Serine-arginine protein kinase-like protein, SrpkF, stimulates both cellobiose-responsive and d-xylose-responsive signaling pathways in Aspergillus aculeatus

Aspergillus aculeatus produces cellulolytic enzymes in the presence of their substrates. We screened a library of 12,000 A. aculeatus T-DNA-inserted mutants to identify a regulatory factor involved in the expression of their enzyme genes in response to inducers. We found one mutant that reduced the expression of FIII-avicelase (chbI) in response to cellulose. T-DNA was inserted into a putative protein kinase gene similar to AN10082 in A. nidulans, serine-arginine protein kinase F, SrpkF. Fold increases in srpkF gene expression in response to various carbon sources were 2.3 (d-xylose), 44 (Avicel(R)), 59 (Bacto((TM)) Tryptone), and 98 (no carbon) compared with d-glucose. Deletion of srpkF in A. aculeatus resulted in a significant reduction in cellulose-responsive expression of chbI, hydrocellulase (cel7b), and FIb-xylanase (xynIb) genes at an early induction phase. Further, the srpkF-overexpressing strain showed upregulation of the srpkF gene from four- to nine-fold higher than in the control strain. srpkF overexpression upregulated cbhI and cel7b in response to cellobiose and the FI-carboxymethyl cellulase gene (cmc1) and xynIb in response to d-xylose. However, the srpkF deletion did not affect the expression of xynIb in response to d-xylose due to the less expression of srpkF under the d-xylose condition. Our data demonstrate that SrpkF is primarily involved in cellulose-responsive expression, though it has a potential to stimulate gene expression in response to both cellobiose and d-xylose in A. aculeatus.

Automated summary

The study revealed that the SrpkF gene in Aspergillus aculeatus plays a crucial role in cellulose-responsive gene expression.