Genetic analysis of the role of peroxisomes in the utilization of acetate and fatty acids in Aspergillus nidulans

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 pexgenes. 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 mutant ts are able to grow oil acetate but are affected ill growth on fatty acids, indicating a requirement For the peroxisomal localization of beta-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 (far)A Delta strain. A mutation affecting a mitochodrial ketoacyl-CoA thiolase and disruption of a mitochondrial hydroxy-acyl-CoA dehydrogenase gene prevented growth on short-chair) 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 beta-oxidation pathway. The mitochondrial pathway is not: reqired for growth on valerate or for long-chain fatty acid utilization.