Plasticity of a key metabolic pathway in fungi

Beta oxidation is the principal metabolic pathway for fatty acid degradation. The pathway is virtually universally present throughout eukaryotes yet displays different forms in enzyme architecture, substrate specificity, and subcellular location. In this review, we examine beta oxidation across the fungal kingdom by conducting a large-scale in silico screen and localization prediction for all relevant enzymes in > 50 species. The survey reveals that fungi exhibit an astounding diversity of beta oxidation pathways and shows that the combined presence of distinct mitochondrial and peroxisomal pathways is the prevailing and likely ancestral type of beta oxidation in fungi. In addition, the available information indicates that the mitochondrial pathway was lost in the common ancestor of Saccharomycetes. Finally, we infer the existence of a hybrid peroxisomal pathway in several Sordariomycetes, including Neurospora crassa. In these cases, a typically mitochondrion-located enzyme compensates for the lack of a peroxisomal one.