| 20173036 |
Murray SL, Hynes MJ: Metabolic and developmental effects resulting from deletion of the citA gene encoding citrate synthase in Aspergillus nidulans. Eukaryot Cell. 2010 Feb 19.
Citrate synthase is a central activity in carbon metabolism. It is required for the TCA cycle, respiration and for the glyoxylate cycle. In Saccharomyces cerevisiae and Arabidopsis thaliana there are mitochondrial and peroxisomal isoforms encoded by separate genes, while in Aspergillus nidulans, a single gene, citA, encodes a protein with predicted mitochondrial and peroxisomal targeting sequences (PTS). Deletion of citA results in poor growth on glucose but not on derepressing carbon sources, including those requiring the glyoxylate cycle. Growth on glucose is restored by a mutation in the creA carbon catabolite repressor gene. Methyl-citrate synthase, required for propionyl-CoA metabolism, has previously been shown to have citrate synthase activity. We have been unable to construct the mcsADelta;citADelta double mutant and the expression of mcsA is subject to CreA mediated carbon repression. Therefore McsA can substitute for the loss of CitA activity. Deletion of citA does not affect conidiation or sexual development but results in delayed conidial germination as well as a complete loss of ascospores in fruiting bodies, which can be attributed to loss of meiosis. These defects are suppressed by the creA204 mutation indicating that McsA activity can substitute for the loss of CitA. A mutation of the putative PTS1 encoding sequence in citA had no effect on carbon source utilisation or development but did result in slower colony extension arising from single conidia or ascospores. CitA-GFP studies showed mitochodrial localisation in conidia, ascospores and hyphae. Peroxisomal localisation was not detected. However a very low and variable detection of punctate GFP fluorescence was sometimes observed in conidia germinated for 5 hours when the mitochondrial targeting sequence was deleted. |
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