maintains two ohnologs, and , for distinct roles in ergosterol gene regulation to mediate sterol homeostasis under azole and hypoxic conditions.

UNLABELLED

exhibits innate resistance to azole antifungal drugs but also has the propensity to rapidly develop clinical drug resistance. Azole drugs, which target Erg11, is one of the major classes of antifungals used to treat infections. Despite their widespread use, the mechanism controlling azole-induced gene expression and drug resistance in has primarily revolved around Upc2 and/or Pdr1. Phylogenetic and syntenic analyses revealed that , following a whole genome duplication event, maintained and , whereas only retained the ortholog, . In this study, we determined the function of two zinc cluster transcription factors, Hap1A and Hap1B, as direct regulators of genes. In Hap1, an ortholog of Hap1A, is a known transcription factor controlling gene expression under aerobic and hypoxic conditions. Interestingly, deleting or in either or respectively, showed altered susceptibility to azoles. In contrast, the strain deleted for did not exhibit azole susceptibility. We also determined that the increased azole susceptibility in a Δ strain is attributed to decreased azole-induced expression of genes, resulting in decreased levels of total ergosterol. Surprisingly, Hap1A protein expression is barely detected under aerobic conditions but is specifically induced under hypoxic conditions, where Hap1A is required for the repression of genes. However, in the absence of Hap1A, Hap1B can compensate as a transcriptional repressor. Our study shows that Hap1A and Hap1B is utilized by to adapt to specific host and environmental conditions.

IMPORTANCE

Invasive and drug-resistant fungal infections pose a significant public health concern. , a human fungal pathogen, is often difficult to treat due to its intrinsic resistance to azole antifungal drugs and its capacity to develop clinical drug resistance. Therefore, understanding the pathways that facilitate fungal growth and environmental adaptation may lead to novel drug targets and/or more efficacious antifungal therapies. While the mechanisms of azole resistance in species have been extensively studied, the roles of zinc cluster transcription factors, such as Hap1A and Hap1B, in have remained largely unexplored until now. Our research shows that these factors play distinct yet crucial roles in regulating ergosterol homeostasis under azole drug treatment and oxygen-limiting growth conditions. These findings offer new insights into how this pathogen adapts to different environmental conditions and enhances our understanding of factors that alter drug susceptibility and/or resistance.