Chitin is an important structural constituent of fungal cell walls composed ofN-acetylglucosamine (GlcNAc) monosaccharides, but catabolism of GlcNAc has not been studied in filamentous fungi so far. In the yeastCandida albicans, the genes encoding the three enzymes responsible for stepwise conversion of GlcNAc to fructose-6-phosphate are clustered. In this work, we analysed GlcNAc catabolism in ascomycete filamentous fungi and found that the respective genes are also clustered in these fungi. In contrast toC. albicans, the cluster often contains a gene for an Ndt80-like transcription factor, which we named RON1 (regulatorofN-acetylglucosamine catabolism 1). Further, a gene for a glycoside hydrolase 3 protein related to bacterialN-acetylglucosaminidases can be found in the GlcNAc gene cluster in filamentous fungi. Functional analysis inTrichoderma reeseishowed that the transcription factor RON1 is a key activator of the GlcNAc gene cluster and essential for GlcNAc catabolism. Furthermore, we present an evolutionary analysis of Ndt80-like proteins in Ascomycota. All GlcNAc cluster genes, as well as the GlcNAc transporter genengt1, and an additional transcriptional regulator gene,csp2, encoding the homolog ofNeurospora crassaCSP2/GRHL, were functionally characterised by gene expression analysis and phenotypic characterisation of knockout strains inT. reesei.
N-acetylglucosamine is the monomeric sugar of the abundant biopolymer chitin. In this work we found that the genes encoding the enzymes for N-acetylglucosamine catabolism are clustered in ascomycete filamentous fungi and that this cluster often contains a gene for a transcription factor with an Ndt80-like DNA-binding domain. Functional analysis of this transcription factor, which we named RON1 (regulator of N-acetylglucosamine catabolism), in Trichoderma reesei showed that it is an essential key activator for N-acetylglucosamine catabolism.