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Monsanto’s James Roberts on Targeting Crop Pests With RNAi

NAME: James Roberts
POSITION: Gene suppression team leader, Monsanto
Postdoc, University of Georgia — 1996-1997
Fellow, Plant Science Center, Australian National University — 1994-1995
Postdoc, Commonwealth Scientific and Industrial Research Organization — 1991-1994
Postdoc, University of Georgia — 1989-1991
PhD, botany, University of Georgia — 1988
BS, biological sciences, State University of New York, Albany — 1981

This week, researchers from Monsanto and DevGen published a paper in Nature Biotechnology showing that dsRNA designed to inhibit certain viral genes could trigger larval stunting and mortality in corn rootworm — a pest that feeds on the roots of corn — when fed to the animals. Further experimentation demonstrated that transgenic corn plants expressing these dsRNA showed a significant reduction in damage caused by the pest.
These findings suggest “that the RNAi pathway can be exploited to control insect pests via in planta expression of a dsRNA,” the papers authors wrote.
RNAi News spoke this week with Monsanto’s James Roberts, the senior author on the Nature Biotechnology paper, about the data and plans for possibly commercializing the approach.
Let’s begin with your research at Monsanto.
This research [detailed in Nature Biotechnology]really started in the insect control program. … We have a fairly big portfolio of insect-protected [genetic] traits on the market. One of the very important ones is corn rootworm control for corn. Currently, we control … corn rootworm through expression of a Bt protein, Cry 3Bb.
One of our focuses here at Monsanto is to provide farmers with robust, integrative resistance-management programs. One part of that is research centered on developing new modes of action for the control of corn rootworm.
Towards that, we started experiments a while back to really see if we could use double-stranded RNA to induce RNAi phenomena in corn rootworm larva. That’s the topic of the paper we published.
How big of a problem is the corn rootworm for the corn industry?
It’s referred to as the billion-dollar pest. Between Northern and Western corn rootworm, [according to] a study Monsanto sponsored back in 2002 before the advent of biotech solutions for corn rootworm, around 14 million acres were treated with various pesticides for corn rootworm. So it’s a widespread problem across the [US] Corn Belt and it has accounted for the application of a lot of traditional pesticides.
Are pesticides still the primary way they are dealt with?
Now, it’s a more varied set of control mechanisms because Monsanto has the biotech trait that helps control the corn rootworm very well — in fact, we think better than traditional pesticides. I believe Pioneer [Hi-Bred] has a biotech trait out this year for controlling corn rootworm.
One of the things about biotech control of the corn rootworm is that it really provides the plant with a much more robust root system. So we get significant protection of the roots, and by having that protection in the root system … corn plants [can] utilize the available water and nutrients a lot better. [As a result], we see a significant increase in yield when you have good root protection.
Could you talk about the RNAi approach to controlling the pest and the findings in the paper?
The paper starts off by illustrating that we can see a biological effect in an in vitro bioassay … we have developed here at Monsanto, [in which] we can deposit corn rootworm eggs on a [specific] diet.
[In this case], we incorporated [into the worm’s diet] double-stranded RNA that were derived from corn rootworm sequences. We noticed that if we took this bioassay out longer than usual — out to about 12 days — we could see significant stunting and mortality in the corn rootworm … depending on the double-stranded RNA that was applied to the diet.
The paper goes on to show that by screening through many different genes, we could find some that were very efficacious at giving mortality and stunting in this in vitro bioassay, [in addition to] being very specific.
One of the main figures in the paper shows that if you feed corn rootworm a double-stranded RNA derived from, say, a V-ATPase gene, the mRNA for that gene declines after [the worm] feeds on double-stranded RNA, but an unrelated messenger RNA does not decline. And vice-versa, if you feed them a double-stranded RNA derived from a tubulin gene, only the tubulin message declines. So it really establishes that this is a specific response that appears to be operating at the level of the messenger RNA.
The paper goes on to show that if we transform corn plants with an expression cassette that makes a small double-stranded RNA with sequence identity to a corn rootworm gene, those corn plants show significant protection in a whole-plant bioassay that we’ve infested with corn rootworm eggs.
With these transformed plants, were there no other changes observed? Have you examined several generations?
This is still a discovery project, but we have looked at more than just the initial transformed plants; we have looked at multiple generations. These tests have been done with hybrid corn plants in a growth chamber assay.
So it seems quite robust, but it is still a discovery project. We still have a lot of field testing and further testing to do.
What’s involved in that further testing before you think about possible commercialization?
The marketplace is very stringent — these new biotech traits need to have positive effects and no negative agronomic effects on the plant.
We have seen no negative agronomic effects on those plants we’ve tested so far, but we’ll continue to test, and we’re looking to have the most efficacious and specific sequence used. Then, the whole transgenic event selection process is quite involved, and there are lots of further safety studies that we will conduct, as well.
Realistically, assuming that everything goes according to plan and there are no unforeseen negative events, when would be the earliest we could see these sorts of crops used?
This is still a discovery-phase project, so it’s really difficult to predict commercialization. But we’re really optimistic about the technology.
Is this [RNAi approach] the kind of thing that Monsanto is looking to apply to other crops?
We are exploring other possible uses for the RNAi technology for insect control, but of course RNAi as a means for gene suppression also has a great number of applications for changing native plant gene expression. There is a lot of excitement about possible applications there.

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