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Small plant plays big role in research

By Kate Ramsayer

(Editor’s Note: This is one in an occasional series of articles spotlighting the organisms important in a variety of biological studies.)

Arabidopsis flower (photo courtesy of Ian Rees)

Gregor Mendel had a monastery garden in which to conduct his famous genetics experiments with peas. Plant scientists these days, especially those at medical schools and smaller universities, don’t often have that luxury of space.

So they’ve turned their focus to Arabidopsis thaliana, a small and fast-growing flowering plant that behaves on a molecular level very similarly to larger plants, ranging from corn to cedar trees. Scientists first started looking at the experimental possibilities of Arabidopsis in the middle of the 19th century, but it didn’t gain popularity as a model organism until the 1980s. Now, Arabidopsis labs are as common as the plant itself.

“You’d be hard pressed to find a biology genetics department in a university that doesn’t have an Arabidopsis person,” said Kendal Hirschi, PhD, an associate professor of pediatrics and of human and molecular genetics at Baylor College of Medicine and the USDA/ARS Children’s Nutrition Research Center at Baylor College of Medicine.

Immature buds and blooms (photo courtesy of Ian Rees)

These little mustard plants have taken off in popularity thanks to their small size, their speedy growth, and their simple genetics.

Arabidopsis seeds start their laboratory life in a petri dish, growing in a special medium in an incubator kept at 22 degrees Celsius. Once the plants are past the seedling stage, researchers can put them in tubs of soil and let them finish growing under heat lights. With Arabidopsis’ generation time of 40 days, researchers can reap almost 10 generations of crops in each year.

The equipment is so simple, said Hirschi, that the plants could be grown anywhere. They’re even popular with schoolteachers and students, who can use them to demonstrate phenomena such as how plants grow towards light.

A model plant

Grown-up scientists can examine any number of questions with Arabidopsis as well.

“It’s a card carrying member of the genetics club,” said Hirschi. “Anything you can do with yeast, you can do with this little weed.” The sequence of the plant’s more than 20,000 genes was published in 2000, and the National Science Foundation has set a goal for scientists to understand the function of each of those genes by the year 2010.

For now, much of the research on Arabidopsis focuses on a few main areas. Many researchers are using the plants as a model to study disease resistance in crops and to identify which genes are involved in self-defense.

Maturing plant (photo courtesy of Ian Rees)

Other scientists are looking for ways to improve the commercial potential of crops, with experiments that examine how to control the growth of grains and fruits, or study how plants respond to the environment around them. Arabidopsis is also a model for the study of plant circadian rhythms, or how the plant keeps internal time.

Knowledge of this model plant can be easily transferred to the more complex crop plants, and specialist plant scientists have figured out how to transfer genes from one organism to another just as easily.

A major problem of using the tiny Arabidopsis is one of biomass. Because the plant is so small, scientists who are trying to isolate proteins have to grind up a lot of leaves to get a sample large enough to analyze. The researchers usually get around this problem by turning on the gene in a larger plant or another organism, and doing their collection there.

Calcium-packed carrots

In Hirschi’s lab, scientists are investigating a protein complex that transports calcium ions into plant cells. When they turn on extra copies of this gene in another plant, like the carrot, it causes the carrot cells to take up twice as much calcium as it would usually.

The scientists are currently doing bioavailability studies to see if eating these carrots gives someone twice the calcium, with the hope of someday seeing these carrots in grocery stores.

While he acknowledges that being a plant biologist in a medical school makes him something of an orphan, Hirschi said that there are benefits as well. He can collaborate with physicians and nutritionists to test the carrots, and with his other affiliation at Texas A&M University, he has access to the expertise of crop scientists who can transfer the genes between one plant species and another.

While his everyday lab work involves the genetics of yeast and plants, Hirschi said that there’s always something else you can look towards as a future goal.

“You can do basic biology everyday but have the fun of imagining how to apply it to world agricultural problems,” he said.

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