Weeds in the Garden

Most gardeners despise the lowly weed as a pest and eyesore. But one of those weeds just might enable us to better understand the growth of plants that humans rely on for food and fiber.

Bonnie Bartel, assistant professor of biochemistry and cell biology, is trying to figure out how levels of the hormone auxin are regulated in the plant Arabidopsis thaliana. Auxin causes plants to bend toward light and also promotes root development. The latter function is what Bartel’s research group observes to identify mutant plants, which tend to sprout irregular roots.

“We would like to understand all the inputs and outputs of the auxin pool in the plant and how the plant regulates them, because this hormone controls the size of cells,” Bartel says. “Our approach is to look for mutant plants that are defective in various aspects of the metabolism of auxin. Those mutants allow us to identify defective genes, which in turn helps us identify the enzyme made by those genes that is important for auxin metabolism.”

Arabidopsis thaliana is ideal for genetic research because it is closely related to other flowering plants, making Bartel hopeful that what she learns about hormone regulation will be useful to agriculture. Also, the weed’s generation time is only six weeks, and all 25,000 genes in its genome have been sequenced. Even so, the research process is time-consuming and tedious. To isolate the mutants, researchers grow tens of thousands of seeds in a solution that contains either auxin or an auxin precursor, a chemical that the plant normally converts to auxin. It takes eight days for the plants to grow enough for their roots to be inspected. Then researchers have to eye each of the plants in search of mutants that reveal a defect in the gene that converts the precursor to the hormone. Seeds from the mutants can be used to grow plants for further study. “It can take several years to identify the gene that is defective,” Bartel says. Bartel’s work is supported by the National Institutes of Health, the National Science Foundation, the U.S. Department of Agriculture, and the Robert A. Welch Foundation.

—B. J. Almond