Davis, California and Los Baños,
The Philippines
August, 2006A gene that
enables rice to survive complete submergence has been identified
by a team of researchers at the
International Rice Research Institute in the Philippines and
at the University of California's
Davis and
Riverside campuses. The
discovery allows for development of new rice varieties that can
withstand flooding, thus overcoming one of agriculture's oldest
challenges and offering relief to millions of poor rice farmers
around the world.
While rice thrives in standing
water, like all crops it will die if completely submerged for
more than a few days. The development and cultivation of the new
varieties is expected to increase food security for 70 million
of the world's poorest people, and may reduce yield losses from
weeds in areas like the United States where rice is seeded in
flooded fields. Results of this study will appear in the Aug. 10
issue of the journal Nature.
"Globally, rice is the most
important food for humans, and each year millions of small
farmers in the poorest areas of the world lose their entire
crops to flooding," said Pamela Ronald, a rice geneticist and
chair of UC Davis' Plant Genomics Program. "Our research team
anticipates that these newly developed rice varieties will help
ensure a more dependable food supply for poor farmers and their
families. And, in the long run, our findings may allow rice
producers in the United States to reduce the amount of
herbicides used to fight weeds."
Background
Rice is the primary food for
more than 3 billion people around the world. Approximately
one-fourth of the global rice crop is grown in rain-fed, lowland
plots that are prone to seasonal flooding. These seasonal flash
floods are extremely unpredictable and may occur at any growth
stage of the rice crop.
While rice is the only cereal
crop that can withstand submergence at all, most rice varieties
will die if fully submerged for too long. When the plant is
covered with water, its oxygen and carbon dioxide supplies are
reduced, which interferes with photosynthesis and respiration.
Because the submerged plants lack the air and sunlight they need
to function, growth is inhibited, and the plants will die if
they remain under water for more than four days.
During any given year, yield
losses resulting from flooding in these lowland areas may range
from 10 percent to total destruction, depending on the water
depth, age of the plant, how long the plants are submerged,
water temperature, rate of nitrogen fertilizer use and other
environmental factors. Annual crop loss has been estimated at
more than $1 billion.
"For half a century,
researchers have been trying to introduce submergence tolerance
into the commonly grown rice varieties through conventional
breeding," said rice geneticist and study co-author David
Mackill, who heads the Division of Plant Breeding, Genetics, and
Biotechnology at the International Rice Research Institute.
"Several traditional rice varieties have exhibited a greater
tolerance to submergence, but attempts to breed that tolerance
into commercially viable rice failed to generate successful
varieties.
"We're especially pleased that
we have been able to use the latest advances in molecular
biology to help improve the lives of the world's poor," Mackill
added. "We're confident that even more important discoveries
like this are in the pipeline."
Results of this study
Using genetic mapping
techniques, the research team identified a cluster of three
genes that appeared closely linked to the biological processes
that either make rice plants vulnerable to flooding or enable
them to withstand the total submergence that occurs during
flooding.
The researchers then focused
their attention on one of those three genes, known as the Sub1A
gene. They found that when this gene is over-expressed, or
hyper-activated, a rice variety that is normally intolerant of
submergence becomes tolerant.
Further studies indicated that
the Sub1A gene is likely successful in conferring submergence
tolerance to rice because it affects the way the plants respond
to hormones, such as ethylene and giberellic acid, that are key
to the plant's ability to survive even when inundated with
water.
Going one step further, the
researchers introduced the Sub1A gene into a rice variety that
is especially suited for growing conditions in India. The
resulting rice plants were not only tolerant of being submerged
in water but also produced high yields and retained other
beneficial crop qualities. Development of submergence-tolerant
varieties for commercial production in Laos, Bangladesh and
India is now well under way.
In addition to providing a more
stable supply of rice in developing countries, the researchers
are hoping that the new gene will be useful in suppressing weeds
and reducing herbicide applications for conventional and organic
rice farmers in developed countries like the United States. If
water can be left on the rice for an additional week, it is
expected that weed populations will be reduced.
The research team is now trying
to identify all the genes that are regulated by Sub1A and to use
this information to further improve tolerance to flooding and
other stresses.
