Transcriptomic analysis reveals Aspergillus oryzae responds to temperature stress by regulating sugar metabolism and lipid metabolism.

Aspergillus oryzae is widely used in industrial applications, which always encounter changes within multiple environmental conditions during fermentation, such as temperature stress. However, the molecular mechanisms by which A. oryzae protects against temperature stress have not been elucidated. Therefore, this study aimed to characterize the fermentative behavior, transcriptomic profiles, and metabolic changes of A. oryzae in response to temperature stress. Both low and high temperatures inhibited mycelial growth and conidial formation of A. oryzae. Transcriptomic analysis revealed that most differentially expressed genes (DEGs) were involved in sugar metabolism and lipid metabolism under temperature stress. Specifically, the DEGs in trehalose synthesis and starch metabolism were upregulated under low-temperature stress, while high temperatures inhibited the expression of genes involved in fructose, galactose, and glucose metabolism. Quantitative analysis of intracellular sugar further revealed that low temperature increased trehalose accumulation, while high temperature increased the contents of intracellular trehalose, galactose, and glucose, consistent with transcriptome analysis. In addition, most DEGs involved in lipid metabolism were significantly downregulated under low-temperature stress. Furthermore, the metabolomic analysis revealed that linoleic acid, triacylglycerol, phosphatidylethanolamine, and phosphoribosyl were significantly decreased in response to low-temperature stress. These results increase our understanding of the coping mechanisms of A. oryzae in response to temperature stress, which lays the foundation for future improvements through genetic modification to enhance A. oryzae against extreme temperature stress.

Inhibition of AoAur1 increases mycelial growth, hyphal fusion and improves physiological adaptation to high-temperature stress in Aspergillus oryzae.

Inositol phosphorylceramide (IPC) participates in hyphal growth and serves as a signaling molecule that enables fungi to adapt to diverse environments. Here, a gene, encodes IPC synthase, was identified from the Aspergillus oryzae 3.042 genome and designated AoAur1. The characteristics, phylogenetic evolution, and resistance to aureobasidin A of AoAur1 were analyzed. The expression pattern of AoAur1 was markedly downregulated under temperature stress. Additionally, an RNAi-AoAur1 strain in which the AoAur1 expression was inhibited had mycelial that grew more quickly, had a higher frequency of hyphal fusion, and was more resistant to high-temperature stress than the control. Gene expression profiles showed that the genes related to IPC biosynthesis were obviously downregulated, while AoCerS, which participates in dihydroceramide biosynthesis, increased in the RNAi-AoAur1 strain at the three temperature treatments. A metabolomic analysis revealed that the intracellular IPC content decreased, and the accumulation of dihydroceramide and galactosylceramide increased significantly in the RNAi-AoAur1 strain. Thus, the inhibition of AoAur1 reduced IPC level followed by an increase in the contents of dihydroceramide and galactosylceramide that promote mycelial growth and the formation of spores in the RNAi-AoAur1 strain. Interestingly, the inhibition of AoAur1 also induced the expression of hyphal fusion-related genes, which promote hyphal fusion, thus, contributing to the transduction of stress signal to enhance the ability of cells to adapt to temperature stress. Our results demonstrated that the downregulation of AoAur1 and a decrease in the accumulation of IPC is one of the mechanisms that enables A. oryzae to adapt low- and high-temperature stress.

Glycosphingolipids in Filamentous Fungi: Biological Roles and Potential Applications in Cosmetics and Health Foods.

Filamentous fungi are a group of economically important fungi used in the production of fermented foods, industrial enzymes, and secondary metabolites. Glycosphingolipids (GSLs) as constituents of lipid rafts are involved in growth, differentiation, and response to environment stress in filamentous fungi. In addition to these key roles, GSLs are also important in the barrier function of skin to retain moisture as a moisturizing ingredient in cosmetics or health products for their strong biological activity as a functional component. GSLs found in filamentous fungi are divided in two major classes: neutral GSLs (glycosylceramides), glucosylceramides (GlcCers), and/or galactosylceramides (GalCers) and acidic GSLs, mannosylinositol phosphorylceramide (MIPC) and mannosyldiinositol phosphorylceramide [M(IP)2C]. Glycosylceramides are one of the abundant GSLs in Aspergillus and known to improve skin-barrier function and prevent intestinal impairment as a prebiotic. Some filamentous fungi of Aspergillus spp., synthesizing both GlcCer and GalCer, would be an amenable source to exploit glycosylceramides that wildly adding in cosmetics as moisturizing ingredients or health food as dietary supplements. In this minireview, the types, structures, and biosynthetic pathways of GSLs in filamentous fungi, and the relevance of GSLs in fungal growth, spore formation, and environmental stress response are explained. Furthermore, the advantage, potential development, and application of GlcCer and GalCer from filamentous fungi Aspergillus spp. are also investigate based on the use of plant GlcCer in health foods and cosmetics.

Genome-wide identification of the GATA transcription factor family and their expression patterns under temperature and salt stress in Aspergillus oryzae.

GATA transcription factors (TFs) are involved in the regulation of growth processes and various environmental stresses. Although GATA TFs involved in abiotic stress in plants and some fungi have been analyzed, information regarding GATA TFs in Aspergillus oryzae is extremely poor. In this study, we identified and functionally characterized seven GATA proteins from A. oryzae 3.042 genome, including a novel AoSnf5 GATA TF with 20-residue between the Cys-X2-Cys motifs which was found in Aspergillus GATA TFs for the first time. Phylogenetic analysis indicated that these seven A. oryzae GATA TFs could be classified into six subgroups. Analysis of conserved motifs demonstrated that Aspergillus GATA TFs with similar motif compositions clustered in one subgroup, suggesting that they might possess similar genetic functions, further confirming the accuracy of the phylogenetic relationship. Furthermore, the expression patterns of seven A. oryzae GATA TFs under temperature and salt stresses indicated that A. oryzae GATA TFs were mainly responsive to high temperature and high salt stress. The protein-protein interaction network of A. oryzae GATA TFs revealed certain potentially interacting proteins. The comprehensive analysis of A. oryzae GATA TFs will be beneficial for understanding their biological function and evolutionary features and provide an important starting point to further understand the role of GATA TFs in the regulation of distinct environmental conditions in A. oryzae.