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August 28, 2007
By Krishna Ramanujan
When soils are too acidic,
aluminum that is locked up in clay minerals dissolves into the
soil as toxic, electrically charged particles called ions,
making it hard for most plants to grow. In fact, aluminum
toxicity in acidic soils limits crop production in as much as
half the world's arable land, mostly in developing countries in
Africa, Asia and South America.
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Aluminum toxicity in acidic soils limits crop production
in as much as half the worldÕs arable land, mostly in
developing countries in Africa, Asia and South America. |
Now,
Cornell Univeristy
researchers have cloned a novel aluminum-tolerant gene in
sorghum and expect to have new genetically-engineered
aluminum-tolerant sorghum lines by next year.
The research, to be published in the September issue of Nature
Genetics, provides insights into how specialized proteins in the
root tips of some cultivars of sorghum and such related species
as wheat and maize can boost aluminum tolerance in crops.
Sorghum is an important food crop in Africa, Central America and
South Asia and is the world's fifth most important cereal crop.
"My lab has been working to identify the physiological
mechanisms of plant aluminum tolerance as well as its molecular
basis," said Leon Kochian, the paper's senior author, a Cornell
adjunct professor of plant biology and director of the U.S.
Department of Agriculture--Agriculture Research Service
(USDA-ARS) Plant, Soil and Nutrition Laboratory at Cornell. "The
reason this is significant is there are extensive areas of the
earth's lands that are highly acidic, with pH of 5 or below [pH
below 7 is considered acidic]. Most of these areas are in the
tropics or subtropics, where many developing countries are
located."
Kochian's research shows that in aluminum-tolerant sorghum
varieties, special proteins in the root tip release citric acid
into the soil in response to aluminum exposure. Citric acid
binds aluminum ions very effectively, preventing the toxic metal
from entering the roots.
Kochian and colleagues, including the paper's first author,
Jurandir Magalhaes, who received his Ph.D. from Cornell in
Kochian's lab and now directs his own lab at the Embrapa Maize
and Sorghum Research Center in Brazil, used genetic mapping to
identify a single gene that encodes a novel membrane-transporter
protein responsible for the citric acid release. The gene, they
discovered, is only turned on to express the protein and
transport citric acid when aluminum ions are present in the
surrounding soil.
The researchers have now used the sorghum gene to engineer
transgenic aluminum-tolerant Arabidopsis thaliana (a small
mustard plant used in plant research because of its small genome
and short life cycle) and wheat plants. Sorghum is harder to
genetically transform, Kochian said.
The map-based cloning of this agronomically important gene in
sorghum is helping advance this species as a model for further
exploring the mechanisms of aluminum tolerance and discovering
new molecular genetic solutions to improving crop yields,
Kochian said.
"This research also has environmental implications for badly
needed increases in food production on marginal soils in
developing countries," said Kochian. "For example, if we can
increase food production on existing lands, it could limit
encroachment into other areas for agriculture."
The research is supported in part by the McKnight Foundation
Collaborative Crop Research Program, the Generation Challenge
Program, the National Science Foundation and the USDA-ARS. |
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