Scientists have high hopes for corn genome

By David Brown
Friday, November 20, 2009

If a biologist had to pick one living thing as the textbook of how genes work, what would it be?

Corn seems to be a good answer.

Now the scientific world has at hand the complete genome sequence of corn, announced by researchers who have collaborated over the past four years and published their results Thursday. A package of 14 research papers in Science and PLoS Genetics accompanying the genome release suggests corn still has some useful secrets to reveal.

Many agronomists hope the information buried in corn's 32,000 genes and 2.3 billion letters of DNA may help sustain the century-long improvement in yield and hardiness into an era of climate change and, possibly, food shortage.

Corn -- or maize, as it's called in most parts of the world -- is mankind's second most widely consumed cereal and a crop of huge importance to animal husbandry, manufacturing and energy production. It is also turning out to be an unusually good teacher of gene action and evolutionary mechanics.

Studies over the past 60 years have revealed numerous hard-to-believe gene actions in corn that were later found to operate in higher organisms, including human beings. Mobile genetic elements -- the "jumping genes" that won corn geneticist Barbara McClintock a Nobel Prize in 1983 -- are perhaps the best-known example.

"The fact that example after example of these unexpected phenomena are also at work in mammals suggests that scientists interested in things like human diseases would be well served to pay attention to what's happening in plants, and in corn in particular," said Virginia Walbot, a molecular geneticist at Stanford University.

Patrick S. Schnable, a geneticist at Iowa State University, where much of the work was done, said simply: "Corn is a good model for biology in general."

The sequencing revealed that an astonishing 85 percent of the corn genome is made up of "transposable elements" -- short stretches of DNA, some perhaps descended from viral invaders -- that show evidence of having moved around in corn's 10 chromosomes at some point in evolution. Their peregrinations provided the basis for new genes, or the on-and-off regulation of existing ones (that is, when they didn't cause a fatal disruption and consign their host to the dustbin of history).

The genome also exemplifies two other engines of evolution -- gene duplication and fusion.

About 70 million years ago, a corn ancestor copied and kept its entire genome, ending up with two of everything. Then, about 5 million years ago, two related ancestral species fused. Both events gave corn a huge amount of raw material for fashioning the tools for survival and adaptation, namely genes.

That genetic diversity descended to teosinte, a Central American grass with coblike seed heads that are smaller than a person's thumb.

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