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BIOLOGICAL SCIENCES / PLANT BIOLOGY
The tiny eukaryote Ostreococcus provides genomic insights into the paradox of plankton speciation
aScripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0202; cJoint Genome Institute and Stanford Human Genome Center, Stanford University School of Medicine, 975 California Avenue, Palo Alto, CA 94304; dU.S. Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598; eLaboratoire Associé de l'Institut National de la Recherche Agronomique (France), Ghent University, Technologiepark 927, B-9052 Ghent, Belgium; fDepartment of Plant Sciences, University of Arizona, 303 Forbes Building, Tucson, AZ 85721-0036; gObservatoire Océanologique, Laboratoire Arago, Centre National de la Recherche Scientifique/Université Pierre et Marie Curie Paris 6, Unité Mixte de Recherche 7628, BP 44, 66651 Banyuls sur Mer Cedex, France; hDepartment of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, Technologiepark 927, B-9052 Ghent, Belgium; iDepartment of Chemistry and Biochemistry, University of California, Box 951569, Los Angeles, CA 90095; jScripps Genome Center, Scripps Institution of Oceanography, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0202; kDepartment of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037; lInstitut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique/Université Paris 6, Unité Mixte de Recherche 7141, 13, Rue Pierre et Marie Curie, 75005 Paris, France; mDépartement de Biologie, Ecole Normale Supérieure, Formation de Recherche en Evolution 2910, Centre National de la Recherche Scientifique, 46, Rue D'Ulm, 75230 Paris Cedex 05, France; nInstitut für Allgemeine Botanik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany; oProgram in Molecular Medicine, University of Massachusetts Medical School, Suite 213, Biotech II, 373 Plantation Street, Worcester, MA 01605; pThe Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850; and qCell Biology and Molecular Genetics, University of Maryland, H. J. Patterson Hall, Building 073, College Park, MD 20742-5815
Edited by Robert Haselkorn, University of Chicago, Chicago, IL, and approved March 13, 2007 (received for review December 12, 2006)
The smallest known eukaryotes, at 
1-µm diameter, are Ostreococcus tauri and related species of marine phytoplankton. The genome of Ostreococcus lucimarinus has been completed and compared with that of O. tauri. This comparison reveals surprising differences across orthologous chromosomes in the two species from highly syntenic chromosomes in most cases to chromosomes with almost no similarity. Species divergence in these phytoplankton is occurring through multiple mechanisms acting differently on different chromosomes and likely including acquisition of new genes through horizontal gene transfer. We speculate that this latter process may be involved in altering the cell-surface characteristics of each species. In addition, the genome of O. lucimarinus provides insights into the unique metal metabolism of these organisms, which are predicted to have a large number of selenocysteine-containing proteins. Selenoenzymes are more catalytically active than similar enzymes lacking selenium, and thus the cell may require less of that protein. As reported here, selenoenzymes, novel fusion proteins, and loss of some major protein families including ones associated with chromatin are likely important adaptations for achieving a small cell size.
green algae | picoeukaryote | genome evolution | selenium | synteny
Author contributions: J.G. and A.A. performed research; B.P., P.R., A.S., N.P., C. Dupont, R.J., E.D., S. Rombauts, K.Z., R.O., S.S.M., S.P., T.G., C.N., K.G., A.M., V.T., O.V., G.P., S.J., M.H., K.J., C.B., M.L., S. Robbens, G.W., I.D., G.J.P., Q.R., I.P., C. Delwiche, J.S., D.R., Y.V.d.P., H.M., and I.V.G. analyzed data; and B.P., P.R., C. Dupont, R.J., K.Z., S.S.M., M.L., H.M., and I.V.G. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The O. lucimarinus genome sequence, predicted genes, and annotations reported in this paper have been deposited in the GenBank database (accession nos. CP000581–CP000601 for Chr 1 through Chr 21). The O. lucimarinus strain (CCE9901) used here has been deposited in the Provasoli-Guillard Culture Collection of Marine Phytoplankton (accession no. CCMP2514).
This article contains supporting information online at www.pnas.org/cgi/content/full/0611046104/DC1.
bTo whom correspondence may be addressed. E-mail: bpalenik{at}ucsd.edu or ivgrigoriev{at}lbl.gov
© 2007 by The National Academy of Sciences of the USA
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