Genetic analysis of the role of peroxisomes in the utilisation of acetate and fatty acids in Aspergillus nidulans
Michael J. Hynes 1*, Sandra L. Murray 1, Gillian S. Khew 1 and Meryl A. Davis 1
1 University of Melbourne
* To whom correspondence should be addressed. E-mail: mjhynes{at}unimelb.edu.au.
Submitted on December 11, 2007
Revised on January 2, 2008
Accepted on 17 January 2008
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Abstract |
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Peroxisomes are organelles containing a diverse array of enzymes. In fungi they are important for carbon source utilisation, 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 localisation of b-oxidation enzymes. However mislocalisation of malate synthase does not prevent growth on either fatty acids or acetate showing that the glyoxalate cycle does not require peroxisomal localisation. Proliferation of peroxisomes is dependent on fatty acids, but not acetate, and on PexK (Pex11), expression of which is activated by the FarA transcription factor. Proliferation was abolished in a farA 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 nor for long chain fatty acid utilisation.
Key Words:
Aspergillus, filamentous fungi, metabolism, peroxisomes, regulation
