The circadian clock gear in cyanobacteria: Assembled by evolution

Abstract

The circadian system of cyanobacteria has a long and complex evolutionary history. Some of its genetic elements are probably as old as cyanobacteria themselves. Currently available data from evolutionary studies suggest that, in the course of evolution, the whole system as well as its elements experienced a number of major structural modifications, which resulted in diversification of the circadian system. There are probably at least three main types of the cir-cadian system in cyanobacteria, which differ by their set of elements. Whether these differences result in any functional modifications or malfunction is yet to be determined. Some evidence exists that major steps in macroevolution of the cyanobacterial circadian system were adaptive and associated with large-scale changes in global environment. Further studies will help to fully reconstruct a scenario by which the circadian system of cyanobacteria evolved into a finely tuned regulatory mechanism.