Plants let chloroplasts know the time

March 14, 2013
Investigating the effect of different wavelengths of light. Image by Antony Dodd/University of Bristol

( —Plant cells communicate information about the time of day to their chloroplasts, the part of their cells that underpins all agricultural productivity on Earth, researchers at the University of Bristol have demonstrated in a study published today in Science.

Plant cells contain an internal clock (the ), which is able to regulate cellular processes so that they occur at the optimal time of day, causing a big increase in . As chloroplasts are the site of photosynthesis, their function is highly dependent on the daily changes in light environment.

It is thought that chloroplasts were originally free-living organisms that were incorporated into the cells of plants very early in plant evolutionary history. A result of this is that chloroplasts have retained some of the cellular machinery required to produce proteins from their own chloroplast DNA. An essential part of this machinery are 'sigma factors', and in present-day plants, they are encoded for by the cell's nuclear DNA.

The researchers were able to show that the production of sigma factors is controlled by the plant's clock. This enables the to regulate the activity of chloroplast genes, and ensure that the production of proteins essential for photosynthesis is co-ordinated with daylight.

Lead author, Dr Antony Dodd of Bristol's School of Biological Sciences said: "This is a major breakthrough that provides a completely new perspective on daily . We have learnt from this work that timing information moves between different parts of the cell, and in particular involves the chloroplast, which is the part of the cell that underpins all agricultural productivity on the planet. It's particularly fascinating that the process we identified makes use of genes that pre-date modern land plants and originates from the bacteria that gave rise to chloroplasts."

Explore further: New research alters concept of how circadian clock functions

More information: 'Circadian Control of Chloroplast Transcription by a Nuclear-Encoded Timing Signal' by Noordally, Z., Ishii, K., Atkins, K., Wetherill, S., Kusakina, J., Walton, E., Kato, M., Azuma, M., Tanaka, K., Hanaoka, M., and Dodd, AN. in Science:

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1 / 5 (1) Mar 16, 2013
The question for astrobiology is whether this circadian mechanism is necessary for life and if so can it be transmuted to other perhaps habitable exoplanets. The recent discovery of deeply buried hydrogen life forms under the oceanic crust would exhibit an alternative biological timing mechanism.
not rated yet Mar 16, 2013
As long as the timing is mutable. it should be OK. And remember, due to our Moon we have had a more varying daily rhythm than most planets, from an initial ~ 8 hours to today's 24 h. Though plants would have only seen the last 20 % change or so.

Modern organisms and cells have a lot of "necessary" mechanisms, by necessity of contingency creating so called "interlocking complexity" (Muller, 1930ish). Say, the nerve that loops down to the hearth before ending up controlling parts of our throat.

Some circadian clock mechanisms have deep ancestry, billions of years. Plenty of times for interlocking systems to form.

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