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Hypoxia, denitrification, and the fitness of Fusarium verticillioides as a fungal pathogen of maize

Blake Oakley: Department of Plant Pathology, The University of Georgia

<div><em>Fusarium verticillioides</em> is a globally distributed fungal pathogen of maize and is of concern both for its impact on grain quality and its contamination of grain with fumonisin mycotoxins. The fungus is noted for its endophytic infection of maize, but it also colonizes plant debris in the soil. Since the plant’s internal tissues and the soil environment are both prone to periods of hypoxia (low oxygen), we hypothesized that <em>F. verticillioides</em> utilizes physiological processes conferring hypoxia tolerance and that the genes encoding these processes are differentially regulated. RNA-seq analysis identified 1444 genes up-regulated at least 8-fold in response to 24 h hypoxic growth. Three of these genes encode a dissimilatory nitrate reductase (10-fold), a dissimilatory nitrite reductase (832-fold), and a P450 nitric oxide reductase (17560-fold), which are all components of denitrification. Deletion mutants were created for these genes and others likely associated with denitrification and other responses to hypoxia. We are evaluating the impact of these genes on <em>F. verticillioides</em> virulence, endophytic infection, and general tolerance to hypoxic growth. Since nitrous oxide (N<sub>2</sub>O) is the final product of fungal denitrification, we are also assessing the impact of these genes on production of this greenhouse gas. This is important since agriculture is the primary source of global emissions of N<sub>2</sub>O, which has 300-times the warming potential of carbon dioxide.</div>