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Modified crops 'silence' insect pests for good

NewScientist.com news service
Andy Coghlan

Genetically modified plants that can kill just about any insect pest without harming beneficial insects or the environment may soon pop up in farmers' fields.

The plants exploit a mechanism called RNA interference (RNAi), which organisms naturally use to switch genes off. To to this, the organism produces a double-stranded piece of RNA (dsRNA) whose sequence matches part of the gene to be silenced. Adding just a few of these to a cell shuts down the target gene.

The dsRNA produced by these modified plants targets genes specific to certain insect pests. When the pest feeds on the plant, the dsRNA it ingests shuts down some of its genes, killing it.

This week, two teams announced that they have independently created crops that act in this way. One team in China primed plants to make dsRNA that kills the larvae of the cotton bollworm moth, which cause $1 billion of damage to cotton crops each year in China alone.

Xiao-Ya Chen and his colleagues at the Shanghai Institutes for Biological Sciences engineered tobacco and thale cress to make dsRNA that targets a gene called CYP6AE14 in the bollworm larvae. This gene usually allows the moth larvae to withstand cotton's natural defence, a toxic chemical called gossypol. In lab tests, the larvae were first fed on the modified plants, and then munched on cotton leaves laced with gossypol (Nature Biotechnology, DOI: 10.1038/nbt1352). "They died within two days," Chen told New Scientist. "Now we're introducing the same RNA into cotton plants."

Meanwhile, Jim Roberts and his colleagues at biotech giant Monsanto in Chesterfield, Missouri, have created maize plants that produce dsRNA which protects against beetle larvae, including southern corn rootworm, the Colorado potato beetle and the western corn rootworm - "called the 'billion-dollar bug' because of all the damage it does", says Roberts.

Roberts and his team were able to modify maize to be resistant to specific species of beetle by producing dsRNA that targets particular variants on the same gene in each species (Nature Biotechnology, DOI: 10.1038/nbt1359).

Both teams speculate that the dsRNA enters the insects by infecting the cells in the lining of the gut. The dsRNA infection ends up spreading to cells throughout the insects' bodies. "If the effect translates from the lab into the field, then it really could be the dawn of a new approach to pest resistance," says Peter Waterhouse of CSIRO Plant Industry, a Canberra-based agricultural branch of the Australian government's research organisation.

Using this RNAi technique yields two clear benefits. Plants can be grown that kill specific pest species, ensuring that other beneficial species of insect - and human consumers of a crop - are unaffected. The technique could also be used to bolster other methods of killing pests. For example, Monsanto proposes adding the production of dsRNA to maize plants already modified to produce the Bt toxin - a substance usually produced by the bacterium Bacillus thuringiensis which is lethal to a wide range of insects.

From issue 2629 of New Scientist magazine, 10 November 2007, page 19

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