St. Louis, Missouri
February 25, 2008
A team of scientists led by
Washington University in St.
Louis has begun to unlock the genetic secrets of corn, a crop
vital to U.S. agriculture. The researchers have completed a
working draft of the corn genome, an accomplishment that should
accelerate efforts to develop better crop varieties to meet
society's growing demands for food, livestock feed and fuel.
Corn, also known as maize, underlies myriads of products, from
breakfast cereal, meat and milk to toothpaste, shoe polish and
ethanol.
The genetic blueprint will be announced on Thursday, Feb. 28, by
the project's leader, Richard K. Wilson, Ph.D., director of
Washington University's Genome Sequencing Center, at the 50th
Annual Maize Genetics Conference in Washington, D.C.
"This first draft of the genome sequence is exciting because
it's the first comprehensive glimpse at the blueprint for the
corn plant," Wilson says. "Scientists now will be able to
accurately and efficiently probe the corn genome to find ways to
improve breeding and subsequently increase crop yields and
resistance to drought and disease."
The $29.5 million project was initiated in 2005 and is funded by
the National Science Foundation (NSF), the U.S. Department of
Agriculture and the U.S. Department of Energy. "Corn is one of
the most economically important crops for our nation," says NSF
director Arden L. Bement Jr. "Completing this draft sequence of
the corn genome constitutes a significant scientific advance and
will foster growth of the agricultural community and the economy
as a whole."
The team working on the endeavor, including scientists at the
University of Arizona in Tucson, Cold Spring Harbor Laboratory
in New York and Iowa State University, has already made the
sequencing information accessible to scientists worldwide by
depositing it in GenBank, an online public DNA database. The
genetic data is also available at maizesequence.org.
The draft covers about 95 percent of the corn genome, and
scientists will spend the remaining year of the grant refining
and finalizing the sequence. "Although it's still missing a few
bits, the draft genome sequence is empowering," Wilson explains.
"Virtually all the information is there, and while we may make
some small modifications to the genetic sequence, we don't
expect major changes."
The group sequenced a variety of corn known as B73, developed at
Iowa State decades ago. It is noted for its high grain yields
and has been used extensively in both commercial corn breeding
and in research laboratories.
The genome will be a key tool for researchers working to improve
varieties of corn and other cereal crops, including rice, wheat
and barley. "There's a lot of great research on the horizon,"
says plant biologist Ralph S. Quatrano, Ph.D., the Spencer T.
Olin Professor and chair of Washington University's Department
of Biology. "The genome will help unravel the basic biology of
corn. That information can be used to look for genes that make
corn more nutritious or more efficient for ethanol production,
for example."
Corn is only the second crop after rice to have its genome
sequenced, and scientists will now be able to look for genetic
similarities and differences between the crops, Quatrano adds.
"The maize genome sequence will be of great interest to maize
geneticists and biologists around the world, but also will be an
important resource for plant breeding and biotechnology
companies," says project collaborator Rob Martienssen, Ph.D., of
Cold Spring Harbor Laboratory. "The maize sequence will be an
invaluable reference for research, especially in renewable
energy and biofuels, similar in significance to the human genome
sequence for biomedical research".
The genetic code of corn consists of 2 billion bases of DNA, the
chemical units that are represented by the letters T, C, G and
A, making it similar in size to the human genome, which is 2.9
billion letters long. By comparison, the rice genome is far
smaller, containing about 430 million bases.
The challenge for Wilson and his colleagues was to string
together the order of the letters, an immense and daunting task
both because of the corn genome's size and its complex genetic
arrangements. About 80 percent of the DNA segments are repeated,
and corn also has 50,000 to 60,000 genes, roughly double the
number of human genes. Mobile genes, or transposons, make up a
significant portion of the genome, further complicating
sequencing efforts.
"Sequencing the corn genome was like putting together a 1,000
piece jigsaw puzzle with lots of blue sky and blue water, with
only a few small sailboats on the horizon," Wilson explains.
"There were not a lot of landmarks to help us fit the pieces of
the genome together."
The United States is the world's top corn grower, producing
44 percent of the global crop. In 2007, U.S. farmers produced a
record 13.1 billion bushels of corn, an increase of nearly 25
percent over the previous year, according to the U.S. Department
of Agriculture. The 2007 production value of corn was estimated
at more than $3 billion. Favorable prices, a growing demand for
ethanol and strong export sales have fueled an increase in
farmland acreage devoted to corn production.
Washington University School of Medicine's 2,100 employed and
volunteer faculty physicians also are the medical staff of
Barnes-Jewish and St. Louis Children's hospitals. The School of
Medicine is one of the leading medical research, teaching and
patient care institutions in the nation, currently ranked fourth
in the nation by U.S. News & World Report. Through its
affiliations with Barnes-Jewish and St. Louis Children's
hospitals, the School of Medicine is linked to BJC HealthCare.
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