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The wheat experiment
We went to Rothamsted Research on Thursday 10th May armed with your questions on the development of the GM wheat and why it is being grown outside.
We met Dr Toby Bruce and Professor Huw Jones who showed us around their labs and greenhouses. Toby Bruce is senior research scientist in the Biological Chemistry department. His research looks at how plants use alarm signals and how insects respond to them. Huw Jones is research leader of the Cereal Transformation Group, studying ways to develop genetic techniques to solve problems growing wheat and other cereals.
Before we start, we’ve got some questions that have come in about why you’re doing this in the first place, and we thought perhaps while you’re sitting here with a cup of tea, we could ask you a few of those, and then perhaps you’ll take us to where it all started.
- The first question is: how have you alighted on this pheromone to repel aphids? Are other plants using other mechanisms?
Toby Bruce: The pheromone is a substance which is naturally produced by aphids to warn them of danger. So one aphid produces this signal to warn the other aphids and they run away when they smell it. This substance is naturally produced by over 400 different species of plant, but not by wheat. Wheat is not a smelly plant.
2. Is this the main way that plants repel aphids?
TB: No, but this is a particularly strong repellent, so we're hoping it might work better because this is the substance that aphids normally use to warn each other when there's a predator about to attack them, and it does make them run away very fast.
3. Another question we’ve had: are aphids the only pest that wheat has to struggle with?
TB: There are some other pests, there's the orange wheat blossom midge as well. This varies from year to year, and we've done quite a lot of work on breeding varieties resistant to it in collaboration with others at Rothamsted, and we've also devised a pheromone monitoring system for that pest.
4. We’ve had a lot of questions about predators and aphids getting used to the signal, becoming immune to these strategies. Does that happen?
TB: With anything that is used against insects, they could evolve resistance. But with this particular repellent, because it's a natural alarm signal if they stopped responding to it they would become vulnerable to predator attack. So this could be something which is more difficult for them to evolve resistance to.
5. Could they evolve into superaphids or superpests?
TB: Well, this is something that happens with the pesticides, which have a toxic mode of action, so when you've got a toxin and use it a lot, then the pest can evolve resistance to it. It happens because there's a particular method for controlling the pest which is used too much, and the pest has very fast generation times.
6. So is there already a problem that aphids are immune to toxic pesticide?
TB: Yes, that is quite an issue. Some aphid species are resistant to a lot of different pesticides. That's the peach potato aphid. There are some indications that the cereal aphids are also starting to evolve resistance to pesticides, so it's good to look for alternative ways of controlling them.
7. We've had a question in from David Owen on Facebook, saying he's having trouble negotiating studies. He asks: are the problems such as pesticide resistance or unintended consequences of GMOs too formidable to overcome? Are they intrinsically GMO problems, or problems of large scale agriculture?
TB: I'd say the latter; they're intrinsic problems of the way agricultural ecosystems are designed. You've got a large area of very lush habitat which is suitable for the pests that feed on that particular plant. GM is just a technique for breeding resistance into the crops, and it's not a harmful technique in itself. The effect depends on what trait is put into the plant. That probably explains the effects that we've seen with some of the GM crops to date, rather than the technology that's been used for engineering their genes.
8. Can we now go and see where you engineer those genes Huw? Could you take us to the transformation lab? How do you make genes?
Huw Jones: Yes, so I'm a researcher on this project, I'm also the technical consent holder, which means I'm the main point of contact. By training I'm a plant molecular geneticist. So we'll have a look around the lab where we make the transgenic wheat, where we move genes from a test tube into a plant cell, and then generate a plant from that cell.
(Lab full of green wheat plants)
HJ: We sow these non-GM wheat plants to have a constant supply, then we take a particular type of cell called the scutellum tissue from an immature seed, and they're the cells that we shoot with the DNA.
(Moving to a small room with a box)
HJ: So, there are two main ways in which we can move DNA into plant cells. One of them is using the gene gun. This box. We apply a vacuum, and use helium to push gold powder, coated with the genes we want to transfer, into wheat cells.
9. A question from Facebook: Do you make a whole new gene? Where do those bits of DNA come from?
HJ: It's all synthesised in the lab, so all the DNA we use is not taken from any organism. We have to use a template, we have to use an idea, like a plan, in order to order that DNA. And we've used different bits. The genes are a reconstruction.
10. Can the plant tell the difference between a manmade gene and a natural one?
HJ: No. The gene is the construction. It is the code for an enzyme or protein. And we choose enzymes - in this case two enzymes that lead to the production of this aphid alarm smell - that would work in a wheat plant.
11. It doesn’t happen here does it? You are getting that gene information from somewhere else. So which bit are you doing here?
HJ: We first decided what enzymes we would need to help our wheat plants make (E)-β-farnesene. Using a computer, we studied the genes of different organisms, and found genes, or templates that are codes for the enzyme we wanted. For one gene ((E)-β-farnesene synthase) we chose a form from the peppermint plant, for the other gene (FPP synthase) we chose one that looked more like an animal form of the code. This second enzyme is found in virtually all living things, including wheat, and we needed to use a form that was different from wheat, so that wheat didn't switch it off. We chose an animal form of the gene and the one we chose happened to have the closest similarity to that from cow.
12. Okay, so then how do you actually create it?
HJ: Again on a computer, you align the nucleotides, the bits of DNA that you want to put together, and then you save that as a string of A, T, G and Cs - the four nucleotides of DNA. You submit an order to a DNA-synthesis company who then synthesise that DNA to your order. They put the A, T, G and Cs together in the string that you want.
