Identification of metabolic engineering targets in C4 carbon assimilation, an efficient photosynthetic pathway in a marine diatom

海洋硅藻高效光合作用途径 C4 碳同化代谢工程目标的鉴定

• 批准号: 1134115
• 负责人: Ganesh Sriram
• 金额: $ 45万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1134115&HistoricalAwards=false
• 关键词: Identification; metabolic; engineering; targets; C4

Abstract#1134115Sriram, Ganesh Relevance and intellectual merit. Photosynthesis converts solar energy and atmospheric CO2 into food, fuel, renewable carbon and molecular oxygen. A rapidly growing human population and an increasing need for renewable fuel and carbon demand a greater increase in photosynthetic output. In this context, understanding the metabolism of photosynthetically efficient organisms will enable metabolic engineering for enhanced photosynthetic productivity.Photosynthetic carbon fixation is typically inefficient because CO2 is sparingly soluble in water and highly diffusible, which prevents it from accumulating at a high concentration around ribulose bisphosphate carboxylase/oxygenase (RuBisCO), the enzyme that catalyzes the first step of photosynthesis. This reduces both the rate and yield of photosynthetic carbon assimilation. A small number of photosynthetic organisms overcome this problem by concentrating or pumping CO2 around RuBisCO through biochemical or biophysical mechanisms. One such biochemical mechanism known as the C4 pathway is found in a small number of crop plants including maize and certain grasses. However, recent circumstantial evidence has suggested that diatoms, a class of unicellular, marine algae, may also operate a C4 pathway. This may explain why diatoms are responsible for 20% to 40% of global photosynthetic output despite surviving in CO2 -depleted environments. This project takes advantage of the availability of isotope-assisted metabolic flux analysis (isotope MFA) and recently established genomic data and reverse genetic tools to investigate the C4 pathway in the model diatom species Phaeodactylum tricornutum. Specifically, the project will employ isotope MFA to measure carbon flow through the CO2 assimilation pathways and identify whether this organism concentrates CO2 exclusively through the C4 pathway. Furthermore, the project will assess the effects of varying environmental conditions on the efficiency of CO2 assimilation and finally, genetically engineer P. tricornutum by silencing key genes in the C4 pathways and identify rate-limiting steps. Broader impacts. The work will reveal the key metabolic steps and the organization of the C4 pathway in diatoms, which may underlie the high photosynthetic efficiency of these unicellular algae. Such knowledge will help pinpoint target genes and rate-limiting steps for future metabolic engineering towards improved photosynthetic productivity in algae and perhaps plants. A long-term goal will be to construct CO2-sequestering devices via synthetic biology approaches. This project will train students at the graduate, undergraduate and high school levels in the interdisciplinary fields of metabolic engineering, biochemistry, plant biology, and systems biology. Additionally, this project will develop metabolic pathway teaching modules for undergraduate and graduate courses in chemical and biomolecular engineering as well as biology, many of which will be disseminated to BioEMB, an NSF-funded repository for biology-intensive course materials in engineering.

摘要#1134115斯里拉姆、加内什的相关性和智力价值。光合作用将太阳能和大气中的二氧化碳转化为食物、燃料、可再生碳和分子氧。人口的快速增长以及对可再生燃料和碳的需求不断增加，这就要求光合作用产量有更大的增长。在这种背景下，了解光合作用高效生物的新陈代谢将使代谢工程能够提高光合作用的生产力。光合成碳固定通常是无效的，因为二氧化碳在水中溶解很少，并且高度扩散，这阻止了它在催化光合作用第一步的核酮糖二磷酸羧基酶/加氧酶(Rubisco)周围以较高的浓度积累。这降低了光合作用碳同化的速率和产量。少数光合作用生物通过生化或生物物理机制在Rubisco周围浓缩或泵送二氧化碳，从而克服了这一问题。其中一种被称为C4途径的生化机制在包括玉米和某些牧草在内的少数农作物中被发现。然而，最近的间接证据表明，硅藻，一类单细胞的海洋藻类，也可能运行C4途径。这可能解释了为什么硅藻在二氧化碳耗尽的环境中生存，但仍占全球光合作用产出的20%至40%。本项目利用同位素辅助代谢通量分析技术(同位素MFA)和最近建立的基因组数据和反向遗传工具来研究模式硅藻三角褐指藻的C4途径。具体地说，该项目将使用同位素MFA来测量通过二氧化碳同化途径的碳流量，并确定这种生物是否只通过C4途径浓缩二氧化碳。此外，该项目将评估不同环境条件对二氧化碳同化效率的影响，并最终通过沉默C4途径中的关键基因来对三角拟青霉进行基因工程，并确定限速步骤。更广泛的影响。这项工作将揭示硅藻中关键的代谢步骤和C4途径的组织，这可能是这些单细胞藻类高光合作用效率的基础。这些知识将有助于精确定位目标基因和限速步骤，为未来的代谢工程提高藻类甚至植物的光合作用生产率提供帮助。一个长期目标将是通过合成生物学方法建造二氧化碳封存设备。该项目将培养代谢工程、生物化学、植物生物学和系统生物学等跨学科领域的研究生、本科生和高中生。此外，该项目将为化学和生物分子工程以及生物学的本科生和研究生课程开发代谢途径教学模块，其中许多模块将传播到BioEMB，这是一个由NSF资助的生物密集型工程课程材料储存库。