Mevalonate Diphosphate Decarboxylase MVD/Erg19 Is Required for Ergosterol Biosynthesis, Growth, Sporulation and Stress Tolerance in Aspergillus oryzae

Functional study of two ER localized sterol C-14 reductases in Aspergillus oryzae

Ergosterol is an important component of fungal cell membrane. Ergosterol biosynthesis involves sterol C-14 reductase, a key enzyme in ergosterol biosynthesis, which has been well studied in Saccharomyces cerevisiae. However, little studies about this important enzyme in Aspergillus oryzae. In this study, two sterol C-14 reductases named AoErg24A and AoErg24B were identified in A. oryzae using bioinformatics analysis. Through phylogenetic tree, expression pattern, subcellular localization, and yeast functional complementation analyses, we discovered that both AoErg24A and AoErg24B are conserved and localized to the endoplasmic reticulum (ER). Both enzymes can partially restore the temperature sensitivity phenotype of a S. cerevisiae erg24 weak mutant. Overexpression of AoErg24A in A. oryzae increased 1.6 times of ergosterol content, while overexpression of AoErg24B led to a slight decrease of ergosterol. Both genes affect the sporulation of A. oryzae. These results uncovered that the two genes function differently in ergosterol biosynthesis. Thus, this study further enhances our understanding of ergosterol biosynthesis in A. oryzae and lays a good foundation for A. oryzae to be used in industrial ergosterol production.

Strategies for the Enhancement of Secondary Metabolite Production via Biosynthesis Gene Cluster Regulation in Aspergillus oryzae

The filamentous fungus Aspergillus oryzae (A. oryzae) has been extensively used for the biosynthesis of numerous secondary metabolites with significant applications in agriculture and food and medical industries, among others. However, the identification and functional prediction of metabolites through genome mining in A. oryzae are hindered by the complex regulatory mechanisms of secondary metabolite biosynthesis and the inactivity of most of the biosynthetic gene clusters involved. The global regulatory factors, pathway-specific regulatory factors, epigenetics, and environmental signals significantly impact the production of secondary metabolites, indicating that appropriate gene-level modulations are expected to promote the biosynthesis of secondary metabolites in A. oryzae. This review mainly focuses on illuminating the molecular regulatory mechanisms for the activation of potentially unexpressed pathways, possibly revealing the effects of transcriptional, epigenetic, and environmental signal regulation. By gaining a comprehensive understanding of the regulatory mechanisms of secondary metabolite biosynthesis, strategies can be developed to enhance the production and utilization of these metabolites, and potential functions can be fully exploited.

Ergosterol Is Critical for Sporogenesis in Cryptococcus neoformans

Microbes, both bacteria and fungi, produce spores to survive stressful conditions. Spores produced by the environmental fungal pathogen Cryptococcus neoformans serve as both surviving and infectious propagules. Because of their importance in disease transmission and pathogenesis, factors necessary for cryptococcal spore germination are being actively investigated. However, little is known about nutrients critical for sporogenesis in this pathogen. Here, we found that ergosterol, the main sterol in fungal membranes, is enriched in spores relative to yeasts and hyphae. In C. neoformans, the ergosterol biosynthesis pathway (EBP) is upregulated by the transcription factor Sre1 in response to conditions that demand elevated ergosterol biosynthesis. Although the deletion of SRE1 enhances the production of mating hyphae, the sre1Δ strain is deficient at producing spores even when crossed with a wild-type partner. We found that the defect of the sre1Δ strain is specific to sporogenesis, not meiosis or basidium maturation preceding sporulation. Consistent with the idea that sporulation demands heightened ergosterol biosynthesis, EBP mutants are also defective in sporulation. We discovered that the overexpression of some EBP genes can largely rescue the sporulation defect of the sre1Δ strain. Collectively, we demonstrate that ergosterol is a critical component in cryptococcal preparation for sporulation.

The expression pattern, subcellular localization and function of three sterol 14α-demethylases in Aspergillus oryzae

Sterol 14α-demethylase catalyzes lanosterol hydroxylation, which is one of the key reactions in the biosynthetic pathway of sterols. There is only one sterol 14α-demethylases gene named Erg11 in Saccharomyces cerevisiae genome. In this study, three sterol 14α-demethylases genes named AoErg11A, AoErg11B and AoErg11C were identified in Aspergillus oryzae genome through bioinformatics analysis. The function of these three genes were studied by yeast complementation, and the expression pattern/subcellular localization of these genes/proteins were detected. The results showed that the three AoErg11s were expressed differently at different growth times and under different abiotic stresses. All of the three proteins were located in endoplasmic reticulum. The AoErg11s could not restore the temperature-sensitive phenotype of S. cerevisiae erg11 mutant. Overexpression of the three AoErg11s affected both growth and sporulation, which may be due to the effect of AoErg11s on ergosterol content. Therefore, this study revealed the functions of three AoErg11s and their effects on the growth and ergosterol biosynthesis of A. oryzae, which may contribute to the further understanding of the ergosterol biosynthesis and regulation mechanism in this important filamentous fungus, A. oryzae.

