ManR, a novel Zn(II)2Cys6 transcriptional activator, controls the β-mannan utilization system in Aspergillus oryzae

Fungal endo-β-mannanases (β-mannanases) are widely used as industrial enzymes; however, no transcriptional regulator of β-mannanases has been identified in fungi or other eukaryotic cells to date. To identify a transcriptional regulator of β-mannanases in Aspergillus oryzae, a gene-disruptant library of transcriptional regulators was screened for mutants exhibiting reduced β-mannanase activity by using konjac glucomannan as the substrate, and ManR, a Zn(II)2Cys6 type DNA binding protein was identified. Moreover, a manR-overexpressing strain showed significantly increased β-mannanase activity. DNA microarray analysis of the manR-disruptant strain further indicated that when konjac glucomannan is used as the carbon source, ManR positively regulates the gene expression of not only β-mannanase, but also the enzymes involved in the degradation of galactomannans and glucomannans such as α-galactosidase, β-mannosidase, acetylmannan esterase, and β-glucosidase. Furthermore, we demonstrated that the presence of 1,4-β-d-mannobiose increased the expression of the endo-β-mannanase gene (manG, AO090010000122), and that ManR plays a key role in the inducible expression of manG in A. oryzae. Therefore, we conclude that ManR is a positive regulator of the β-mannan utilization system in A. oryzae. This is the first study to identify a transcriptional regulator of this system in eukaryotic cells.

► A transcriptional activator for β-mannan utilization system (ManR) was found in Aspergillus oryzae. ► manR was found to encode a Zn(II)2Cys6 type DNA binding protein. ► ManR is able to bind the promoter region of an endo-β-mannanase (manG) gene directly. ► β-1,4-d-Mannobiose caused increased expression of manG. ► ManR plays a key role in the inducible expression of manG in the presence of β-1,4-d-mannobiose.