AsianScientist (Nov. 2, 2016) – Researchers in Japan, China and the US have uncovered the mechanisms through which cryptochrome 2—a key photoreceptor that allows plants to respond to blue light—is switched on and off, allowing plants to remain responsive to light. The research was published in Science.
Though it was long known that blue light played a key role in activating plants’ response in the natural light environment, through the action of cryptochromes and other photoreceptors, the mechanism through which the response was turned on and off remained elusive. In recent years, it was hypothesized that the receptors were activated and inactivated through a process of photoreduction, a system like that used in the process of photosynthesis where electrons are transferred, moving energy across molecules.
To determine whether this was the real mechanism, the group began by screening transgenic lines of Arabidopsis, a model grass used in plant genetics, using the FOX library developed by Drs. Takanari Ichikawa and Minami Matsui of the former RIKEN Plant Science Center, to find lines that expressed phenotypes similar to a mutant strain that does not respond properly to blue light. They identified lines that overexpress a protein, named BIC1, which corresponded to the mutant phenotype and showed that it blocks the action of the cryptochrome 2 photoreceptor.
Through a series of experiments, they were able to show that BIC1’s activity was not a process of photoreduction. It turns out that cryptochrome 2 undergoes a conformational change—taking a dimer form—when exposed to blue light, and that this homodimer form is the active form. The dimer form, however, disappeared in the presence of the BIC1 protein.
“We have shown that there is a desensitization mechanism, where the photoactivated photoreceptor is regulated in blue light to avoid excess response. This is important as it allows plants to maintain the homeostasis of their blue light responsiveness in order to adapt to the fluctuating light environment in nature,” said Matsui, one of the leaders of the study.
The article can be found at: Wang et al. (2016) Photoactivation and Inactivation Mechanisms of Arabidopsis Cryptochrome 2.
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Source: RIKEN; Photo: Pixabay.
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