Genomics of Algae

Marc Heijde, Biologie Moléculaire des Organismes Photosynthétiques, France
Chris Bowler, Biologie Moléculaire des Organismes Photosynthétiques, France

Published online: September 2009

DOI: 10.1002/9780470015902.a0021254

Algae are dominant contributors to primary production and have a major impact on biogeochemical cycles because of their unique metabolisms. Few algal genomes have so far been characterized, although whole genome sequences have now been generated from representatives of the green, red and brown algae. In addition, numerous projects are progressing to define algal transcriptomes using expressed sequence tags (ESTs) and microarrays. Multiple efforts based on comparative and functional genomics approaches have already generated an influx of exciting data about evolutionary origins and functional innovations of different algal species dispersed throughout the eukaryotic tree of life.

Key concepts:

  • Algal species have little common phylogeny and are widely dispersed throughout the eukaryotic tree of life.
  • Red and green algae lie within the Archaeplastida whereas brown algae lie within the Stramenopile and Alveolata lineages.
  • Brown algae have secondary plastids, thought to be derived from secondary endosymbiosis.
  • Chlamydomonas reinhardtii represents the best-studied experimental system for algae.
  • Diatom genomes are highly chimeric in nature, with genes derived from both partners of the secondary endosymbiosis, as well as large numbers of bacterial genes acquired by horizontal gene transfer.
  • The existence of C4 photosynthesis in algae has not yet been conclusively demonstrated.
  • Distinct algal species often comprise ecotypes optimized for growth in specific environmental conditions.

Keywords: algal genome; biofuel; chlamydomonas; diatom; prasinophyte; transcriptome

Figure 1. Schematic representation of current views of plastid evolution in eukaryotic phytoplankton. (a) Engulfment of a cyanobacterial ancestor and subsequent reduction to a primary plastid by a eukaryotic host initially led to the formation of three lineages with primary plastids: the chlorophytes and land plants, rhodophytes and glaucophytes. (b) The subsequent uptake of a green or a red alga by independent hosts to form secondary endosymbioses resulted in euglenophytes, chlorarachniophytes and the monophyletic Chromalveolates. Chromalveolates, which represent the association of chromists (Stramenopiles, Haptophyta and Cryptophyta) and the Alveolata (Apicomplexa, Perkinsidae, Dinophyta and Ciliata), unite an extremely diverse array of protists. (c) Different Dinophyta have replaced their original secondary plastid with a green alga-derived plastid either by serial secondary endosymbiosis (Lepidodinium) or even tertiary endosymbioses, for example, Karlodinium harbours a tertiary plastid of haptophyte origin. The heterokontophyte Rhopalodia gibba appears to have engulfed a cyanobacterial Cyanothece spp.
Figure 2. Placement of the ongoing or completed (in bold) algal genome sequencing projects in the tree of eukaryotic life. Reproduced by the permission of the Editorial Office of Journal of Systematics and Evolution, Baldauf (2008).
Figure 3. Schematic representation of diatom evolution. The origin of the diatom ‘melting pot’ genome finds its origins in successive gene transfers after the primary and secondary endosymbioses that permitted gene transfer from prey nucleus to host nucleus as well as from organelles to nucleus. Diatoms also seem to have acquired genes through lateral gene transfer both before and after the diversification of pennates and centrics. Other driving forces of diversification have been proposed to be through the action of mobile transposable elements and by selective gene loss/expansions during niche adaptation (Bowler et al., 2008).
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Related Sub-Topics:

Basic Cell Biology, Protein, RNA and DNA | Genomes and Chromosomes | Microbial Evolution and Taxonomy | Algae | Plant Evolution | Plant Genetics and Molecular Biology
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Article Title: Genomics of Algae
 
How to Cite close
Heijde, Marc, and Bowler, Chris(Sep 2009) Genomics of Algae. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021254]