Transcriptional response of Candida auris to the Mrr1 inducers methylglyoxal and benomyl

Candida auris is an urgent threat to human health due to its rapid spread in healthcare settings and its repeated development of multidrug resistance. Diseases that put individuals at a higher risk for C. auris infection, such as diabetes, kidney failure, or immunocompromising conditions, are associated with elevated levels of methylglyoxal (MG), a reactive dicarbonyl compound derived from several metabolic processes. In other Candida species, expression of MG reductase enzymes that catabolize and detoxify MG are controlled by Mrr1, a multidrug resistance-associated transcription factor, and MG induces Mrr1 activity. Here, we used transcriptomics and genetic assays to determine that C. auris MRR1a contributes to MG resistance, and that the main Mrr1a targets are an MG reductase and MDR1, which encodes an drug efflux protein. The C. auris Mrr1a regulon is smaller than Mrr1 regulons described in other species. In addition to MG, benomyl (BEN), a known Mrr1 stimulus, induces C. auris Mrr1 activity, and characterization of the MRR1a-dependent and independent transcriptional responses revealed substantial overlap in genes that were differentially expressed in response to each compound. Additionally, we found that an MRR1 allele specific to one C. auris phylogenetic clade, clade III, encodes a hyperactive Mrr1 variant, and this activity correlated with higher MG resistance. C. auris MRR1a alleles were functional in Candida lusitaniae and were inducible by BEN, but not by MG, suggesting that the two Mrr1 inducers act via different mechanisms. Together, the data presented in this work contribute to the understanding Mrr1 activity and MG resistance in C. auris. ImportanceCandida auris is a fungal pathogen that has spread since its identification in 2009 and is of concern due to its high incidence of resistance against multiple classes of antifungal drugs. In other Candida species, the transcription factor Mrr1 plays a major role in resistance against azole antifungals and other toxins. More recently, Mrr1 has been recognized to contribute to resistance to methylglyoxal (MG), a toxic metabolic byproduct. Here, we show that C. auris MRR1a, the closest ortholog to MRR1 in other species, contributes to resistance to MG, and that Mrr1a strongly co-regulates expression of MGD1, encoding a methylglyoxal reductase enzyme and MDR1, encoding an efflux protein involved in resistance to azole drugs, antimicrobial peptides and bacterial products. We found that one major clade of C. auris has a constitutively active Mrr1 despite high azole resistance due to other mutations, and that this high Mrr1a activity correlates with higher MG resistance. Finally, we gain insights into the activities of MG and another Mrr1 inducer, benomyl, to better understand C. auris regulation of phenotypes relevant in vivo.