Collaborative Research: Nitroplast: A Light-Driven, Synthetic Nitrogen-Fixing Organelle

为了获得最佳产量，农作物需要氨或硝酸盐肥料形式的固定氮，但这需要大量的化石燃料投入，还可能导致径流污染含水层和河口。与一些有能力固定大气氮的微生物不同，植物没有这种能力。这项研究的最终目标是设计一种新型的合成固氮细胞器，长期目标是在非豆科作物中实现有效的固氮。然而，在实现这一目标之前存在重大障碍，包括高代谢能源成本和克服该过程的氧气敏感性。在这个项目中，将使用合成生物学的工具将固氮工程设计成一个简单的模型系统。蓝藻是单细胞生物，在进化上与植物质体有亲缘关系。在蓝藻中，工程目标应该是易于处理的，构成了导致植物质体固氮工程的技术垫脚石。为了使这个项目取得成功，需要实现几个目标。首先，需要确定固氮所需的理想候选基因簇。其次，利用这些信息，可以精确控制的可调固氮基因模块将被构建并转移到蓝藻中。最后，为了应对这一过程的高代谢能源成本，将采用一种新的策略，通过该策略将额外的光吸收能力工程到蓝藻中。这些目标是复杂和多方面的，需要参与实验室之间的密切协调。这项研究的成功完成将导致一种工程合成的、可控制的固氮基因簇，它与光能能量相连，最终可以被转移到作物的叶绿体中，形成“硝化体”。这一挑战的核心是非豆科作物对氮的同化问题。该项目的目标是在蓝藻中构建一种新型的合成、可控的固氮模块。为了实现这一目标，已经组建了一支来自生物物理、生物化学、分子遗传学和合成生物学领域的科学专家团队。这项研究的结果预计将通过开发蓝藻的新工具，以及通过在植物中引入固氮等产品，使学术界的基础研究人员以及应用科学家受益。该项目是美国和英国科学家之间方法交流的独特机会，也是开发可供合成生物学和蓝藻研究社区免费使用的工具的独特机会。如果成功，这项工作也将使传统农业研究受益。培养下一代科学家是这个跨学科团队的一大目标。这项研究将通过在本科生、研究生和博士后层面进行密集的研究培训，以及通过美英合作者之间的国际交流、出版物和在科学会议上的陈述，使高等教育受益。这项工作产生的新技术应该提供工具和知识，以提高可能对农业产生重大影响的固氮能力。

INTELLECTUAL MERIT For optimal yields, crop plants require fixed nitrogen in the form of ammonia or nitrate fertilizers, but this requires large fossil fuel inputs and can also result in runoff which contaminates aquifers and estuaries. Unlike some microbes that have the capacity to fix atmospheric nitrogen, plants do not have this ability. The ultimate goal of this research is to engineer a novel synthetic nitrogen fixing organelle, with the long-term aim of conferring efficient nitrogen fixation in non-leguminous crop plants. However, there are significant hurdles before realizing this goal, which include high metabolic energy costs and overcoming oxygen sensitivity of the process. In this project, tools of synthetic biology will be used to engineer nitrogen fixation into a simple model system. Cyanobacteria are single-celled organisms that are evolutionarily related to plant plastids. In cyanobacteria, the engineering goals should be tractable, constituting a technological stepping stone that would lead to the engineering of nitrogen fixation into plant plastids. For this project to be successful, several objectives need to be met. First, ideal candidate gene clusters required for nitrogen fixation need to be identified. Second, using this information, tunable nitrogen-fixing gene modules, which can be precisely controlled, will be built and moved into cyanobacteria. Finally, to deal with the high metabolic energy costs of the process, a novel strategy will be employed by which extra light absorption capacity is engineered into cyanobacteria. These objectives are complex and multi-faceted, requiring tight coordination between participating laboratories. Successful completion of this research will lead to an engineered synthetic, controllable nitrogen fixing gene cluster linked energetically to light energy, which can ultimately be transferred into plastids of crop plants in the form of a 'nitroplast'.BROADER IMPACTSOne of the major challenges of the twenty-first century is to ensure food security for the world's people. At the core of this challenge is the problem of nitrogen assimilation by non-leguminous crop plants. The goal of this project is to build a novel synthetic, controllable nitrogen-fixing module into a cyanobacterium. To achieve this goal, a team of scientific experts have been assembled from the fields of biophysics, biochemistry, molecular genetics and synthetic biology. The outcome of this research is expected to benefit basic researchers in academia as well as applied scientists through the development of new tools for cyanobacteria, and through products such as the introduction of nitrogen fixation into plants. This project is a unique opportunity for methodology exchange between U.S and U.K. scientists and for developing tools that will be freely available to the synthetic biology and cyanobacterial research communities. If successful, the work will also benefit traditional agricultural research. The preparation of the next generation of scientists is a major goal of this interdisciplinary team. The research will benefit higher education through intensive research training at the undergraduate, graduate and postdoctoral levels and through international exchange between US and UK collaborators, publications and presentations at scientific meetings. The new technologies derived from this work should provide tools and knowledge to boost nitrogen fixation capacity that could strongly impact agriculture.