Mini Eukaryote

Wenche Eikrem and Jahn Throndsen / University of Oslo

E. Derelle et. al., "Genome analysis of the smallest free-living eukaryote Ostreococcus tauri unveils many unique features," Proc Natl Acad Sci, 103:11647-52, 2006. (Cited in 74 papers)

French, Belgian, and US scientists sequenced the genome of Ostreococcus tauri, an ancient species of green algae at the base of the green plant lineage and the marine food chain. Its phylogenetic position gave insight into the divergence between plant and animal lineages since it shared gene homologies to both, says Arthur Grossman, at Stanford University, who was not involved in the study.

O. tauri's strikingly compact genome, with just one region of reduplication, contained unexpected evidence of complexity in the form of two heterogenous chromosomes, says Alexandra Worden of Stanford University, an author on the study.

Two of O. tauri's 18 chromosomes carry most of the genome's transposons; one of them, C2, contains sole copies of essential housekeeping genes. The intron and gene content of C2 suggested it may be a sex chromosome. Related species of algae sequenced since also have such oddball chromosomes, pointing to a common speciation mechanism, says Pierre Rouzé of Ghent University and lead author.

Comparing the tiny O. tauri genome to O. lucimarinus, an open ocean alga sequenced the following year, and other related species is shedding light on the evolution of environment-specific features such as metabolism.