Sip4p Regulates the Transcription of Enzymes for Gluconeogenesis in Nakaseomyces glabratus

Abstract

To survive in glucose poor niches within the host, the opportunistic pathogen Nakaseomyces glabratus must assimilate alternative carbon sources. In many yeasts, pathways for alternative carbon metabolism are regulated at the transcriptional level by Zn2Cys6 transcription factors, a class of proteins that are unique to fungi. Here, we investigated the transcriptional regulation of alternative carbon metabolism pathways by the Zn2Cys6 transcription factors Cat8p, Sip4p, and Rds2p in the opportunistic pathogen N. glabratus. Phenotypic screens of transcription factor knockout strains grown on alternative carbon sources identified that deletion of CAT8, a transcription factor required for growth in the closely related model organisms Saccharomyces cerevisiae, did not affect the growth of N. glabratus, but deletion of SIP4 resulted in growth defects. We further probed the changes in gene expression that occur upon treatment with lactate or ethanol using RNA-seq. In the wild type strain, genes related to gluconeogenesis, the TCA cycle, and the glyoxylate cycle were upregulated in the presence of alternative carbon sources, and transcription of PCK1, encoding the gluconeogenesis enzyme phosphoenolpyruvate carboxykinase, was induced over 2000-fold. Deletion of SIP4 resulted in a 4-fold decrease in PCK1 gene expression in lactate and ethanol treated cells, and a 6-fold decrease in the cytosolic malate dehydrogenase MDH2 in lactate treated cells. Taken together, our results have uncovered transcriptional rewiring and a role for Sip4p in the regulation of alternative carbon metabolism in N. glabratus.