Expression profiles of amylolytic genes in AmyR and CreA transcription factor deletion mutants of the black koji mold Aspergillus luchuensis

Different Putative Methyltransferases Have Different Effects on the Expression Patterns of Cellulolytic Genes

Putative methyltranferase LaeA and LaeA-like proteins, conserved in many filamentous fungi, regulate fungal growth, development, virulence, the biosynthesis of secondary metabolites, and the production of cellulolytic enzymes. Penicillium oxaliucm is a typical fungus that produces cellulolytic enzymes. In this study, we reported the biological function of eight putative methyltransferases (PoMtr23C/D/E/F/G/H and PoMtr25A/B) containing a methyltransf_23 or methyltransf_25 domain, with a focus on their roles in the production of cellulolytic enzymes. In P. oxalicum, various methyltransferase genes displayed different transcriptional levels. The genes Pomtr23C and Pomtr25A exhibited high transcriptional levels, while Pomtr23D/E/F/G/H and Pomtr25B were transcribed constantly at low levels. The gene deletion mutants (Δmtr23C/D/E/F/G/H and Δmtr25A/B) were constructed. Various mutants have different patterns in cellulolytic enzyme production. Compared to the WT, the largest increase in filter paper activity (FPA, indicating total cellulase activity) was observed in the Δmtr23G mutant, the only mutant with a cellulolytic halo surrounding the colony. Three mutants (Δmtr23C/D and Δmtr25A) also showed increased cellulolytic enzyme production. The Δmtr23E and Δmtr25B mutants displayed decreased FPA activity, while the Δmtr23F and Δmtr23H mutants displayed similar patterns of cellulolytic enzyme production compared with the WT. The assay of transcriptional levels of cellobiohydrolase gene Pocbh1 and β-1,4-endoglucanase Poeg1 supported that higher cellulolytic gene transcription resulted in higher production of cellulolytic enzymes, and vice versa. The transcriptional levels of two transcription factors, activator XlnR and repressor CreA, were measured. The high transcription level of the PoxlnR gene in the Δmtr23D mutant should be one reason for the increased transcription of its cellulolytic enzyme gene. Both XlnR and CreA transcriptional levels increased in the Δmtr23G mutant, but the former showed a more significant increase than the latter, indicating that the activation effect predominated. The PoMtr25A is localized in the nucleus. The catalytic subunit SNF2 of the SWI/SNF chromatin-remodeling complex was found as one of the interacting proteins of PoMtr25A via tandem affinity purification coupled with mass spectrometry. PoMtr25A may affect not only the transcription of repressor CreA but also by recruiting SWI/SNF complexes that affect chromatin structure, thereby regulating the transcription of target genes.

The white koji fungus Aspergillus luchuensis mut. kawachii

The white koji fungus, Aspergillus luchuensis mut. kawachii, is used in the production of shochu, a traditional Japanese distilled spirit. White koji fungus plays an important role in the shochu production process by supplying amylolytic enzymes such as α-amylase and glucoamylase. These enzymes convert starch contained in primary ingredients such as rice, barley, buckwheat, and sweet potato into glucose, which is subsequently utilized by the yeast Saccharomyces cerevisiae to produce ethanol. White koji fungus also secretes large amounts of citric acid, which lowers the pH of the shochu mash, thereby preventing the growth of undesired microbes and enabling stable production of shochu in relatively warm regions of Japan. This review describes the historical background, research tools, and recent advances in studies of the mechanism of citric acid production by white koji fungus.