Designing Nitrogen Fixing Ability in Oxygenic Photosynthetic Cells

本项目的总体目标是发展设计原则，以建立单细胞蓝藻，集胞藻6803，一种产氧光合生物的固氮能力。氮是植物生长所必需的营养元素。虽然少数植物通过与微生物共生获得固定氮，但大多数植物通过从土壤中吸收含氮化合物获得氮。含氮肥料的施用被广泛用于促进植物生长。然而，人造肥料价格昂贵，对环境有严重的负面影响，包括土壤质量和径流的退化以及水源的污染。解决作物氮可用性问题的一个方法是改造植物细胞，使其具有将大气氮固定为可用化合物的能力。 目前，开发这样一个系统的一个主要挑战是叶绿体中的光合作用产生氧气，氧气是固氮酶的有效抑制剂，固氮酶是固氮的关键酶。 有趣的是，许多蓝藻菌株都有能力进行固氮和产氧光合作用，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来设计非固氮蓝细菌来固定氮，从而确定在光合细胞（包括作物细胞）中发生固氮的最低要求。如果成功，这一努力将迎来一个新的范例，整合光合细胞中看似不相容的代谢功能。更广泛的影响提高作物产量是这个星球上不断增长的人口对粮食、饲料和燃料生产的迫切需求，而有效利用氮是满足这一需求的关键因素。本计画所建立之知识库，将直接应用于固氮作物之工程设计，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生物。特别是，重点将放在（1）为本科生开发机构间iGEM（国际遗传工程机器）培训计划;（2）在印度的两个学术机构的国际合作伙伴的参与。这两套活动将与本项目的研究目标密切相关，旨在为科学，技术，工程和数学（STEM）学生提供实践培训机会。

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).