|Chang, Perng Kuang|
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2003
Publication Date: 6/1/2004
Citation: Wilson, R.A., Chang, P.-K, Dobrzyn, A., Ntambi, J.M., Zarnowski, R., Keller, N.P. 2004. Two delta 9-stearic acid desaturases are required for Aspergillus nidulans growth and development. Fungal Genetics and Biology. 41:501-509.
Interpretive Summary: Aflatoxin contamination of oilseed crops by Aspergillus flavus and A. parasiticus remains a persistent problem in many countries. To interrupt the infection cycle, one approach would involve reducing the production of spores, the main disseminating mechanism for fungal propagation, such that fewer spores are produced for the next round of infection. To this end, an understanding of the factors that influence fungal development is necessary. Unsaturated fatty acids are important constituents of cell membranes and are required for normal fungal growth and development. To investigate the relationship between fatty acid metabolism and spore production, we disrupted genes necessary for the production of the fatty acids, palmitoleic- and oleic acid, in A. nidulans. This study has elucidated the role of specific fatty acid in Aspergillus development. New strategies that reduce spore loads of toxigenic strains in the field through the manipulation of fungal fatty acid metabolism thus are feasible. Success would lead to a net reduction in aflatoxin contamination of oilseed crops during growing seasons, and a net increase in profitability to the growers.
Technical Abstract: Unsaturated fatty acids are important constituents of all cell membranes and are required for normal growth. In the filamentous fungus Aspergillus nidulans, unsaturated fatty acids and their derivatives also influence asexual (conidial) and sexual (ascospore) sporulation processes. To investigate the relationship between fatty acid metabolism and fungal development, we disrupted the A. nidulans sdeA and sdeB genes, both encoding delta 9-stearic acid desaturases responsible for the conversion of palmitic acid (16:0) and stearic acid (18:0) to palmitoleic acid (16:1) and oleic acid (18:1). The effects of sdeA deletion on development were profound, such that growth, conidial, and ascospore production were all reduced at 22 degrees C and 37 degrees C. Total fatty acid content was increased over three fold in the delta sdeA strain, reflected in up-regulation of the expression of the fasA gene encoding the alpha chain of the fatty acid synthase, compared to wild type. Stearic acid accumulated approximately three fold compared to wild type in the delta sdeA strain, while unsaturated fatty acid production was decreased. In contrast, disruption of sdeB reduced fungal growth and conidiation at 22 degrees C, but did not affect these processes at 37 degrees C compared to wild type. Interestingly, ascospore production was increased at 37 degrees C for delta sdeB compared to wild type. Total fatty acid content was not increased in this strain, although stearic acid accumulated two fold compared to wild type, and unsaturated fatty acid production was decreased. Combining the delta sdeA and delta sdeB alleles created a synthetic lethal strain requiring the addition of oleic acid to the medium for a modicum of growth. Taken together, our results suggest a role for sdeA in growth and development at all temperatures, while sdeB is involved in growth and development at lower temperatures.