Scientists throw light on the mechanism of plants’ ticking clock

Posted on Friday 25 July 2014

In a study published in the journal eLife they pinpoint a protein that plays a key role in the way the Circadian Clock – the internal mechanism which governs plants’ daily cycles -- can anticipate dark and light intensity and duration of light.

These internal clocks control how multiple genes are switched ‘on’ or ‘off’ at different times in every 24-hour period.  Because light and ambient temperatures also vary with time of day, many organisms, including humans, use these external signals as cues to reset their own internal clocks. As daylight hours and temperature vary around the world, and with the seasons, plants and animals must be able to change how these external signals influence their internal clocks to enable them to stay in tune with the day/night cycle. However, it is not clear how they do this.

The researchers, from the Department of Biology at York working with colleagues from Max Planck Institute for Plant Breeding Research, explored this question by growing plants that were from a cross between two types of the model plant Arabidopsis thaliana from different environments -- one from Germany, and the other from Tajikistan in Central Asia.

These offspring were also genetically engineered so that an enzyme that could give off light was produced under the control of the internal clock. The scientists found that the plants continued to glow and fade with an almost daily rhythm even after external cues, such as changes in temperature or light, had been removed.

Various offspring plants glowed and faded with different rhythms with some having, for example, a 21-hour day and others a 28-hour day. These distinctions were caused by many genes that differed from the original German and Tajikistan parent plants, and the researchers "mapped" one of these genetic differences to a single gene.

Offspring that inherited a version of a gene called ELF3 from the Tajikistan parent had internal clocks that ran faster when the plant was under the light. These plants also gradually stopped glowing as brightly as the German parent when they were kept in the dark, suggesting that their internal clocks were "ticking more softly". It was already known that the ELF3 gene affected the circadian clock in plants, and the research team concluded that the plants with Tajikistan version of this gene -- ELF3-Sha -- were also less able to reset their internal clocks to synchronize in response to external cues.

The researchers also showed that the normal ELF3 protein is more likely to be found in the nucleus of a plant cell than the ELF3-Sha version, which might suggest that this protein is involved in switching genes off. Further research is now needed to uncover exactly how the ELF3 protein does this to keep the plant’s internal clock "ticking" correctly.

One of the research team, Professor Seth Davis, of the Department of Biology at York and formerly of the Max Planck Institute for Plant Breeding Research, said: “The challenge now is to convert this fundamental research to change clock genes in crop plants so they can better respond to different environmental influences and mitigate the forces of climate change.”