Circadian clock does not allow plants to grow until before dawn

24/01/2018

American researchers Jeffrey C. Hall, Michael Rosbash and Michael W. Young were awarded the 2017 Nobel Prize in Medicine. The Nobel Assembly at the Karolinska Institute in Stockholm, Sweden, said it recognized them for their "discoveries of the molecular mechanisms that control the circadian rhythm", that is, our biological clock.

Thanks to the discoveries that these scientists made using Drosophila, family of the fruit fly, today we know that organisms have an internal clock built from a set of cellular proteins whose quantity oscillates in periods of 24 hours. These oscillations, which are maintained autonomously, explain how living organisms adapt their biological rhythm to synchronize it with the revolutions of the Earth.

The term circadian comes from the Latin words "circa" (around) and "die" (day). As an example, this biological clock is responsible for making us sleepy at night and influences our mood, alertness and even our risk of suffering cardiac arrest.

Rosbash and Hall began collaborating at Brandeis University, in Boston, more than 30 years ago to study the circadian rhythm of Drosophila. Both were the first to clone the circadian rhythm gene of this fly in 1984.

The plants

On the other hand, Spanish scientists have identified certain components of the circadian clock that limit the growth of plants until the end of the night.

Plants, like animals, also have an internal clock. In fact, the first hypotheses about the existence of a circadian clock in living organisms arose with the observation of the movements of leaves and flowers in plants.

The plant lengthens the stem just before dawn, when the days are short (winter) and studies of recent years have shown that stem elongation in young seedlings is controlled by PIF proteins, whose cellular accumulation depends on sunlight . Therefore, light promotes the degradation of PIF proteins during the day, while at night, PIF proteins accumulate inside the cell and, just before dawn, promote the growth of the stem of the plant.

Why does it grow only before dawn?

The answer to this question was obtained thanks to a work published in 2016, by a group led by the researcher of the Superior Council of Scientific Research (CSIC), in the Center for Research in Agricultural Genomics (CRAG), Elena Monte, who discovered that an internal clock protein (TOC1 or PRR1) acts as a gate during the night, allowing PIF to act only at the end of the night.

Like the watch proteins described by the Nobel Prize winners, the amount of the different PRR proteins (PRR1, PRR5, PRR7 and PRR9) oscillates sequentially in periods of 24 hours. At the end of the night, the total amount of PRR proteins in the cell reaches its minimum, which allows the action of the PIF proteins, which, due to the absence of light, are at their peak maximum concentration. Therefore, although some PIF proteins are detected during the day, they can not promote the extension of the stem until the end of the night, when the door is opened, coinciding with the optimum conditions of humidity for growth.

'Our results show that plant growth regulation has evolved in plants to encompass the orchestrated sequential action of PRRs. This demonstrates the dual role of PRRs: as regulators of the components of the central clock and as physiological repressors of growth," explains Elena Monte.

"Since these three laureates made these transcendental discoveries, circadian biology has become a broad and very dynamic field of research, with repercussions on our health and well-being," said the representative of the Nobel Assembly when presenting the USD 1,1 prize. .XNUMX million to scientists.

Text with information from Current Biology

Source: Martín Carrillo O. - Blueberries Consulting