( The analysis of DNA sequences from tiny...)Puzzling plankton yield secrets to role in evolution/global photosynthesis

The analysis of DNA sequences from tiny green algae have provided new insights into the mystery of how new species of plankton evolve—and further highlights their critical role in managing the global cycling of carbon. These findings, by a group led by the DOE Joint Genome Institute (DOE JGI); the Scripps Institution of Oceanography, University of California, San Diego; and the Pierre & Marie Curie University, were published this week in the Proceedings of the National Academy of Sciences (PNAS).

Ocean-dwelling phytoplankton from the genus Ostreococcus emerge at the primitive root of the green plant lineage, dating back nearly 1.5 billion years. Today, these microscopic, free-living creatures, among the smallest eukaryotes ever characterized, barely a micron in diameter, contribute to a significant share of the world’s total photosynthetic activity. These "picophytoplankton" also exhibit great diversity that contrasts sharply with the dearth of ecological niches available to them in aquatic ecosystems. This observation, known as the "paradox of the plankton," has long puzzled biologists.

Plumbing the depths of molecular-level information of related species, genomics offers a novel glimpse into this paradox. The researchers compared the genomes of two Ostreococcus species, O. lucimarinus and O. tauri, and saw dramatic changes in genome structure and metabolic capabilities.

"We found several striking features of genome organization," said DOE JGI’s Igor Grigoriev, the PNAS paper’s senior author. "Overlapping genes conserved across the species may enable them to cross-regulate their expression, while species-specific chromosomes with horizontally transferred genes can account for changes in the cell surface to adapt to different ecological niches." Grigoriev and his colleagues noted the abundance of selenium-rich proteins that surfaced in their analysis, which he said allows the organisms to horde nutrients and reduced their appetit
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Source:DOE/Joint Genome Institute

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