Funding for this study was
provided by the U.S. Department of Agriculture's Cooperative
State Research, Education and Extension Service - National
Research Initiative; the U.S. Agency for International
Development; and the German Federal Ministry for Economic
Cooperation and Development.
In addition to Ronald and
Mackill, this international research team included Kenong Xu,
Xia Xu and Patrick Canlas, all of UC Davis; Takeshi Fukao and
Julia Bailey-Serres, both of UC Riverside; and Reycel
Maghirang-Rodriguez, Sigrid Heuer and Abdelbagi Ismail, all of
the International Rice Research Institute in the Philippines.
Nature
Rice made to breathe underwater
http://www.nature.com/news/2006/060807/full/060807-8.html
Source:
SciDev.Net
Gene
discovery could lead to flood-resistant rice
Hepeng Jia, SciDev.Net
Scientists have identified a gene that enables rice to survive
for up to two weeks underwater, raising the possibility of
breeding varieties that can withstand what would otherwise be
damaging floods.
A
quarter of the world's rice grows in areas prone to flooding,
which costs rice farmers in South and South-East Asia more than
US$1 billion a year.
Although rice thrives in standing water, most varieties die
within a week of being completely submerged. But others can
tolerate being totally submerged for up to two weeks.
The researchers, who published their findings today (10 August)
in Nature, studied the DNA of one such variety. They found it
has a gene that intolerant varieties lack.
When they introduced the gene into a high-yielding rice variety
grown widely in Asia, they found it kept its high yield but
could also tolerate being totally submerged.
David Mackill of the International Rice Research Institute in
the Philippines, and Pamela Ronald of the University of
California in Davis, United States, led the international team.
Mackill told SciDev.Net that scientists would be able to
crossbreed submergence-tolerant rice with varieties that are
already popular with farmers.
Link to full paper in Nature
Link to related commentary
article in Nature
RELATED
RELEASE: UC Riverside researchers develop
flood-tolerant California rice
Source:
University of California Davis
http://indica.ucdavis.edu/research/index.php?research=tolerance
RESEARCH OVERVIEW
Submergence tolerance in rice
More than 22 million hectares
of rice paddies are prone to transient flooding due to seasonal
rains. Cultivars that can survive temporal flooding of fields
are highly desired to enhance yield. Furthermore, sowing of
submergent tolerant seed into fields flooded to 15 to 20 cm
would effectively limit weed growth and eliminate the need for
herbicides.
An international effort,
focused on the characterization of the genetic determinants of
submergence tolerance, identified an indica landrace, FR13A, as
the world's most tolerant of flooding. In collaboration with D.
Mackill (International Rice
Research Institute) we have now cloned the submergence
tolerance (Sub1) locsu from FR13A using a map-based cloning
approach. The Sub1 locus encodes three putative transcription
regulators of the AP2 class and RNA blot analysis indicates that
the Sub1A mRNA levels increase dramatically in response to O2
deprivation in sub1 seedlings; whereas Sub1C levels decrease.
The sub1A-2 allele possesses a single nucleotide change as
compared to the Sub1A-1 allele. All five sequenced sub1A-2
(intolerant) alleles encode a proline at this position whereas
the Sub1A-1 alleles from three tolerant lines examined encode a
serine. Transgenic lines overexpressing the Sub1A-1 gene into a
submergence intolerant line display enhanced submergence
tolerance.
Once we confirm these results,
we will examine the expression profiles of the Sub1 vs sub1
lines, determine the significance of the serine to proline
mutation and investigate whether the submergence tolerance
phenotype of rice involves differential regulation of other
signal transduction pathways (in collaboration with Julia
Bailey-Serres, UCR). These studies will help us determine if
genetic manipulation of this pathway can be used to improve
seedling survival and seed development under submergence stress.
Xu K, Xu X, Ronald PC, Mackill
DJ. 2000. A high-resolution linkage map in the vicinity of
the rice submergence tolerance locus Sub1. MGG. 263. 681-689 (pdf)
Kenong Xu, Xia Xu, Takeshi Fukao, Patrick Canlas, Sigrid
Heuer, Julia Bailey-Serres, Abdel Ismail, Ronald, P.C, David J.
Mackill. 2006. Sub1A encodes an ethylene responsive-like
factor that confers submergence tolerance to rice. Provisional
Acceptance Nature.
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