Fungal Morphology, Iron Homeostasis, and Lipid Metabolism Regulated by a GATA Transcription Factor in Blastomyces dermatitidis

Abstract

In response to temperature, Blastomyces dermatitidis converts between yeast and mold forms. Knowledge of the mechanism(s) underlying this response to temperature remains limited. In B. dermatitidis, we identified a GATA transcription factor, SREB, important for the transition to mold. Null mutants (SREBΔ) fail to fully complete the conversion to mold and cannot properly regulate siderophore biosynthesis. To capture the transcriptional response regulated by SREB early in the phase transition (0–48 hours), gene expression microarrays were used to compare SREB∆ to an isogenic wild type isolate. Analysis of the time course microarray data demonstrated SREB functioned as a transcriptional regulator at 37°C and 22°C. Bioinformatic and biochemical analyses indicated SREB was involved in diverse biological processes including iron homeostasis, biosynthesis of triacylglycerol and ergosterol, and lipid droplet formation. Integration of microarray data, bioinformatics, and chromatin immunoprecipitation identified a subset of genes directly bound and regulated by SREB in vivo in yeast (37°C) and during the phase transition to mold (22°C). This included genes involved with siderophore biosynthesis and uptake, iron homeostasis, and genes unrelated to iron assimilation. Functional analysis suggested that lipid droplets were actively metabolized during the phase transition and lipid metabolism may contribute to filamentous growth at 22°C. Chromatin immunoprecipitation, RNA interference, and overexpression analyses suggested that SREB was in a negative regulatory circuit with the bZIP transcription factor encoded by HAPX. Both SREB and HAPX affected morphogenesis at 22°C; however, large changes in transcript abundance by gene deletion for SREB or strong overexpression for HAPX were required to alter the phase transition.

Genome-wide Identification of the Aspergillus oryzae GATA Transcription Factor Gene Family and expression Analysis under Temperature or Salt Stresses

“…Apart from the regulation of siderophore biosynthesis and iron metabolism, GATA TF SreA is also related with the maintenance of cell wall integrity and negatively impacts resistance as ΔsreA increases resistance to H 2 O 2 , calco uor white, and Congo red [10,14].The expression level of AoSreA was signi cantly downregulated under 40 ℃ and high salt stresses, which indicates AoSreA might negatively impact high-temperature and high salt resistance. In contrast, AoSreA was signi cantly upregulated at 22 ℃, and there is a report that the SreB strongly expresses and contributes to lamentous growth at 22 ℃ via lipid metabolism in Blastomyces dermatitidis [17]. AoSreA and SreB shared the same conserved ZnF_GATA domain ( Figure S2), which demonstrates that overexpression AoSreA in A. oryzae might also enhance the growth of mycelium at 22 ℃.…”

“…Fungal GATA TFs are mainly involved in the relation of nitrogen metabolism [12,31], light responses [13,29], siderophore biosynthesis and mating-type switching [10; 36]. Few GATA TFs in fungus also take part in response to the abiotic stresses, such as the SreA, SreB, LreA, LreB, GLN3 and GAT1 [10,13,17,18,29]. The number of the GATA TFs is conserved among A. clavatus, A. avus, A. fumigatus, A. nidulans, A. niger and A. oryaze that possess six GATA TFs, suggesting that lamentous fungi share an identical composition of GATA TFs with each other [26].…”

“…Transcription factors (TFs) are one of the key transcriptional regulators governing gene regulation and exhibit different expression pro les under distinct physiological and environmental conditions and act as synchronizing elements between stimuli and response. Many studies have revealed the GATA TFs are involved in the regulation of various abiotic stress responses in plants and few fungi [8,9,10,13,17,18,37]. The temperature and salt concentration are two of the most important environmental factors affecting the growth of A. oryzae during fermentation process [21,22,23,24,25].…”

“…For example, in Alternaria alternata, GATA TF SreA is related with the maintenance of cell wall integrity, and the ΔsreA increases resistance to calco uor white, Congo red and H 2 O 2 [10]. SreB strongly expresses and contributes to lamentous growth at 22 ℃ via lipid metabolism in Blastomyces dermatitidis [17]. Additionally, GLN3 and GAT1 of GATA TFs have been shown to be involved in salt tolerance in Saccharomyces cerevisiae [18].…”

Clinical Manifestations and Treatment of Blastomycosis

“…Recent genetic analyses identified a GATA transcription factor encoded by SREB that mediates the conversion from yeast to mycelia after a drop in temperature from 37 to 22°C. 34 SREB null mutants (SREBΔ) exhibit a defect in the morphologic shift that corresponds to a reduction in neutral lipid (ergosterol, triacylglycerol) biosynthesis and lipid droplet formation. In B. dermatitidis and H. capsulatum, N -acetylglucosamine transporters NGT1 and NGT2 accelerate the transition to mycelia at 22°C.…”