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Scientists Discover How Phytochromes Signal Light Sources to Bacteria and Plants

Joanna Lawrence
15th August, 2016

Scientists have now observed how phytochromes, light-sensitive proteins, operate on a molecular scale. A team of researchers used x-ray scattering to study structural changes in activated phytochromes, providing new insight into how photosynthetic organisms detect light. The findings are in a paper just published in the journal Science Advances. Phytochromes are pigment proteins that detect and respond to light sources. They are generally found in photosynthetic organisms, such as plants, fungi, and certain bacteria. Phytochromes also help maintain circadian rhythms and other time-based events. For example, many plants rely on phytochromes to signal ideal flowering times. Phytochromes have been studied in the laboratory but there was no viable way to examine the entire intact protein. Researchers from the University of Gothenburg collaborated with a team from the University of Jyväskylä. They studied a full-length phytochrome from a bacteria species called Deinococcus radiodurans. The research team used time-resolved x-ray scattering to observe the phytochrome in action. The researchers found that the phytochrome underwent minor structural changes when exposed to light. Parts of the protein were refolded and this change set off a cascade of signals to the organism. All of this took place in one motion and the entire process took mere milliseconds. These simple changes are enough to tell the bacteria how much light there is and where it’s located. Bacteria use these signals to move to places where they’ll have a better chance of survival. The findings will help researchers understand how phytochromes send signals to plants and other organisms. Previously, scientists were unable to study a full-length phytochrome on the molecular scale. Thanks to x-ray scattering, we now know how these pigment proteins work. One possible application of this knowledge would be the development of artificial proteins for medical purposes. The proteins could be modified to target specific areas in the body, based on the mechanisms found in phytochromes. REFERENCE Bjo rling et al. Structural photoactivation of a full-length bacterial phytochrome. Science Advances (2016).