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Silencing Pests: Altered plants make RNA that keeps insects at bay

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12:16pm, November 7, 2007
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Two teams of researchers have modified plants to produce genetic material that disables critical genes in insects that eat the plants. The technique could provide a new strategy for agricultural-pest control.

Looking for a new way to protect corn plants, James Roberts with Monsanto in Chesterfield, Mo., and his colleagues turned to a mechanism known as RNA interference, in which segments of the genetic molecule RNA block the translation of information from a target gene (SN: 7/2/05, p. 7). The researchers found RNA sequences that would target critical genes in the western corn rootworm and two other related pests, and then modified corn so that it would generate those sequences.

In rootworms that fed on the modified corn, RNA from the plants shut down the target gene, stunting or killing the insects' larvae, the researchers report. Modified corn plants infested with corn-rootworm eggs suffered less root damage than did normal corn.

In the other study, Xiao-Ya Chen and his colleagues at the Chinese Academy of Sciences in Shanghai used a similar trick to increase the cotton bollworm's sensitivity to gossypol, a defense chemical produced by the cotton plant.

Although large doses of gossypol stunt the growth of bollworm caterpillars, the pests can tolerate the chemical at low concentrations. Chen and his colleagues found the insect gene responsible for this tolerance, and then modified Arabidopsis, a widely used lab plant, to produce silencing RNA for that gene. Insects that feasted on the modified lab plants ingested the RNA, and stopped growing when fed gossypol. The researchers are trying to reproduce their results with cotton plants.

Both teams report their findings in the November Nature Biotechnology.

Previous research had shown that RNA injected into insects could shut down specific genes. The critical innovation of the new work is oral delivery of the silencing RNA from plant to insect, Roberts says.

The Monsanto researchers "have produced protection of a crop plant against a real pest," says Peter Waterhouse of CSIRO Plant Industry in Canberra, Australia. Although the Shanghai-based study uses a model plant to deliver the RNA, it "has a very ingenious strategy ... to kill off the insects' counterdefense against a defense chemical," he adds.

For many years, farmers have planted crops engineered to possess a bacterial gene that produces an insect poison known as Bt. But this poison doesn't work on all insects, and scientists worry that pests could eventually evolve resistance to it (see Spying Genetically Engineered Crops).

With the appropriate choice of target gene, "in principle, the [RNA] strategy is applicable to any herbivorous insect," Chen says. And the ability to carefully design the RNA sequence could allow researchers to evade insect-resistance strategies, Waterhouse says.

More research will be needed to show how applicable the technique is to other pests and how well it would work in the field, he adds. Government regulatory bodies would have to grant permission before such crops could be grown in open fields. But Waterhouse says the initial results suggest that RNA interference could be a powerful strategy for controlling insect pests.

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