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

令许多人惊讶的是，地球是由寒冷的生态系统主导的。微生物是占据这些极端生境的主要生命形式。南极的绿色细菌，衣原体属UWO 241（UWO 241）已经成为研究得最好的嗜冷光合微生物之一，也就是“嗜冷的”光合微生物，并且被认为是研究光合适应极端环境的新兴模式系统，该极端环境结合了寒冷、高盐和6个月的黑暗！考虑到预测的全球变暖的气候变化情景，这些嗜冷微生物代表了评估边缘生命恢复力的特殊生物标志物。UWO 241的特征在于独特的光合装置，其通过光系统I循环电子流（PSI-CEF）来调节能量流，而不是像所有其他藻类和植物那样通过状态转换。阐明UWO 241的表型可塑性和光合适应极端环境的复杂性的分子机制仍然是一个挑战。因此，我的研究计划的长期目标是阐明UWO 241通过状态转换及其与这种新生物的嗜冷性之间的联系来平衡能量的独特无能的分子基础。UWO 241突变体的产生是我阐明这种光合-嗜冷表型的分子基础的目标中的关键一步。因此，第一个目标是通过插入诱变产生UWO 241的突变体，通过一种新的合成基因组方法，涉及细菌和绿色细菌UWO 241之间的接合基因转移，结合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的结构和功能的类囊体蛋白激酶已知的管理状态转换和阐明的嗜冷菌，UWO 241的高生长温度限制的分子基础。除了是一个嗜冷菌，UWO 241也适应延长每年的光/暗周期与南半球的夏季和冬季。第四个目标是评估从长时间黑暗到光照的过渡过程中光合作用重新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。我提出的研究不仅有助于这项国际努力，而且还将UWO 241确定为研究极端边缘生活适应性的微生物光合自养生物的首选。它还将创造一个特殊的生物技术机会，利用这种绿色植物作为生物工厂，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.