Structural and Genomic Information Laboratory, UMR7256 CNRS, Aix-Marseille University, Mediterranean Institute of Microbiology (FR3479), Marseille, FR-13385, France.
Genome Biol. 2012 May 25;13(5):R39. doi: 10.1186/gb-2012-13-5-r39.
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.
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).
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.
对于生命适应极地极端环境条件的机制，我们知之甚少。本文呈现了绿藻门衣藻目的单细胞绿藻 Coccomyxa subellipsoidea C-169 的基因组序列，下文将其简称为 C-169。这是首个测序的极地真核微生物。
该 48.8Mb 基因组包含在 20 条染色体中，与同属的 Chlorella variabilis 和 Chlamydomonas reinhardtii 的染色体具有显著的同线性保守性。基因的顺序在同线性块内高度重排，表明染色体内重排比染色体间重排更为普遍。值得注意的是，Zepp 反转录转座子以严格每个染色体一个簇的嵌套元件簇的形式出现，可能位于着丝粒处。在 C. subellipsoidea 中高度过表达的几个蛋白家族包括参与脂代谢、转运蛋白、纤维素合酶和短醇脱氢酶的蛋白。相反，C-169 缺乏所有其他已测序的绿藻中存在的蛋白，包括糖基磷脂酰肌醇锚定系统的组成部分、丙酮酸磷酸二激酶和光系统 1 反应中心亚基 N（PsaN）。
我们认为这些基因的缺失和获得可能有助于适应低温。将这些基因组特征与嗜冷微生物的适应策略进行比较表明，原核生物和真核生物采取了类似的进化途径来适应寒冷环境。
