Critics of genetically modified (GM) crops worry that herbicide resistance genes could be transferred to wild plants in pollen blown from a field of GM plants. Now researchers have shown that GM genes carried in maternally inherited chloroplasts are rarely transferred through pollen to other plants.
"Determining the Transgene Containment Level Provided by Chloroplast Transformation" by Stephanie Ruf, Daniel Karcher, and Ralph Bock, Proceedings of the National Academy of Sciences (volume 104), April 24, 2007, pages 6998-7002.
Jan Witkowski: Welcome to DNA Today, I’m Jan Witkowski…
Dave Micklos: … and I’m Dave Micklos. We’re here at Cold Spring Harbor Laboratory discussing news about DNA.
JW: Today’s new is about genetically modified, or GM, crops.
DM: What’s so new about that? It’s been done in Mesopotamia for a long time.
JW: Where is Mesopotamia?
DM: The Fertile Crescent, about ten thousand years ago.
JW: Your history in geography is better than mine. Anyway, the difference these days of course is that, with recombinant DNA and genetic engineering, you can transfer genes between species. And in the topic we are covering today, you can take a gene from a bacteria cell, a gene that is involved in herbicide resistance. You can put that into important agricultural crops like cotton, canola, soy, or corn. This means a farmer can plant a field with these crops, allow them to grow, and then treat the whole field with herbicide, selectively killing off just the weeds in the field, and leaving the crop intact.
DM: Now, farmers use GM crops because they improve yield, that’s what they are really after, of course. But they also save tilling, which improves the soil fertility and cuts down on runoff, so these are great things. The majority of people in the United States would be surprised to learn that most of the fresh vegetables and processed foods we eat have some genetically modified component. Now in Europe this isn’t the case, where the majority of people really distain GM foods.
JW: One of the concerns is, particularly in term of herbicide resistance, is that these herbicide resistance genes will escape from the crops and enter the wild plants. You can imagine having superweeds that are now not killed off by any sort of herbicide.
DM: Now, one way you could potentially get around this is to put the genetically modified gene in a compartment within the plant cell, called the chloroplast. This is the part of the cell that produces sugar, but also makes the plant green. Now, chloroplasts are inherited entirely from the mother plant, so that means that a pollen grain does not have any chloroplast. If you were to genetically engineer a new gene into a chloroplast, the chances of it escaping into the wild by wind and pollinating a wild plant would presumably be pretty small.
JW: A group in Germany has just tried to determine how often this happens experimentally. They made tobacco plants that were transgenic for jellyfish protein, green fluorescent protein that fluoresces when you shine light on it. And they took pollen from those plants and used them to fertilize non-transgenic tobacco plants – and they examined over two million seedlings for any sign of green color. Of those 2 million seedlings, they only found about six that showed evidence of transmission of the green fluorescent protein via the pollen, which is about one in three hundred thousand.
DM: Now, this was in a laboratory experiment, or as you would say it, lab-or-atory experiment. It’s a pretty small rate of transmission, so the authors of the paper thought that, in fact, the transmission in the wild would be even smaller. Now, you’re European, so, how do you think this story will square with Europeans?
JW: I don’t think it will have much effect on the critics.
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