The unicellular green alga Chlamydomonas sp. ICE-L thrives in polar sea ice, where it tolerates extreme low temperatures, high salinity, and broad seasonal fluctuations in light conditions. Despite the high interest in biotechnological uses of this species, little is known about the adaptations that allow it to thrive in this harsh and complex environment. Here, we assembled a high-quality genome sequence of ∼542 Mb and found that retrotransposon proliferation contributed to the relatively large genome size of ICE-L when compared to other chlorophytes. Genomic features that may support the extremophilic lifestyle of this sea ice alga include massively expanded gene families involved in unsaturated fatty acid biosynthesis, DNA repair, photoprotection, ionic homeostasis, osmotic homeostasis, and reactive oxygen species detoxification. The acquisition of multiple ice binding proteins through putative horizontal gene transfer likely contributed to the origin of the psychrophilic lifestyle in ICE-L. Additional innovations include the significant upregulation under abiotic stress of several expanded ICE-L gene families, likely reflecting adaptive changes among diverse metabolic processes. Our analyses of the genome, transcriptome, and functional assays advance general understanding of the Antarctic green algae and offer potential explanations for how green plants adapt to extreme environments.

单细胞绿藻衣藻sp. ICE-L 在极地海冰中茁壮成长，在那里它可以忍受极端低温、高盐度和光照条件下的广泛季节性波动。尽管对该物种的生物技术用途非常感兴趣，但对其在这种恶劣而复杂的环境中茁壮成长的适应性知之甚少。在这里，我们组装了一个约 542 Mb 的高质量基因组序列，发现与其他叶绿植物相比，反转录转座子增殖导致 ICE-L 的基因组大小相对较大。可能支持这种海冰藻极端嗜极生活方式的基因组特征包括大量扩展的基因家族，这些基因家族涉及不饱和脂肪酸生物合成、DNA 修复、光保护、离子稳态、渗透稳态和活性氧解毒。通过假定的水平基因转移获得多种冰结合蛋白可能促成了 ICE-L 嗜冷生活方式的起源。其他创新包括在非生物胁迫下几个扩大的 ICE-L 基因家族的显着上调，可能反映了不同代谢过程之间的适应性变化。我们对基因组、转录组和功能分析的分析促进了对南极绿藻的普遍了解，并为绿色植物如何适应极端环境提供了潜在的解释。可能反映了不同代谢过程之间的适应性变化。我们对基因组、转录组和功能分析的分析促进了对南极绿藻的普遍了解，并为绿色植物如何适应极端环境提供了潜在的解释。可能反映了不同代谢过程之间的适应性变化。我们对基因组、转录组和功能分析的分析促进了对南极绿藻的普遍了解，并为绿色植物如何适应极端环境提供了潜在的解释。