Scientists Scrutinize A Plant to Uncover Some Genetic Secrets

THANKS to a humble little plant called mouse-ear cress, Julian Schroeder has taken a giant step toward learning how to protect plants from crop-killing salt in soil.

Dr. Schroeder, a geneticist at the University of California at San Diego, and his colleagues have identified the gene that controls the way sodium (from salt) gets into plant cells. He says it now seems possible to amend the genetic instructions this gene represents to enable plants to keep out unwanted sodium and perhaps some other toxic metals.

Schroeder calls this "an exciting breakthrough" for botanical applications of basic genetic knowledge. But he notes that the larger significance of such research lies in the fact that it is applicable to animals as well as plants. There is a great deal of commonality among genes that govern fundamental processes in plant and animal cells, he explains.

This is the kind of information that now is flowing from a multinational program to decode the entire genome (genetic blueprint) of mouse-ear cress - or Arabidopsis thaliana to use its botanical name. While the much larger effort to decode the human genome has captured public attention, this quieter, less ambitious program to decode an entire plant genome is moving more rapidly toward its goal. The Arabidopsis genome is far simpler than its human counterpart. Nevertheless, it is opening up a new world of

basic knowledge for geneticists.

The plants are small. Many thousands can be grown in a laboratory at one time. They produce abundant seeds. They go through a full seed-to-mature-plant cycle in five to six weeks. The genome also is relatively small. It has only about 3 percent as much genetic material as corn. This makes the genome relatively ease to decode. Thus, in Arabidopsis, geneticists have a plant that is easy to work with, yet undergoes the same processes as do higher plants. Pappachan Kolattukudy, director of the Biotechnology Center at Ohio State University in Columbus, explains that Arabidopsis "really is a most convenient model plant if you want to know everything about the genome."

Techniques to analyze DNA - the molecule that carries genetic information - through the power of computer data processing reached levels a few year ago where it became feasible to tackle the Arabidopsis genome. A multinational coordinated research project was launched in 1990 to take advantage of this new research opportunity. Resource centers to serve the scientists involved were set up at the University of Nottingham in England, at the Max Planck Institute in Cologne in Germany, and at Ohio State Unive rsity.

Dr. Kolattukudy says the genome mapping has progressed so fast it has reached "the point of maturity" where researchers are picking out specific genes to study. According to the second annual progress report of the program, which was released last month, "we will soon begin to see applications of these advances to improvement of plants of economic significance."

Kolattukudy, like Schroeder, also notes that the results have an even wider significance. Many of the genes being investigated govern fundamental biological processes in animals.

As team members reported in a paper in the magazine Science earlier this month, they have shown that a gene found in Arabidopsis governs the channel by which plant cells take in potassium, an essential nutrient. This is a so-called inward channel in the cell membrane that acts like a one-way gate. It lets in ions (electrically charged atoms) of potassium. It generally keeps other ions out. But some ions of sodium or of a poisonous metal such as aluminum can sneak in. If genetic engineers can modify this gene to improve the effectiveness of the one-way gate, crop plants, which have the same gene, might gain salt tolerance.

Schroeder notes that animals, including humans, have similar ion channels that regulate electrical activity in their muscle and nerve cells. He adds that the gene governing an animal ion channel would "very likely" contain the same genetic information as does the plant gene.