Life at the edge: photosynthetic adaptation and phenotypic plasticity in extreme environments

令许多人吃惊的是，地球被寒冷的生态系统所支配。微生物是占据这些极端栖息地的主要生命形式。南极绿藻，Chlamydomonas sp. UWO241 （UWO241）已成为研究得最好的嗜冷（即“爱冷”）光合微生物之一，被认为是研究光合适应寒冷、高盐和6个月黑暗极端环境的新兴模式系统！考虑到预测的气候变化情景和全球变暖，这些嗜冷微生物代表了评估边缘生命恢复能力的特殊生物标记。UWO241具有独特的光合机制，通过光系统I循环电子流（PSI-CEF）调节能量流动，而不是像其他所有藻类和植物那样通过状态转换。阐明UWO241表型可塑性的分子机制和极端环境下光合适应的复杂性仍然是一个挑战。因此，我的研究计划的长期目标是阐明控制UWO241通过状态转换来平衡能量的独特能力的分子基础，以及它与这种新型生物的嗜冷性的联系。UWO241突变体的产生是我阐明这种光合-嗜冷表型分子基础的关键一步。因此，第一个目标是通过一种新的合成基因组方法，通过插入诱变产生UWO241突变体，该方法涉及细菌和绿藻之间的接合基因转移，以及涉及生长温度和状态转换的双重筛选来选择突变体。我的第二个和第三个目标是利用这些突变体来表征已知控制状态转变的类囊体蛋白激酶的结构和功能，并阐明嗜冷性物质UWO241高生长温度限制的分子基础。除了是一种嗜冷植物外，uwo241还适应与南方夏季和南方冬季有关的延长的年度光/暗周期。第四个目标是评估从长时间的黑暗到开始有光的过渡期间光合作用再激活的机制和动力学。2014年，国际南极研究科学委员会将“适应极端环境的基因组、分子和细胞基础”确定为6个优先研究领域之一。我提出的研究不仅将有助于这项国际努力，而且还将建立UWO241作为研究极端边缘生命适应的微生物光自养生物的选择。它还将创造一个特殊的生物技术机会，利用这种绿藻作为生物工厂，通过分子农业生产医药产品，并提高生物燃料的生产。

Astonishing to many, Earth is dominated by cold ecosystems. Micro-organisms are the major life forms occupying these extreme habitats. The Antarctic green alga, Chlamydomonas sp. UWO241 (UWO241) has become one of the best studied psychrophilic, that is, "cold loving", photosynthetic microbes and is considered an emerging model system for the study photosynthetic adaptation to an extreme environment which combines cold, high salt and 6 months of darkness! Given the predicted climate change scenarios regarding global warming, these psychrophilic microbes represent exceptional biological markers to assess the resilience of life at the edge. UWO241 is characterized by a unique photosynthetic apparatus which regulates energy flow by Photosystem I cyclic electron flow (PSI-CEF) rather than through state transitions as do all other algae and plants. Elucidation of the molecular mechanisms underlying the phenotypic plasticity and the complexity of photosynthetic adaptation of UWO241 to extreme environment remains a challenge. Thus, the long-term goal of my research programme is to elucidate the molecular basis governing the unique inability of UWO241 to balance energy through state transitions and its link to the psychrophilic nature of this novel organism. The generation of UWO241 mutants is a critical step in my goal to elucidate the molecular basis of this photosynthetic-psychrophilic phenotype. Thus the first objective is to generate mutants of UWO241 by insertional mutagenesis via a novel synthetic genomic approach involving conjugative gene transfer between a bacterium and the green alga, UWO241, coupled with a double screen involving growth temperature and state transitions to select the mutants. My second and third objectives are to exploit these mutants to characterize the structure and function of the thylakoid protein kinases known to govern state transitions and to elucidate the molecular basis of the high growth temperature limitation of the psychrophile, UWO241. In addition to being a psychrophile, UWO 241 is also adapted to extended annual light/dark cycles associated with austral summer and austral winter. The fourth objective is to assess the mechanism and kinetics of reactivation of photosynthesis during the transition from prolonged darkness to the onset of light. In 2014, the international Scientific Committee on Antarctic Research identified the “genomic, molecular and cellular bases of adaptation” to extreme environments as one of 6 priority research areas. My proposed research will not only contribute to this international effort but also establish UWO241 as the microbial photoautotroph of choice for study of adaptation to life at the extreme edge. It will also create an exceptional biotechnological opportunity to exploit this green alga as a biofactory for the generation of medicinal products through molecular farming as well as for enhanced biofuel production.