Characterization of the mbsA Gene Encoding a Putative APSES Transcription Factor in Aspergillus fumigatus

Abstract

The APSES family proteins are transcription factors (TFs) with a basic helix-loop-helix domain, known to regulate growth, development, secondary metabolism, and other biological processes in Aspergillus species. In the genome of the human opportunistic pathogenic fungus Aspergillus fumigatus, five genes predicted to encode APSES TFs are present. Here, we report the characterization of one of these genes, called mbsA (Afu7g05620). The deletion (Δ) of mbsA resulted in significantly decreased hyphal growth and asexual sporulation (conidiation), and lowered mRNA levels of the key conidiation genes abaA, brlA, and wetA. Moreover, ΔmbsA resulted in reduced spore germination rates, elevated sensitivity toward Nikkomycin Z, and significantly lowered transcripts levels of genes associated with chitin synthesis. The mbsA deletion also resulted in significantly reduced levels of proteins and transcripts of genes associated with the SakA MAP kinase pathway. Importantly, the cell wall hydrophobicity and architecture of the ΔmbsA asexual spores (conidia) were altered, notably lacking the rodlet layer on the surface of the ΔmbsA conidium. Comparative transcriptomic analyses revealed that the ΔmbsA mutant showed higher mRNA levels of gliotoxin (GT) biosynthetic genes, which was corroborated by elevated levels of GT production in the mutant. While the ΔmbsA mutant produced higher amount of GT, ΔmbsA strains showed reduced virulence in the murine model, likely due to the defective spore integrity. In summary, the putative APSES TF MbsA plays a multiple role in governing growth, development, spore wall architecture, GT production, and virulence, which may be associated with the attenuated SakA signaling pathway.

The C 2 H 2 transcription factor SltA is required for germination and hyphal development in Aspergillus fumigatus

“…The GT biosynthesis genes gliA , gliF , gliT , gliM , and gliG were upregulated in the ∆ sltA strain. The gliA , gliT , and gliM genes were also upregulated in A. fumigatus ∆ mbsA and ∆ rgdA strains which resulted in a fivefold higher production of GT in both strains ( 56 , 57 ). Virulence, however, of the ∆ sltA , ∆ mbsA , and ∆ rgdA strains were reduced in neutropenic mice when compared to the WT strain ( 16 , 56 , 57 ).…”

Identification of a Novel Pleiotropic Transcriptional Regulator Involved in Sporulation and Secondary Metabolism Production in Chaetomium globosum

“…Investigations into pleiotropic regulatory genes in microorganisms have revealed that secondary metabolite production is often closely associated with morphological development and nutrient availability. In a previous study, inactivation of the mbsA gene (Afu7g05620) in Aspergillus fumigatus caused a significant reduction in spore germination rates and chitin synthesis capacity; however, antibiotic resistance and mRNA levels of gliotoxin biosynthetic genes increased markedly [ 44 ]. Disruption of urdA gene expression in A. nidulans increased sterigmatocystin yield in a light-dependent manner, which was achieved by the up-regulation of aflR and stcU expression.…”

The Lysine Demethylases KdmA and KdmB Differently Regulate Asexual Development, Stress Response, and Virulence in Aspergillus fumigatus

“…The expression ratios were normalized to the expression level of the reference gene ef1α [ 25 , 26 ] and calculated using the ΔΔCq method [ 27 ]. The expression stability of ef1α and efficiencies of PCRs of the target genes were determined as previously described [ 28 ]. Expression levels of target gene mRNAs were analyzed using appropriate oligonucleotide pairs ( Table S1 ).…”

“…After incubation at 37 °C for 48 h, MIC values were determined as the zone edge intersecting the strips. The production of secondary metabolites and GT was determined as described previously [ 28 , 29 ]. GT standard was purchased from Sigma-Aldrich (Burlington, MA, USA).…”

“…The virulence assay was conducted as previously described [ 28 , 36 ]. Briefly, for the immunocompromised mouse model, we used outbred CrlOri: CD1 (ICR) (Orient Bio Inc., Seongnam, Korea) female mice (6–8 weeks old, average weighing 30 g), which were housed at a density of five per cage and provided access to food and water ad libitum.…”