A nitric oxide reductase is a key enzyme target for eliminating fungal emissions of nitrous oxide

Authors: OAKLEY, BLAKE - University Of Georgia; Mitchell, Trevor; Read, Quentin; HIBBS, GARRETT - University Of Georgia; BALDWIN, THOMAS - North Dakota State University; Pierce, Larry; Gold, Scott; Glenn, Anthony

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2025
Publication Date: 9/23/2025
Citation: Oakley, B.A., Mitchell, T.R., Read, Q.D., Hibbs, G.T., Baldwin, T.T., Pierce, L.A., Gold, S.E., Glenn, A.E. 2025. A nitric oxide reductase is a key enzyme target for eliminating fungal emissions of nitrous oxide. Fungal Genetics and Biology. https://doi.org/10.1016/j.fgb.2025.104038.
DOI: https://doi.org/10.1016/j.fgb.2025.104038

Interpretive Summary: Nitrous oxide (N2O) is a harmful gas that comes from various sources, including from farming. When farmers use a lot of synthetic nitrogen fertilizer, especially during periods of heavy rain, it leads to more N2O being released into the air. This happens because of a natural microbial process called denitrification. In this study, an enzyme named NOR1 was shown to be essential for production of N2O by fungi commonly found in agricultural environments. Specifically the function of NOR1 was assessed in Fusarium verticillioides, a pathogen of maize that is notorious for its production of mycotoxins. When the NOR1 gene was deleted from the fungus, N2O was no longer produced. Likewise, when the gene was added back into the F. verticillioides mutant, the fungus started producing N2O again. Relative denitrification was assessed in other fungal species as well, and an analysis of fungal genomes showed that NOR1 is only found in a group of fungi called Ascomycota. Thus, targeting the NOR1 enzyme in these fungi could help reduce N2O emissions from agricultural soils and keep the nitrogen in the soil and available for plants to use.

Technical Abstract: Nitrous oxide (N2O) derived from agricultural activity is a major contributor to Earth’s greenhouse effect. Synthetic nitrogen fertilizer applied at high levels, particularly combined with heavy rainfall events, generates hot spots of N2O emissions in agricultural fields due to the process of microbial denitrification. Here, a key conserved fungal denitrification enzyme necessary for N2O emissions was identified. Functional characterization of the p450nor nitric oxide reductase encoding gene, NOR1, in the soil-borne denitrifying maize pathogen, Fusarium verticillioides, showed that this enzyme is critical for fungal N2O production. Deletion of the single copy NOR1 gene in F. verticillioides eliminated N2O emissions. Complementation of deletion mutants via the NOR1 gene add-back restored wild type N2O emission levels and segregation analysis further corroborated the pivotal role of NOR1 for N2O emissions. NOR-containing plant pathogenic Fusarium species exhibited drastic differences in N2O production based on denitrification potential. Phylogenetic analysis revealed that fungal NOR1-like genes, with rare exceptions, are highly conserved and confined to the phylum Ascomycota. We suggest targeting of the NOR1 enzyme as an effective strategy to reduce fungal-based N2O emissions and the loss of plant-available N.