In the past few years, researchers have identified more than a dozen genes that make plants resistant to bacteria, viruses, and fungi. Now, in today's issue of Science,* a team of European researchers reports nabbing the first one for resistance to an animal pest: voracious threadworms known as nematodes that destroy about $100 billion in crops worldwide each year. The new work could pave the way for engineering nematode resistance into major commercial crops such as oilseed rape.
The new gene, which originated from a wild beet plant, wasn't easy to track down. In fact, it took 8 years and a lucky break to find it.
In the past, plant breeders tried to capitalize on the natural nematode resistance of plants such as wild beets by breeding them with susceptible crops such as the sugar beet, but the hybrids only had partial resistance and were unsuitable for commercial use. Those hybrids gave researchers a clue to the location of the resistance gene, however. A team that included plant breeder Christian Jung, of the Institute of Crop Science and Plant Breeding at the University of Kiel in Germany, and his colleagues at the University of Aarhus in Denmark and at the Centre for Plant Breeding and Reproduction Research in Wageningen, the Netherlands, found that some of the hybrids carried the nematode-resistance gene from wild beet on a tiny stretch of DNA where two chromosomes had broken and joined abnormally. This was "a very, very fortunate find," says nematologist Valerie Williamson of the University of California, Davis, because it allowed the researchers to focus their gene hunt on the section of the wild beet genome that carried the breakpoint.
Additional clues, such as the knowledge that resistance genes are often rich in the amino acid leucine, ultimately enabled the researchers to pinpoint their quarry. The team confirmed its finding by transferring the gene into susceptible beet roots in culture and showing that the transformed roots resisted damage by nematodes.
It's still unclear how the gene confers resistance. That's one question Jung and his colleagues hope to answer. They also want to use the gene to create new lines of resistant sugar beets and other crops. But they anticipate a challenge in coaxing the cells used for the gene transfers to grow into whole plants. "Sugar beet is a notoriously recalcitrant variety," Jung notes. Moreover, a gene that offers resistance to one strain of nematode may not work against others. Still, a team that has spent 8 years hunting the gene isn't easily put off: Jung has organized a large team of plant biologists to work on the problem. "We hope to have disease-resistant plants in the lab by the end of the year," he says.
* For more details, Science Online subscribers can link to the full text of the Report.