Robust, coherent and synchronized circadian clock-controlled oscillations along anabaena filaments

Circadian clocks display remarkable reliability despite significant stochasticity in biomolecular reac-tions. We study the dynamics of a circadian clock-controlled geneattheindividualcelllevelinAnabaena sp. PCC 7120, a multicellular filamentous cyanobacterium. Wefoundsignificantsynchronizationandspa-tial coherence along filaments, clock coupling due to cell-cell communication, and gating of the cell cycle. Furthermore, we observed low-amplitude circadian oscillatory transcription of kai genes comprising the post-transcriptional core oscillatory circuit, and high-amplitude oscillations of rpaA coding for the master regulator transducing the core clock output. Transcriptional oscillations of rpaA suggest an additional level of regulation. A stochastic, one-dimensional toy model of coupled clock cores and their phosphorylation states shows that demographic noise can seed stochastic oscillations outside the region where deterministic limit cycles with circadian periods occur. The model reproduces the observed spatio-temporal coherence along filaments, and provides a robust description of coupled circadianclocksinamulticellularorganism. NTRODUCTION.