Chaetosphaeridium globosum

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Chaetosphaeridium globosum is a one-celled algae which is thought to represent an ancient lineage of the green plants. This organism exists in a filamentous form with one flagella per cell. It is a freshwater species. The flagellum is covered in scales in a 3-prong irregular shape called ‘maple leafs’.

Researchers have found that the mitochondrial DNA of Chaetosphaeridium is markedly different than that of land plants, indicating that land plants developed mitochondria separately from their protist progenitors. A very slight similarity exists between liverwort mtDNA and Chaetosphaeridium. The chloroplast DNA is markedly similar, however, indicating that a close relationship had existed between the Viridiplantae and the clade that includes Chaetosphaeridium. This seems to argue that chloroplasts in green plants originated in prehistoric green algae; the family which includes Chaetosphaeridium globosum.

Chloroplasts are known to be captured (symbiotic) cyanobacteria with their own genetic code. This code is both transferred to the nucleus and retained in the chloroplast for the continuation of metabolic processes. This symbiosis, now proven by modern genomics, has shown us how Chaetosphaeridium globosum links ancient cyanobacteria with modern green plants like those in our garden.

References

• Hausmann, Klaus. Hülsmann, Norbert. Radek, Renate. Protistology. E.Schweizerbart’sche Verlagsbuchhandlung. Third edition. 2003
• Turmel, Monique. Otis, Christian. Lemieux, Claude. The Chloroplast and Mitochondrial Genome Sequences of the Charophyte Chaetosphaeridium globosum: Insights into the Timing of the Events That Restructured Organelle DNAs Within the Green Algal Lineage That Led to Land Plants. PNAS. August 20, 2002. Vol. 99 No. 17. 11275-11280.
• Turmel, M. Otis, C. Lemieux, C. The Complete Chloroplast DNA Sequences of the Charophycean Green Algae Staurastrum and Zygnema Reveal that the Chloroplast Genome Underwent Extensive Changes During the Evolution of the Zygnemateles. BMC Biol 2005 Oct 20; 3:22.
• Raven, John. Allen, John. Genomics and Chloroplast Evolution: What did Cyanobacteria Do For Plants? Genome Biol. 2003; 4(3): 209