Tiny Green Algae Reveal Large Genomic Variation

First complete picture of standing genetic variation within a natural population.

The Science

TEM image of O. tauri strain RCC4221. Credit: Herve Moreau

TEM image of O. tauri strain RCC4221. (Martin Hohmann-Marriott)

Ostreococcus are tiny green algae that are the bases of many marine food webs. A decade after the complete representative genomes of three Ostreococcus picoplankton groups were sequenced, researchers have sequenced and analyzed the genomes of 13 members of a natural Ostreococcus population. The analysis revealed that the O. tauri population is larger than anticipated, with high genetic and phenotypic diversity that is influenced by the algae’s natural resistance to ocean viruses.

The Impact

Ostreococcus is considered a model species to study marine picophytoplankton. Though microscopic, Ostreococcus and other picoplankton are significant primary producers in the oceans and contribute to the global carbon cycle. Understanding the genetic variability of various Ostreococcus strains will help researchers understand how environmental changes affect their abundance and ability to photosynthesize.

Summary

By their name, picophytoplankton such as Ostreococcus are invisible to the naked eye. Despite their size, their global abundance means 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 U.S. Department of Energy Joint Genome Institute (DOE JGI), a DOE Office of Science user facility, sequenced one of the Ostreococcus strains. That genome, along with other genome sequences from 3 groups of the picophytoplankton 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 (CSP).

BER Contact

Daniel Drell, Ph.D.
Program Manager
Biological Systems Sciences Division
Office of Biological and Environmental Research
Office of Science
US Department of Energy
daniel.drell@science.doe.gov

PI Contacts

Igor Grigoriev
Fungal Genomics Program Head
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

Funding

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

Publication

R. Blanc-Mathieu et al. “Population genomics of picophytoplankton unveils novel chromosome hypervariability.” Science Advances. 2017 Jul 5. DOI: 10.1126/sciadv.1700239