Engineering Synthetic Symbiosis Between Plant and Bacteria to Deliver Nitrogen to Crops

PI: John W. Peters（蒙大拿州立大学）CoPIs: Jean-Michel Ane（威斯康星大学麦迪逊分校），Michael Udvardi（塞缪尔·罗伯茨诺贝尔基金会）和Christopher A. Voigt（麻省理工学院）主要合作者：Giles E. Oldroyd（英国约翰英纳斯中心）和Phillip S. Poole（英国牛津大学约翰英纳斯中心）氮是地球上生物分子和生命的基本元素。可利用氮的缺乏限制了微生物、植物和动物的生长。农业土壤中氮的缺乏限制了植物粮食、饲料、纤维和燃料的生产。自然界通过一种重氮营养菌的生物固氮进化解决了氮的限制问题，重氮营养菌能够将大气中的N2还原为NH3， NH3很容易被吸收成生物分子。生物固氮是由一种复杂的含金属酶促进的，这种酶被称为氮酶，它的氧敏感性可能解释了它在细菌中的有限分布。一些植物，包括大多数豆科植物和少数非豆科植物，与重氮营养体形成亲密的固氮共生关系，为植物提供氨。因此，数千年来，豆类一直是可持续农业系统的一个组成部分。不幸的是，许多重要的食物物种，包括禾草、玉米、水稻和小麦，不能与重氮营养体建立有效的固氮共生关系，使它们依赖氮肥来获得高产。大规模使用工业生产的氮肥使进入陆地生物地球化学氮循环的氮增加了一倍，对人类健康和自然环境产生了严重的负面影响。因此，农业中大量氮肥投入的长期可持续性受到质疑。该项目汇集了来自美国和英国的跨学科研究团队，通过在模型和作物植物物种中开发有效的内生（根内细菌）和结合（根外附着细菌）固氮共生，解决发达国家氮肥过度使用和发展中国家土壤氮素缺乏的双重氮问题。该项目的总体目标是在模型C4-grass， Setaria viridis以及相关作物品种Zea mays与内生细菌Rhizobium sp. IRBG74以及伴生细菌假单胞菌荧光假单胞菌Pf5之间建立有效的固氮共生关系。生物固氮在模型草或作物草上的成功应用将为第二次绿色革命铺平道路，为资源贫乏的农民增加作物产量，减少富裕农民使用工业氮肥和对环境的影响。该项目将为植物-微生物相互作用的研究建立一个强大的新模型系统，并展示合成生物学在工程中的力量，新的关联关系和相互依赖关系有可能普遍适用于所有作物植物。它将在重要作物玉米上测试这种潜力。美英综合研究伙伴关系将为学生和博士后提供独特的培训机会，并在两国的学术实验室和研究基金会之间积极交流人员。研究中产生的数据和材料，包括质粒结构和转基因细菌和植物物种，将通过在美国和英国维护的网站提供。为了扩大这项工作的影响，将使用传统和非传统的外展策略来帮助K-12教师、学生和公众了解跨学科研究的基础和好处，以及合成生物学对下一代农业生物技术解决方案的影响。

PI: John W. Peters (Montana State University)CoPIs: Jean-Michel Ane (University of Wisconsin - Madison), Michael Udvardi (The Samuel Roberts Nobel Foundation) and Christopher A. Voigt (Massachusetts Institute of Technology)Key Collaborators: Giles E. Oldroyd (John Innes Centre, UK) and Phillip S. Poole (John Innes Centre, Oxford University, UK)Nitrogen is an essential element of biological molecules and life on earth. Lack of usable nitrogen limits growth of microbes, plants, and animals. Scarcity of nitrogen in agricultural soils limits plant production of food, feed, fiber and fuel. Nature solved the nitrogen limitation problem via evolution of biological nitrogen fixation in a type of bacteria, diazotrophs, that are able to reduce atmospheric N2 to NH3, which is readily assimilated into biological molecules. Biological nitrogen fixation is promoted by a complex metal containing enzyme called nitrogenase, whose oxygen-sensitivity may explain its restricted distribution amongst bacteria. Some plants, including most legumes and a few non-legumes form intimate, nitrogen-fixing symbioses with diazotrophs that provide the plants with ammonia. As a consequence, legumes have been an integral part of sustainable agricultural systems for thousands of years. Unfortunately, many important food species, including the grasses maize/corn, rice, and wheat cannot establish effective nitrogen-fixing symbioses with diazotrophs, making them dependent on nitrogenous fertilizers for high yield. Large-scale use of industrially-produced nitrogen-fertilizer has doubled the influx of nitrogen into the terrestrial biogeochemical nitrogen-cycle, with serious negative consequences for human health and the natural environment. Therefore, the long-term sustainability of massive nitrogen-fertilizer inputs in agriculture has come into question. This project brings together an interdisciplinary team of investigators from the US and UK to solve the dual nitrogen problems of nitrogen-fertilizer over-use in developed countries and soil nitrogen-paucity in developing countries by developing effective endophytic (bacteria inside the root) and associative (bacteria attached outside the root) nitrogen-fixing symbioses in a model and a crop plant species. The overarching goal of the project is to develop effective N2-fixing symbioses between the model C4-grass, Setaria viridis, as well as the related crop species, Zea mays, with the endophytic bacterium, Rhizobium sp. IRBG74, as well as the associative bacterium, Pseudomonas fluorescenes Pf5. Successful deployment of biological nitrogen fixation in model or crop grass species will pave the way for a second Green Revolution to increase crop yields for resource-poor farmers and decrease the use and environmental-impact of industrial nitrogen-fertilizers by wealthier farmers. This project will establish a powerful new model system for the study of plant-microbe interactions and demonstrate the power of synthetic biology in engineering new associative relationships and interdependencies that have the potential to be universal for all crop plants. It will test this potential in the important crop, maize. The integrated US-UK research partnership will provide a unique training opportunity for students and post-doctoral associates with active exchange of personnel between academic laboratories and research foundations in both countries. Data and materials generated in the study including plasmid constructs and genetically modified bacterial and plant species will be made available via websites maintained in the US and the UK. To broaden the impact of the work, traditional and non-traditional outreach strategies will be used to help K-12 teachers, students, and the public understand the fundamentals and benefits of interdisciplinary research and the implications of synthetic biology for the next generation of biotechnological solutions in agriculture.