07/05/2017

Tiny Green Algae Reveal Large Genomic Variation

First complete picture of genetic variations in a natural algal population could help explain how environmental changes affect global carbon cycles.

The Science

Although they are invisible to the unaided eye, tiny green algae called Ostreococcus play a big role in how carbon, including carbon dioxide, cycle through our world. Researchers have sequenced and analyzed the complete set of genes (the genome) of 13 members of a natural Ostreococcus population. The analysis revealed that the O. tauri population is larger than anticipated. It’s also diverse in terms of its genetics and appearance. The algae’s natural resistance to ocean viruses influenced it’s diversity.

The Impact

Ostreococcus is a microscopic model species for algal studies in marine environments. These picoplankton use sunlight together with carbon dioxide (CO2) to create organic matter. The algae are significant primary producers (i.e., they convert CO2 into biomass) and thus contribute to the global carbon cycle. This study offers insights into the genetic variability of various Ostreococcus strains. The results will help scientists see how environmental changes affect algae’s ability to survive and thrive.

Summary

Picophytoplankton such as Ostreococcus are invisible to the naked eye. Despite their size, their global abundance means they are a widespread primary producer and form the bases of several marine food webs. In coastal areas, they account for as much as 80 percent of the available biomass. A decade ago, the Joint Genome Institute (JGI), a U.S. Department of Energy (DOE) Office of Science user facility, sequenced one of the Ostreococcus strains. That genome, along with other genome sequences from three groups of Ostreococcus, revealed the tiny algae’s diversity and adaptation to different ecological niches around the world.

Now, a team led by researchers at the Oceanological Observatory of Banyuls, France, and including scientists at the DOE JGI, has resequenced and analyzed 13 members of a natural population of Ostreococcus tauri from the northwest Mediterranean Sea. The analysis offers a complete picture on the surprisingly large population and correspondingly high genetic and phenotypic diversity within O. tauri species. The team identified two large candidate mating type loci, consistent with the pervasive evidence of recombination and thus sexual reproduction within the population. The work reported in Science Advances was enabled in part by the DOE JGI’s Community Science Program. A deeper understanding of algal genomic diversity and potential will help scientists track carbon (and nitrogen) traffic through marine ecosystems as well as provide insights into the structure and operation of algal plant communities.

Principal Investigator(s)

Igor Grigoriev
DOE Joint Genome Institute
ivgrigoriev@lbl.gov

Gwenael Piganeau
Integrative Biology of Marine Organisms Lab, Oceanological Observatory of Banyuls, France
gwenael.piganeau@obs-banyuls.fr

Related Links

Funding

Work was conducted by the U.S. Department of Energy (DOE) Joint Genome Institute, a DOE Office of Science user facility (contract DE-AC02-05CH11231). This work was also supported by the European Community’s 7th Framework program FP7 and the Agence Nationale de la Recherche (contract ANR-13-JSV6-0005).

References

R. Blanc-Mathieu, M. Krasovec, M. Hebrard, S. Yau, E. Desgranges, J. Martin, W. Schackwitz, A. Kuo, G. Salin, C. Donnadieu, Y. Desdevises, S. Sanchez-Ferandin, H. Moreau, E. Rivals, I. Grigoriev, N. Grimsle, A. Eyre-Walker, and G. Piganeau, “Population genomics of picophytoplankton unveils novel chromosome hypervariability.” Science Advances 3(7), e1700239 (2017). [DOI: 10.1126/sciadv.1700239]