One of the reasons that many people with solid scientific backgrounds have concerns about the use of genetic modification techniques in agriculture is the degree to which the potential for unintended consequences seems to be downplayed. This is especially true when microbial genetic material is involved. Unlike more complex organisms, bacteria can spread changes to their genomes through methods other than traditional reproduction; “horizontal gene transfer” across species is said to be responsible for up to 10% of evolutionary changes to bacterial genes. The use of microbial DNA in agricultural biotechnology risks increasing the possibility of horizontal transfer, particularly between bacterial species that don’t normally have contact.
Given the overwhelming concern these days about bacteria acquiring antibiotic resistance, one would expect that this would be an area that plant bioengineers would be extra-careful about. One would be wrong. It turns out that genes for a particular type of antibiotic resistance are part of many plant modifications, for reasons explained below. Fortunately, researchers in Tennessee have come across a set of plant genes that impart similar resistance to antibiotics, but cannot be transferred—horizontally or otherwise—to bacteria. The adoption of this technique won’t allay all reasonable concerns about GMOs, but it would go a long way to preventing one particularly nasty outcome.
Genetic modification is a tricky business. It’s actually quite difficult to get one species to accept genetic material from another, and most attempts to make that happen fail. But if the modification one is attempting doesn’t have an obvious external effect—making the species glow, for example, or change color in the presence of land mines—determining whether or not one is successful can be difficult. For that reason, agricultural biotechnologists often use “marker” genes that can signal whether or not a transfer is successful, but otherwise don’t affect the function of the organism.
A common marker is a bacterial gene complex that imparts resistance to the antibiotic kanamycin. The ostensibly modified plants are grown in soil containing kanamycin; plants where the genetic transfer was successful do well, while plants without the marker—hence without the rest of the transfered genes—wither due to the chemical. According to one of the Tennessee scientists, Dr. Neal Stewart, about 60-70% of modified plants discussed in scientific literature between 2000 and 2002 included this antibiotic marker.
What Dr. Stewart’s team found is that a gene complex from Arabidopsis thaliana—a very widely-researched plant species—can also impart resistance to kanamycin, but cannot be transferred to bacteria.
The gene increases production of a protein called an ATP binding cassette (ABC), and - by a mechanism which is not fully understood - makes the plants kanamycin-resistant.
“I would like to see a science-based approach to the regulation of GM crops,” said Professor Stewart, “and this could do something to mitigate the regulation and public perception hurdles.
“We have been trying to simulate what would happen if this gene was transferred to microbes; and we can show that if this ABC gene is inserted into E. coli, for example, it does not make them kanamycin-resistant.”
Reactions to this discovery are mixed, but fairly predictable. Opponents of GMOs aren’t enthusiastic, noting that foods with the bacterial antibiotic gene are already available, and that insufficient research has been done as to the other effects this change might have (true, but such research seems a good next step); GMO industry organizations are somewhat more welcoming, but hasten to assert that the use of bacterial antibiotic genes is completely harmless (a claim that’s fairly easy to make, as proving that horizontal gene transfer happened due to a GMO crop is next to impossible).
My take is this: it is pretty much a given that global warming-induced climate disruption will lead to severely negative impacts on global agriculture; it is likely that careful use of genetic modification, along with more conventional “smart breeding” practices, will be needed to help agricultural plants adjust to an altered climate. If so, we need to make certain that such modifications are done as safely as possible, with minimal ecosystem consequences. If this plant-based antibiotic resistance gene proves not to have other disruptive effects, it appears to be a very good step in the right direction for agricultural biotech.
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