Regulation of genes encoding cellulolytic enzymes by Pal-PacC signaling in Aspergillus nidulans

Cellulosic biomass represents a valuable potential substitute for fossil-based fuels. As such, there is a strong need to develop efficient biotechnological processes for the enzymatic hydrolysis of cellulosic biomass via the optimization of cellulase production by fungi. Ambient pH is an important factor affecting the industrial production of cellulase. In the present study, we demonstrate that several Aspergillus nidulans genes encoding cellulolytic enzymes are regulated by Pal-PacC-mediated pH signaling, as evidenced by the decreased cellulase productivity of the palC mutant and pacC deletants of A. nidulans. The deletion of pacC was observed to result in delayed induction and decreased expression of the cellulase genes based on time course expression analysis. The genome-wide identification of PacC-regulated genes under cellobiose-induced conditions demonstrated that genes expressed in a PacC-dependent manner included 82 % of ClrB (a transcriptional activator of the cellulase genes)-regulated genes, including orthologs of various transporter and beta-glucosidase genes considered to be involved in cellobiose uptake or production of stronger inducer molecules. Together with the significant overlap between ClrB- and PacC-regulated genes, the results suggest that PacC-mediated regulation of the cellulase genes involves not only direct regulation by binding to their promoter regions but also indirect regulation via modulation of the expression of genes involved in ClrB-dependent transcriptional activation. Our findings are expected to contribute to the development of more efficient industrial cellulase production methods.