Table_4_Cold Adaptation Mechanisms of a Snow Alga Chlamydomonas nivalis During Temperature Fluctuations.xlsx

Cold environments, such as glaciers and alpine regions, constitute unique habitats for organisms living on Earth. In these harsh ecosystems, snow algae survive, florish, and even become primary producers for microbial communities. How the snow algae maintain physiological activity during violent ambient temperature changes remains unsolved. To explore the cold adaptation mechanisms of the unicellular snow alga Chlamydomonas nivalis, we compared its physiological responses to a model organism from the same genus, Chlamydomonas reinhardtii. When both cell types were exposed to a shift from 22°C to 4°C, C. nivalis exhibited an apparent advantage in cold tolerance over C. reinhardtii, as C. nivalis had both a higher growth rate and photosynthetic efficiency. To determine the cold tolerance mechanisms of C. nivalis, RNA sequencing was used to compare transcriptomes of both species after 1 h of cold treatment, mimicking temperature fluctuations in the polar region. Differential expression analysis showed that C. nivalis had fewer transcriptomic changes and was more stable during rapid temperature decrease relative to C. reinhardtii, especially for the expression of photosynthesis related genes. Additionally, we found that transcription in C. nivalis was precisely regulated by the cold response network, consisting of at least 12 transcription factors and 3 RNA-binding proteins. Moreover, genes participating in nitrogen metabolism, the pentose phosphate pathway, and polysaccharide biosynthesis were upregulated, indicating that increasing resource assimilation and remodeling of metabolisms were critical for cold adaptation in C. nivalis. Furthermore, we identified horizontally transferred genes differentially expressed in C. nivalis, which are critical for cold adaptation in other psychrophiles. Our results reveal that C. nivalis adapts rapid temperature decrease by efficiently regulating transcription of specific genes to optimize resource assimilation and metabolic pathways, providing critical insights into how snow algae survive and propagate in cold environments.

冰川、高山区域等寒冷环境，是地球生物的独特栖息生境。在这类严苛的生态系统中，雪藻得以存活、繁衍，甚至成为微生物群落的初级生产者。然而，雪藻如何在剧烈波动的环境温度下维持生理活性，这一问题至今尚未得到解答。为解析单细胞雪藻——雪衣藻（Chlamydomonas nivalis）的低温适应机制，本研究将其与同属模式生物莱茵衣藻（Chlamydomonas reinhardtii）的生理响应进行了对比分析。当两类细胞均经历22℃至4℃的温度骤降时，雪衣藻在耐寒性上展现出显著优势：其生长速率与光合效率均高于莱茵衣藻。为阐明雪衣藻的耐寒机制，本研究采用RNA测序（RNA sequencing）技术，对两类物种在1小时低温处理（模拟极地地区的温度波动）后的转录组进行了对比分析。差异表达分析结果显示：相较于莱茵衣藻，雪衣藻在快速降温过程中转录组变化更少，稳定性更强，这一特征在光合相关基因的表达上尤为突出。此外，本研究发现雪衣藻的转录过程受到低温响应网络的精准调控，该网络至少包含12种转录因子与3种RNA结合蛋白。同时，参与氮代谢、磷酸戊糖途径以及多糖生物合成的基因均出现上调，这表明提升资源同化能力与代谢重塑，对雪衣藻的低温适应至关重要。进一步地，本研究在雪衣藻中鉴定出了差异表达的水平转移基因，这类基因在其他嗜冷生物的低温适应过程中发挥关键作用。本研究结果表明：雪衣藻通过高效调控特定基因的转录以优化资源同化与代谢通路，从而适应快速降温的环境；该发现为解析雪藻在寒冷环境中的存活与繁殖机制提供了重要理论参考。