Introducing Biological Nitrogen Fixation to Plants

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Nitrogen is the main limiting nutrient for crops, and we currently synthesize over 100MMt of fertilizer annually. This revolutionized crop yield but at substantial economic and environmental costs (Good and Beatty, 2011). However, if we are to feed the future 9B people on the planet in 2050, we would need to increase the amount of fixed N by an additional 51MMt. Even if this was possible, the environmental consequences would be so significantly deleterious as to bring new meaning to the statement, “To foul your own nest”. Therefore there is no question that we need to address the ways in which we fix N, either through the production of N based fertilizers or by biological nitrogen fixation (BNF). This level of fixed N for agriculture is unsustainable, Industrially fixed N (IFN) is produced using the Haber-Bosch process. However, certain microorganisms have the ability to fix atmospheric nitrogen under ambient temperature and pressure conditions. In principle, the ability to biologically-fixed nitrogen could be introduced into plants, allowing them to fix atmospheric nitrogen directly and when needed. This would keep the environment almost “untouched”, by eliminating excess N loss into the environment. This proposal focuses on implementing a series of experiments that will allow us to determine whether it is possible to introduce biological N fixation into crop plants. IFN requires significant amounts of energy both to produce and ship, while biologically-fixed nitrogen influences the global nitrogen cycle substantially less than IFN. Recently there has been renewed interest in bioengineering N2 fixing cereals and significant advances in our understanding of the biology of N2 fixation have been made in the last two decades. We now understand the complete biosynthesis pathway for nitrogenase, the enzyme that performs the BNF reaction, and we are in a position to assay each step in the assembly pathway in vitro. Finally, with the rapid advances in synthetic biology, we can now synthesize novel genes, regulatory components and pathways and introduce them into organisms of our choice. N2-fixing cereal crops would benefit developed area farmers (ie Alberta) by lowering N fertilizer expenses while developing area farmers would have access to N2 fixing cereal plants. We want to reduce the cereal crop dependence on applied fertilizers by engineering crop plants that fix their own nitrogen to sustain growth and yield. This is a timely project that will build on decades of research on the N2 fixing bacteria/plant symbioses, the genetic and protein components of the bacterial N2 fixing nitrogenase complex, the full genomic sequences of cereal organelle genomes, and the recent development of techniques for the transient expression of multiple genes.