Scientists in five nations complete first genetic map of a plant

Scientists for the first time have mapped the entire genetic sequence of a plant. It's neither a towering redwood tree nor a fragrant rose, but an obscure, spindly weed with leaves resembling mouse

Wednesday, December 13th 2000, 12:00 am

By: News On 6

Scientists for the first time have mapped the entire genetic sequence of a plant. It's neither a towering redwood tree nor a fragrant rose, but an obscure, spindly weed with leaves resembling mouse ears.

Arabidopsis thaliana _ gardeners know it as thale cress _ joins the fruitfly, yeast, the nematode worm and two dozen bacteria as organisms that have revealed their entire DNA blueprints.

Scientists selected Arabidopsis as the poster plant for the genetics revolution over 250,000 flowering competitors because it's biologically simple and grows quickly _ as many as eight generations per year.

Like the animal models, it is easily manipulated in laboratory experiments and widely used as a reliable stand-in for more complex organisms.

In the wild, this homely member of the mustard family sprouts innocuously along pathways and dry, rubble-strewn hillsides in Europe.

Suddenly, Arabidopsis is indispensable. The small plant's 25,500 genes already are being manipulated in some of science's most revolutionary _ and controversial experiments. Chief among them, to boost the yields and nutritional content of rice, wheat and other staple crops that feed billions of people in poor, crowded countries.

In industrial nations, scientists hope to turn corn fields into renewable sources of industrial oils and chemicals, replacing fossil fuels.

Even medicine could benefit by learning how the plant's DNA repairs itself after infection or injury.

``Arabidopsis now is the reference plant for all others,'' said Jeff Dangl, a plant geneticist at the University of North Carolina. He works extensively with Arabidopsis, but did not contribute to the mapping report.

``It has all the genes that more complicated plants have for roots, seeds, flowers and fighting diseases,'' Dangl said. ``Now we know what it essentially takes to make a flower.''

Hundreds of researchers in five nations contributed to the plant gene mapping project, which was funded by government agencies in the United States and the European Union. The results of the five-year effort are published in the latest issue of the journal Nature. The map was announced in news conferences in Washington, London, Brussels and Tokyo.

Additional work was published separately in Science, the Washington-based research journal.

Biologists praised the map's completion as a scientific milestone. But knowing the genes' locations within the plant's five chromosomes isn't enough, they said.

In the project's second phase, researchers hope by 2010 to determine the biological function controlled by each of the plant's 25,500 genes.

``Almost half of the genes in Arabidopsis don't match anything with a known function,'' said Iowa State University corn geneticist Patrick Schnable. ``Once we know what each gene does, we need to figure out how and why that function is important to the plant. We don't know how to do that now.''

Compared to more familiar plants, Arabidopsis is a simple organism. Its genes are compact and they contain a small total of DNA. An Arabidopsis cell has 118.7 million base pairs of amino acids in its nuclear DNA. Rice has 425 million. Corn has 3 billion. (So do humans.) Wheat has five times more than corn.

But Arabidopsis contained some surprises, too. The mapping project revealed that 70% of its genetic code is duplicated in various patterns that remain poorly understood.

Some repeats might serve as backups for important genes. Others may cooperate in complex functions. Scientists said the map enables them to knock out specific genes or gene groups and see what happens when they grow the plant again.

Scientists said they already are testing Arabidopsis genes to breed crops with more specific and reliable traits.

The result: more food, added nutrition and hardier crops that will grow vigorously in meager soil baked by global warming. Such crops, they said, could curtail the need to plow tropical rainforests into marginal farms.

Other crops are genetically modified to resist certain pests and diseases, reducing the use of environmentally damaging synthetic chemicals and fertilizers, researchers said.

Opponents fear that tinkering with the genes of widely-planted crops will result in unforeseen health and environmental consequences that could upend millions of years of evolution and threaten the survival of already vulnerable species.

Its a simmering issue in the United States, where thousands of products on supermarket shelves already contain genetically modified ingredients.

In Europe, the debate is boiling over. Demonstrators block ships from unloading cargo and disrupt trade meetings. EU officials are considering stringent regulations on genetic modifications.

Ironically, the plant gene map might also provide breakthroughs in medicine and evolution, too.

Arabidopsis contains numerous genes that are equivalent to human genes involved in aging and disease, including cancer.

And it contains master genes controlling basic cell growth and behavior that have been at work since flowering plants appeared more than 125 million years ago.

Understanding their functions could be a keyhole into the basic molecular pathways of disease and, perhaps, reveal the roots of evolution of complex organisms.

Quite a legacy for a little weed, biologists said.

``It's amazing that humans and plants share a number of genes,'' said Rod Wing, who is mapping the rice genome at Clemson University. ``It provides further evidence that we do have a common origin. Having the whole genome of a plant opens so many questions about evolution. How related are we?''