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。在白天，植物和其他光合生物利用太阳能固定二氧化碳，并将多余的碳储存为碳聚合物，如淀粉或糖原。到了晚上，这些储存的碳被分解，成为黑暗生存的能量来源。从黑暗到光明的转变代表了光合生物普遍面临的环境压力。例如，由于在黑暗中进行的代谢反应，光暴露时光合反应所需的许多代谢物受到限制或耗尽。重要的是光合生物具有适当的机制来科普这种压力并确保在暴露于光时的健康光合性能。光合生物如何实现这种从暗到亮的转变仍然不清楚。该研究项目应用尖端的生物化学和系统生物学方法来剖析分子机制，使这种黑暗到光明的转变发生在一个模型光合蓝绿色植物。从这项研究中获得的知识将如何储存聚合物，如糖原铺平道路，二氧化碳固定发生在黑暗到光明的过渡，并最终导致提高作物生产的光合效率的方法。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也被整合到一个集群教育计划中，并以合成生物学专题课程的形式，以扩大培训机会，加强本科生和研究生的科学素养。蓝细菌在每日光/暗循环下经历剧烈的代谢变化。从黑暗到光明的平稳代谢过渡对于健康的光合性能和光养生物的整体适应性至关重要。已知在蓝细菌细长聚球藻PCC 7942中，糖原代谢参与支持暗-光转换期间Calvin-Benson-Bassham（CBB）循环反应的起始。然而，糖原代谢如何支持光合作用的分子机制尚不清楚。本计画应用蛋白质组学、代谢组学、代谢通量分析及光化学分析等方法，探讨蓝细菌在暗-光转换胁迫下的因应机制。研究活动将说明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，以及保护光系统I在黑暗到光明的过渡期间免受光抑制。该研究的发现将大大推进对光合生物科普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光反应和碳固定之间能量平衡的认识。该研究的结果也有利于光合作用在合成生物学领域的重新设计研究，以实现可持续的粮食供应。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.