C-terminus of serine–arginine protein kinase-like protein, SrpkF, is involved in conidiophore formation and hyphal growth under salt stress in Aspergillus aculeatus

Abstract

Abstract The serine–arginine protein kinase-like protein, SrpkF, was identified as a regulator for the cellulose-responsive induction of cellulase genes in Aspergillus aculeatus. To analyze various aspects of SrpkF function, we examined the growth of the control strain (MR12); C-terminus deletion mutant, which produced SrpkF1–327 (DCsrpkF); whole gene-deletion mutant of srpkF (DsrpkF), srpkF overexpressing strain (OEsprkF), and the complemented strain (srpkF+) under various stress conditions. All test strains grew normally on minimal medium under control, high salt (1.5 M KCl), and high osmolality (2 M sorbitol and 1.0 M sucrose). However, only DCsrpkF showed reduced conidiation and hyperbranched hyphal growth on 1.0 M NaCl media. Conidiation of DCsrpkF on 1.0 M NaCl media was reduced to 12% compared with that of srpkF+. By contrast, deletion of srpkF did not affect hyphal growth and conidiation under the same conditions. We then quantified the transcripts of the regulators involved in the central asexual conidiation pathway in A. aculeatus. The findings revealed that the expression of brlA, abaA, wetA, and vosA was reduced in DCsrpkF under salt stress. These data suggest that in A. aculeatus, SrpkF regulates conidiophore development. The C-terminus of SrpkF seems to be important for regulating SrpkF function in response to culture conditions.