What kind of GMOs are currently on the American market? And what are they spliced from?
-A curious adult from California
April 10, 2008
Farmers have been genetically modifying crops for thousands of years. So much so that some modern plants and animals barely resemble their ancestors. For example, modern corn looks almost nothing like the wild grass it came from.
In the past, farmers had to use careful breeding to get plants that grew better or were more flavorful. Today, scientists can use transgenics to change crops. This is where scientists add a new gene to a plant instead of trying to coax a trait out of the genes that are already there. Here in the U.S. we've been eating this kind of genetically-modified (GM) food since the 1990's.
In 1994, the FDA approved the first modern GM crop, the Flavr Savr® tomato. Today supermarkets have many more GM foods for sale. The most common ones are soybeans, corn, and canola.
Any time you buy something from the grocery store with any of these three ingredients, you might be getting some GM food. In fact, about 70-75% of processed foods include at least a small amount of GM crops. And items like canola oil are often made completely from GM crops.
So how do scientists make these transgenic crops? First they need to find the right gene to do the job they're looking for.
In the last 50 years, we have learned a lot about DNA and genes. Not only do we know what DNA is, but we can also trace things like tomato color back to the gene that makes it that way. Even more, we have figured out how to add to or change the DNA of other organisms.
At first scientists focused on making crops that would need fewer pesticides. Or that might cause less damage to the soil. Lately they've set their sights on making crops that are healthier. And they have found plenty of genes that can give plants these properties!
Most GM foods on the market use bacterial genes. GM foods also have genes from the bay laurel plant, soybeans, and other plants. Other GM foods like papayas have modified plant virus genes that can protect the plant from getting the real virus.
The majority of the GM crops in use today have genes from bacteria for herbicide and pest resistance. One of the most common genes is from soil bacteria that makes plants resistant to an herbicide called Round Up®. This allows farmers to spray these crops with herbicide and only kill the weeds. And it eliminates the need to till the land for weed control, which reduces soil erosion and greenhouse gas emissions.
To make plants bug resistant, scientists added a gene from a bacterium called Bacillus thuringiensis, or Bt. Bt grows in the soil and makes a toxin so that when the bug eats it, the bug dies from holes in its stomach. This toxin only works in the stomachs of a certain family of bugs (and can't work in people or other animals).
At first, the Bt bacteria were sprayed on plants to help get rid of bugs (this is still used as an organic pesticide). To cut out all that spraying, what if the plant itself could make the Bt protein instead?
This would mean the plants would spray themselves! To do this, scientists need to get the Bt gene into plants. They do this by using another type of bacteria -- a plant bacterium.
Making Bt Resistant Plants
Scientists found a special kind of bacteria called Agrobacterium tumefaciens that can insert its own DNA into plants. Scientists use this bacterium to add the genes they want into a crop plant.
In the wild, agrobacterium give plants tumors by inserting bad DNA into the plants. But in the lab, agrobacterium can be changed so they can now be used to put any other DNA sequence into the plant. Say, the Bt gene that makes the toxin for bug resistance.
First scientists put the Bt bug-resistance gene into agrobacteria. It is fairly easy to put new DNA into bacteria -- much easier than putting DNA into a plant. (Click here and select "Manipulation" to learn more about moving genes around in bacteria.)
Next, the modified agrobacteria is mixed with small pieces of plant stems or leaves in the lab. The agrobacteria do their job and some of the plant pieces get the Bt gene.
To make sure ALL of the plants actually get the Bt gene, scientists add a "marker" to the new DNA. The marker is a way to get rid of any plant pieces that don't have the new DNA.
Usually the marker is another gene, such as a gene for antibiotic resistance. So when the plant pieces are grown in the drug, only pieces with the Bt gene will survive because they also got the marker gene.
Finally, the genetically-modified plant pieces are used to make a whole plant. That new plant has to go through lots of testing before approval. For crops with the Bt toxin gene, scientists had to prove that the toxin was not harmful to people or animals. And that Bt crops wouldn't hurt traditional corn.
Future GM Crops
While herbicide and bug resistance are neat, farmers and consumers want more. Now there is a lot of focus on making transgenic crops with added nutritional benefits.
Researchers have made rice called "golden rice" that makes extra vitamin A. Enriched plants like these aren't used yet, but they have the potential to help areas of the world where a vitamin deficiency is a major health problem. For example, golden rice could help eliminate blindness caused by vitamin A deficiency.
Other plants have been developed to make healthier fats and oils. And there are even potatoes that absorb less fat when fried. So French fries would be healthier. So far, only a few altered crops have reached the US market. These include soybeans and canola with healthier fats for people and corn with more protein that is used to feed animals.
In the future, much more of our diet could be affected by genetic engineering. You might even be able to get vaccines by eating bananas!
Colleen Brady, Stanford University