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By Roger Segelken
A new
strategy to genetically engineer rice and other crops to make them more
tolerant of drought, salt and temperature stresses, while improving their yields,
is being reported by molecular biologists at Cornell.
In releasing
their research, the biologists emphasize that the technique, which involves
adding genes to synthesize a naturally occurring sugar called trehalose, should
satisfy critics of genetically modified foods because the chemical composition
of edible parts of plants, such as rice grains, remains unchanged.
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Cornell molecular biologists Ajay
Garg, left, with 'normal' rice, and Ray Wu, with transgenic rice grown under
the same environmental stresses, are placing the new technology in the public
domain to make seeds for stress-tolerant crops available worldwide. Frank DiMeo/University
Photography
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Para ahli
biologi menggambarkan strategi baru untuk membantu tanaman mengatasi tiga
penyebab utama kegagalan panen dalam Prosiding National Academy of Sciences
(PNAS), diterbitkan pekan dari 25 Nov. The biologists describe the new
strategy to help plants overcome three of the main causes of crop failure in Proceedings
of the National Academy of Sciences ( PNAS ), published the week of
Nov. 25.
"We
have demonstrated the feasibility of engineering rice for increased tolerance
of major environmental stresses and for enhanced productivity," said Ray
J. Wu, Cornell professor of molecular biology and genetics. He is director of a
laboratory in the College of Agriculture and Life Sciences where
stress-tolerant rice has been under development since 1996, with support from
the Rockefeller Foundation.
The Cornell
biologists showed stress tolerance by introducing the genes for trehalose
synthesis into Indica rice varieties, which represent 80 percent of rice
grown worldwide and include the widely eaten basmati rice. But the same
strategy, they note, should also work in Japonica rice varieties, as
well as in a range of other crops, including corn, wheat, millet, soybeans and
sugar cane.
The
researchers plan to report on their claims of increased food productivity from
the resulting transgenic rice plants in a subsequent article. They say the
trehalose gene technology will be placed in the public domain -- instead of
being sold exclusively to commercial seed companies -- so that improved crop
varieties can be cultivated in resource-poor parts of the world where the need
is greatest.
Co-authors
of the PNAS report, "Trehalose accumulation in rice plants confers
high tolerance levels to different abiotic stresses," include Cornell
biologists Ajay K. Garg, research associate and lead author of the article;
Thomas G. Owen, associate professor of plant biology; Anil P. Ranwala, a
horticulture research associate; and Leon V. Kochian, research leader at the US
Department of Agriculture-Agricultural Research Service Plant, Soil and
Nutrition Laboratory, located on the Cornell campus. Other authors are South
Koreans Ju-Kon Kim, a biologist at Myongji University, and Yang D. Choi of
Seoul National University's School of Agricultural Technology.
Garg, a
plant molecular biologist, explains why trehalose (generally pronounced
TREE-hal-lows) was chosen in the first place: "Trehalose is a simple sugar
that is produced naturally in a wide variety of organisms -- from bacteria and
yeasts to fungi, including mushrooms, and in many invertebrates, particularly
insects. But there is normally not much trehalose in plants, with the exception
of the so-called resurrection plants that can survive prolonged droughts in the
desert. Drought-stressed resurrection plants look like they are dead and gone
forever; then they pop back to life when moisture is available," Garg
said. "That's the power of trehalose in combating stress, and it gave us
an idea to help important crop plants survive stress."
In their
experiment, the Cornell biologists used two different E. coli
genes that are fused together and are responsible for trehalose synthesis in
bacteria. (Previous attempts in other laboratories had used only one type of
trehalose gene and had been less successful because the resulting transgenic
plants showed so-called pleiotrophic effects, including stunted growth, and had
little tolerance for stresses.)
The Cornell
biologists also learned how to add custom-designed "promoter"
sequences to the fused genes, to allow precise "when-and-where"
control over gene expression. Depending on the need, the trehalose genes can be
turned on in the transgenic plants when stresses occur -- the onset of colder
temperatures, for example. Or the gene sequence can be regulated to make
trehalose in particular parts of the plant -- such as the leaf but not the
edible grains.
So far the
transgenic rice plants with the trehalose-enhancement gene sequences have been
tested through five generations -- from seed-producing plants to seedlings and
more seed-producing plants, again and again -- and the desirable,
stress-tolerance characteristics have held true. Compared with non-engineered
rice plants that lack the trehalose-enhancement gene sequences, the transgenic
rice plants are much more robust under a variety and combination of
environmental stresses.
Even when
the transgenic plants are not under stress, their processes of photosynthesis
(converting light to energy) are more efficient, the Cornell scientists report,
accounting, in part, for the increased productivity. Better utilization of soil
micronutrients, such as zinc and iron, also has been noted in the transgenic plants.
All the
benefits -- and any potential liabilities -- of trehalose have yet to be
explored fully, Garg noted. At the cellular level in plants, trehalose helps
maintain individual cell structure and function during severe environmental
stresses that would kill most plants. Then the sugar appears to help plant
cells regain function and efficiency when stress is gone. But, Garg added,
"We still have a lot to learn about trehalose in important crop
plants."
Likewise,
several years of research-and-development work, safety testing and
certification are ahead before large-scale production and distribution of
transgenic rice seeds to farmers can begin. The Cornell scientists are seeking
patent protection of the trehalose-enhancement technologies, not to control the
market and profit from the work, but to ensure that the technologies can be
offered in the public domain, Wu said.
"World
population continues to increase at an explosive rate, our arable land is
deteriorating, fresh water is becoming scarce and increasing environmental
stresses pose ever more serious threats to global agricultural production and
food security," said Wu. "Anything we can do to help crop plants cope
with environmental stresses will also raise the quality and quantity of food
for those who need it most."
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December 5, 2002
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