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Shared roots - Hormones took control long before plants and animals went their separate ways

点击量:   时间:2017-10-22 05:01:09

By Andy Coghlan A KEY secret of how plants regulate their growth has been unlocked by the discovery of a new kind of hormone receptor. It is the strongest evidence yet that plants and animals share the same types of receptors for some hormones. By tinkering with plant receptors, it might be possible to produce better crops. Richard Hooley and his colleagues at the Institute for Arable Crops Research near Bristol knew of the “G protein-coupled receptors”, or GPCRs, found in mammals. This group of receptors includes the light-sensitive receptors in the retina, a multitude of odour and taste receptors, and the receptors for serotonin and adrenaline. Hooley’s team hit on a plant counterpart of the mammalian gene that makes GPCRs after trawling through gene sequences of the cress Arabidopsis thaliana. “The gene was expressed at very low levels in roots, shoots and leaves of seedlings and mature plants,” says Hooley, who presented his results at a meeting of the Royal Society in London last week. Named GCR-1, short for G coupled receptor 1, the molecule is also referred to as a “serpentine” receptor because it snakes in and out of cell surfaces, breaching the membrane at seven points. The researchers set about finding out its function by genetically engineering the cress so that the gene making GCR-1 was blocked. The altered cress had abnormally low levels of leaf expansion and cotyledon growth, which the researchers suspected was due to the suppression of cytokinins. This important group of plant hormones governs vital functions, including cell division and flowering. Subsequent experiments backed this theory. Roots in the altered cress failed to stop growing as they usually would when treated with cytokinins, for example. With the receptor blocked, the usual cytokinin message was failing to get through. And pores in the altered plants wouldn’t open as they should when exposed to cytokinins. Yet the plants with the blocked receptor responded perfectly normally to other plant hormones. “We can’t say for certain that it’s the receptor until we prove cytokinins bind to it,” says Hooley. “But it’s strongly implicated.” If the receptor does prove to be the molecular button that cytokinins press, it will be only the second kind of plant hormone receptor discovered. A family of receptors for ethylene, which accelerates ripening, is known, the first being identified in the early 1990s. However, the ethylene receptors are of a type apparently unique to plants and some bacteria. Confirmation that the new receptor is a hormone receptor like those in animals adds weight to the idea that they have a common ancestor in which the receptors originally evolved. Tony Bleecker of the University of Wisconsin at Madison, one of the botanists who discovered ethylene receptors, hailed the new findings. “It’s been a major question whether that huge class of receptors is present in plants,” he says. “This is the best evidence for it.” Hooley, whose institute has a patent on the receptor, thinks its discovery will have a major impact on agriculture, enabling genetic improvement of crop yields and food quality. His results appear in Current Biology (vol 8,