PhD Dissertation Defense: Walker Huso

Abstract:

Filamentous fungi are tough and resilient organisms. The cell wall plays an important role in maintaining the strong exterior protection necessary for fungal growth in stressful environments. This study focuses on the fungi Aspergillus nidulans and the signaling and repair mechanisms that defend against cell wall stress. Phosphoproteomics was used to study the well conserved mitogen-activated protein kinase cascades (MAPK’s), specifically the Cell Wall Integrity (CWI) pathway, and the response to cell wall stress. MpkA is the final kinase in the CWI pathway and plays an important role in homeostasis as well as the response to the echinocandin, micafungin. To better understand the role of MpkA under ideal, steady-state growth conditions, a single
endpoint phosphoproteomic study was carried out to compare changes in protein phosphorylation and gene expression between a mpkA deletion mutant and the isogenic control strain. This study suggests that MpkA is crucial for maintaining cell wall strength as well as playing an important role in branching and iron homeostasis.

Next, a dynamic phosphoproteomic approach was used to characterize the normal cellular response to cell wall stress. A multi-omic approach was used to capture dynamic changes in both phosphorylation and transcription over time using phosphoproteomics and transcriptomic studies. A multivariate adaptive regression splines (MARS) analysis was used to model the dynamic behavior in both datasets in response to micafungin treatment. This approach identified 431 dynamic phosphorylation sites and 1810 dynamic transcripts after cell wall
perturbation. The kinases that exhibited dynamic behavior were further characterized by testing kinase deletion strains. These strains were tested to determine the impact the deletion had on cell wall strength and micafungin sensitivity. This approach revealed novel connections and crosstalk mediated by the CWI pathway with the high osmolarity- glycerol (HOG) pathway and the septation initiation network (SIN).

Agenda: