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点击量:   时间:2019-03-07 09:05:17

By Marina Chicurel in Santa Cruz PLANTS may coordinate their growth and responses to the environment by ferrying genetic messengers along an information superhighway. So say scientists who have seen molecules that carry genetic information coursing through the vascular systems of pumpkin plants. What goes on in one part of a plant often affects other parts. Sunlight falling on a leaf, for example, can influence the flowering of a distant bud. In the past, researchers have put these influences down to the movement of small hormone molecules. But recent studies have hinted that important messages are also carried by larger molecules—not only proteins but also messenger RNAs (mRNAs), which carry genetic information. To investigate this, Roberto Ruiz-Medrano and his team at the University of California at Davis hunted for mRNAs in the vascular tubes called phloem of pumpkin plants. They found mRNAs coding for proteins that regulate plant development, such as one called CmNACP, and other mRNAs of unknown function. To test whether the mRNAs were moving through the phloem, the scientists grafted a cutting from a cucumber plant onto the stem of a pumpkin plant. Cucumbers do not produce CmNACP RNA. So when the team picked up this RNA in the cucumber cutting, they knew it was travelling in the phloem ( Development, vol 126, p 4405). Further experiments showed that not all mRNAs move in the same way. Many never venture into the phloem, others travel only short distances, and still others seem to trek far into the growing tips of plants. This suggested to William Lucas, who led the team, that plants use them to coordinate global responses. Travelling RNAs might switch genes on and off, and choreograph the activity of cells. “I think we will probably find some pretty damn novel information-processing molecules,” says Lucas. “One can’t even begin to imagine how much it may open up the field of signalling.” Robert Singer of the Albert Einstein College of Medicine in New York, an expert in mRNA movement, points out that the real purpose of the mRNA transport is not yet clear. “The question is: does it really have any significance or physiological impact?” he asks. “At some point one has to find out what happens if the RNAs don’t move,” adds plant physiologist Sarah Hake of the University of California at Berkeley. Lucas and his colleagues are now setting up experiments to test this. Whether or not mRNA traffic is essential, the findings may spur biologists to rethink their ways of studying plant genes. Genes are often assumed to be active when mRNA is spotted nearby. If mRNAs can romp throughout the plant, this assumption may not always hold true. And the results suggest a powerful new tool for manipulating plant genes. Scientists recently discovered that the activity of a gene in one plant cell can silence genes in distant cells. If, as suspected, the silencer is RNA, then researchers could hijack the phloem network to silence genes in whole plants. “This technique is going to sweep through the plant literature—in fact, it’s already started to do that,