CAREER: Glycogen metabolism kick-starts photosynthesis in cyanobacteria

地球上的生命依靠光合作用来获取太阳能。白天，植物和其他光合作用生物利用太阳能固定二氧化碳，并以淀粉或糖原等碳聚合物的形式储存多余的碳。到了晚上，这些储存碳被分解，成为黑暗生存的能量来源。从暗到光的转变代表了光合作用生命形式普遍存在的环境胁迫。例如，光照时光合作用所需的许多代谢物由于在黑暗中进行的代谢反应而受到限制或耗尽。对于光合作用的有机体来说，重要的是有一种机制来应对这种压力，并确保在光照下健康的光合作用表现。光合作用的生物体是如何实现这种从暗到亮的转变的，目前还不清楚。这项研究项目应用尖端的生化和系统生物学方法来剖析在一个光合作用蓝藻模型中发生这种从暗到光转变的分子机制。从这项研究中获得的知识将如何为糖原等储存聚合物为二氧化碳的固定铺平道路，并最终导致提高作物生产的光合作用效率的方法。该研究项目还为一名博士后研究员、一名研究生和几名本科生提供了培训机会。这项研究的组成部分还被纳入集群教育计划以及合成生物学专题课程的形式，以扩大本科生和研究生的培训机会并加强科学素养。蓝藻在每天的光/暗循环中经历着剧烈的代谢变化。从暗到光的平稳代谢过渡对于健康的光合作用表现和光养生物的整体适合性至关重要。已知糖原代谢参与支持蓝藻细长聚球藻PCC7942从暗到光转变过程中Calvin-Benson-Bassham(CBB)循环反应的启动。然而，糖原代谢如何支持光合作用的分子机制尚不清楚。本项目应用蛋白质组学、代谢组学、代谢通量分析和光化学分析等方法，研究蓝藻对光-暗过渡胁迫的应对机制。这些研究活动将阐明CBB循环停滞的状态，并了解糖原代谢如何帮助补充和重新启动碳固定反应，以及在从暗到光的转变中保护光系统I免光抑制。这项研究的发现将极大地促进人们对光合作用生命体应对从暗到光过渡胁迫的基本机制的理解，并进一步加深我们对光合作用光反应和固碳之间的能量平衡的认识。这项研究的结果也有利于可持续食品供应合成生物学领域的光合作用重新设计研究。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Life on Earth depends on photosynthesis to harvest solar energy. During the day, plants and other photosynthetic organisms use solar energy to fix carbon dioxide and store excess carbon as carbon polymers such as starch or glycogen. At night, these storage carbons are broken down as the energy source for dark survival. The dark-to-light transition represents a universal environmental stress for photosynthetic lifeforms. For example, many metabolites necessary for photosynthetic reactions upon light exposure are limited or depleted due to metabolic reactions conducted in dark. It is important for photosynthetic organisms to have a mechanism in place to cope with this stress and ensure healthy photosynthetic performance upon exposure to light. How photosynthetic organisms achieve this dark-to-light transitions remains unclear. This research project applies cutting-edge biochemical and systems biology approaches to dissect the molecular mechanisms that allow this dark to light transition to occur in a model photosynthetic blue green alga. Knowledge gained from this research will how storage polymers like glycogen pave the way for carbon dioxide fixation to occur during the dark to light transition and eventually lead to ways to improve photosynthetic efficiency for crop productions. The research project also provides training opportunities for one postdoctoral researcher, one graduate student, and several undergraduate students. Components of this research are also integrated in a cluster education program as well as in the form of a special topics course on Synthetic Biology to broaden the training opportunity and strengthen scientific literacy for both undergraduate and graduate students. Cyanobacteria experience drastic metabolic changes under daily light/dark cycles. The smooth metabolic transition from dark to light is crucial for healthy photosynthetic performance and the overall fitness of phototrophs. It is known that glycogen metabolism is involved in supporting the initiation of the Calvin-Benson-Bassham (CBB) cycle reactions during dark-to-light transitions in the cyanobacterium Synechococcus elongatus PCC 7942. However, the molecular mechanisms of how glycogen metabolism supports photosynthesis are not clear. This project applies proteomics, metabolomics, metabolic flux analysis, and photochemical analyses to characterize the coping mechanism of cyanobacteria for the dark-to-light transition stress. The research activities will illustrate the status of a stalled CBB cycle, and understand how glycogen metabolism helps replenish and restart carbon fixation reactions, as well as protecting Photosystem I from photoinhibition during dark-to-light transitions. Discoveries from the research will significantly advance the understanding on a fundamental mechanism employed by photosynthetic lifeforms to cope with the dark-to-light transition stress and further our knowledge on energy balance between photosynthetic light reactions and carbon fixation. Results from the study also benefit photosynthesis redesign research in the field of synthetic biology for sustainable food supply.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.