Designing Nitrogen Fixing Ability in Oxygenic Photosynthetic Cells

这个项目的总体目标是开发设计原则，以建立单细胞蓝藻，聚球藻6803的固氮能力，聚球藻是一种产氧的光合作用生物。氮是植物生长所必需的营养物质。虽然少数植物通过与微生物共生来获得固定氮，但大多数植物通过从土壤中吸收含氮化合物来获得氮。氮肥的应用被广泛应用于促进植物生长。然而，人工肥料价格昂贵，对环境有严重的负面影响，包括土壤质量和径流退化，以及水源污染。解决作物氮素有效性问题的一种方法是改造植物细胞，使其能够将大气中的氮素固定成可用的化合物。目前，开发这一系统的一个主要挑战是叶绿体的光合作用产生氧，氧是固氮的关键酶固氮酶的有效抑制物。有趣的是，一些蓝藻菌株具有同时执行固氮和充氧光合作用的能力，使用巧妙的策略将这两个过程暂时分开。该项目使用合成生物学工具设计了一种非重氮营养的蓝藻来固定氮，从而确定了包括作物在内的光合作用细胞中固氮的最低要求。如果成功，这一努力将带来一种在光合作用细胞中整合看似不相容的新陈代谢功能的新范式。作物产量的提高是为地球上日益增长的人口生产食物、饲料和燃料的迫切需要，而有效利用氮气是满足这种需求的关键因素。本项目建立的知识库将直接应用于固氮作物工程，具有巨大的社会效益潜力。该项目团队在蓝藻系统生物学、计算建模和合成生物学方面拥有广泛的专业知识，并计划开发创新的跨学科教育计划，重点是将这些方法应用于光合作用生物体。重点将特别放在(1)为本科生开发机构间国际基因工程机器(IGEM)培训计划；以及(2)在印度的两个学术机构与国际合作伙伴的参与。这两套活动都将与该项目的研究目标密切相关，旨在为学生提供科学、技术、工程和数学(STEM)方面的实践培训机会。

INTELLECTUAL MERITThe overall goal in this project is to develop the design principles to establish nitrogen fixing ability in the unicellular cyanobacterium, Synechocystis 6803, an oxygenic photosynthetic organism. Nitrogen is an essential nutrient for plant growth. While a few plants acquire fixed nitrogen via symbioses with microorganisms, most plants obtain nitrogen through uptake of nitrogenous compounds from the soil. The application of nitrogen-containing fertilizers is widely used to enhance plant growth. However, artificial fertilizers are expensive and have serious negative environmental effects, including degradation of soil quality and runoff and contamination of water sources. A solution to the problem of nitrogen availability to crop plants is to engineer plant cells with the ability to fix atmospheric nitrogen into usable compounds. Presently, a major challenge in developing such a system is the fact that photosynthesis in chloroplasts generates oxygen, a potent inhibitor of nitrogenase, the key enzyme for nitrogen fixation. Interestingly, a number of cyanobacterial strains have the ability to perform both nitrogen fixation and oxygenic photosynthesis, using ingenious strategies that separate these two processes temporally. This project uses synthetic biology tools to engineer a non-diazotrophic cyanobacterium to fix nitrogen, thereby defining the minimum requirements for nitrogen fixation to occur in photosynthetic cells including those in crop plants. If successful, this effort will usher a new paradigm for integrating seemingly incompatible metabolic functions in a photosynthetic cell.BROADER IMPACTSEnhanced production of crop plants is an urgent need for the production of food, feed and fuel for an ever-increasing human population on this planet, and efficient use of nitrogen is a key factor to meet such a need. The knowledgebase created in this project will be directly applicable to engineer nitrogen-fixing crop plants, and will thus have enormous potentials for societal benefits. The project team has broad expertise in cyanobacterial systems biology, computational modeling, and synthetic biology, and plans to develop innovative interdisciplinary educational programs focused on the application of such approaches to photosynthetic organisms. In particular, emphasis will be placed on (1) Development of an inter-institutional iGEM (International Genetically Engineered Machine) training program for undergraduate students; and (2) Engagement of international partners at two academic institutions in India. Both set of activities will be intimately linked to the research goals of this project, and will be aimed at providing hands on training opportunities for students in Science, Technology, Engineering and Mathematics (STEM).