Cyanobacteria respond to cytokinin

We studied the effects of trans-zeatin (10−9–10−5 M) on the RNA synthesis in the in vitro transcriptional system containing DNA and RNA polymerase of a cyanobacterium Synechocystis sp. PCC 6803. The cytokinin enhanced transcription in this system, and its action depended on the concentration applied: trans-zeatin exerted its highest effects at the concentrations of 10−8–10−6 M. Adenine, which derivatives are trans-zeatin and other purine cytokinins, did exert such an effect. Its wide range of concentrations (10−7–10−4 M) did not affect 3H-UMP incorporation into RNA. This indicates a specificity of trans-zeatin action. Culturing of cyanobacteria for 3 days in the presence of synthetic cytokinin benzyladenine (10−6 M) also enhanced 3H-UMP incorporation into RNA. A cytokinin-binding protein isolated earlier from plant chloroplasts, which is involved in the cytokinin-dependent control of chloroplastic transcription, enhanced substantially the response of the cyanobacterial transcriptional system to cytokinin. The results obtained show that cyanobacteria, evolutionary ancestors of chloroplasts, own the system of cytokinin signal recognition, which might be transferred to the plant cell. This inspires further investigation of the systems of cytokinin signal perception and transduction in cyanobacteria and elucidation of common and different traits of these systems in plants and cyanobacteria.