Welcome to another edition of “What’s the Deal?”, the blog that rearranges its nucleotides to strengthen its spam filter (read: I get a lot of spam).
In this week’s post, we’ll discuss new research on Genetically Modified Crops and their co-evolution with pests and also look at the wider advance of GMOs; checking on their brief history, and contrasting public visions of how genetic advances should be part of our agricultural production.
Mainstream farmers have been planting crops that have been genetically engineered for many years. Some types of crops, such as corn and cotton, have been genetically altered to produce a chemical that is harmless to humans and most animals, but kills certain insect pests that can decimate crop fields. The chemical, a toxin known as Bt, is derived from the protein Cry1Ab in the bacterium Bacillus thuringiensis (hence the initials Bt) and has kept pests (mainly, the European Corn borer and the Cotton Bollworm moth) at bay and greatly increased crop yields.
In a report presented this spring at the Proceedings of the U.S. National Academy of Sciences, new evidence came to light of developing insect resistance to Bt. In some ways, this may not seem like a surprise given that the insecticide has been used on crops for decades, and that certain pests have developed some genetic mutations that allow them to survive the toxin in the plants. The cause for concern with this report is not that these pests have evolved a resistance, but the type and speed of resistance.
The study, carried out by researchers from the University of Arizona in Northern China, examined resistance to Bt by the caterpillar of the cotton bollworm moth, Helicoverpa armigera, a common pest of cotton in the region. The study looked at bollworm genetic mutations for Bt resistance found in laboratory conditions versus mutations developed in field conditions. In the laboratory, resistance developed from recessive mutant alleles (rare types of genes) as expected, but samples with mutations from the field were developed from dominant alleles.
Why is this important, and what’s an allele? Get ready for a 9th grade biology refresher.
Before we get back into drawing punnet squares, here’s a quick summary sentence: The importance of the bollworm developing a mutation from dominant alleles means that resistance to Bt can be conferred more quickly to the bollworm population at large, eventually making the toxin ineffective against them as the bollworms with the resistant gene will be advantageously selected.
Before we begin, let’s put our safety glasses on. Safety first.
Now, let’s first start with the obvious: the bollworms with the genetic mutation for resistance to Bt will survive better than their non-mutant counterparts; they won’t die when they munch on cotton plants. This genetic mutation developed over many generations of bollworm populations who had been exposed to the toxin. The mutated gene that developed was rare and indeed was a recessive trait, or not the normal (wild-type) type of gene expressed by the insect.
Normal genes for the bollworm do not confer a resistance to Bt. Therefore for the recessive gene to be expressed in one bollworm, a mother and father bollworm from the previous generation had to carry one mutant allele of this resistant gene (out of a possible two; there is a pair of alleles or type of gene, one from each of your parents). This possibility of two carriers, or parents with hybrid genotypes, was very rare.
From the samples from the field grown moths from the new report, it’s clear that evolutionary selection has chosen the mutant gene fairly quickly, and it has developed rapidly in the bollworm to become the homozygous dominant trait, or both formerly mutant alleles are now the normal, wild-type trait. This means, that for each new generation of bollworms, there will be a greater and greater percentage of Bt resistant moths, free to happily eat away at cotton crops.
This counter-evolution is the latest victory for pests in the never-ending evolutionary war between insects and plants. This will put pressure on humans who created the Bt plants, to come up with a new method of keeping the pests off of important crops. The method will most likely come from genetically engineering the plants.
History of GMOs (and more science!)
In the history of agriculture, modifying plants to increase yields, change appearance, or derive a new product has taken place for thousands of years. The methods of agriculture fundamentally changed the ancestors of modern food plants to resemble something very different today. Creating plants with desirable traits through cross-breeding, seed selection, and other methods was essentially a type of primitive genetic engineering, though this was not known at the time.
