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“Missouri has been a hotbed of plant genetics for a long time,” Walker says. The MU husband and wife team of Ernie and Lotti Sears bred domesticated wheat with the rust resistance of wild wheat. And Barbara McClintock, who was awarded the Nobel Prize for the discovery of the “jumping gene” phenomenon — genes that can “jump” into random areas of a chromosome – also worked at the University.

Walker points through a window of the Christopher S. Bond Life Sciences Center where he works to a nearby complex of greenhouses. He has one row of the greenhouse, a strip about 20 feet long by 72 feet wide. Inside it are growing about 100,000 Arabidopsis plants.

Walker is also cultivating hundreds of thousands more plants in the Bond Life Sciences Center. Palates of them fill incubator-like machines called growth chambers and climate-controlled rooms where the plants often get 16 hours of light each day.

“We grow them as fast as we can, so we use long days,” he says. Walker enters one of the rooms. It’s about the size of a large walk-in closet. It’s warm and bright and has the earthy smell of rich soil.

Row after row of Arabidopsis plants line the shelves. Like dandelions, the plants have leaves that lie low to the ground. Their stalks rise about five inches, although when fully grown, they can be a couple of feet tall.

Arabidopsis flowers have tiny white petals. And it is here that Walker’s detective work into the genetics of abscission begins.

The petals of wild Arabidopsis plants have abscission zones. The petals drop after the plant’s seed pod is fertilized by pollen. Walker flicks a couple of plants with his finger and the petals fall.

But in a mutated variety of Arabidopsis, the petals stay firmly in place. “I can flick them all day long and they never fall off,” Walker says.

These plants provided the clues for tying the abscission process to certain genes that Walker already had identified as suspects.

Scientists have long known that different signals, such as pollination or fewer hours of daylight, trigger the production of enzymes that dissolve the bonds between cells in the abscission zone. “But there’s always been this big, black box between the [triggering] signal and the event, the pathway the signal travels,” Walker says. “We’ve identified a lot of the genetic components in that pathway.”

Genes communicate the signal by producing proteins called enzymes that act on receptor genes that in turn turn on more enzymes. “What you have is a cascade of enzymes that activate enzymes that activate other enzymes,” Walker says. “It’s the proteins talking to the proteins.”

But out of the 30,000 genes in Arabidopsis, which ones are involved in abscission? “We knew what all the genes in Arabidopsis looked like, so we could make a guess at what they do,” Walker said. “We let the plant tell us.”

Walker and his IPG colleague Shuqun Zhang found certain genes that expressed proteins that were concentrated exclusively in the abscission zones of Arabidopsis petals. In the mutated plants that don’t lose their petals, these genes no longer produce the proteins.

So far, Walker and his group have linked four genes that make up the midsection of the abscission pathway. “We identified that these genes all play together,” he says.

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Published by the Office of Research.

©2009 Curators of the University of Missouri. Click here to contact the editor.

 

Illumination home. Spring 2009 Table of Contents.