Hormogonium

About: Hormogonium is a research topic. Over the lifetime, 128 publications have been published within this topic receiving 6660 citations.

The Molecular Biology of Cyanobacteria

Abstract: Preface. Color Plates. 1. Molecular Evolution and Taxonomy of the Cyanobacteria A. Wilmotte. 2. The Oceanic Cyanobacterial Picoplankton N.G. Carr, N.H. Mann. 3. Prochlorophytes: the 'Other' Cyanobacteria? H.C.P. Matthijs, et al. 4. Molecular Biology of Cyanelles W. Loffelhardt, H.J. Bohnert. 5. Chloroplast Origins and Evolution S.E. Douglas. 6. Supramolecular Membrane Organization E. Gantt. 7. Phycobilisome and Phycobiliprotein Structures W.A. Sidler. 8. The Use of Cyanobacteria in the Study of the Structure and Function of Photosystem II B.A. Barry, et al. 9. The Cytochrome b6f Complex T. Kallas. 10. Photosystem I in Cyanobacteria J.H. Golbeck. 11. The F-type ATPase in Cyanobacteria: Pivotal Point in the Evolution of the Universal Enzyme W.D. Frasch. 12. Soluble Electron Transfer Catalysts of Cyanobacteria L.Z. Morand, et al. 13. Cyanobacterial Respiration G. Schmetterer. 14. The Biochemistry and Molecular Regulation of Carbon Dioxide Metabolism in Cyanobacteria F.R. Tabita. 15. Physiological and Molecular Studies on the Response of Cyanobacteria to Changes in the Ambient Inorganic Carbon Concentration A. Kaplan, et al. 16. Assimilatory Nitrogen Metabolism and its Regulation E. Flores, A. Herrero. 17. Biosynthesis of Cyanobacterial Tetrapyrrole Pigments: Hemes, Chlorophylls, and Phycobilins S.I. Beale. 18. Carotenoids in Cyanobacteria J. Hirschberg, D. Chamovitz. 18. Genetic Analysis of Cyanobacteria T. Thiel. 20. The Transcription Apparatus and the Regulation of Transcription Initiation S.E. Curtis, J.A. Martin. 21. The Responses of Cyanobacteria to Environmental Conditions: Light and Nutrients A.R. Grossman, et al. 22. Short-Term and Long-Term Adaptation of the Photosynthetic Apparatus: Homeostatic Properties of Thylakoids Y. Fujita, et al. 23. Light-Responsive Gene Expression and the Biochemistry of the Photosystem II Reaction Center S.S. Golden. 24. Thioredoxins in Cyanobacteria: Structure and Redox Regulation of Enzyme Activity F.K. Gleason. 25. Iron Deprivation: Physiology and Gene Regulation N.A. Straus. 26. The Cyanobacterial Heat-Shock Response and the Molecular Chaperones R. Webb, L.A. Sherman. 27. Heterocyst Metabolism and Development C.P. Wolk, et al. 28. Differentiation of Hormogonia and Relationships with Other Biological Processes N. Tandeau de Marsac. Organism Index. Gene and Gene Product Index. Subject Index.

Heterocyst Metabolism and Development

Abstract: Heterocysts are differentiated cells that are specialized for fixation of N2 in an aerobic environment. In heterocysts in the light, Photosystem I generates ATP, but no photosynthetic production of O2 takes place. Instead, reductant moves into heterocysts from vegetative cells. In return, fixed nitrogen moves from heterocysts to vegetative cells. In neither case is there certainty about the identity of the traffic molecules. Pathways of electron-donation to N2 have been extensively investigated, but their in-vivo importance remains to be critically tested. Nitrogenase in heterocysts is protected from inactivation by O2 by a variety of means, principally by enhanced respiration and by a barrier, the heterocyst envelope, to entry of O2. However, the respiratory apparatus and the biosynthetic processes that result in synthesis of the barrier have been little studied. The detailed mechanisms underlying metabolic, environmental, and developmental control of nitrogenase are under investigation. Studies of heterocyst development are being greatly facilitated by recent advances in the genetics of Anabaena sp. An autoregulated gene, hetR, that is activated shortly after nitrogen-stepdown is critical for the differentiation of heterocysts. Two enigmas remain to be answered: how is it determined which cells will differentiate; and, after differentiation is initiated, what intercellular interactions and intracellular mechanisms regulate the progression of the differentiation process? An evolutionary and biochemical relationship between the processes leading to the formation of heterocysts and akinetes is suggested.

