Nitrous oxide (N2O) is a potent atmospheric pollutant that is removed biologically by a bacterial enzyme called prokaryotic nitrous oxide reductase (N2OR). In high yield agricultural soils N2OR is often inadequately active. Thus, N2O has been continuously increasing in post-industrial atmosphere, so that it accounts for about 12% of present radiative forcing by greenhouse gases. N2O is also a significant ozone depleting chemical. A novel and potentially transformative solution to agricultural emissions of N2O will be investigated in this project.
N2OR will be expressed in plant mitochondria so that it is active continuously, removing N2O from soil and atmosphere. N2OR has been reported to be active under anoxic conditions in vitro in extracts of plants conventionally transformed with nosZ, the structural gene for N2OR. Using the expertise that the investigators have developed in their lab for the construction of novel synthetic genetic vectors for phytoremediation, they will express nosZ modified with the amino acid sequences that target the proteins to the mitochondria matrix and inner periplasmic membrane of the mitochondria. The mitochondrion is the site of respiratory reduction in the cell, i.e., the site of oxygen consumption, and is analogous to the site of N2O reduction in denitrifying bacteria. This is a high-risk project, but with great potential benefits of global importance. With one year of funding, the project seeks to determine: 1. whether N2O reduction in whole plants is possible using current nosZ sequences and mitochondrial targeting sequences, 2. whether the putative helper genes in the nos operon, nosXDFYL, are necessary for optimal N2OR expression, and 3. whether N2OR expressing plants can prevent N2O emissions from fertilized soils. If N2OR can be made to be active in plants and if this technology is applied on a large scale to crops such as maize and rice, it is expected that N2O emissions from grain cultivation could be cut significantly, resulting in a sudden reduction in N2O increases. Potentially this reduction could be accomplished sustainably with little to no additional energy expenditure. This would be a major and welcome cut in greenhouse gas and ozone depleting emissions, unanticipated by present IPCC projections.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
