Sep. 6, 2002 MADISON -- Plants have never impressed anyone with their intelligence, but they do measure the seasons and tell time. After all, a Christmas cactus blooms only in winter and an evening primrose opens just at dusk. Now, scientists led by University of Wisconsin-Madison researchers report that they have discovered a gene that regulates when plants flower and is critical for keeping a plant's 24-hour clock running accurately. The researchers will publish their findings in the Friday, Sept. 6, issue of the scientific journal Nature.
The discovery adds a new piece to the still-unfinished puzzle of how plants regulate the transition from vegetative growth to flowering, and control their daily rhythmic activity. Mark Doyle, the article's lead author, says the discovery may aid agriculture, as farmers want to maximize vegetative growth from crops such as alfalfa and spinach, or control the timing of flowering and seed production.
"Our primary interest is in understanding what this new gene does to control flowering, but it may be difficult to separate that from its effects on the clock that determines plant rhythms," says Doyle, a research assistant in the College of Agricultural and Life Sciences.
Working with plant molecular biologist Richard Amasino in the Department of Biochemistry, Doyle identified the new gene, which they called early flowering 4 (ELF4).
"So far, scientists haven't found any genes similar to ELF4 outside the plant kingdom," Amasino says. "All organisms have these internal clocks, but there are different molecular mechanisms that operate them."
The Wisconsin scientists discovered the gene in Arabidopsis thaliana, a small plant used worldwide to study plant genetics, physiology and molecular biology. Arabidopsis plants typically flower quickly when days have 12 hours of light or more but take a long time to begin flowering when the day length is eight hours. Scott Michaels and Fritz Schomburg in Amasino's lab created tens of thousands of plants with individual genes inactivated and Doyle grew them in conditions where the day length was eight hours. He identified a plant that bloomed early despite the eight-hour days because the plant was a mutant in which the ELF4 gene was inactivated. He then isolated ELF4.
Doyle and Amasino sent plants with and without a functioning ELF4 gene to Andrew Millar's lab at the University of Warwick in England. When the Warwick group held the plants in continuous light or darkness, those with the ELF4 continued their daily patterns of leaf movement and gene expression. Plants without a functioning ELF4 gene quickly lost those rhythmic 24-hour patterns.
When Doyle restored a functioning ELF4 gene to plants lacking one, those plants could again maintain daily patterns even under constant light or darkness.
"ELF4 is critical to keeping the clock working accurately," says Doyle. However, he notes that there are five or six other genes that play a role in the plant's clock. "Scientists still have a lot of work to do before we can explain the molecular circuitry by which these genes, and the proteins produced from them, keep plants on a 24-hour cycle."
Joining the Wisconsin researchers as co-authors of the Nature paper are: Andrew J. Millar, Seth J. Davis, Ruth M. Bastow, and Harriet G. McWatters from the University of Warwick in England; and László Kozma-Bognár and Ferenc Nagy from the Institute of Plant Biology at the Biological Research Center in Hungary.
The UW-Madison research was supported by state funding to the College of Agricultural and Life Sciences, by a training grant from the National Institutes of Health, and by research grants from the USDA and National Science Foundation.
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