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Fighting blight

点击量:   时间:2019-03-07 09:05:06

By Andy Coghlan GENETICALLY modified potatoes that would have prevented the Irish potato famine in the 19th century have been developed in Canada. The potatoes thwart Phytophthora infestans, the fungal blight which devastated Irish potato harvests in the 1840s. William Kay, who led the team developing the potatoes at the University of Victoria in British Columbia, says the GM tubers also resist fusarium wilt, another fungal disease, as well as Erwinia soil bacteria, which rot potatoes. The potatoes owe their hardiness to the combined effects of two peptides—amino acid chains—which respectively protect honeybees and moths from microbes. Cecropin, a peptide isolated from the giant silkworm moth, was genetically spliced with melittin, a peptide from bee venom. Previous experiments with these two substances suggested that a hybrid of the two would kill a wider range of fungi and bacteria than either alone. To test this idea, Kay’s team made msrA1, a synthetic gene which makes the hybrid. Next, they tethered it to the CMV promoter, a switch which turns the gene on. They then used a bacterium to insert the gene into Desiree and Russet Burbank potatoes. The tubers remained healthy despite heavy exposure to harmful bacteria and fungi, including potato blight. Kay says that the results were all the more surprising because the potatoes made such tiny amounts of the hybrid peptide. “We could scarcely detect them,” he says. Now, the team is preparing to test the potatoes in field trials. “We’ve been doing everything in greenhouses up to now,” he says. Experiments to assess whether the potatoes are safe to eat are under way too, even though the peptides would be destroyed by cooking. “Preliminary animal testing in rats shows they are harmless,” says Kay. He points out that similar substances occur throughout nature, even in humans and other mammals. Kay is confident that bacteria and fungi will find it hard to develop resistance against the peptides. Unlike conventional antibiotics, which kill bacteria by interfering with bacterial biochemistry, the peptides inflict physical damage which is almost impossible to combat, punching lethal holes in bacterial and fungal cell walls. Kay accepts that like all genetically engineered crops, the potatoes will meet a wall of consumer resistance, especially in Europe. But the Victoria team points out that a combination of the same two peptides they have inserted in the potatoes is already being tested in people: it is undergoing clinical trials as an antibiotic, and has already shown its potential for killing methicillin-resistant Staphylococcus aureus, the most notorious superbug lurking in hospitals (New Scientist, 22 June 1996, p 20). Sue Mayer of GeneWatch UK, an environmental lobby group, fears that benign bacteria and fungi could be caught in the firing line, damaging soil ecology. Mayer, who has previously studied similar peptides made by cows and humans,