Abstract
Aspergillus nidulans has one gene for alternative oxidase (EC 1.10.3.11). To investigate the relationship between this mitochondrial terminal oxidase and the formation of the mycotoxin sterigmatocystin, the encoding aodA gene was both deleted and overexpressed. Relative to the wild-type, the cyanide-resistant fraction of respiration in the late stationary stage—when sterigmatocystin production occurs—doubled in the overexpressing mutant carrying three aodA gene copies, but decreased to 10% in the deletant. Essentially identical results were obtained regardless whether the cultures were illuminated or protected from light. In contrast, sterigmatocystin yield in the aodA deletant was about half of that in the control when grown in the dark, while aodA overexpression resulted in up to 70% more sterigmatocystin formed, the yield increasing with alternative oxidase activity. Results were quite different when cultures were illuminated: under those conditions, sterigmatocystin volumetric yields were considerably lower, and statistically unvarying, regardless of the presence, absence, or the copy number of aodA. We conclude that the copy number of aodA, and hence, the balance between alternative- and cytochrome C-mediated respiration, appears to correlate with sterigmatocystin production in A. nidulans, albeit only in the absence of light.
Highlights
IntroductionAlternative oxidase (AOX) (systematic name: ubiquinol:oxygen oxidoreductase, nonelectrogenic; EC 1.10.3.11) occurs in many organisms: in plants and fungi, and in animals and protists [1,2,3,4,5,6]
Alternative oxidase (AOX) occurs in many organisms: in plants and fungi, and in animals and protists [1,2,3,4,5,6].This cyanide-resistant terminal oxidase is located on the matrix side of the inner mitochondrial membrane (IMM)
Unlike most of the cytochrome C oxidase (COX) subunits, alternative oxidase is encoded in the nuclear genome and it provides an “alternative” for the electron flow opposite to the Toxins 2018, 10, 168; doi:10.3390/toxins10040168
Summary
Alternative oxidase (AOX) (systematic name: ubiquinol:oxygen oxidoreductase, nonelectrogenic; EC 1.10.3.11) occurs in many organisms: in plants and fungi, and in animals and protists [1,2,3,4,5,6]. This cyanide-resistant terminal oxidase is located on the matrix side of the inner mitochondrial membrane (IMM). The alternative pathway after NADH: ubiquinone oxidoreductase (complex I), which oxidizes NADH to NAD+ and reduces ubiquinone to ubiquinol while translocating four protons, moves fewer protons across the inner mitochondrial membrane to generate a proton gradient, and provides less ATP by oxidative phosphorylation [7]. Many ascomycetous filamentous fungi harbour two or even three homologue genes encoding an AOX in their genome, Aspergillus nidulans—a model system for biochemical and genetic research in multicellular fungi—features only a single alternative oxidase gene named aodA
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