needed to confer a selective advantage. A possible exception is that some of these ‘wild’ plants are smart enough to realize they don’t need the pesticide-resistant gene to survive in places where they aren’t exposed to the pesticide. Therefore they choose not to express the gene and subsequently don’t waste any energy doing so, and can therefore compete with the wild-type plants. (As an aside, the loss of expression of introduced genes is a real problem (for the farmer) even back in the farmer’s field).
Now you might ask the question – what happens to the non-expressed pesticide gene mentioned above? Isn’t it still a threat? You are probably aware that the human genome is composed of mostly ‘junk’ DNA – well the pesticide-resistance gene has now become part of the ‘junk.’ Theoretically, it COULD be re-expressed days, weeks, years, or millions of years later. More likely is that it will lie dormant forever, or evolve into a completely different type of gene. In many ways, the genome of an organism is a blank slate waiting to be molded by the environment – after all 1.5 billion years ago all life on earth was in the same primordial form, and now like at the incredible diversity. Interestingly, this incredibly diversity came about completely in the absence of those awful gene-altering corporations and gave us sinister entities such as the HIV and ebola viruses, tasty things such as brussel sprouts, friendly organisms such as cocker spaniels, and bizarre, difficult-to-classify organisms such as Mr. G.W. Bush.
To understand how this genetic diversity arose, let’s consider one gene that is of interest to the GMO folk. That would be the gene for a fish antifreeze protein which has been introduced into strawberries and/or tomatoes (obviously, to allow these plants to withstand frost). Leaving aside these latter day maniputions, an interesting question is where did the fish get this protein from in the first place, with the timing of the ‘first place’ being approximately 14 million years ago according this paper:
Expansion of genome coding regions by acquisition of new genes.
Genetica. 2002 May;115(1):65-80. Review.
PMID: 12188049 .
OK, there was no Prestone Corporation 14 million years ago to supply the fish with antifreeze, but no matter, it was able to solve the problem on it’s own, as described in a quote from the paper cited above:
"Figure 2 summarizes the mechanism in which these antifreeze protein genes originated. Given the common elements in the sequence, it seems that the AFGP gene in Antarctic notothenioid fish was born as a trypsinogen gene that underwent a big deletion and a series of tandem duplications of a nine nucleotide (Thr-Ala-Ala) motif. Thr is glycosylated and that allows the protein to bind ice. The spacers provide sites of postranscriptional proteolytic cleavage. A completely new function was born from pieces and an intron of the trypsinogen gene. This occurred under the appropriate selective pressure allowing a species to adapt to a new environment."
What happened here is that the trypsinogen gene, which originally existed to digest proteins (a crucial metabolic process in each and every cell), has now taken on a very, very different role (note that the fish likely had multiple copies of the trypsinogen gene in its genome, so even though one copy was converted to become the antifreeze protein, others would remain and retain their original function. Getting back to the pesticide-resistant gene that was introduced into plants by genetic engineering methods (as considered earlier in this post), what’s to say the same thing won't happen with it? Well, sure it could happen, as the example just cited shows, genes really are blank slates that can be dramatically altered under the appropriate selective pressure. However, it is very important to realize that the very same process could take place with any one of the many thousands of naturally-occurring genes found within an organism (which is what happened in the development of the fish anti-freeze protein).
OK, maybe I’ve convinced you that the genomes of organisms are dynamic and constantly under change? If not, or you are interesting in learning more about this fascinating subject, the scientific journal (with ‘scientific’ meaning peer-reviewed, hence reliable as compared to most Google-obtained information) Genetica has an issue devoted to this topic available free of charge at this link:
http://www.kluweronline.com/issn/0016-6707/contents (note – you may have to then click on the ‘Issue 1, May 2002’ link)
The bottom line is that naturally-occurring genetic change absolutely dwarfs any conceivable efforts by the genetic engineer. In a way, the genetic engineer will always be battling nature, because nature will take the ‘new’ genes and twist them in new and probably un-imagined ways, making the original efforts obsolete after a few generations of the organism in question. However, this genetic in-stability can hardly be regarded as threatening because the very same thing is happening on a much larger scale with all organisms complements of naturally-occurring genes.
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