Genome-Wide Gene Expression Analyses of the AtfA/AtfB-Mediated Menadione Stress Response in Aspergillus nidulans

Total transcriptome response for tyrosol exposure in Aspergillus nidulans

Although tyrosol is a quorum-sensing molecule of Candida species, it has antifungal activity at supraphysiological concentrations. Here, we studied the effect of tyrosol on the physiology and genome-wide transcription of Aspergillus nidulans to gain insight into the background of the antifungal activity of this compound. Tyrosol efficiently reduced germination of conidia and the growth on various carbon sources at a concentration of 35 mM. The growth inhibition was fungistatic rather than fungicide on glucose and was accompanied with downregulation of 2199 genes related to e.g. mitotic cell cycle, glycolysis, nitrate and sulphate assimilation, chitin biosynthesis, and upregulation of 2250 genes involved in e.g. lipid catabolism, amino acid degradation and lactose utilization. Tyrosol treatment also upregulated genes encoding glutathione-S-transferases (GSTs), increased specific GST activities and the glutathione (GSH) content of the cells, suggesting that A. nidulans can detoxify tyrosol in a GSH-dependent manner even though this process was weak. Tyrosol did not induce oxidative stress in this species, but upregulated "response to nutrient levels", "regulation of nitrogen utilization", "carbon catabolite activation of transcription" and "autophagy" genes. Tyrosol may have disturbed the regulation and orchestration of cellular metabolism, leading to impaired use of nutrients, which resulted in growth reduction.

Coordination of two regulators SscA and VosA in Aspergillus nidulans conidia

Airborne fungal spores are a major cause of fungal diseases in humans, animals, and plants as well as contamination of foods. Previous studies found a variety of regulators including VosA, VelB, WetA, and SscA for sporogenesis and the long-term viability in Aspergillus nidulans. To gain a mechanistic understanding of the complex regulatory mechanisms in asexual spores, here, we focused on the relationship between VosA and SscA using comparative transcriptomic analysis and phenotypic studies. The ΔsscA ΔvosA double-mutant conidia have lower spore viability and stress tolerance compared to the ΔsscA or ΔvosA single mutant conidia. Deletion of sscA or vosA affects chitin levels and mRNA levels of chitin biosynthetic genes in conidia. In addition, SscA and VosA are required for the dormant state of conidia and conidial germination by modulating the mRNA levels of the cytoskeleton and development-associated genes. Overall, these results suggest that SscA and VosA play interdependent roles in governing spore maturation, dormancy, and germination in A. nidulans.

Global Transcriptomic Changes Elicited by sodB Deletion and Menadione Exposure in Aspergillus nidulans

Manganese superoxide dismutases (MnSODs) play a pivotal role in the preservation of mitochondrial integrity and function in fungi under various endogenous and exogenous stresses. Deletion of Aspergillus nidulans mnSOD/SodB increased oxidative stress sensitivity and apoptotic cell death rates as well as affected antioxidant enzyme and sterigmatocystin productions, respiration, conidiation and the stress tolerance of conidiospores. The physiological consequences of the lack of sodB were more pronounced during carbon starvation than in the presence of glucose. Lack of SodB also affected the changes in the transcriptome, recorded by high-throughput RNA sequencing, in menadione sodium bisulfite (MSB)-exposed, submerged cultures supplemented with glucose. Surprisingly, the difference between the global transcriptional changes of the ΔsodB mutant and the control strain were relatively small, indicating that the SodB-dependent maintenance of mitochondrial integrity was not essential under these experimental conditions. Owing to the outstanding physiological flexibility of the Aspergilli, certain antioxidant enzymes and endogenous antioxidants together with the reduction in mitochondrial functions compensated well for the lack of SodB. The lack of sodB reduced the growth of surface cultures more than of the submerged culture, which should be considered in future development of fungal disinfection methods.