McmA‐dependent and ‐independent regulatory systems governing expression of ClrB‐regulated cellulase and hemicellulase genes in Aspergillus nidulans

Abstract

Fungal cellulolytic and hemicellulolytic enzymes are promising tools for industrial hydrolysis of cellulosic biomass; however, the regulatory network underlying their production is not well understood. The recent discovery of the transcriptional activators ClrB and McmA in Aspergillus nidulans implied a novel regulatory mechanism driven by their interaction, experimental evidence for which was obtained from transcriptional and DNA-binding analyses in this study. It was found that ClrB was essential for induced expression of all the genes examined in this study, while McmA dependency of their expression was gene-dependent. DNA-binding studies revealed McmA assisted in the recruitment of ClrB to the cellulose-responsive element (CeRE) in the promoters of eglA and eglB, expression of which was significantly reduced in the mcmA mutant. The CCG triplet within the CeRE served as the recognition sequence for the ClrB monomer. In contrast, ClrB did not require McmA for binding as a homodimer to the CGGN CCG sequences in the promoter of mndB, expression of which was affected less in the mcmA mutant than in all other examined genes. Thus, there are two types of ClrB-mediated regulation: McmA-assisted and McmA-independent. This novel McmA-ClrB synergistic system provides new insights into the complex regulatory network involved in cellulase and hemicellulase production.

Blocking utilization of major plant biomass polysaccharides leads Aspergillusniger towards utilization of minor components

“…2, Cluster C). These are all enzymes that are negatively affected by the single clrB deletion, and the promoter sequences of their corresponding genes contain the putative ClrB binding site (CGGN 8 CCG) (Li et al, 2016) (Table S2), suggesting direct regulation of the Cluster C genes by ClrB. A broad range of other CAZymes showed highly reduced abundance or absence in the quadruple mutant compared with any single deletion strain (Fig.…”

“…Binding sites were searched using the 'DNA Pattern Matching' algorithm, with the default parameters of 'search on both strands' and 'prevent overlapping matches'. The reported putative binding motifs 5 0 -GGCTAR-3 0 (de Vries et al, 2002) and 5 0 -CGGNTAAW-3 0 (Ishikawa et al, 2018) for XlnR, 5 0 -CGGDTAAW-3 0 (Ishikawa et al, 2018) for AraR, 5 0 -CGGN 8 CCG-3 0 (Li et al, 2016) for ClrB and 5 0 -CGGN 8 CGG-3 0 (Petersen et al, 1999) for AmyR were analysed in this study. Relative growth has been estimated after 6, 8 and 10 days of incubation at 30°C.…”

Combinatorial control of gene expression in Aspergillus niger grown on sugar beet pectin

“…Another study showed that an interaction of two TFs, ClrB and McmA, is necessary for regulation of the endoglucanase encoding genes eglA and eglB in A . nidulans 28 , while in A . niger , expression of cbhA , eglC and xynA was shown to be co-dependent on both XlnR and ClrB 29 .…”

Transcriptome analysis of Aspergillus niger xlnR and xkiA mutants grown on corn Stover and soybean hulls reveals a highly complex regulatory network

“…ClrA and ClrB are two TFs involved in the regulation of cellulose degradation, which have been partially characterized in A. niger [27]. It was shown that the interaction of two TFs, ClrB and McmA, is necessary for the regulation of eglA and eglB in A. nidulans [46], while in A. niger , expression of cbhA , eglC and xynA was shown to be affected by both XlnR and ClrB [45]. Expression of clrA was not affected on SBH at any time point tested in either of the deletion mutants.…”