Functional characterization of a putative alternative oxidase in Sporisorium reilianum f. sp. zeae.

Sporisorium reilianum is a pathogenic basidiomycete fungus with two formae speciales, each capable of infecting corn (SRZ) or sorghum (SRS), respectively. This fungus is also a dimorphic variety, meaning it can switch between its haploid, yeast-like sporidia and diploid teliospore stages over the course of its life cycle (Schirawski). When S. reilianum is found in a haploid state and conditions are favorable, it will mate with a compatible non-self mating type to begin filamentous growth and proliferation in the plant host (Zhao). S. relianum, like most fungi, utilizes the four classical components of the electron transport chain to produce the high energy molecule, adenosine triphosphate (ATP), via oxidative phosphorylation in the mitochondrion (Horne). Some fungal species such as Ustilago maydis, a sister species to S. reilianum, possess additional components to this process, e.g., alternative oxidase (Aox), which serves as an alternate route of electron transfer to produce basal levels of ATP if the classical electron transport chain were compromised (O. G. Juarez). Using bioinformatics, Aox was previously identified in S. reilianum by the Perlin lab (Culver). The focus of the following experiments was on the characterization of Aox and the potential effects on pathogenicity and growth it may have in SRZ. Additionally, the investigation of potential differential expression of the gene encoding Aox during two energetically distinct stages of the fungus’ life cycle was of interest. This study further confirmed the presence of an alternative oxidase as part of the ETC of SRZ. The activity of this protein renders respiration in SRZ antimycin-resistant by providing an alternate terminal point for electron transport if the classical cytochrome c pathway is compromised. The alternative oxidase of SRZ was determined to play a role in the fungus’ pathogenic stage, as its absence significantly decreases mean disease severity. Differential expression of Aox was made evident in distinct stages of the fungal life cycle and is in concordance with their specific metabolic needs