Synchronization of the circadian clock in cyanobacteria with the day/night cycle proceeds without an obvious photoreceptor, leaving open the question of its specific mechanism. The circadian oscillator can be reconstituted in vitro,where the activities of two of its proteins, KaiA and KaiC, are affected by metabolites that reflect photosynthetic activity: KaiC phosphorylation is directly influenced by the ATP/ADP ratio, and KaiA stimulation of KaiC phosphorylation is blocked by oxidized, but not reduced, quinones. Manipulation of the ATP/ADP ratio can reset the timing of KaiC phosphorylation peaks in the reconstituted in vitro oscillator. Here, we show that pulses of oxidized quinones reset the cyanobacterial circadian clock both in vitro and in vivo. Onset of darkness causes an abrupt oxidation of the plastoquinone pool in vivo, which is in contrast to a gradual decrease in the ATP/ADP ratio that falls over the course of hours until the onset of light. Thus, these twometabolicmeasures of photosynthetic activity act in concert to signal both the onset and duration of darkness to the cyanobacterial clock.
Publication Source (Journal or Book title)
Proceedings of the National Academy of Sciences of the United States of America
Kim, Y., Vinyard, D., Ananyev, G., Dismukes, G., & Golden, S. (2012). Oxidized quinones signal onset of darkness directly to the cyanobacterial circadian oscillator. Proceedings of the National Academy of Sciences of the United States of America, 109 (44), 17765-17769. https://doi.org/10.1073/pnas.1216401109