GMOs: a Primer

The “March Against Monsanto” took place over Memorial Day weekend, where groups of activists protest the use of genetically modified organisms (GMOs), specifically those used in agriculture and patented by the corporation Monsanto. What is a genetically modified organism, anyway?

Humans have been breeding plants and animals for 1000s of years, shaping them to fit their needs and desires. Corn is one example; its wild relative, teosinte, at first glance looks nothing like modern corn, being more grass-like and lacking the giant cobs of kernels we are used to seeing.1 We all know that dogs are the descendants of wolves, but have you stopped to think just how different a wolf is from a pug? How did it get that way?

It’s all in the genes. A gene is a unit of heredity, encoded within an organism’s DNA. Even before people knew about genes, they knew that if they bred an organism with a desirable trait to a second organism, the trait they wanted might be passed on. And so they would breed the offspring, and the parent, and the offspring, until the organisms they had bred “true” for the trait. This type of breeding is commonly called “artificial selection,” i.e., humans are the ones selecting for desired traits, not nature.2   In the case of pugs, you can imagine how many generations of breeding dogs it would take to produce a canine so dissimilar from the parental wolf.

Along comes genetic engineering. What if it was possible to select exactly what traits (genes) you wanted in an organism and, well, put them in there? GMOs are created in this manner. Whereas artificial selection relies on genes created by “nature” (some plant breeders do utilize radiation or chemicals to induce changes – mutations – in genes which are then screened for desired traits3), scientists use a variety of techniques to insert specific genes into organisms, producing GMOs. In the case of plants, two of the most common methods used to transfer genetic material are 1) the “gene gun” (where tungsten pellets are coated with DNA and literally shot into the cells) and, 2) bacterial vectors such as Agrobacterium tumefaciens.4 Agrobacterium naturally infect plants and transfer their genetic material into them; scientists remove the pathogenic (disease-causing) genes of Agrobacterium and replace them with the genes they want to transfer into the plant. The science used to create GMOs is not so sophisticated yet as to know exactly where the genes will be inserted into the plant genome, which is why GM plants are tested for the stability and inheritability of the desired gene over generations. Overall plant health and any effect on animals fed them are also assessed during this time.

Examples of GMOs:

Plants are usually the first things people think of as being GMO. GM soybeans, alfalfa, corn, cotton, canola, and sugarbeets have been altered to resist the herbicide glyphosate (trade name Roundup).5 The premise behind Roundup Ready (RR) GMOs is that farmers can use Roundup to spray their fields, killing weeds while leaving valuable crops undamaged. RR GMOs have been patented by Monsanto6 and are the bulls-eye on “March Against Monsanto’s” target. The US also grows its fair share of GM corn and cotton, which have been modified to express Bt protein (derived from Bacillus thuringiensis bacteria, which are common in soil). The bacterial Bt protein is a natural insecticide that is only active once it enters an insect’s gut.7 Scientists have further modified the Bt gene to create different proteins that are effective against a variety of insects. Interestingly, whereas Bt corn and cotton have been engineered to produce their own Bt proteins, organic and conventional farming uses exogenous BT in insecticide sprays.8,9 Bt corn and cotton are also manufactured by Monsanto.

Hawaiian Rainbow papaya was engineered to “self-vaccinate” against ringspot virus, which devastated papayas grown on the island in the 1990s.10 Seventy-seven percent of papayas now grown in Hawaii are of the rainbow variety, and these plants actually help non-GM/organic papayas by decreasing the viral burden on the island.11

After many years in development12, GM Golden Rice will soon be available for consumption. Golden Rice contains up to 35 μg of beta-carotene per gram of rice, which is effectively converted to vitamin A in humans.13 Golden Rice was developed to help curb vitamin A-malnutrition in rice-dependent, poor populations which cannot afford a diversified diet. Another GM plant on the horizon is the Arctic Apple, which is engineered to not brown once cut or peeled. The interesting spin on GM apples is that instead of adding genes, these apples have been modified to have the genes which facilitate browning silenced (turned off).14

Bacteria, virus, and yeast. The food and drug industries produce lots of these types of GMOs. As a biologist who studies viruses, I have created my fair share genetically modified bacteria that produce viral proteins that I want to study. Virologists also readily employ viruses modified to glow green (or cyan, or red) by inserting a fluorescent protein found in jellyfish.15 This fluorescent technology was a major scientific breakthrough and is now widely used to study just about everything in biology; bacteria, mice, fish, and even cats have all been genetically modified in this manner.

GM E. coli, modified to produce human insulin, is used to treat diabetes. GMOs are also widely used to make vaccines. A recombinant rabies vaccine used to immunize wildlife is actually a genetically modified vaccinia virus that 1) has been engineered to express a rabies protein, and 2) has genes deleted to make it less virulent (disease-causing).16 GM yeast is used to make the human vaccines for hepatitis B and human papilloma virus (GardisilTM).17,18 In the food industry, GM yeast were engineered to produce a milk-coagulating protein central to making cheese.19 Have you noticed that your Cheerios are now GMO-free? Have you also noticed that they now contain fewer vitamins and minerals? That’s because some vitamins and minerals that are added to foodstuffs are manufactured directly from GMOs (like bacteria) or encapsulated with (possibly GM) corn or soy to prevent them from degrading.20

Animals. While not apparent to most people, transgenic mice are critical tools for scientists.21 GM pigs are currently being tested to grow human organs for donation, and GM cows to produce hypo-allergenic milk.22,23,24

As you can see, GMOs are currently used for more things than most of us are probably aware of. Ultimately, genetic engineering is a tool (one among many) that scientists, farmers, doctors, etc., can use. It is a technique that has risks and benefits just like any other. While I’ve only described GMOs currently in use, there are a great many GMOs that have been developed by scientists and failed. GMOs are not a magic bullet that will solve all the world’s problems, but they are not the devil’s handmaidens either. And they make delicious cheese.

References/Further Reading

12. Potrykus I. 2010. Lessons from the ‘Humanitarian Golden Rice’ project: regulation prevents development of public good genetically engineered crop products. New Biotechnology. 27: 466-472.
13. Tang G, J Qin, GG Dolnikowski, RM Russell, MA Grusak. 2009. Golden Rice is an effective source of vitamin A. Am. J. Clin. Nutr. 89: 1776-1783.
18. Bryan JT. 2007. Developing an HPV vaccine to prevent cervical cancer and genital warts. Vaccine. 25: 3001-3006. Review.
22. Klymiuk N, B Aigner, G Brem, E Wolf. 2010. Genetic modification of pigs as organ donors for xenotransplantation. Mol. Reprod. Dev. 77: 209-221. Review.
23. Jabed A, S Wagner, J McCracken, DN Wells, G Laible. 2012. Targeted microRNA expression in dairy cattle directs production of β-lactoglobulin-free, high-casein milk. PNAS. 109: 16811-16816.