title: The stringent response regulates adaptation to darkness in the cyanobacterium Synechococcus elongatus.
abstract: The cyanobacterium Synechococcus elongatus relies upon photosynthesis to drive metabolism and growth. During darkness, Synechococcus stops growing, derives energy from its glycogen stores, and greatly decreases rates of macromolecular synthesis via unknown mechanisms. Here, we show that the stringent response, a stress response pathway whose genes are conserved across bacteria and plant plastids, contributes to this dark adaptation. Levels of the stringent response alarmone guanosine 3'-diphosphate 5'-diphosphate (ppGpp) rise after a shift from light to dark, indicating that darkness triggers the same response in cyanobacteria as starvation in heterotrophic bacteria. High levels of ppGpp are sufficient to stop growth and dramatically alter many aspects of cellular physiology, including levels of photosynthetic pigments and polyphosphate, DNA content, and the rate of translation. Cells unable to synthesize ppGpp display pronounced growth defects after exposure to darkness. The stringent response regulates expression of a number of genes in Synechococcus, including ribosomal hibernation promoting factor (hpf), which causes ribosomes to dimerize in the dark and may contribute to decreased translation. Although the metabolism of Synechococcus differentiates it from other model bacterial systems, the logic of the stringent response remains remarkably conserved, while at the same time having adapted to the unique stresses of the photosynthetic lifestyle.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720;
authors.forename: Rachel D
authors.initials: RD
authors.lastname: Hood
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720;
authors.forename: Sean A
authors.initials: SA
authors.lastname: Higgins
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720;
authors.forename: Avi
authors.initials: A
authors.lastname: Flamholz
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720;
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Nichols
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720; Department of Chemistry, University of California, Berkeley, CA 94720; Energy Biosciences Institute, University of California, Berkeley, CA 94720 savage@berkeley.edu.
authors.forename: David F
authors.identifier: 0000-0003-0042-2257
authors.initials: DF
authors.lastname: Savage
mesh_terms: D000064:Acclimatization; D000222:Adaptation, Physiological; D004261:DNA Replication; D003624:Darkness; D015964:Gene Expression Regulation, Bacterial; D006159:Guanosine Tetraphosphate / Q000032:analysis / Q000502:physiology; D010788:Photosynthesis; D046940:Synechococcus / Q000502:physiology*
chemical_list: D006159:Guanosine Tetraphosphate
keywords: (p)ppGpp; Synechococcus; cyanobacteria; hibernation promoting factor; stringent response