ScienceDaily (July 9, 2010) — One of the most pivotal steps in evolution-the transition from unicellular to multicellular organisms-may not have required as much retooling as commonly believed, found a globe-spanning collaboration of scientists led by researchers at the Salk Institute for Biological Studies and the US Department of Energy's Joint Genome Institute.
This is Volvox carteri. (Credit: Courtesy of Dr. David Kirk, Washington University, St. Louis)
"If you think of proteins in terms of lego bricks Chlamydomonas already had a great lego set," says James Umen, Ph.D., assistant professor in the Plant Molecular and Cellular Biology Laboratory at the Salk Institute. "Volvox didn't have to buy a new one, and instead could experiment with what it had inherited from its ancestor."
Altogether the findings, published in the journal Science, suggest that very limited protein-coding innovation occurred in the Volvox lineage. "We expected that there would be some major differences in genome size, number of genes, or gene families sizes between Volvox and Chlamydomonas," says Umen. "Mostly that turned out not to be the case."
The evolution of multicellularity occurred repeatedly and independently in diverse lineages including animals, plants, fungi, as well as green and red algae. "This transition is one of the great evolutionary events that shaped life on earth," says co-first author Simon E. Prochnik, Ph.D., a Computationial Scientist at the DOE Joint Genome Institute. "It has generated much thought and speculation about what makes multicellular organisms different or more complex than their unicellular ancestors."
In most cases the switch from a solitary existence to a communal one happened so long ago-over 500 million years-that the genetic changes enabling it are very difficult to trace. An interesting exception to the rule are volvocine green algae. For them, the transition to multicellularity happened in a series of small, potentially adaptive changes, and the progressive increase in morphological and developmental complexity can still be seen in contemporary members of the group (see slide show).
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Vol. 329. no. 5988, pp. 223 - 226
DOI: 10.1126/science.1188800
Genomic Analysis of Organismal Complexity in the Multicellular Green Alga Volvox carteri
Simon E. Prochnik,1,* James Umen,2,*, Aurora M. Nedelcu,3 Armin Hallmann,4 Stephen M. Miller,5Ichiro Nishii,6 Patrick Ferris,2 Alan Kuo,1 Therese Mitros,7 Lillian K. Fritz-Laylin,7 Uffe Hellsten,1Jarrod Chapman,1 Oleg Simakov,8 Stefan A. Rensing,9 Astrid Terry,1 Jasmyn Pangilinan,1Vladimir Kapitonov,10 Jerzy Jurka,10 Asaf Salamov,1 Harris Shapiro,1 Jeremy Schmutz,11Jane Grimwood,11 Erika Lindquist,1 Susan Lucas,1 Igor V. Grigoriev,1 Rüdiger Schmitt,12 David Kirk,13Daniel S. Rokhsar1,7,
The multicellular green alga Volvox carteri and its morphologically diverse close relatives (the volvocine algae) are well suited for the investigation of the evolution of multicellularity anddevelopment. We sequenced the 138–mega–base pair genome of V. carteri and compared its ~14,500 predicted proteins to those of its unicellular relative Chlamydomonas reinhardtii. Despite fundamental differences in organismal complexity and life history, the two species have similar protein-coding potentials and few species-specific protein-coding gene predictions. Volvox is enriched in volvocine-algal–specific proteins, including those associated with an expanded and highly compartmentalized extracellular matrix. Our analysis shows that increases in organismalcomplexity can be associated with modifications of lineage-specific proteins rather than large-scale invention of protein-coding capacity.
1 U.S. Department of Energy, Joint Genome Institute, Walnut Creek, CA 94598, USA.
2 The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
3 University of New Brunswick, Department of Biology, Fredericton, New Brunswick E3B 5A3, Canada.
4 Department of Cellular and Developmental Biology of Plants, University of Bielefeld, D-33615 Bielefeld, Germany.
5 Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21250, USA.
6 Biological Sciences, Nara Women’s University, Nara-shi, Nara Prefecture 630-8506, Japan.
7 Center for Integrative Genomics, Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA.
8 European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
9 Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.
10 Genetic Information Research Institute, 1925 Landings Drive, Mountain View, CA 94043, USA.
11 HudsonAlpha Institute for Biotechnology, Huntsville, AL 35806, USA.
12 Department of Genetics, University of Regensburg, D-93040 Regensburg, Germany.
13 Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: umen@salk.edu (J.U.); dsrokhsar@gmail.com (D.S.R.)
The multicellular green alga Volvox carteri and its morphologically diverse close relatives (the volvocine algae) are well suited for the investigation of the evolution of multicellularity anddevelopment. We sequenced the 138–mega–base pair genome of V. carteri and compared its ~14,500 predicted proteins to those of its unicellular relative Chlamydomonas reinhardtii. Despite fundamental differences in organismal complexity and life history, the two species have similar protein-coding potentials and few species-specific protein-coding gene predictions. Volvox is enriched in volvocine-algal–specific proteins, including those associated with an expanded and highly compartmentalized extracellular matrix. Our analysis shows that increases in organismalcomplexity can be associated with modifications of lineage-specific proteins rather than large-scale invention of protein-coding capacity.
1 U.S. Department of Energy, Joint Genome Institute, Walnut Creek, CA 94598, USA.
2 The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
3 University of New Brunswick, Department of Biology, Fredericton, New Brunswick E3B 5A3, Canada.
4 Department of Cellular and Developmental Biology of Plants, University of Bielefeld, D-33615 Bielefeld, Germany.
5 Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21250, USA.
6 Biological Sciences, Nara Women’s University, Nara-shi, Nara Prefecture 630-8506, Japan.
7 Center for Integrative Genomics, Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA.
8 European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
9 Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.
10 Genetic Information Research Institute, 1925 Landings Drive, Mountain View, CA 94043, USA.
11 HudsonAlpha Institute for Biotechnology, Huntsville, AL 35806, USA.
12 Department of Genetics, University of Regensburg, D-93040 Regensburg, Germany.
13 Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: umen@salk.edu (J.U.); dsrokhsar@gmail.com (D.S.R.)
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