Researchers have identified an enzyme involved in the production of auxin, a plant growth hormone that influences many aspects of plant growth, including cell division and flowering. Although auxin has been studied for more than 100 years, scientists have not had a good grasp of how the hormone is synthesized by plants.

In an article published in the January 12, 2001, issue of the journal Science, Howard Hughes Medical Institute investigator Joanne Chory and colleagues at the Human BioMolecular Research Institute in San Diego and the University of Minnesota reported identifying a new flavin monooxygenase (FMO)-like enzyme that is central to auxin biosynthesis. The finding reveals an important pathway for auxin synthesis and is likely to offer clues that will aid researchers studying similar enzymes in mammals. The role of the FMO-like enzymes was discovered when the scientists created a mutant form of the plant Arabidopsis that had growth characteristics indicative of auxin overproduction. Arabidopsis, a small flowering plant that is a relative of the mustard plant, is the basic model organism used in plant biology research.

"We were randomly inserting into the Arabidopsis genome DNA sequences called enhancer sequences that promote gene activity," said Chory, who is at The Salk Institute for Biological Studies. "Specifically, we were looking for mutants in the light-responsive pathway. One measure of the light-responsive pathway in plants is the length of the primary stem, or hypocotyl, under various light conditions," Chory explained. "Normally, light represses stem growth so that the stem becomes thicker and can support more leaves. In plants that dont respond well to light due to mutations, the hypocotyl elongates."

According to Chory, one mutant produced during their experiments showed signs of overgrowth that is characteristic of auxin over
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
11-Jan-2001