Algal Pan-Genome Fills Gap in Tree of Life
To World War II soldiers, “The White Cliffs of Dover” was a morale-boosting song that lifted spirits in dark times. To scientists, the white cliffs are towering structures made of the chalky, white calcium carbonate exoskeleton that envelop the single-celled photosynthetic alga known as Emiliania huxleyi or “Ehux.” In some marine ecosystems, Ehux can trap as much as 20 percent of organic carbon derived from CO2 , making it a critical player in the marine carbon cycle . The Department of Energy’s Joint Genome Institute (DOE JGI) has sequenced the Ehux genome and compared it with sequences from other algal isolates. The Ehux genome turned out to be large and complex. Also, Ehux does not exist as a clearly defined species with a uniform genome, but as a more diffuse community—a “pan-genome”—with different individuals possessing a shared core of genes, supplemented by different gene sets to cope with the particular challenges of a local environment. DOE JGI and its collaborators compared 13 Ehux strains, revealing the first ever algal pan-genome. Ehux ’s genomic variability helps explain its ability to thrive in oceans from the equator to the subarctic. The researchers found that the core gene sets include genes that enable Ehux to survive in low levels of phosphorus and to assimilate and break down nitrogen-rich compounds. Additionally, the algal genome offers hints that Ehux may be involved in the global sulfur cycle, as it is able to produce a compound that can influence cloud formation and the climate.
Read, B. A., J. Kegel, M. J. Klute, A. Kuo, S. C. Lefebvre, F. Maumus, C. Mayer, J. Miller, A. Monier, A. Salamov, J. Young, M. Aguilar, J.-M. Claverie, S. Frickenhaus, K. Gonzalez, E. K. Herman, Y.-C. Lin, J. Napier, H. Ogata, A. F. Sarno, J. Shmutz, D. Schroeder, C. de Vargas, F. Verret, P. von Dassow, and et al. 2013. “Pan Genome of the Phytoplankton Emiliania Underpins Its Global Distribution,” Nature 499 , 209–13. DOI: 10.1038/nature12221.