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发布时间：2022-04-24 11:37
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时间：2023-05-04 12:36
Tweaking Genes to Help Plants Survive Elements
For centuries, farmers have sought to discover and modify crops that can grow in otherwise inhospitable areas -- places that are too dry, too salty and too cold. While plant breeding has led to some advances, the progress has been slow, and frost, drought and high salinity still greatly limit global agriculture.
But new research has begun to explain how plants adapt to hostile conditions, and advances in biotechnology have allowed scientists to start to use and significantly expand those adaptations.
Using genetic material already in a plant, researchers have been able to supercharge the plant's natural defenses, and allow it to survive usually fatal drought, cold and salinity. Other scientists have been able to move genes from organisms able to withstand great water and temperature stress into other plants, with significant success.
Most of this work has been done in greenhouses and growth chambers, and the technology is not ready for regulatory review or commercial use. But researchers are optimistic that crops in the future can be designed to withstand far more adversity than today. And if they can, the benefits could be substantial.
"At this point, I think the science is moving much faster than our ability to apply it," said John O'Toole of the Rockefeller Foundation, which has a $25 million, five-year program to encourage the development of drought-resistant rice for Asia and corn for Africa.
"The combination of conventional breeding and high-skilled biotechnology tools has taught us an enormous amount about how plants can be made more tolerant of harsh conditions," he said. "Places like China and India are running out of water, so the need for these improvements is pressing."
As a sign that the technology is getting close to becoming practical, major companies such as Monsanto and Pioneer Hi-Bred International, as well as some small biotechnology start-ups, have begun pouring resources into developing crops, timber trees, grass for golf courses and even ornamental plants that can withstand drier, colder and saltier conditions. To some, it looks like genetically engineered stress tolerance could be the next major arena for agricultural biotechnology.
"This looks to us like the late '80s, when we were making discoveries that led to insect and [weed] protection technologies and procts," said Robert Fraley, Monsanto's chief technology officer. "The fundamental breakthroughs have been made, and now we're in the process of adapting them to a wide range of plants."
One of the key discoveries in the field of plant tolerance to stress has been that most plants have some ability, controlled by their genes, to stabilize membranes against cold and dry conditions. Microbiologists found that by turning up the activity of several of the genes involved in this response -- using "promoter genes" from the same or other plants -- they can make the plant adapt to increasingly hostile conditions.
While investigation has been done in the Arabidopsis plant, a relative of the mustard plant that is the lab rat of plant genetics, researchers have found the same cold-response pathway in wheat, rye and even tomatoes.
In addition, researchers have identified "osmoprotectants," compounds that shield proteins and membranes from the effects of dehydration in some plants. Microbiologists at the University of Illinois at Urbana-Champaign took the gene that proces the osmoprotectants from the ice plant, a hardy groundcover, and introced it into the tobacco plant. The modified tobacco was better able to survive drought, though not enough to make a difference in the field.
Researchers now generally view the stresses of drought and cold as largely the same on a molecular level. A freezing plant, they found, essentially died of dehydration because its water crystallizes and is no longer available for use.
Michael Thomashow of Michigan State University and his team were early researchers in the field, and they helped discover the genetic mechanism that controls activity of the cold-response genes that protect plants. They initially worked with the Arabidopsis plant and found they could manipulate the genes so the plant would over-express the cold tolerance. Later research found that the genes did protect greenhouse plants subjected to cold or dry conditions.
"With this technology, you are activating or optimizing a system already present in the plants," Thomashow said. In the often contentious world of biotechnology, the system has the advantage of not requiring the introction of genes from other plants or organisms, making it perhaps less of a "Frankenfoods" creation.
Some rights to the Michigan State discovery were licensed to a California start-up company, Mendel Biotechnology, which is developing the technology as "Weathergard." Company Vice President William Goure said Mendel has received federal grants of almost $600,000 to work on the project, especially on the "promoter" gene that would switch the tolerance trait on and off at the proper times. If the gene was constantly over-expressing the drought or cold-resistant trait, then the plant would not grow normally, making it useless commercially.
"So far, we haven't found any plants that don't have the Weathergard gene, and they are easy to get out of the plants," Goure said. "Finding the proper promoter gene to turn the trait on is more complicated, but we're having success."
In parallel research, a team led by Eardo Blumwald of the University of California at Davis has significantly changed the ability of tomatoes, rice and alfalfa to withstand salty conditions by over-expressing a particular gene in the plant. Using genes from the Arabidopsis plant, the modified crops are able to shunt salt into storage cavities, allowing the plant to thrive in otherwise impossible conditions. Because salts often build up on irrigated land, the technology could be useful in the vast farmlands of central California and Arizona.
"This is revolutionary technology," said Blumwald, whose creations are being field tested by a small company in California. "But for it to work, we need to marry it to the discipline of the plant breeders. What we need is transformed transgenic plants in the background of varieties that have already shown promise in the field."
Major technical and regulatory challenges remain before these kind of stress-resistant plants can become commercial, and public acceptance of genetically modified foods is no longer a given. But researchers are optimistic that their new technologies will some day make progress in pushing back the most traditional limitations on agriculture worldwide.
