The genome of the polar eukaryotic microalga Coccomyxa subellipsoidea reveals traits of cold adaptation.
BACKGROUND
Little is known about the mechanisms of adaptation of life to the extreme environmental conditions encountered in polar regions. Here we present the genome sequence of a unicellular green alga from the division chlorophyta, Coccomyxa subellipsoidea C-169, which we will hereafter refer to as C-169. This is the first eukaryotic microorganism from a polar environment to have its genome sequenced.


RESULTS
The 48.8 Mb genome contained in 20 chromosomes exhibits significant synteny conservation with the chromosomes of its relatives Chlorella variabilis and Chlamydomonas reinhardtii. The order of the genes is highly reshuffled within synteny blocks, suggesting that intra-chromosomal rearrangements were more prevalent than inter-chromosomal rearrangements. Remarkably, Zepp retrotransposons occur in clusters of nested elements with strictly one cluster per chromosome probably residing at the centromere. Several protein families overrepresented in C. subellipsoidae include proteins involved in lipid metabolism, transporters, cellulose synthases and short alcohol dehydrogenases. Conversely, C-169 lacks proteins that exist in all other sequenced chlorophytes, including components of the glycosyl phosphatidyl inositol anchoring system, pyruvate phosphate dikinase and the photosystem 1 reaction center subunit N (PsaN).


CONCLUSIONS
We suggest that some of these gene losses and gains could have contributed to adaptation to low temperatures. Comparison of these genomic features with the adaptive strategies of psychrophilic microbes suggests that prokaryotes and eukaryotes followed comparable evolutionary routes to adapt to cold environments.
Structural and Genomic Information Laboratory, UMR7256 CNRS, Aix-Marseille University, Mediterranean Institute of Microbiology (FR3479), Marseille, FR-13385, France. guillaume.blanc@igs.cnrs-mrs.fr
Guillaume
G
Blanc
Irina
I
Agarkova
Jane
J
Grimwood
Alan
A
Kuo
Andrew
A
Brueggeman
David D
DD
Dunigan
James
J
Gurnon
Istvan
I
Ladunga
Erika
E
Lindquist
Susan
S
Lucas
Jasmyn
J
Pangilinan
Thomas
T
Pröschold
Asaf
A
Salamov
Jeremy
J
Schmutz
Donald
D
Weeks
Takashi
T
Yamada
Alexandre
A
Lomsadze
Mark
M
Borodovsky
Jean-Michel
JM
Claverie
Igor V
IV
Grigoriev
James L
JL
Van Etten
D000222:Adaptation, Physiological; D000460:Chlorophyta / Q000235:genetics* / Q000502:physiology*; D003080:Cold Temperature; D019143:Evolution, Molecular; D016678:Genome; D023281:Genomics; D010802:Phylogeny; D026801:Synteny