Author ORCID Identifier:
Date of Graduation
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Cell & Molecular Biology (PhD)
Degree Level
Graduate
Department
Cell & Molecular Biology
Advisor/Mentor
Egan, Martin
Committee Member
Rojas, Alejandro
Second Committee Member
Srivastava, Vibha
Third Committee Member
Wang, Yong
Keywords
Appressorium; Magnaporthe oryzae; NADPH Oxidases; Reactive Oxygen Species; Rice blast
Abstract
Rice blast is a devastating disease of cultivated rice, wheat, and other grasses, caused by the ascomycete Magnaporthe oryzae, also known as the blast fungus. M. oryzae initiates infection with a specialized pressure-generating cell called an appressorium to penetrate the leaf cuticle and access the host tissue. Remarkably, successful appressorium morphogenesis and functionality rely on the production of reactive oxygen species (ROS) by two NADPH oxidases, Nox1 and Nox2. These enzymes are homologs of the phagocyte NADPH oxidase gp91phox and are regulated by NoxR, a homolog of the phagocyte regulatory subunit p67phox. A third NADPH oxidase, Nox3 is also present in the genome of M. oryzae. It has an EF-hand calcium-binding domain absent in Nox1 and Nox2, and its role remains elusive. Nox2-derived ROS are essential for remodeling a higher-order septin ring-like structure in the base of the appressorium, a morphogenetic step critical for appressorium functionality. Furthermore, Nox2- derived ROS are thought to modulate actin-binding proteins through redox control, thereby influencing septin cytoskeleton dynamics. Despite the known importance of Nox2-derived ROS, the precise mechanism influencing the remodeling of higher-order septin structures and the spatiotemporal regulation of the Nox2 complex are not well characterized. In this study, we provide a time-resolved and quantitative analysis, including genetic deletion and pharmacological methods, to dissect how the absence of Nox2 and NoxR affects septin and F- actin dynamics. Our results support the critical role of Nox2-derived ROS in F-actin-mediated septin remodeling. To further understand the regulated production of ROS by the Nox complex formed by the catalytic subunit Nox2 and the regulatory subunit NoxR, we conducted proximity- dependent proteomics to identify novel components of the complex in M. oryzae. This approach identified several candidate proteins that may contribute to the spatial and temporal regulation of Nox2-derived ROS production. Lastly, to our knowledge, we conduct a functional characterization of Nox3 in M. oryzae, an isoform that has not been characterized in many fungal species. We report that Nox3, unlike Nox1 and Nox2, is dispensable for the pathogenicity of M. oryzae, but important for normal germ tube extension and spore generation. In summary, this work advances our understanding of the role of the ROS produced by the Nox2/NoxR NADPH oxidase complex, its importance for signaling the F-actin and septin cytoskeleton remodeling during appressorium morphogenesis, and its role in the pathogenicity of M. oryzae. Furthermore, we characterized the role of Nox3 in M. oryzae. These insights pave the way for exploring new targets within the NADPH oxidase complex, critical for the pathogenicity and development of filamentous fungi.
Citation
Rodriguez, C. M. (2025). NADPH Oxidase-Derived Reactive Oxygen Species: Key Signaling Molecules that Promote Blast Fungus Pathogenicity. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6027
