Regulatory Genes Controlling Fatty Acid Catabolism and Peroxisomal Functions in the Filamentous Fungus Aspergillus nidulans

Abstract

The catabolism of fatty acids is important in the lifestyle of many fungi, including plant and animal pathogens. This has been investigated in Aspergillus nidulans, which can grow on acetate and fatty acids as sources of carbon, resulting in the production of acetyl coenzyme A (CoA). Acetyl-CoA is metabolized via the glyoxalate bypass, located in peroxisomes, enabling gluconeogenesis. Acetate induction of enzymes specific for acetate utilization as well as glyoxalate bypass enzymes is via the Zn 2 -Cys 6 binuclear cluster activator FacB. However, enzymes of the glyoxalate bypass as well as fatty acid beta-oxidation and peroxisomal proteins are also inducible by fatty acids. We have isolated mutants that cannot grow on fatty acids. Two of the corresponding genes, farA and farB, encode two highly conserved families of related Zn 2 -Cys 6 binuclear proteins present in filamentous ascomycetes, including plant pathogens. A single ortholog is found in the yeasts Candida albicans, Debaryomyces hansenii, and Yarrowia lipolytica, but not in the Ashbya, Kluyveromyces, Saccharomyces lineage. Northern blot analysis has shown that deletion of the farA gene eliminates induction of a number of genes by both short-and long-chain fatty acids, while deletion of the farB gene eliminates short-chain induction. An identical core 6-bp in vitro binding site for each protein has been identified in genes encoding glyoxalate bypass, beta-oxidation, and peroxisomal functions. This sequence is overrepresented in the 5 region of genes predicted to be fatty acid induced in other filamentous ascomycetes, C. albicans, D. hansenii, and Y. lipolytica, but not in the corresponding genes in Saccharomyces cerevisiae.It has become increasingly clear that the breakdown of fatty acids is important in the metabolism, development, and pathogenicity of many fungi. Catabolism occurs via the beta-oxidation pathway, in which fatty acids are activated to the corresponding acyl coenzyme A (CoA) and then oxidation by a series of enzyme steps releases acetyl-CoA and an acyl-CoA shortened by two carbons, which can undergo additional cycles of beta-oxidation. In mammals, beta-oxidation of long-chain fatty acids occurs in peroxisomes, while medium-and shortchain fatty acids undergo beta-oxidation in the mitochondria (reviewed in references 16 and 84). In contrast, in Saccharomyces cerevisiae fatty acids are metabolized entirely in peroxisomes (reviewed in reference 29). In fungi, where fatty acids can serve as sole sources of carbon and energy, the acetyl-CoA must be converted to C 4 compounds via the glyoxalate bypass, comprising the enzymes isocitrate lyase and malate synthase, allowing gluconeogenesis (40, 64). Isocitrate lyase and malate synthase are usually, but not always, located in peroxisomes. It has been found that mutations affecting isocitrate lyase, malate synthase, and peroxisomal functions can affect the pathogenicity of both plant and animal pathogens (33,37,45,46,66). Furthermore it has been found that genes encoding enzymes for fatty acid catabol...

Transcriptional Control of Gluconeogenesis in Aspergillus nidulans

“…The FacB activator, which is similar to the Cat8/Sip4 proteins, is specific for the regulation of genes required for acetate utilization. The enzymes of the glyoxalate cycle that are required for growth on both acetate and fatty acids are additionally controlled by fatty acid induction independently of FacB, and regulatory genes involved in this have been identified (Hynes et al 2006). In S. cerevisiae, the glyoxalate cycle genes are not regulated by fatty acid induction but only by Cat8/Sip4 (Hiltunen et al 2003).…”

“…Molecular techniques: Standard methods for DNA manipulations, RNA isolation, nucleic acid blotting, and hybridization have been described (Sambrook et al 1989;Todd et al 2005;Hynes et al 2006).…”

Rearrangements of the transcriptional regulatory networks of metabolic pathways in fungi

“…The regulatory proteins involved in this process comprise the transcription factors (TFs) Adr1, Cat8, Oaf1 and Pip2 [26]. In Aspergilus nidulans, the TFs FarA and FarB were recently identified as central regulators of lipid utilization genes and were shown to bind the CCGAGG sequence: a farA mutant has a reduced peroxisomal proliferation and perturbs the oleate gene expression response [27]. Interestingly, both the CCGAGG cisregulatory element and the FarA protein are conserved in most ascomycetes, with the exception of Ashbya gossypii, Kluvyeromyces lactis, C. glabrata, S. cerevisiae and other Saccharomyces species [27] (Figure 1a).…”

“…In Aspergilus nidulans, the TFs FarA and FarB were recently identified as central regulators of lipid utilization genes and were shown to bind the CCGAGG sequence: a farA mutant has a reduced peroxisomal proliferation and perturbs the oleate gene expression response [27]. Interestingly, both the CCGAGG cisregulatory element and the FarA protein are conserved in most ascomycetes, with the exception of Ashbya gossypii, Kluvyeromyces lactis, C. glabrata, S. cerevisiae and other Saccharomyces species [27] (Figure 1a). The ortholog of FarA in C. albicans, Ctf1, is required for growth on oleate and different lipidic carbon sources while the TFs Cat8 and Adr1 are dispensable and Oaf1 and Pip2 are missing in C. albicans and related species [28,60].…”

Differential gene expression analysis of Paracoccidioides brasiliensis during keratinocyte infection

“…Infection of NOKs resulted in elevated expression of short-chain fatty acid CoA ligase (43 sequences) and glucosamine-6-phosphate isomerase (14 sequences) in the fungus, the high number of clones for these genes indicating that the main limitation to infection by P. brasiliensis is the acquisition of nutrients. Short-chain fatty acid CoA ligase, which catalyses the formation of acyl-CoA from a shortchain fatty acid, has a central role in the metabolism, development and pathogenicity of many fungi (Hynes et al, 2006). Fatty acids can serve as sole sources of carbon and energy, whilst acyl-CoAs serve as important intermediates in diverse metabolic functions such as fatty acid transport, oxidative degradation of fatty acids and phospholipid biosynthesis, as well as enzyme activation, cell signalling and transcriptional regulation (Morgan-Kiss & Cronan, 2004).…”