Mutations in <i>TAC1B</i> drive increased <i>CDR1</i> and <i>MDR1</i> expression and azole resistance in <i>Candida auris</i>

<i>Candida auris</i> has emerged as a fungal pathogen of particular concern owing in part to its propensity to exhibit antifungal resistance, especially to the commonly prescribed antifungal fluconazole. A mutation in <i>TAC1B</i>, which encodes a zinc cluster transcription factor, has been shown to confer increased resistance to fluconazole. In this work, we aimed to determine how mutations in <i>TAC1B</i> exert this effect. <i>TAC1B</i> mutations leading to A640V, A657V, and F862_N866del, found in fluconazole-resistant clinical isolates, were introduced into two susceptible Clade I backgrounds using CRISPR-Cas9 gene editing. These <i>TAC1B</i> mutations conferred increased fluconazole resistance, as well as increased resistance to other triazoles as measured by broth microdilution. RNA-seq revealed that the ATP-binding cassette (ABC) transporter gene <i>CDR1</i> as well as the major facilitator superfamily (MFS) transporter gene <i>MDR1</i> were both upregulated in the presence of these <i>TAC1B</i> mutations. Disruption of <i>CDR1</i> increased susceptibility in strains with <i>TAC1B</i> mutations, whereas disruption of <i>MDR1</i> had little to no effect. However, disruption of both <i>CDR1</i> and <i>MDR1</i> resulted in an additional increase in susceptibility as compared with disruption of <i>CDR1</i> alone. <i>TAC1B</i> mutations, leading to A640V, A657V, and F862_N866del all result in increased resistance to fluconazole and other triazole antifungals and increased expression of both <i>CDR1</i> and <i>MDR1</i> in <i>C. auris</i>. Together, these data suggest <i>CDR1</i> is the primary driver of resistance conferred by these <i>TAC1B</i> mutations.