Identification of Six Thiolases and their Effects on Fatty Acid and Ergosterol Biosynthesis in Aspergillus oryzae

Thiolase plays important roles in lipid metabolism. It can be divided into degradative thiolases (Thioase I) and biosynthetic thiolases (thiolases II), which are involved in fatty acid β-oxidation and acetoacetyl-CoA biosynthesis, respectively. The Saccharomyces cerevisiae (S. cerevisiae) genome harbors only one gene each for thioase I and thiolase II, namely, Pot1 and Erg10, respectively. In this study, six thiolases (named AoErg10A-AoErg10F) were identified in Aspergillus oryzae (A. oryzae) genome using bioinformatics analysis. Quantitative reverse transcription-PCR (qRT-PCR) indicated that the expression of these six thiolases varied at different growth time and under different forms of abiotic stress. Subcellular localization analysis showed that AoErg10A was located in the cytoplasm, AoErg10B and AoErg10C in the mitochondria, and AoErg10D-AoErg10F in the peroxisome. Yeast heterologous complementation assays revealed that AoErg10A, AoErg10D, AoErg10E, AoErg10F and cytoplasmic AoErg10B (AoErg10B^ΔMTS) recovered the phenotypes of S. cerevisiae erg10 weak and lethal mutants, and that only AoErg10D-F recovered the phenotype of the pot1 mutant that cannot use oleic acid as the carbon source. Overexpression of AoErg10s either affected the growth speed or sporulation of the transgenic strains. In addition, the fatty acid and ergosterol content changed in all the AoErg10-overexpressing strains. This study revealed the function of six thiolases in A. oryzae and their effect on growth, and fatty acid and ergosterol biosynthesis, which may lay the foundation for genetic engineering for lipid metabolism in A. oryzae or other fungi. Importance Thiolase including thioase I and thiolase II, plays important roles in lipid metabolism. A. oryzae, one of the most industrially important filamentous fungi, has been widely used for manufacturing oriental fermented food such as sauce, miso, and sake for a long time. Besides, A. oryzae has a high capability in production of high lipid content and has been used for lipid production. Thus, it is very important to investigate the function of thiolases in A. oryzae. In this study, six thiolase (named AoErg10A-AoErg10F) were identified by bioinformatics analysis. Unlike other reported thiolases in fungi, three of the six thiolases showed dual function of thioase I and thiolase II in S. cerevisiae, indicating the lipid metabolism is more complex in A. oryzae. The reveal of function of these thiolases in A. oryzae can lay the foundation for genetic engineering for lipid metabolism in A. oryzae or other fungi.

Synthesis of aminoacylated ergosterols: A new lipid component of fungi

Aminoacylated ergosterol such as 1-ergosteryl aspartate (Erg-Asp) is a new lipid component recently discovered in fungi. In order to study physiological functions of this novel sterol derivative and to develop potential antifungal agents, we established the method to synthesize aminoacylated ergosterol derivatives. Herein, we report the synthesis of Erg-Asp as well as some other aminoacylated ergosterols (Erg-Gly, Erg-Ala, Erg-Leu, Erg-Ile, and Erg-Val) using Boc protected amino acids.

Effects on Gene Transcription Profile and Fatty Acid Composition by Genetic Modification of Mevalonate Diphosphate Decarboxylase MVD/Erg19 in Aspergillus Oryzae

Mevalonate diphosphate decarboxylase MVD/Erg19 is required for ergosterol biosynthesis, growth, sporulation, and stress tolerance in Aspergillus oryzae. In this study, RNA-seq was used to analyze the gene transcription profile in AoErg19 overexpression (OE) and RNAi strains. There were 256 and 74 differentially expressed genes (DEGs) in AoErg19 OE and RNAi strains, respectively, compared with the control strain (CK). The most common DEGs were transport- and metabolism-related genes. Only 22 DEGs were obtained that were regulated in both OE and RNAi strains. The transcriptomic comparison between CK and AoErg19 overexpression strain (CK vs. OE), and between CK and AoErg19 RNAi strain (CK vs. RNAi) revealed that the greatest difference existed in the number of genes belonging to the cytochrome P450 family; 12 were found in CK vs. OE, whereas 1 was found in CK vs. RNAi. The expression patterns of lipid biosynthesis and metabolism related genes were altered in OE and RNAi strains, either by gene induction or suppression. Moreover, the total fatty acid content in the RNAi strain was 12.1% greater than the control strain, but no difference in total acid content was found between the overexpression strain and the control strain. Therefore, this study highlights the gene expression regulation within mevalonate (MVA), ergosterol biosynthesis, and fatty acid biosynthesis pathways.