Librais, G. M. | Search bioRxiv

bioRxiv2025

Distinct Ire1-driven transcriptional responses control morphogenesis in Candida albicans

The pathogenic yeast Candida albicans relies on morphogenesis--the transition from spherical yeast to filamentous hyphal forms--for infection. While morphogenesis requires Ire1, a transmembrane protein that canonically initiates the Unfolded Protein Response (UPR) through HAC1 mRNA splicing, the specific mechanisms linking Ire1 to filamentation remain unclear. Using transcriptome analysis, we found that the Ire1-dependent transcriptional response driving morphogenesis is fundamentally distinct from the canonical UPR response to proteotoxic stress, with minimal overlap between programs. Remarkably, morphogenesis occurs without detectable HAC1 splicing, and HAC1 deletion only partially impairs filamentation, unlike complete loss with IRE1 deletion. These findings establish that Ire1 regulates hyphal development through previously uncharacterized HAC1-independent pathways. Our data reveal decreased transcription of secretory proteins in an Ire1-dependent manner, providing compelling evidence that C. albicans possesses regulated Ire1-dependent decay (RIDD) activity--a post-transcriptional mechanism not previously characterized in this pathogen. Additionally, we identify cell wall integrity as a key HAC1-independent mechanism, with Ire1--but not Hac1--essential for cell wall stress tolerance and upregulation of cell wall biosynthesis genes during filamentation. Given Ire1s essential role in pathogenesis and extensive development of Ire1-targeting compounds for mammalian systems, our findings position Ire1 as a highly promising druggable target for novel antifungal therapeutics and development of fungal-specific inhibitors.

cell biology↗

bioRxiv2023

Evolutionary diversity of the control of the azole response by Tra1 across yeast species

Tra1 is an essential co-activator protein of the yeast SAGA and NuA4 acetyltransferase complexes that regulate gene expression through multiple mechanisms including the acetylation of histone proteins. Tra1 is a pseudokinase of the PIKK family characterized by a C-terminal PI3K domain with no known kinase activity. However, mutations of specific arginine residues to glutamine in the PI3K domains (an allele termed tra1Q3) result in reduced growth and increased sensitivity to multiple stresses. In the opportunistic fungal pathogen Candida albicans, the tra1Q3 allele reduces pathogenicity and increases sensitivity to the echinocandin antifungal drug caspofungin, which disrupts the fungal cell wall. Here, we found that loss of Tra1 function, in contrast to what is seen with caspofungin, increases tolerance to the azole class of antifungal drugs, which inhibits ergosterol synthesis. In C. albicans, tra1Q3 increases expression of genes linked to azole resistance, such as ERG11 and CDR1. CDR1 encodes a multidrug ABC transporter associated with efflux of multiple xenobiotics, including azoles. Consequently, cells carrying tra1Q3 show reduced intracellular accumulation of fluconazole. In contrast, a tra1Q3 S. cerevisiae strain displayed opposite phenotypes: decreased tolerance to azole, decreased expression of the efflux pump PDR5 and increased intracellular accumulation of fluconazole. Therefore, our data provide evidence that Tra1 differentially regulates the antifungal response across yeast species.

genetics↗