Grandfather time keeps plants ticking over

Scientists at Royal Holloway, University of London, have identified that plants use a mechanism similar to a grandfather clock to activate a gene that regulates when they flower. The study 'Coordinated transcriptional regulation underlying the circadian clock in Arabidopsis,' is published in the journal Nature Cell Biology.

Image shows a plant containing a bioluminescent 'reporter'

The scientists used a bioluminescent "reporter" to follow the activity of the Early Flowering gene (ELF4) in living plants so that when the gene is activated the plants would glow. The plants showed a beautiful daily rhythm of luminescence and the academics were then able to determine just how the cycle of ELF4 activity was regulated.

Dr Paul Devlin, from the School of Biological Sciences at Royal Holloway, explains: "In almost all organisms there exists a daily clock which regulates many metabolic, development and physiological processes which is known as the "circadian clock". Rather than just responding to dawn or dusk, the circadian clock is an internal rhythm which allows anticipation of these changes. Our own body's daily rhythms are one example but plants can also "tell the time". They can prepare their metabolism for photosynthesis before the sun rises or for the chill of night before the sun sets. Many plants also use their circadian clock to measure day length and so determine when to flower."

He adds: "For the first time we have identified the mechanism that the plant clock uses. In a grandfather clock, the mechanism is driven by some force, a weight or a spring, that moves the hands forward while a pendulum forms a timekeeping mechanism to regulate that movement. In plants we show that light provides that driving force. Light acts through a group of proteins including FHY3 which are normally degraded in the dark but which are stabilised by light and then directly bind to the ELF4 gene, activating it."

The "pendulum" is another of the genes in this clock loop, a negative-acting component called Circadian Clock Associated (CCA1). The CCA1 gene is activated during the night but activity declines again during the day. The product of this gene, the CCA1 protein, binds to FHY3 preventing its association with the ELF4 gene. Thus, the ELF4 gene is activated during the day and deactivated again during the night. We went on to confirm that this process can continue just a well in constant light as in day / night cycles, forming a genuinely internal timing mechanism.

Dr Devlin says: "We could, hopefully, really benefit from better understanding of the clock mechanism in terms of crop productivity. As an example of it's importance it was recently revealed that the clock also regulates how a plant invests its reserves. As a result, there's a strong link to crop productivity. For example, plants will ration investment of their stored reserves over each night so that they just run out exactly at dawn: the plant is never left with an uninvested surplus and, conversely, will never starve overnight."

Source: Royal Holloway, University of London