On your markers

 作者:季碇     |      日期:2019-03-07 11:13:09
By Andy Coghlan WILL a spoonful of sugar help genetically modified food go down? Novartis clearly hopes so. The Swiss multinational has developed a sugar-based replacement for the controversial antibiotic resistance marker genes used in some GM foods. Because genetic engineering is a hit-and-miss affair, marker genes are used to reveal if cells have taken up packages of new genes. After adding the genes to plant cells, the cells are exposed to antibiotics. The unmodified cells die, leaving botanists with the live ones that have taken up the new genes. Some scientists fear that when people eat GM foods that contain such marker genes, they might spread to potentially harmful gut bacteria, making them resistant to antibiotics. Novartis says there is no evidence this has ever happened, and that marker genes in products such as its GM maize pose no risks. Earlier this year, however, tests in the Netherlands showed that DNA could survive in the intestine for several minutes, suggesting that marker genes could be transferred to bacteria (New Scientist, 30 January, p 4). And some countries have been reluctant to approve crops that contain such genes. So to allay such concerns, researchers at Novartis’s molecular biology lab in Rayleigh, North Carolina, have developed a sugar-based alternative to antibiotic-resistance marker genes. “We’ve already transformed a dozen crops, including maize, wheat, rice, sugar beet, oilseed rape cotton and sunflowers,” says Willy DeGreef, head of regulatory affairs at Novartis. “Several are already in field tests and, if all goes well, we hope to apply for commercial release of at least one of them as early as 2001,” he says. Novartis’s new marker gene, manA, enables plants to digest a simple sugar called mannose-6-phosphate. Most plants can’t handle this sugar, and so die when fed mannose alone. The manA gene codes for an enzyme called phosphomannose isomerase, which converts mannose-6-phosphate into fructose-6-phosphate, another sugar that all plants can digest. The system cannot work in all plants because some, such as soya and other legumes, already have the manA gene. “But we are lucky because most higher plants don’t have it,” says DeGreef. The fact the gene already exists in many familiar crops should increase confidence in the safety of the system, he says. “It’s in many of our foodstuffs and in most of the animals we eat, and all mammals including us,” he says. It also exists in many species of gut bacteria. Novartis unveiled the new marker system this week in London at a conference organised by Nature Biotechnology. The British Medical Association, which opposes the use of antibiotic resistance markers in food, welcomes Novartis’s development. “The industry is beginning to take seriously the expressed concerns of others,” says Vivienne Nathanson,