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Abstract
Cyanobacterial circadian clock composed of the Kai oscillator has been unraveled in the model strain Synechococcus elongatus PCC 7942. Recent studies with nitrogen-fixing Cyanothece sp. ATCC 51142 show rhythmic oscillations in the cellular program even in continuous light albeit with a cycle time of ~11 h. In the present study, we investigate correlation between cellular rhythms, KaiC1 phosphorylation cycle, ATP/ADP ratio, and the redox state of plastoquinone pool in Cyanothece. KaiC1 phosphorylation cycle of Cyanothece was similar to that of Synechococcus under diurnal cycles. However, under continuous light, the cycle time was shorter (11 h), in agreement with physiological and gene expression studies. Interestingly, the ATP/ADP ratio also oscillates with an 11 h period, peaking concomitantly with the respiratory burst. We propose a mathematical model with C/N ratio as a probable signal regulating the clock in continuous light and emphasize the existence of a single timing mechanism regardless of the cycle time.
Acknowledgements
This work was partially supported by grant from Department of Biotechnology, Ministry of Science and Technology, Government of India (grant number BT/EB/PAN IIT/2012) awarded to P.P.W. Authors acknowledge Prof Louis A. Sherman, Purdue University for providing anti-NifH antibody.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Department of Biotechnology, Ministry of Science and Technology, Government of India [grant number BT/Indo-Aus/04/04/2009].