Corn Genome Unraveled

A group of scientists have completed a working draft of the genome sequence of corn, also known as maize, a widely grown crop that is vital to US agriculture. They hope the unraveling of this genome will speed up the development of better crop varieties to meet growing demand for food, animal feed and fuel.

The team, led by Dr. Richard K. Wilson, director of Washington University's Genome Sequencing Center in St. Louis, Missouri, will reveal its work today, Thursday 28th February, at the 50th Annual Maize Genetics Conference in Washington, DC.

The draft includes about 95 per cent of the corn genome. Wilson and colleagues hope to complete the rest by the end of the year.

"Although it's still missing a few bits, the draft genome sequence is empowering," said Wilson.

"Virtually all the information is there, and while we may make some small modifications to the genetic sequence, we don't expect major changes," he added.

Maize, or corn, is an underlying foodstuff used in the manufacture of a wide variety of foods and other products, from the more familiar breakfast cereal to ethanol, shoe polish and toothpaste. It is also a vital food for cattle and other animals.

Wilson said that this first draft is "exciting" because:

"It's the first comprehensive glimpse at the blueprint for the corn plant."

"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," he added.

There are 2 billion DNA nucleotide bases in the corn genome, making it about the same size as the human genome. This is significantly larger than the rice genome which has about 430 million bases.

A DNA nucleotide base is a chemical building block of which there are four kinds, each represented by a letter: A for adenine, G for guanine, C for cytosine, and T for thymine.

The hardest part of the work Wilson and colleagues faced was to get the order of the bases right. About 80 per cent of the DNA sequence is repeated, and corn has 50,000 to 60,000 genes, about twice as many as humans. Many of these genes are mobile (transposons), making them much more difficult to "count" compared to the stationary ones.

Genes are large groups of nucleotide pairs that either code for a type of protein or cell component, or regulate the expression of other genes. An organism's complexity does not depend on the number of genes in its genome. And some genes have sequences in common with other genes. The concept of a gene is not fixed and still changing as scientists discover more about them.

Wilson explained that the task of 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."

"There were not a lot of landmarks to help us fit the pieces of the genome together," he added.

Other cereal crops could also benefit from this research, not just other varieties of corn, but also rice, wheat and barely, and other applications.

The research project, backed by the National Science Foundation (NSF), the US Department of Agriculture and the US Department of Energy, with a budget of nearly 30 million dollars, started in 2005.

NSF director Arden L. Bement Jr. stressed the importance of corn as "one of the most economically important crops for our nation".

"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," he said.

The rest of the team includes scientists from the University of Arizona in Tucson, Cold Spring Harbor Laboratory in New York and Iowa State University.

Wilson and colleagues have been sharing the sequencing information they have unraveled through the online public DNA database, GenBank and maizesequence.org.

The precise variety of corn that Wilson and colleagues have been studying is called B73, which was developed at Iowa State University several decades ago. B73 is known for its high yield and is widely used for commercial breeding of corn and also for research.

Plant biologist Dr. Ralph S. Quatrano, who is Spencer T. Olin Professor and chair of Washington University's Department of Biology spoke of the range of applications of this discovery:

"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."

The genome sequence of rice has already been unraveled, so sequencing a second grain crop will help scientists to find the genetic similarities and differences between them, said Quatrano.

Project collaborator Dr. Rob Martienssen of Cold Spring Harbor Laboratory, was also enthusiastic about this:

"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."

"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," added Martienssen.

Over 40 per cent of the world's corn is produced in the US, where a record 13.1 billion bushels were grown in 2007, representing a 25 per cent increase on 2006, according to the US Department of Agriculture.

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