Ostreococcus tauri

As of today, the green alga Ostreococcus tauri (O. tauri) is the smallest described eukaryotic organism and has the smallest known genome for a photosynthetic eukaryote. This alga is widespread in all the seas and is part of the phytoplankton. Together with cyanobacteria and photosynthetic picoeukaryotes, O.tauri constitutes the basis of the oceans food chain, using solar energy and fixing carbon dioxide to produce organic matter that other organisms feed on. The photosynthetic process of these organisms produce about 50% of the oxygen we breathe.

The appeal of this unicellular planktonic green alga for research can be explained both by its interest as a model organism for studying marine phytoplankton, and by its evolutionary position, leading to higher plants. Thus, O. tauri shares many physiological and molecular mechanisms with plants. Most of the genes present specifically in plants are found in O. tauri. The genomes of three Ostreococcus strains have been fully sequenced and studies to elucidate the function of the genes conserved between these “primitive” algae and higher plants will lead to a better understanding of the function and regulation of homologous genes in plants, as well as how they have evolved.