Roles of Elm1 in antifungal susceptibility and virulence in Candida glabrata

Delving into the molecular initiating event of cadmium toxification via the dose-dependent functional genomics approach in Saccharomyces cerevisiae

Determining dose-response relationship is essential for comprehensively revealing chemical-caused effects on organisms. However, uncertainty and complexity of gene/protein interactions cause the inability of traditional toxicogenomic methods (e.g., transcriptomics, proteomics and metabolomics) to effectively establish the direct relationship between chemical exposure and genes. In this work, we built an effective dose-dependent yeast functional genomics approach, which can clearly identify the direct gene-chemical link in the process of cadmium (Cd) toxification from a genome-wide scale with wide range concentrations (0.83, 2.49, 7.48, 22.45, 67.34, 202.03 and 606.1 μM). Firstly, we identified 220 responsive strains, and found that 142, 110, 91, 34, 8, 0 and 0 responsive strains can be respectively modulated by seven different Cd exposure concentrations ranging from high to low. Secondly, our results demonstrated that these genes induced by the high Cd exposure were mainly enriched in the process of cell autophagy, but ones caused by the low Cd exposure were primarily involved in oxidative stress. Thirdly, we found that the top-ranked GO biological processes with the lowest point of departure (POD) were transmembrane transporter complex and mitochondrial respiratory chain complex III, suggesting that mitochondrion might be the toxicity target of Cd. Similarly, nucleotide excision repair was ranked first in KEGG pathway with the least POD, indicating that this dose-dependent functional genomics approach can effectively detect the molecular initiating event (MIE) of cadmium toxification. Fourthly, we identified four key mutant strains (RIP1, QCR8, CYT1 and QCR2) as biomarkers for Cd exposure. Finally, the dose-dependent functional genomics approach also performed well in identifying MIE for additional genotoxicity chemical 4-nitroquinoline-1-oxide (4-NQO) data. Overall, our study developed a dose-dependent functional genomics approach, which is powerful to delve into the MIE of chemical toxification and is beneficial for guiding further chemical risk assessment.

The Gcn5-Ada2-Ada3 histone acetyltransferase module has divergent roles in pathogenesis of Candida glabrata

Candida glabrata is an opportunistic fungal pathogen and the second most prevalent species isolated from candidiasis patients. C. glabrata has intrinsic tolerance to antifungal drugs and oxidative stresses and the ability to adhere to mucocutaneous surfaces. However, knowledge about the regulation of its virulence traits is limited. The Spt-Ada-Gcn5 acetyltransferase (SAGA) complex modulates gene transcription by histone acetylation through the histone acetyltransferase (HAT) module comprised of Gcn5-Ada2-Ada3. Previously, we showed that the ada2 mutant was hypervirulent but displayed decreased tolerance to antifungal drugs and cell wall perturbing agents. In this study, we further characterized the functions of Ada3 and Gcn5 in C. glabrata. We found that single, double, or triple deletions of the HAT module, as expected, resulted in a decreased level of acetylation on histone H3 lysine 9 (H3K9) and defective growth. These mutants were more susceptible to antifungal drugs, oxidative stresses, and cell wall perturbing agents compared with the wild-type. In addition, HAT module mutants exhibited enhanced agar invasion and upregulation of adhesin and proteases encoding genes, whereas the biofilm formation of those mutants was impaired. Interestingly, HAT module mutants exhibited enhanced induction of catalases (CTA1) expression upon treatment with H2O2 compared with the wild-type. Lastly, although ada3 and gcn5 exhibited marginal hypervirulence, the HAT double and triple mutants were hypervirulent in a murine model of candidiasis. In conclusion, the HAT module of the SAGA complex plays unique roles in H3K9 acetylation, drug tolerance, oxidative stress response, adherence, and virulence in C. glabrata.

Forward and reverse genetic dissection of morphogenesis identifies filament-competent Candida auris strains

Candida auris is an emerging healthcare-associated pathogen of global concern. Recent reports have identified C. auris isolates that grow in cellular aggregates or filaments, often without a clear genetic explanation. To investigate the regulation of C. auris morphogenesis, we applied an Agrobacterium-mediated transformation system to all four C. auris clades. We identified aggregating mutants associated with disruption of chitin regulation, while disruption of ELM1 produced a polarized, filamentous growth morphology. We developed a transiently expressed Cas9 and sgRNA system for C. auris that significantly increased targeted transformation efficiency across the four C. auris clades. Using this system, we confirmed the roles of C. auris morphogenesis regulators. Morphogenic mutants showed dysregulated chitinase expression, attenuated virulence, and altered antifungal susceptibility. Our findings provide insights into the genetic regulation of aggregating and filamentous morphogenesis in C. auris. Furthermore, the genetic tools described here will allow for efficient manipulation of the C. auris genome.

Some isolates of the emerging fungal pathogen Candida auris can form cellular aggregates or filaments. Here, Santana and O’Meara use Agrobacterium-mediated transformation and a CRISPR-Cas9 system to identify several genes that regulate C. auris morphogenesis.