The efforts of modifying crops became more refined in the 19th and early 20th Century, but the identity of the true carrier of genetic information, and therefore the code behind the plants, was not recognized as DNA until 1944 and its structure not pictured as a double helix until the 1950s. With the idea that you could alter the code to directly get a better product, the path to GMOs became an exponentially expanding effort.
To have an organism manufacture a specific protein, toxin, or hormone that is not naturally produced requires inserting a foreign organism’s DNA (the organism that does naturally produce this item) into the DNA of the desired living thing in a specific location. The information for coding this protein is transcribed from the DNA sequence (gene) into messenger RNA, then translated into transfer RNA which attaches chains of amino acids that correspond to the specific tRNA code, and fold themselves into the desired hormone, protein complex, or toxin producing protein. The process of DNA – mRNA – tRNA – Protein is known as the central canon of biology.
The complicated mechanisms for accomplishing the feat of genetic engineering came about by first being able to identify the gene, or stretch of DNA, that is responsible for producing the desired protein. Then, scientists had to find a way to “cut out” the desired gene from the donor organism and a way to insert the DNA into the new organism. This was accomplished by using “restriction enzymes” or enzymes found naturally in bacteria that cut DNA at specific locales (a very useful find). Introduction of DNA into a new animal cell is accomplished via direct injection, or through a vector, such as a virus and using another enzyme, DNA ligase, to reattach the DNA to the host genome.
With these tools and knowledge, Stanley Cohen and Herbert Boyer developed the technique of gene splicing in 1972 by using yeast cells and a borrowed circular DNA strand (plasmid) from bacteria. They were able to produce human hormones such as HGH and insulin in bacteria via this method.
If the new organism happens to be a plant, as is the case with our protagonist Bt Cotton, a more complicated method had to be discovered. Plant cells, as you may remember from your 9th grade microscopy adventures, are surrounded by a thick cell wall made of cellulose, a fibrous chain of carbohydrates. the challenge is getting the specific gene into the DNA of the plant. Direct injection of DNA was insufficient to the task, and using a viral vector also fell short.
In 1976, researchers from the University of Washington discovered a certain soil bacteria, Agrobacterium tumefaciens, infects flowering plants (dicots) and causes a wound/tumor, making entry possible into cells. Agrobacterium contains a large plasmid (circular strand of bacterial DNA) called a Ti plasmid, which in itself contains what is called T DNA. The T DNA are the sequences used in genetic engineering, by replacing the bacterial T DNA sequences with the selected DNA sequence for a desired protein. The plasmid is then used to gain entry into plant cells, allowing the selected DNA to be incorporated into the plant genome, to be able to produce the desired product.
Thus, modern crops could now produce their own insecticides, fungal resistant antibiotics, and growth hormones. These desired traits didn’t become widely used in modern agriculture until the 1990s as many tests for safety and creation of policy was needed. Indeed, crop spraying was still widely used until the early 1990s when Bt crops really began to take off commercially and become widely accepted.
An Ethical and Safety Backlash?
Since their introduction to agriculture, GMOs have been controversial; we humans have been understandably unsure of our role of “playing god” by altering the genetic makeup of the plants and animals we eat. We have also been unsure of the role GMOs may have on the outside environment and to our own health.
For better or for worse, GMOs have made it on the mainstream in modern agriculture. In 2008, 92% of soyabeans and 80% of corn grown in the U.S. were of a GMO variety. Given the entrenchment of GMOs in the production of our food and biofuels, Americans have generally accepted (or may just plead ignorance) that much of what ends up on our plate may have been genetically engineered. We have also accepted much larger crop yields, less decimation from pests and fungi, and crops that provide extra nutritional value for developing agricultural nations. The controversial conversation over GMOs is far from over, however.
A recent FDA approval of genetically modified salmon with a growth hormone and antifreeze gene from two different fish species has been consistently stalled since 2010 because of opposition from green groups and an apparent uncertainty of what would happen if the GMO fish came into contact with wild species. This debate over salmon that would grown twice as fast as normal farmed Atlantic salmon remains unsolved.
Most recently, the debate over GMOs has focused on legislation that would require labeling products that come from plants that have been genetically altered. In the most recent farm bill before Congress, there has been much popular public advocacy for the labeling of GMOs. Many large industry groups oppose the measures requiring GMO labeling because they say it would destroy consumer confidence in the food supply. The FDA has maintained that labeling GMO foods is unnecessary, that they pose no threat to human health, and that the food is essentially the same as other foods (though bigger/greener). Advocacy groups like Just Label It have formed a coalition to get this measure through in this years farm bill. According to a Mellman Poll conducted in February, some 64% of people believe there is a difference between GM foods and non-GM foods, so perhaps the industry groups have some evidence to back their side. Then again, how difficult would it be just to slap a label on a product next to the nutrition facts? Hmm… this is a tough one.
This issue has led to many farms who aren’t organic farms, but who use non-GMO seeds to market themselves as non-GMO. This has interestingly led to some potential problems, such as cross pollination with GMO farms.
One last problem people have with GMOs is the leading figures of the industry. The leading developers and producers of genetically modified seeds and crops like Bt corn and cotton have little or no competition in “the field.” The most famous of these is Monsanto, a seed giant, and manufacturer of the famous weed killer, Roundup. Monsanto developed genetically modified plants that could withstand the presence of Roundup, that way farmers could get rid of weeds without the toxic poison killing their crops as well. In addition, Monsanto developed a strain of Bt corn that killed another famous pest, the corn borer. Novartis, a Swiss based chemical and pharmaceuticals company also developed Bt crops.
The controversy regarding Monsanto is their very strong presence in the agriculture industry. Their market dominance and lobbying power for their industry often have forced the hand of farmers to grow GMO crops against their wishes. The economic interests of industry giants like Monsanto has put enormous pressure on Congress to not push forward the GMO labeling requirement, as mentioned above. Notably, Monsanto has also pioneered crops such as “Golden Rice” that provide extra nutritional value for people suffering malnutrition. This positive note is tarnished, critics say, by Monsanto’s unwillingness to relinquish control of the product and its distribution in developing nations; in other words, Monsanto wants to be able to have a significant presence in the agricultural market and production of these nations as well. In essence, the “health and safety issues” of GMOs (which are arguably nill) are actually economic.
We’ve covered a great deal here; perhaps meandering a bit too far in one subject or another, but I have faith that we can pull this all together into something useful.
- Humans have been genetically altering plants to produce bigger, tastier, and specific crops since the beginning of settled agriculture.
- The discovery of DNA as the genetic carrier in living things led to great developments in the ability to manipulate specific parts of domesticated plants and animals.
- While still very controversial, GMOs are now a huge part of modern agriculture whether we like it or not.
On the science side,
- The discovery of a soil bacterial that infects flowering plants allowed scientists to genetically engineer plants.
- The discovery of the “safe” toxin Bt, from a bacteria, has been produced by genetically engineered cotton and corn crops and has led to significantly greater crop yields.
- Insect resistance to the toxin Bt has been confirmed in a new study, putting new pressure on scientists to come up with a new method of keeping high crop yields.
So, the fact that those pesky cotton plant-eating bollworms will develop resistance to Bt plants at a much faster rate is the latest example of a counter evolution in the war of domesticated plants (and humans) versus pests. The public debate over GMOs will continue; whether the labeling issue or industry entrenchment will change will be fascinating to cover.
Hopefully I didn’t go too overboard with the biology for this one, but I have to get some use out of these old text books.
Until the next bug evolves faster than us,
Your Faithful Historian,
Eric G. Prileson
Sources and Further Reads:
Genetics: A Genomics Perspective Fifth Edition, Daniel Hartl and Elizabeth Jones
U.S. Department of Agriculture Economic Research Service, “Adoption of Genetically Engineered Crops in the U.S.,”http://www.ers.usda.gov/Data/BiotechCrops/