雪藻驱动极地碳循环及适应低温和高辐射的机制

Snow algae including Chlamydomonas nivalis can grow and propagate on polar regions covered with snow and ice. They can fix about 2300 µmol CO2 per day and per square meter. So they play a vital role in the carbon cycle in polar regions. However, the mechanisms of acclimation to low temperature and high irradiation, and driving the carbon cycle of polar microbial communities in Chlamydomonas nivalis remain unclear. In this proposal, we will study the distribution, community composition and succession of snow algae in the polar regions, focus on the carbon metabolism such as selection of carbon resource, the transport and concentration of CO2, fixation of CO2 and secretion of acetate. To study the acclimation of carbon metabolism to low temperature, we will compare the metabolic change, the alteration of membrane fluidity and the activities of key metabolic enzyme when Chlamydomonas nivalis is shifted from normal temperature to low temperature. To study the adaption of carbon metabolism to high irradiation, our work will concentrate on the change of transcriptional regulation, the adjustment of ROS and redox system, the accumulation of astaxanthin . The above results will be further verified in Chlamydomonas reinhardtii, a model organism closely related to Chlamydomonas nivalis. Moreover, we will cooperate with Chinese polar research stations and artificial polar system to study the effect of the growth and propagation of snow algae on polar carbon cycling and the succession of microbial community. Our research will reveal the functions of snow algae in driving carbon cycle and the succession of the microbial community in polar regions, and deepen our knowledge in the microbial acclimation mechanism to low temperature and high irradiation.

雪藻在极地冰雪表面繁衍，每天每平方米能固定CO2达2300µmol，在极地碳循环中起着举足轻重的作用。但极地雪藻适应低温、高辐射/光强，高效固定CO2以及驱动极地碳循环的机理还不清楚。本项目在研究雪藻分布、群落组成及演替的基础上，围绕雪衣藻在碳源选择、CO2运输和浓缩，CO2固定以及有机碳分泌这一碳代谢的主线，从低温下代谢产物变化、膜的流动性改变及酶活性的维持等方面，研究雪衣藻碳代谢对低温的适应；从雪衣藻在高辐射/光强下转录调控的改变、ROS及抗氧化系统的调整、虾青素的积累等方面来研究雪衣藻碳代谢与高光强/辐射的适应机理。然后在雪衣藻近缘的模式生物莱茵衣藻中验证以上研究得到的结论。将利用我国极地考察站和人工模拟，研究雪藻群落繁衍及对极地碳循环的影响。该研究将揭示雪藻在驱动极地碳等元素循环以及极地生物群落演替中的作用，丰富对微生物适应低温和高辐射的机制的认识。

雪藻是极地重要的初级生产者，不仅驱动极地元素循环，还能高效合成色素，降低冰雪返照率，加速冰雪消融。研究雪藻演化和环境的互作有助于理解极地水圈生境演变的规律和趋势，但是极地雪藻适应低温、高辐射，高效固定CO2的机理还不清楚。.本项目利用两次极地考察，分离纯化真核雪藻和极地细菌，建立了极地雪藻群落种质资源库和雪藻系统生物学分析平台，完成拟衣藻属雪藻高质量基因组组装、比较转录组和蛋白质组分析，开发了适用于绿藻的精确基因编辑技术。利用上述平台，本项目得到以下重要结论：1.雪藻基因组与地球协同演化，碳代谢相关Rubisco小亚基和光保护蛋白基因家族显著扩张，雪藻通过基因水平转移从细菌获得冰结合蛋白，氰酸盐裂解酶等基因适应极地环境；2.温度骤降时雪藻转录组较为稳定，利用Dead box RNA解旋酶调控冷响应代谢网络，氮代谢、磷酸戊糖途径和多糖生物合成代谢通路上调；3.低温时雪藻依赖光系统I的环式电子传递，耗散过量光能，同时合成ATP维持细胞活动；4.解析了真核绿藻DNA甲基化修饰调控高光辐射适应的机制：去甲基化酶CMD1以维生素C为底物催化5-甲基胞嘧啶生成5-甘油基-甲基胞嘧啶，该机制调控光保护蛋白的表达；5.完成南极菲尔德斯半岛有色雪与淡水湖中雪藻多样性分析，发现磷酸盐和温度是影响雪藻群落的关键生态因子，建立了有色雪藻群落中真核藻类与原核生物的关联模型。.本项目实现了极地雪藻采集分离培养、雪藻遗传功能与地球生物学等多学科研究平台的整合，阐明了雪藻碳代谢适应极地低温和高辐射的机制，在真核绿藻中发现了全新的DNA修饰机制，鉴定了雪藻群落结构组成和相关生态因子，有助于未来系统开展极地雪藻多样性和雪藻群落的研究，开发耐极端气候农作物所需的遗传模块，建立雪藻群落演替与全球气候变化的关联模型。