GlcNAc induces GlcNAc catabolic genes and inhibits filamentation via YlRep1-YlNgs1 signaling in the dimorphic yeast <i>Yarrowia lipolytica</i>

Many fungal species can utilize <i>N</i>-acetylglucosamine (GlcNAc) as a carbon source. Studies in the pathogenic yeast <i>Candida albicans</i> have revealed that GlcNAc utilization and the induction of GlcNAc catabolic genes depend on the Ndt80 family transcription factor CaRep1 and the histone acetyltransferase CaNgs1. Additionally, GlcNAc induces filamentation via both alkalinization of the medium and CaNgs1 signaling. However, the roles of YlRep1 and YlNgs1 in GlcNAc catabolism and filamentous growth are not clear in the dimorphic yeast <i>Yarrowia lipolytica</i>. In this study, we demonstrate that YlRep1 and YlNgs1 are essential for the induction of GlcNAc catabolic genes in <i>Y. lipolytica</i>, which is similar to the function of CaRep1 and CaNgs1. YlRep1 and YlNgs1 interact physically and exhibit transcriptional activation activity on a reporter gene. Interestingly, unlike in <i>C. albicans</i>, GlcNAc inhibits filamentation in <i>Y. lipolytica</i>. This inhibition requires YlRep1-YlNgs1 but does not depend on the alteration of ambient pH. We show that YlRep1 and YlNgs1 co-repress a set of transcription factor and cell wall protein genes, some of which are associated with filamentation. Notably, this repression is independent of GlcNAc catabolism but requires the GlcNAc kinase, YlNag5.IMPORTANCEGlcNAc has been used previously to induce filamentation in <i>Yarrowia lipolytica</i>, but often in combination with a citrate buffer at near-neutral pH. The exact role of GlcNAc in regulating filamentous growth is unclear. In this study, we report that GlcNAc inhibits rather than promotes filamentation in <i>Y. lipolytica</i>, and this function does not require GlcNAc catabolism or the alteration of ambient pH by GlcNAc catabolism. We show that YlRep1-YlNgs1 signaling, which activates GlcNAc catabolic genes, represses a set of filamentation-related genes and is a key regulator in the inhibition of filamentation by GlcNAc. This finding indicates that YlRep1-YlNgs1 has dual roles, functioning both in the activation of GlcNAc catabolic genes and the repression of filamentation-related genes in response to GlcNAc. These findings provide new insights into the regulatory mechanisms of GlcNAc catabolism and signaling in <i>Y. lipolytica</i>.