<<返回上一页

Fast and loose

发布时间:2019-03-08 07:09:05来源:未知点击:

By Andy Coghlan PLANTS that don’t interbreed can still exchange DNA using go-betweens such as fungi, viruses or aphids, new research suggests. The findings are likely to be seized on by opponents of genetic engineering, who fear the spread of modified genes from crops to wild plants. But the scientists behind the research stress that such DNA transfers are very rare events. Jeff Palmer and his colleagues at Indiana University in Bloomington have discovered a stowaway gene segment in scores of unrelated flowering plants, including coffee, bananas, cucumbers, periwinkles and foxgloves. They speculate that the segment originated in fungi, as fungal species including baker’s yeast (Saccharomyces cerevisiae) are known to carry it. “We think there was at least one original donation from a fungus to a plant,” says Palmer. Since then, it may have been shuttled from plant to plant by aphids or viruses. Palmer’s group screened 335 families of flowering plants for the segment, a chunk of DNA called an intron. Introns are junk DNA that is clipped out of genes before they are transcribed into proteins. The stowaway intron, which buries itself in the same gene whichever plant it invades, appeared in 48 of the families, the researchers report in the latest Proceedings of the National Academy of Sciences (vol 95, p 14 244). Through analysis of plant family trees, Palmer and his colleagues have found that in 32 of these 48 cases, the intron spread “laterally” between unrelated species rather than “vertically” through inheritance. “We normally think of lateral transfer as a very rare event between plants, especially those that lost the ability to mate with one another millions of years ago,” says Palmer. “What’s novel is finding this massive wave of intron movements.” Scaling up to the 13 000 known families of flowering plants, Palmer says the intron must have jumped species at least 1000 times. The promiscuous intron studied by Palmer carries a molecular tool for jemmying itself into DNA. This tool, the gene for an enzyme called an endonuclease, always wedges the intron into cox1, a gene vital for energy metabolism in plants. Sequences lacking endonuclease genes are probably much less mobile, says Palmer. “It makes it difficult to say how often other genes without these elements move around,” he says. And even with its endonuclease, the stowaway intron has probably jumped species perhaps just once every 5 million years. Given the limits to lateral DNA transfer, Palmer doesn’t think that the risks posed by genetically engineered plants need to be reassessed in the light of his research. “I doubt this lateral transfer occurs often enough to cause concern on a human timescale,” he says. Nevertheless, Phil Dale of the John Innes Centre in Norwich, a member of Britain’s Advisory Committee on Releases to the Environment, says: