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Adaptations of Exophiala dermatitidis in Stressful Environments
Extremotolerant organisms live in extreme conditions of temperature, acidity, alkalinity, or salinity. Studying these organisms not only expands our knowledge on the diversity of life, but can also provide significant insight into how organisms adapt to stressful environments. We use the black yeast Exophiala dermatitidis as our model to investigate the molecular basis of physiological and morphological traits that allow organisms to survive extreme environments. The accumulation of pigments such as melanin and carotenoids likely play a key role in the stress tolerance of E. dermatitidis In addition to their expected roles in hyphal morphogenesis, functional characterization of the monomeric GTPases Cdc42 and Rac1 suggested a novel role in the regulation of carotenoid production in E. dermatitidis. Notably, in the presence of light, visible carotenoids fail to accumulate in the absence of Cdc42. Further experiments demonstrated that this is due to significantly reduced expression of the carotenoid biosynthetic gene cluster. To determine whether the deletion of cdc42 affects any other stress-related functions besides the carotenoid synthesis pathway, we performed RNAseq on wildtype E. dermatitidis and a set of cdc42 and rac1 mutants. Functional annotation using GO enrichment analysis identified several additional stress response pathways whose expression required Cdc42. DNA Motif analysis using upstream sequences from differentially expressed genes predicted transcription factors with known roles in the regulation of melanin biosynthetic and osmotic stress signaling pathways as potential downstream targets of Cdc42 signaling. To further investigate the role of light in the regulation of pigment production and other stress responses, we first verified the conservation of known light response pathways in E. dermatitidis. Notably, this analysis revealed that a homologue of the master circadian regulator FRQ is unexpectedly present in E. dermatitidis and other members of the Chaetothyriales. As a first step towards understanding the function of this homologue, we examined its expression under different light/dark incubation regimens but did not observe any obvious circadian rhythmicity. Additional experiments were undertaken to determine the effects of light on E. dermatitidis responses to diverse abiotic stresses such as reactive oxygen, UV light, and cell wall damage. These studies did not uncover any obvious affect, but did show that light has a previously undescribed role in the control of morphological transitions.
Kumar, Jyothi, "Adaptations of Exophiala dermatitidis in Stressful Environments" (2018). ETD collection for University of Nebraska - Lincoln. AAI10792984.