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，也可能导致径流污染含水层和河口。不像一些微生物有能力固定大气中的氮，植物没有这种能力。因此，本研究的目标是设计一种新的合成固氮细胞器，以实现非豆科作物高效固氮的长期目标。然而，在将固氮引入植物中存在重大障碍，其中包括高代谢能量成本和克服该过程的氧敏感性。为了达到这一目标，合成生物学的工具将被用于将固氮工程设计成一个简单的模型系统。蓝藻是与植物质体进化相关的单细胞生物。在蓝藻中，工程目标应该是可处理的，构成一个技术垫脚石，将导致工程固氮进入植物质体。要使这个项目取得成功，需要满足几个目标。首先，需要确定固氮所需的理想候选基因簇。利用这些信息并将其与合成生物学技术相结合，需要构建可精确控制的可调固氮基因模块。接下来，这些合成的固氮基因模块需要被转移到蓝藻中。最后，为了解决该过程的高代谢能量成本，将采用一种新的策略，通过将额外的光吸收能力设计到蓝藻中。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与光能紧密相连，最终可以以“硝化质体”的形式转移到作物的质体中。

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. So the 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 in introducing nitrogen fixation into plants, which includes high metabolic energy costs and overcoming oxygen sensitivity of the process. To reach this goal, 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. Using this information and coupling it to synthetic biology techniques, tunable nitrogen fixing gene modules, which can be precisely controlled, need to be built. Next, these synthetic nitrogen fixing gene modules need to be 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'.