Expert response from Wayne Parrott
Professor, Crop Breeding and Genetics, University of Georgia
Friday, 09/10/2015 11:15
The short answer is no there are no health effects, and yes, there are tests.
For the long answer, it first helps to define what is meant by ‘promoter.’ Genes in general have three parts to them.
- The promoter is the first part of the gene, and is equivalent to a switchbox that determines when and where that gene will be making its protein.
- The second, or middle part, is the coding sequence, which is the business part of a gene—and in most genes, is where the information needed to make a given protein resides.
- The third part, often called the terminator, marks the end of the gene.
The cauliflower mosaic virus, or CaMV for short, is a virus that infects cole crops (cabbage, kale, cauliflower, broccoli, etc). As such, humans have been eating CaMV as long as they have been eating cole crops, which is some thousands of years. Usually, it is aphids that carry the virus from plant to plant; infected plants can show the typical symptoms of viral plant disease—usually streaked, misshapen leaves.
The CaMV only has six genes controlled by two promoters; its small size is why it lends itself to laboratory work. When the one of these promoters, known as the 35S (the name comes from the measure of its size) CaMV promoter, is placed in front of coding sequence and engineered into plants, it does a very good job of expressing the coding sequence in the new plant. Hence, it has been used to ensure that several GMO crops express their new trait adequately.
However, it was discovered that the 35S CaMV promoter used in several of these GMOs also contains part of the coding sequence of CaMV gene 6, which is found in front of the 35S promoter. Although this partial coding sequence is in front of the promoter, rather than after it, it is conceivable that it could be expressed under certain conditions, and the protein made by the gene 6 (called P6 for short) would then be inside the plant.
It is worth noting that the gene 6 protein is what gives infected plants their distinctive appearance. Hence, GMO critics were quick to claim that these symptoms are a sign that P6 is toxic to plants, and could therefore be toxic to humans.
Several things must be pointed out:
- Humans have been eating P6 inside their cole crops for thousands of years, with no indication of any harm. There is no reason to think that a P6 that is harmless in cauliflower would be harmful in corn or any other crop.
- The P6 has no properties that would indicate it is toxic or could cause allergies.
- The symptoms P6 creates in plants are due to its ability to alter gene expression. For that to happen, the P6 protein would have to be inside the affected cell to begin with.
- There is no known way by which whole proteins from our food can enter human cells in the body. The same goes for DNA from our food.
In conclusion, the chances of having a partial P6 protein due to the CaMV promoter in a GMO are very small. In contrast, the chances are high if one is eating a non-GMO cole crop. Regardless, there is no biological reason to suspect an adverse health effect in humans or other animals.
To answer the final question, yes it is possible to detect the presence of the virus in infected plants, and of the CaMV promoter in food, but only if the food has not been too processed.
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