La Jolla, CA, August 4, 2000 – Scientists at The Scripps Research Institute (TSRI) have cloned a gene that regulates circadian rhythms in plants, providing an increased understanding -- on a molecular level -- of the processes that enable organisms to anticipate and adapt to daily variations in the environment. According to Steve Kay, Ph.D., Professor of Cell Biology and an author of the study, "The work moves scientists in the direction of understanding how this gene helps plants keep accurate track of time, an extremely important capacity for organisms that are completely dependent on the daily cycle of light."
Further, researchers believe that understanding internal "clocks" in plants might also elucidate how clocks work in other species, including humans.
The study, "Cloning of the Arabidopsis Clock Gene TOC1, an Autoregulatory Response Regulator Homolog," appears in today's issue of Science. Its authors are Drs. Carl Strayer, Tokitaka Oyama, Thomas F. Schultz, Ramanujam Raman, David E. Somers, Paloma Mas, Satchidananda Panda, Joel A. Kreps, and Steve A. Kay.
Many biological processes -- the growth of fungi, activity of insects, changes in blood pressure in humans -- fluctuate daily, rising and falling at predictable times of day or night. They do so because the organisms possess internal clocks that time the rhythms. Plants, for example, use their clocks to get a jump on the day, gearing up their photosynthetic machinery and raising their leaves just before dawn. They also use their clocks to measure day length and in that way anticipate changes in the seasons – a system that determines when they shed their leaves or produce seeds or tubers in the fall, or make flowers or fruit in the spring.
Scientists have provided evidence of the existence of internal clock mechanisms by placing organisms in isolation chambers where they are prevented from seeing day/night cycles and in spite of this, their rhythms recur approximately every 24 hours. In the current study, scientists in the Kay lab worked with a mutant plant whose clock ran too fast, cycling approximately once every 21 hours.
To identify the gene responsible for this defect, the Kay group combined old-fashioned genetic techniques with modern technologies. They bred the mutant variety to normal plants and analyzed rhythms in the descendents. Using a gene from fireflies, regulated by the plant's clock, they could visualize the plants' glow rhythms. They also used information from a plant genome project, similar to the human genome project, to help correlate the defect in the glow rhythm with a particular region of a plant chromosome. Once the clock gene, called TOC1, was identified, researchers borrowed another glow gene – this one from a jellyfish – and hooked it up to TOC1 to see where it works within cells.
TOC1 was found in a member of the mustard family, a species named Arabidopsis, but similar genes likely regulate timing in species including corn, rice and wheat.
The study was funded by the National Institutes of Health and the National Science Foundation.
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