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A Delicate Balancing Act: Genes Governing Redox and Lipid Homeostasis Are Essential to the Biotrophic Growth of the Rice Blast Fungus Magnaporthe oryzae
Plant pathogens pose a major threat to global food security, accounting for up to 15% of annual crop losses, with fungal plant pathogens causing the bulk of plant diseases. The ascomycete fungus, Magnaporthe oryzae, is the causal agent of the devastating blast disease on rice ( Oryza sativa), which destroys 10-30% of the annual rice harvest—enough to feed up to 60 million people. M. oryzae grows undetected in the rice host before forming necrotic lesions. This requires tight regulation of shifts in metabolic requirements. Prior to host invasion, M. oryzae forms a specialized infection structure called an appressorium which forces a penetration peg through the rice cuticle. To build enough turgor pressure, via high osmolarity, lipid droplets, and other storage compounds must be degraded from the spore. Although, much is known about the role lipid metabolism plays in appressoria formation, little is known about how M. oryzae regulates metabolic shifts once inside the host, or the role lipid metabolism plays during proliferation. To gain insight, we characterized an acyl-CoA binding protein (Acbp1). Loss of ACBP1 results in changes to the lipid profile which leads to a shift in infection strategy by M. oryzae. Once inside the host, M. oryzae grows biotrophically, scavenging nutrients without being detected by the rice host. To grow undetected, M. oryzae must neutralize host oxidative bursts—which produce damaging reactive oxygen species (ROS)—to avoid triggering more robust host defense responses. How M. oryzae balances its oxidative stress response with its metabolic requirements is currently unknown. We sought to identify additional components of the antioxidation pathway linked with basic metabolism in M. oryzae. Here, we characterized a negative regulator of antioxidation, RXH1. Even though loss of RXH1 resulted in upregulation of antioxidation genes, it also led to loss of pathogenicity due to metabolic constraints, confirming the vital role redox homeostasis plays. Overall, the research presented in this dissertation expands our knowledge of previously unknown metabolic requirements and infection strategies employed by the rice blast fungus. This research can be used to assist in eradicating rice blast disease and ensure global food security.^
Segal, Lauren M, "A Delicate Balancing Act: Genes Governing Redox and Lipid Homeostasis Are Essential to the Biotrophic Growth of the Rice Blast Fungus Magnaporthe oryzae" (2018). ETD collection for University of Nebraska - Lincoln. AAI10793032.