NITROPLAST: A LIGHT-DRIVEN, SYNTHETIC NITROGEN-FIXING ORGANELLE

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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'.