Deciphering the Tac1a / Tac1b network of azole resistance in Candidozyma auris§

Abstract Candidozyma auris (formerly Candida auris ) is a pathogenic yeast of concern because of its ability to develop antifungal resistance and to cause nosocomial outbreaks of invasive candidiasis. Resistance to azoles (mainly fluconazole) is a hallmark of most C. auris clinical isolates and the efflux pump Cdr1 plays a key role in this process. The transcription factor Tac1b is known to regulate CDR1 . TAC1b is located on chromosome 5 in tandem with TAC1a , whose function is not yet elucidated. This study aimed at investigating the respective roles of Tac1a and Tac1b in azole resistance. Hyperactivation of Tac1a using a tagging strategy resulted in markedly decreased fluconazole susceptibility similar to Tac1b hyperactivation. Tac1a and Tac1b shared a large common set of downstream targets, including CDR1 , and use the same DNA-binding motif in their target gene promoters according to ChEC-seq analysis. Other common targets included the efflux pump Cdr4_1, with no role in azole resistance, and the transcription factors Zcf13 and Mrr1b, which demonstrated minor impact on azole susceptibility independently from Cdr1. Our results suggest that Tac1a could bind to the TAC1b promoter (and not inversely) and is therefore located upstream of Tac1b in this regulatory pathway. While gain-of-function mutations of azole resistance have been characterized in Tac1b, our attempts to induce such mutations in Tac1a were unsuccessful. We concluded that Tac1a and Tac1b have redundant functions but with distinct roles in the evolutionary process of azole resistance with Tac1a being the ancestral conserved gene and Tac1b having evolved to trigger azole resistance.