Mechanism and function of non standard circadian clock systems in cyanobacteria

• Applicants: Professorin Dr. Ilka Maria Axmann; Professorin Dr. Annegret Wilde
• Subject Area: Plant Physiology ; Plant Biochemistry and Biophysics
• Term: from 2010 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 173875897

The Earth rotates around its own axis once in 24 hours thereby determining the day-night cycle. Nearly all eukaryotic organisms are able to anticipate this rhythm to prepare themselves for the transitionbetween light and darkness. We have a feeling of this inner clock when we are traveling long distances and suffer from jetlag. Our clock maintains the old time for a while before adapting to the time shift. This already depicts two important characteristics of a circadian clock: it has a free running period, which is independent of environmental cues but can be entrained again. In addition, the 24-hours cycle is temperature compensated. According to this definition cyanobacteria are the only prokaryotes having a true circadian clock. There are no evolutionary connections between the mechanisms of cyanobacterial and eukaryotic clock systems. In cyanobacteria the central oscillator consists of only three proteins (KaiA, KaiB, KaiC), which can be entrained by the environment and transfers the information about time to a cell response using different signalling components. The mechanism of the prokaryotic clock is well understood and many components of the downstream signal transduction chains are known. But nearly all research has been performed using the cyanobacterium Synechococcus 7942 which exhibits a very robust and sustained circadian rhythm. There is increasing evidence that the well established model is not simply transferable to many widely distributed, ecological and biotechnological relevant cyanobacterial species. In this project, we are mainly investigating the timing system of Synechocystis 6803, a model organism for basic and applied science. The genome of this cyanobacterium encodes three KaiC protein variants having different biochemical properties. Two of the KaiC variants show sequence similarities to proteins present in several non-photosynthetic bacteria and Archaea. Using a combination of bioinformatics, biochemical and genetic approaches we answered several questions about the distribution and function of different Kai proteins in the previous funding period. We have analysed diurnal and circadian gene expression in Synechocystis 6803 in detail and compared this to the function of the oscillator. For the next funding period, we particularly plan to further analyse the function of the clock in Synechocystis 6803 focussing on the non-standard Kai proteins and on signal transduction of time information to specific regulators of cell responses. Investigations on the interactions between potential oscillator components and on the characteristics of various KaiC-protein variants of cyanobacteria and other prokaryotes will be another focus.

• DFG Programme: Research Grants
• International Connection: Netherlands
• Co-Investigator: Professor Dr. Markus Kollmann
• Cooperation Partner: Professor Dr. Albert J. R. Heck