Part of the plant’s circadian clock acts like a stopwatch (Adapted from image by Sui-setz (CC BY-SA 3.0)

Fine-tuning the circadian clock

Scientists have pinpointed a single chemical bond that helps to keep a plant’s internal clocks in pace with the day-night cycle.

Many living organisms track the 24-hour cycle of day and night via collections of proteins and other molecules that together act like an internal clock. These clocks, also known as circadian clocks, help these organisms to predict regular changes in their environment, like light and temperature, and adjust their activities according to the time of day.

Plants use circadian clocks to predict, for example, when dawn will occur and get ready to harness sunlight to fuel their growth. A plant called Arabidopsis thaliana has a light-sensitive protein called ZEITLUPE (or ZTL for short) that helps it keep its circadian clock in sync with the cycle of night and day. Previous studies have shown that light activates this protein causing part of it to change shape and then revert back after a period of about an hour and a half. However, it was unclear if this timing was important for ZEITLUPE to allow plants to keep track of time.

To help answer this question, Ashutosh Pudasaini and colleagues set out to identify a specific chemical event behind ZEITLUPE’s changes in shape. A chemical bond forms when light activates ZEITLUPE, and it turns out that how long this bond lasts before it breaks plays an important role in allowing plants to maintain a 24-hour circadian clock. This chemical bond controls the shape changes that guide the protein’s activities and, when Pudasaini and colleagues modified ZEITLUPE so that it took much longer for this bond to break, they could tune how fast the plant’s internal clocks run. In essence, the time between the bond forming and breaking acts like a countdown on a stopwatch, and it must be precisely timed to keep the clock in pace with the environment.

These findings improve our understanding of how light can regulate an internal biological clock. This improved understanding could, in the future, allow researchers to manipulate how plants and other organisms respond to their environment. This in turn could change how these organisms develop, and how much they grow. As such, extending these findings into agricultural crops may one day lead to new ways to increase crop yields.

To find out more

Read the eLife research paper on which this eLife digest is based: “Kinetics of the LOV domain of ZEITLUPE determine its circadian function in Arabidopsis (February 28, 2017).
eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.
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