The Cys2-His2 zinc finger transcription factor NsdC regulates hyphal branching, conidiation and mycelial pellet morphology in Aspergillus oryzae

Abstract

Hyper-branching morphology boosts protein production in filamentous fungi as protein secretion occurs predominantly at the actively growing apical hyphal tip. However, mechanisms regulating hyphal morphology in fungi remain poorly characterized. In this paper, we report that the Cys2-His2 Zinc finger transcription factor NsdC negatively regulates both conidiation and hyphal branching in Aspergillus oryzae. The ∆nsdC A. oryzae mutants produced 10-fold more conidia than the wild type (WT) strain and overexpressed BrlA which is the master transcription factor for the conidiation pathway. The mutant also produced hyphae that were more branched in comparison to the WT strain. Analysis of macro-morphology of ∆nsdC mutant strain expressing human lysozyme in protein production medium (5 × DPY) revealed that it formed large mycelial clumps compared to compact pellets in the WT strain. However, lysozyme secretion in the ∆nsdC mutants was comparable to the WT strain, indicating that hyper-branching does not necessarily result in increased protein secretion. Our results also demonstrate that NsdC is a critical regulator of conidiation, hyphal branching and mycelial macro-morphology in A. oryzae.