C. albicans Zn Cluster Transcription Factors Tac1 and Znc1 are Activated by Farnesol to Up Regulate a Transcriptional Program Including the Multi-Drug Efflux Pump CDR1

Farnesol, a quorum-sensing molecule, inhibits C. albicans hyphal formation, affects its biofilm formation and dispersal, and impacts its stress response. Several aspects of farnesol’s mechanism of action remain incompletely uncharacterized. Among these are a thorough accounting of the cellular receptors and transporters for farnesol. This work suggests these themes are linked through the Zn cluster transcription factors Tac1 and Znc1, and their induction of the multi-drug efflux pump Cdr1. Specifically, we have demonstrated that Tac1 and Znc1 are functionally activated by farnesol through a mechanism that mimics other means of hyperactivation of Zn cluster transcription factors. This is consistent with our observation that many genes acutely induced by farnesol are dependent on TAC1, ZNC1 , or both. A related molecule, 1-dodecanol, invokes a similar TAC1/ZNC1 response, while several other proposed C. albicans quorum sensing molecules do not. TAC1 and ZNC1 both bind to and up-regulate the CDR1 promoter in response to farnesol. Differences in inducer and DNA binding specificity lead to Tac1 and Znc1 having overlapping, but non-identical, regulons. TAC1 and ZNC1 dependent farnesol induction of their target genes was inversely related to the level of CDR1 present in the cell, suggesting a model in which induction of CDR1 by Tac1 and Znc1 leads to an increase in farnesol efflux. Consistent with this premise, our results show that CDR1 expression, and its regulation by TAC1 and ZNC1 , facilitates growth in the presence of high farnesol concentrations in C. albicans , and certain strains of its close relative C. dubliniensis .