The worm turns - controlling nematodes by engineering crops with sex-determining gene - Brief Article

NEMATODES, OR ROUNDWORMS, ARE one of the most abundant animals on Earth, ranging in size from microscopic soil dwellers to 23-foot-long parasitic horrors that torment whales. They are also terribly destructive to crops. Species like the root-knot nematode and the soybean-cyst nematode cause $78 billion a year in damage worldwide. Pesticides sometimes work, but at a price. "They are very toxic, and one after another of them has been banned by the Food and Drug Administration," says William Wood, a geneticist at the University of Colorado at Boulder. "So people are looking for ways to control nematode infections that don't involve poisonous chemicals."

Wood may have found an alternative: a gene isolated from the tiny Caenorhabditis elegans worm that determines whether a fertilized egg will become a male worm. The gene, called her-1, is turned on only in males. It produces a protein that turns on other genes that lead to male development.

That suggests a way of hobbling nematode pests, says Wood. In nematodes like the root-knot and soybean-cyst worms, only females cause crop damage--and the sex of a developing worm is somehow determined by the health of the plant it's born on. If the plant is not healthy, the larvae sense that, develop into males, migrate out of the plant without harming it, and live in the soil, where they wait for a chance to fertilize feamales. If the plant is healthy, however, the larvae develop into females, feed on the plant, and lay more eggs in the roots (female nematodes are hermaphrodites and can fertilize themselves if need be). That savages the plant.

"The sort of pie-in-the-sky idea," Wood says, "is to engineer a plant that would produce the her-1 protein when it is infected by a nematode." Other researchers have already found a plant gene that responds to nematode invasions, turning on certain genes. If the her-1 gene were put in a plant and turned on at the right time, the protein might seep from plant cells into all the worm eggs, turning them into harmless emigrating males.

C. elegans is just a worm geneticists like to study; Wood does not know yet whether root-knot and soybean-cyst nematodes also have the her-1 gene. "Obviously, that is a key question that we need to answer," he says. "We know that some fairly closely related nematodes do become masculinized if we introduce her-1, and all nematodes are pretty similar anatomically. But as far as sex determination goes, we don't know how general this gene will be."

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