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

点击翻译按钮获取中文摘要

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.