Genetic Analysis of the Role of Peroxisomes in the Utilization of Acetate and Fatty Acids in Aspergillus nidulans

Abstract

Peroxisomes are organelles containing a diverse array of enzymes. In fungi they are important for carbon source utilization, pathogenesis, development, and secondary metabolism. We have studied Aspergillus nidulans peroxin (pex) mutants isolated by virtue of their inability to grow on butyrate or by the inactivation of specific pex genes. While all pex mutants are able to form colonies, those unable to import PTS1 proteins are partially defective in asexual and sexual development. The pex mutants are able to grow on acetate but are affected in growth on fatty acids, indicating a requirement for the peroxisomal localization of b-oxidation enzymes. However, mislocalization of malate synthase does not prevent growth on either fatty acids or acetate, showing that the glyoxylate cycle does not require peroxisomal localization. Proliferation of peroxisomes is dependent on fatty acids, but not on acetate, and on PexK (Pex11), expression of which is activated by the FarA transcription factor. Proliferation was greatly reduced in a farAD strain. A mutation affecting a mitochodrial ketoacyl-CoA thiolase and disruption of a mitochondrial hydroxy-acyl-CoA dehydrogenase gene prevented growth on short-chain but not long-chain fatty acids. Together with previous results, this is consistent with growth on even-numbered short-chain fatty acids requiring a mitochondrial as well as a peroxisomal b-oxidation pathway. The mitochondrial pathway is not required for growth on valerate or for long-chain fatty acid utilization.

Peroxisomal and Mitochondrial β-Oxidation Pathways Influence the Virulence of the Pathogenic Fungus Cryptococcus neoformans

“…Indeed, as described below, deletion analysis revealed that loss of HAD1 in C. neoformans caused phenotypes comparable to those from the loss of HAD1 in U. maydis. We also targeted the HAD1-encoded 3-OH-acyl-CoA dehydrogenase step in the mitochondrial ␤-oxidation pathway because loss of this enzyme caused the accumulation of inhibitory intermediates in A. nidulans (26,44,45). We reasoned that this might also reduce virulence for C. neoformans and therefore provide an additional incentive to target fungal ␤-oxidation as an antifungal strategy.…”

“…To test the possibility that defects in ␤-oxidation caused accumulation of toxic intermediates as seen in other fungi, the wildtype strain and the mutants were grown on the alternative carbon sources galactose, lactose, and acetate (16,26,40,44,45,48). No growth was observed on lactose, and galactose generally behaved like glucose as a catabolite-repressing carbon source (Fig.…”

“…A defect in peroxisomal ␤-oxidation influences the stress response and extracellular protease activity. As indicated above, the inability of cells to catabolize fatty acids can lead to the accumulation of toxic fatty acids or their metabolites (16,26,40,44,45,48). In addition, a defect in ␤-oxidation can alter the lipid composition of the plasma membrane due to the absence of specific fatty acids and phospholipids (42).…”

“…However, recent in silico surveys of the pathways encoded in more than 50 fungal genomes revealed that most fungi possess both mitochondrial and peroxisomal pathways (10,69). Mitochondrial ␤-oxidation has also been convincingly demonstrated in the saprophytic ascomycete Aspergillus nidulans (26,44,45).…”

Matching the proteome to the genome: the microbody of penicillin-producing Penicillium chrysogenum cells

“…For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article to be a microbody protein in A. nidulans (Valenciano et al 1998). Recently, it was shown that import of A. nidulans ICL1 in microbodies depends on the PTS2 receptor Pex7p (Hynes et al 2008). In all filamentous ascomycetes, including P. chrysogenum, ICL1 lacks a recognizable PTS, while in some yeast species and certain basidiomycetes, the protein contains a PTS1 (for alignment, see Supplementary Fig.…”