13. Okay, so you get those back then in test tubes? Take them out and put them into your gene gun here?
HJ: We coat the DNA on to gold powder. You can use tungsten or gold. Gold has a certain mass, so you can shoot it at a reasonable speed. It's inert so it doesn't affect the cell, and over the years we've preferred gold.
TB: I'd like to make a point about this 'cow gene'. There are two GM lines, and one is just based on the peppermint gene, and there's another one which has got this extra gene. They supply the building blocks to make the aphid repellent smell. And it's quite possible that we might only need the gene from the peppermint. It might not actually be necessary to have the additional one. Wheat isn't a very smelly plant, so we put this extra gene in for making more of the building blocks, to make the repellent smell from, just in case there wasn't enough of it. Our preliminary evidence suggests that there is enough of the substance for repelling the aphids with just the gene which is based on peppermint. And so it might actually not be necessary to continue further development. But we need to get the data first, to see what's happening in the field.
14. Can we also ask about these traits for antibiotic resistance, because we've had questions on that and there were a lot of references last week on the twitter discussion, to the fact that there are traits for antibiotic resistance in what you're using. Is that right?
TB: Yes, there is an antibiotic resistance gene that's used as a marker, as part of the transformation process. Both our risk assessment internally, and the risk assessment by the independent scientists working for the government agency ACRE deemed this, in the context of our small scale contained field trial, completely safe. There is a theoretical hazard that genes can move from plants to other organisms like bacteria; but this is an exceedingly rare event hardly ever seen in nature. You can force it in the lab. That's the basis for these concerns, that the antibiotic resistance genes may somehow move from our plant cells into soil bacteria, and make those antibiotic resistant. But the gene we're using as a marker comes from soil bacteria anyway. There are plenty of antibiotic resistance genes in soil, which is why the risk assessment deemed this safe.
15. And that’s what’s used as the marker, then, to check that the gene has been taken up by the cells that you shoot it into?
TB: We've got two markers, so we've got the antibiotic resistance gene, that's really useful in an earlier stage. The plant selection marker is a herbicide tolerance gene, and that is also there in the plant cell, and that is also used to distinguish between plant cells that have taken up our DNA and those that haven't.
16. So these are research tools?
HJ: Yes indeed. Neither of those marker genes have any influence over the aphid resistance characteristics that we've moved to our wheat plants. Of course if this was going to be taken forward in any commercial way, then those marker genes could be removed.
TB: An important point here is the size of the trial. What we're talking about is eight 6-metre by 6-metre plots, so it's a very small scale research experiment. If this was going to be done on a larger scale, then there would be further refinements to the type of plant that is made. But at this stage, it's experimental and extremely small, and it's been through a very thorough risk assessment.
17. Here’s another question: how do you get from a cell to a seed to a plant?
HJ: Well, you go from a cell that's been shot with the gun. The cells then are grown on a substance that's rich in sugar and certain hormones. Cells start to divide. On these ones here you can see some little green structures forming; these are new shoots that are very young wheat plants. In a few more weeks, these turn into much larger clumps and leaves and stems form and grow into a young wheat plant.
HJ: This is where the selection is working. In this food gel at the bottom, we've added a herbicide that only the transgenic plants, the plants that have taken up the DNA, can tolerate. It's about 1 in 20-30. All the other plants die.
18. Could you have got that gene into wheat in any other way than the way you have just described?
HJ: Well there are various ways of getting DNA into a cell, like agro-bacterium or electroporation. There are lots of ways of doing that, but it would all be called transformational - transforming a cell.
19. We've also had the question: is there a non-GM way that you could have got this into the wheat?
HJ: No, because the genes we are using turn the wheat from a non-smelly plant into a plant that makes lots of (E)-β-farnesene. Those genes aren’t available in the gene pool that’s available to normal plant breeders. We have to use a GM approach to move the genes from, say peppermint, into wheat.
20. There are no other means? People have talked about mutagenesis, other sorts of techniques that are used by plant breeders. None of those things would work?
HJ: No, there's no feasible way that I can see of getting (E)-β-farnesene synthase as a functional enzyme into wheat, because wheat doesn’t contain that enzyme, other than a GM approach.
21. So Huw, that’s the problem that you’ve solved in this lab.
TB: Yes, these are very nice plants because they produce large amounts of the (E)-β-farnesene and they don’t make any other smells, so it’s really a good achievement, what Huw’s done here in the lab. With conventional breeding you can’t just take one particular gene and move it into a crop, there’s a lot of other genes that come with it; and you’ve got this problem of linkage drag, that’s what geneticists refer to when you’ve got other traits that come along with the trait of interest.
22. You’ve selected the plants that have taken up that gene by growing them with that herbicide. What happens then, where do you grow those shoots?
HJ: They get potted up into our GM glasshouse, which is a small but contained glasshouse area where we have a permanent authority to grow GM plants. It’s inside.
TB: One further point about conventional wheat breeding. There’s a widespread assumption that this is all entirely natural, but it isn’t. There’s this approach called mutagenesis breeding where the plants are exposed to high doses of radiation or mutagenic chemicals to increase the number of genes available for the plant breeders to select from. And this induces random mutations in the plant, and it is a lot less controlled than the sort of approaches we’re using to introduce individual targeted genes into the plant.