Chlamydomonas reinhardtii

Taxonomic lineage

cellular organisms - Eukaryota - Viridiplantae - Chlorophyta - Chlorophyceae - Chlamydomonadales - Chlamydomonadaceae - Chlamydomonas - Chlamydomonas reinhardtii

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Brief facts

• Chlamydomonas is haploid and has a controlled sexual cycle with the possibility of tetrad analysis.
• Its photosynthetic apparatus is closely related to that of vascular plants, and it is also a eukaryote, with photosynthesis genes encoded by both the nuclear and chloroplast genomes.
• Like a plant cell, the cell of Chlamydomonas has a cell wall.
• Chlamydomonas ability to grow heterotrophically allows the isolation of viable mutants that are unable to perform photosynthesis.
• Like animal sperm cells, Chlamydomonas has a flagellum, which enables it to carry out phototaxis, moving towards or away from light to maximize light perception for photosynthesis and minimizing photodamage.
• Chlamydomonas can adopt an anaerobic metabolism, producing hydrogen gas and metabolites such as formate and ethanol.
• Chlamydomonas is the only known eukaryote in which the nuclear, chloroplast and mitochondrial genomes can all be transformed.
• Thus, in some aspects, Chlamydomonas most closely models plant cells and in others, animal cells which makes it a powerful and versatile system for the study of a variety of molecular and cellular processes.

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Life cycle

Generation time takes approximately 5 hours.

• Vegetative cell Haploid cells reproduce asexually by fission: the protoplast dividing to form 4-8 zoospores similar to the parent.
• Gametogenesis
  MeSH Under conditions of nitrogen starvation vegetative cells develop into gametes of two mating types: mt+ and mt-.
• Adhesion Gametes of opposite mating types are attracted to each other and form aggregates.
• Gamete activation Release of cell walls; formation of mating structures.
• Fusion Fusion of mt+ fertilization tubule with mt- mating structure.
• Zygote MeSH Complete cell fusion; zygote is not flagellated and serves as a dormant form of the species in the soil.
• Meiosis MeSH Zygote undergoes meiosis to form 4 haploid zoospores.

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Mating type

Mating can take place only between individuals of opposite mating types due to the interaction of cell surface components. The equivalent in lower organisms of the sexes in higher organisms; the mating types typically differ only physiologically and not in physical form.

• mt+ Activation of cells of mating type mt+ results in production of a long membrane-enclosed fetilization tubule covered with a glycoprotein, and containing polymerized actin filaments.
• mt- Cells of mating type mt- move membrane proteins to the specific region of the plasma membrane and produce a short-lived tubule with no microfilaments.

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Strains

• 137C wild type; ancestral to many mutants; mt+; originates from an isolate made near Amherst, Massachusetts, in 1945
• C9 mt-
• CC-125 wild type; mt+
• CC-1690 wild type; mt+
• CC-1691 mt-
• CC-2290 also called S1D2; mt-

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References

• Boyle NR, Morgan JA. Flux balance analysis of primary metabolism in Chlamydomonas reinhardtii. BMC Syst Biol. 2009 Jan 7;3:4.

  

  Distribution of enzymes and metabolites. Distribution of enzymes and metabolites in the reconstructed model of Chlamydomonas reinhardtii. Almost half of both the enzymes and metabolites are localized to the chloroplast, followed by the cytosol and mitochondria. There are also a large number of transport reactions, indicating the importance of metabolite exchange between compartments.

  

  Reconstructed metabolic network of C. reinhardtii. Based on predicted target peptide sequences, the following localization of pathways was determined. Chloroplast: fatty acid synthesis, amino acid synthesis, nucleotide synthesis, starch synthesis and chlorophyll synthesis. Mitochondria: TCA cycle, amino acid synthesis. Cytosol: glycolysis, amino acid synthesis and fatty acid synthesis.

  

  Autotrophic central metabolism flux map. The thickness of the arrows has been normalized to the total carbon dioxide uptake of 100 moles. The green compartment represents the chloroplast and the orange compartment is the mitochondria.

  

  Heterotrophic central metabolism flux map. The thickness of the arrows has been normalized to the total acetate uptake of 100 moles. The green compartment represents the chloroplast and the orange compartment is the mitochondria.

• Feldman JL, Geimer S, Marshall WF. The mother centriole plays an instructive role in defining cell geometry. PLoS Biol. 2007 Jun;5(6):e149.

  

  Chlamydomonas cell geometry. Flagella (f) extend from the centrioles (white), which are located apically and are attached to the nucleus (yellow) by centrin-containing fibers. The pyrenoid (p; blue), a starch-containing structure, is located basally and is embedded in a cup-like mass of chloroplast (green). The eyespot (e; red), the light-sensing organelle, is located laterally at a reproducible angle relative to the centrioles.

• Manuell AL, Mayfield SP. A bright future for Chlamydomonas. Genome Biol. 2006;7(9):327.

  

  Hydrogen production in the C. reinhardtii chloroplast. Normally, the protein ferredoxin (FD) transfers electrons to an enzyme that reduces NADP+ to NADPH, which is required for chloroplast metabolic processes. Reduced ferredoxin (FD(red)) can instead transfer electrons to a chloroplast hydrogenase, which produces molecular hydrogen (H2) from protons (H+). Hydrogen production thus acts as an alternate electron sink. Reduced ferredoxin can also be produced via glycolysis from the breakdown of starch, which enables hydrogen production in the absence of photosynthesis. FNR, ferredoxin NADP+ oxidoreductase; PFOR, pyruvate ferredoxin oxidoreductase. Figure courtesy of and adapted from M. Posewitz.

• Grossman AR et al. Chlamydomonas reinhardtii at the crossroads of genomics. Eukaryot Cell. 2003 Dec;2(6):1137-50.
• Stauber EJ, Hipper M. Chlamydomonas reinhardtii proteomics. Plant Physiol Biochem. 2004 Dec;42(12):989-1001. Epub 2005 Jan 18.
• PubMed free full-text articles: major topic "Chlamydomonas"

Websites

• Chlamydomonas Center

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