New Study Explains How Plants “See” Blue Light

Plants have been known to perceive and respond to light in a wide range of the electromagnetic spectrum. Now, a new study specifically notes how plants react to blue light.

The latest study comes from Professor Nitzan Shabek's laboratory, within the Department of Plant Biology, College of Biological Sciences, at the University of California Davis. Prof. Shabek himself noted that "Plants can see much better than we can."

Shabek's team reports the crystal structure found in a part of the blue-light receptor, cryptochrome-2, in the model plant Arabidopsis thaliana. Results of their work are submitted to the journal Nature Communications Biology, January 4.

Plants Seeing Colors

Plants, unlike animals, have no dedicated organs or structures for "seeing" light. What they have, however, are different receptors sensitive to different wavelengths. Among these plant receptors are cryptochromes, photoreceptors that respond particularly to blue light when cryptochromes detect a photon's presence - a minute "packet" of light - and trigger a particular physiological response in the plant.

Cryptochromes are also known, through their color-detecting capabilities, to help regulate the plants' circadian rhythm. They were believed to have appeared billions of years ago together with the first living bacteria. These structures have become largely similar across bacteria, plants, and animals. It is even present within human eyes, mostly performing the same function for color detection and circadian rhythm moderation. However, its structural changes in response to light and its photochemistry remain to be fully explored.

Also known as CRYs, the photocycle for these molecules have been known to involve the reduction of a substance known for its flavine adenine dinucleotide (FAD) - bound chromophore. This material totally oxidizes in the dark.

In the work from Shabek's laboratory, they discovered that the light-detecting part of the cryptochrome molecule actually changes its structure in reaction to contact with photons. Starting from a single-unit structure, it then changes into a tetramer - a structure of four interlinked units.

A Trigger for Gene Activation

"This rearrangement process, called photo-induced oligomerization, is also very intriguing because certain elements within the protein undergo changes when exposed to blue light," explains Shabek in a press release from UC Davis. "Our molecular structure suggests that these light-induced changes release transcriptional regulators that control the expression of specific genes in plants."

With aid from the Advanced Light Source X-Ray facility located at the Lawrence Berkeley National Laboratory, researchers were able to better observe and analyze the structure of cryptochrome-2.

Shabek also added that the recently published study is a part of the laboratory's long-term goals of understanding the plant mechanisms in plants. Their previous works focus on hormone perceptions and light signaling pathways in these organisms.

The UC Davis laboratory first identified the crystal structure of the blue light receptor cryptochrome two years ago, through a combination of biochemical and crystallographic techniques. However, with the recent advancements in structural biology and plant science, their team could update the model and offer a clearer illustration of this light-detecting mechanism.