No abstract

In filamentous fungi, asexual development involves cellular differentiation and metabolic remodeling leading to the formation of intact asexual spores. The development of asexual spores (conidia) in Aspergillus is precisely coordinated by multiple transcription factors (TFs), including VosA, VelB, and WetA. Notably, these three TFs are essential for the structural and metabolic integrity, i.e., proper maturation, of conidia in the model fungus Aspergillus nidulans. To gain mechanistic insight into the complex regulatory and interdependent roles of these TFs in asexual sporogenesis, we carried out multi-omics studies on the transcriptome, protein-DNA interactions, and primary and secondary metabolism employing A. nidulans conidia. RNA sequencing and chromatin immunoprecipitation sequencing analyses have revealed that the three TFs directly or indirectly regulate the expression of genes associated with heterotrimeric G-protein signal transduction, mitogen-activated protein (MAP) kinases, spore wall formation and structural integrity, asexual development, and primary/secondary metabolism. In addition, metabolomics analyses of wild-type and individual mutant conidia indicate that these three TFs regulate a diverse array of primary metabolites, including those in the tricarboxylic acid (TCA) cycle, certain amino acids, and trehalose, and secondary metabolites such as sterigmatocystin, emericellamide, austinol, and dehydroaustinol. In summary, WetA, VosA, and VelB play interdependent, overlapping, and distinct roles in governing morphological development and primary/secondary metabolic remodeling in Aspergillus conidia, leading to the production of vital conidia suitable for fungal proliferation and dissemination. IMPORTANCE Filamentous fungi produce a vast number of asexual spores that act as efficient propagules. Due to their infectious and/or allergenic nature, fungal spores affect our daily life. Aspergillus species produce asexual spores called conidia; their formation involves morphological development and metabolic changes, and the associated regulatory systems are coordinated by multiple transcription factors (TFs). To understand the underlying global regulatory programs and cellular outcomes associated with conidium formation, genomic and metabolomic analyses were performed in the model fungus Aspergillus nidulans. Our results show that the fungus-specific WetA/VosA/VelB TFs govern the coordination of morphological and chemical developments during sporogenesis. The results of this study provide insights into the interdependent, overlapping, or distinct genetic regulatory networks necessary to produce intact asexual spores. The findings are relevant for other Aspergillus species such as the major human pathogen Aspergillus fumigatus and the aflatoxin producer Aspergillus flavus.

Fungal development and metabolism are genetically programmed events involving specialized cellular differentiation, cellular communication, and temporal and spatial regulation of gene expression. In genus Aspergillus , the global regulators VeA and LaeA govern developmental and metabolic processes by affecting the expression of downstream genes, including multiple transcription factors and signaling elements.

Glutathione (GSH) is an abundant tripeptide that plays a crucial role in shielding cellular macromolecules from various reactive oxygen and nitrogen species in fungi. Understanding GSH metabolism is of vital importance to deciphering redox regulation in these microorganisms. In the present study, to better understand the GSH metabolism in filamentous fungi, we investigate functions of the dugB and dugC genes in the model fungus Aspergillus nidulans. These genes are orthologues of dug2-3 involved in cytosolic GSH degradation in the yeast. The deletion (Δ) of dugB, dugC, or both resulted in a moderate increase in the GSH content in the mycelia grown on glucose, reduced conidia production, and disturbed sexual development. In agreement with these observations, transcriptome data showed that genes encoding MAP kinase pathway elements (e.g. steC, sskB, hogA, mkkA) or regulatory proteins of conidiogenesis and sexual differentiation (e.g. flbA,C,E, nosA, rosA, nsdC,D) were down-regulated in the ΔdugBΔdugC mutant. Deletion of dugB and/or dugC slowed down the depletion of GSH pools under carbon starvation. It also reduced accumulation of reactive oxygen species, decreased autolytic cell wall degradation and enzyme secretion but increased sterigmatocystin formation. Transcriptome data demonstrated that enzyme secretions - in contrast to mycotoxin production - were controlled at post-transcriptional level. We suggest that GSH connects starvation and redox regulation to each other: Cells utilize GSH as stored carbon source during starvation. The reduction of GSH content alters the redox state activating regulatory pathways responsible for carbon starvation stress responses. Importance Glutathione (GSH) is a widely distributed tripeptide in both eukaryotes and prokaryotes. Owing to its very low redox potential, antioxidative character and high intracellular concentration, GSH profoundly shapes the redox status of cells. Our observations suggest that GSH metabolism and/or the redox status of cells plays a determinative role in several important aspects of fungal life, including oxidative stress defense, protein secretion, secondary metabolite production (including mycotoxin formation) as well as sexual and asexual differentiations. We demonstrated that even a slightly elevated GSH level can substantially disturb the homeostasis of fungi. This information could be important for development of new GSH producing strains or for any biotechnologically relevant processes where the GSH content, antioxidant capacity or oxidative stress tolerance of a fungal strain is manipulated.

Aspergillus flavus is an agriculturally and medically important filamentous fungus that produces mycotoxins, including aflatoxins, which are potent carcinogens. Here, we generated short- and long-read transcript sequence data from the growth of A. flavus strain NRRL 3357 under both typical and stress conditions to produce a new annotation of its genome.