Regulation of arabinose-induced gene expression in Aspergillus niger
The AraR transcription factor of Aspergillus niger encodes a Zn(II)2Cys6 transcription factor required for the induction of several arabinolytic genes. One of the target genes of AraR is AbfA encoding an arabinofuranosidase that is specifically induced on arabinan and arabinose in an AraR-dependent way. Expression of AbfA as well as other arabinolytic genes in A. niger requires the presence of L-arabinose as an inducer to activate AraR.
With the goal to isolate mutants that constitutively express arabinolytic genes independent on the presence of L-arabinose as an inducer, we designed a positive selection method using the arabinose-responsive promoter (PabfA) fused to the acetamidase (amdS) reporter gene. Expression of the amdS gene enables the fungus to grow on acetamide as the sole nitrogen source. Hence, mutants constitutively expressing the amdS gene can be selected on agar-plates with acetamide as a N-source. Growth analysis of the PabfA-amdS reporter strain indicated that abfA is specifically induced by arabinose, arabitol and arabinan. The in vivo reporter strain was also used to monitor carbon catabolite repression control. The PabfA-amdS reporter was repressed by glucose, fructose and sorbitol in a concentration dependant manner. CreA is important in mediating carbon catabolite repression and deletion of the creA gene in the PabfA-amds reporter strain abolished repression by glucose, fructose and sorbitol. Interestingly, the PabfA-amdS reporter construct in the ∆creA background was induced not only by arabinose but also by xylose indicating a regulatory overlap between AraR and XlnR transcription factors.