Regulation of Cellular Differentiation in Filamentous Cyanobacteria in Free-Living and Plant-Associated Symbiotic Growth States

Abstract: Summary: Certain filamentous nitrogen-fixing cyanobacteria generate signals that direct their own multicellular development. They also respond to signals from plants that initiate or modulate differentiation, leading to the establishment of a symbiotic association. An objective of this review is to describe the mechanisms by which free-living cyanobacteria regulate their development and then to consider how plants may exploit cyanobacterial physiology to achieve stable symbioses. Cyanobacteria that are capable of forming plant symbioses can differentiate into motile filaments called hormogonia and into specialized nitrogen-fixing cells called heterocysts. Plant signals exert both positive and negative regulatory control on hormogonium differentiation. Heterocyst differentiation is a highly regulated process, resulting in a regularly spaced pattern of heterocysts in the filament. The evidence is most consistent with the pattern arising in two stages. First, nitrogen limitation triggers a nonrandomly spaced cluster of cells (perhaps at a critical stage of their cell cycle) to initiate differentiation. Interactions between an inhibitory peptide exported by the differentiating cells and an activator protein within them causes one cell within each cluster to fully differentiate, yielding a single mature heterocyst. In symbiosis with plants, heterocyst frequencies are increased 3- to 10-fold because, we propose, either differentation is initiated at an increased number of sites or resolution of differentiating clusters is incomplete. The physiology of symbiotically associated cyanobacteria raises the prospect that heterocyst differentiation proceeds independently of the nitrogen status of a cell and depends instead on signals produced by the plant partner.

An overview of the genome of Nostoc punctiforme, a multicellular, symbiotic cyanobacterium.

Abstract: Nostoc punctiforme is a filamentous cyanobacterium with extensive phenotypic characteristics and a relatively large genome, approaching 10 Mb. The phenotypic characteristics include a photoautotrophic, diazotrophic mode of growth, but N. punctiforme is also facultatively heterotrophic; its vegetative cells have multiple developmental alternatives, including terminal differentiation into nitrogen-fixing heterocysts and transient differentiation into spore-like akinetes or motile filaments called hormogonia; and N. punctiforme has broad symbiotic competence with fungi and terrestrial plants, including bryophytes, gymnosperms and an angiosperm. The shotgun-sequencing phase of the N. punctiforme strain ATCC 29133 genome has been completed by the Joint Genome Institute. Annotation of an 8.9 Mb database yielded 7432 open reading frames, 45% of which encode proteins with known or probable known function and 29% of which are unique to N. punctiforme. Comparative analysis of the sequence indicates a genome that is highly plastic and in a state of flux, with numerous insertion sequences and multilocus repeats, as well as genes encoding transposases and DNA modification enzymes. The sequence also reveals the presence of genes encoding putative proteins that collectively define almost all characteristics of cyanobacteria as a group. N. punctiforme has an extensive potential to sense and respond to environmental signals as reflected by the presence of more than 400 genes encoding sensor protein kinases, response regulators and other transcriptional factors. The signal transduction systems and any of the large number of unique genes may play essential roles in the cell differentiation and symbiotic interaction properties of N. punctiforme.

Tansley Review No. 107. Heterocyst and akinete differentiation in cyanobacteria

Abstract: Summary 3 I. introduction 4 II. the cyanobacteria 7 III. the heterocyst 9 1. Function and metabolism 9 2. Heterocyst structure 12 (a) Overview 12 (b) The polysaccharide (homogeneous) layer 12 (c) The glycolipid (laminated) layer 12 (d) The septum and microplasmodesmata 12 3. Nitrogen regulation and heterocyst development 12 4. Heterocyst development 13 (a) The proheterocyst 13 (b) Proteolysis associated with heterocyst development 14 (c) RNA polymerase sigma factors 14 (d) Developmental regulation of heterocyst cell wall and nitrogenase gene expression 14 (e) Genome rearrangements associated with heterocyst development 15 5. Genes essential for heterocyst development 15 (a) hetR 15 (b) Protein phosphorylation and the regulation of hetR activity 16 (c) hetR in nonheterocystous cyanobacteria 16 (d) Other heterocyst-specific genes 16 6. Heterocyst spacing 18 (a) Patterns of heterocyst differentiation 18 (b) Genes involved in heterocyst spacing 18 (c) Disruption of heterocyst pattern 18 7. Filament fragmentation and the regression of developing heterocysts 20 8. The nature of the heterocyst inhibitor 20 9. Cell selection during differentiation and pattern formation 20 (a) Cell division 20 (b) DNA replication and the cell cycle 21 (c) Competition 21 10. Models for heterocyst differentiation and pattern control 21 IV. the akinete 23 1. Properties of akinetes 23 2. Structure, composition and metabolism 24 3. Relationship to heterocysts 24 4. Factors that influence akinete differentiation 24 5. Extracellular signals 25 6. Akinete germination 25 7. Genes involved in akinete differentiation 26 V. conclusion 26 Acknowledgements 27 References 28 Cyanobacteria are an ancient and morphologically diverse group of photosynthetic prokaryotes. They were the first organisms to evolve oxygenic photosynthesis, and so changed the Earth's atmosphere from anoxic to oxic. As a consequence, many nitrogen-fixing bacteria became confined to suitable anoxic environmental niches, because the enzyme nitrogenase is highly sensitive to oxygen. However, in the cyanobacteria a number of strategies evolved that protected nitrogenase from oxygen, including a temporal separation of oxygenic photosynthesis and nitrogen fixation and, in some filamentous strains, the differentiation of a specialized cell, the heterocyst, which provided a suitable microaerobic environment for the functioning of nitrogenase. The evolution of a spore-like cell, the akinete, almost certainly preceded that of the heterocyst and, indeed, the akinete may have been the ancestor of the heterocyst. Cyanobacteria have the capacity to differentiate several additional cell and filament types, but this review will concentrate on the heterocyst and the akinete, emphasizing the differentiation and spacing of these specialized cells.