CPCR1, but not its interacting transcription factor AcFKH1, controls fungal arthrospore formation in Acremonium chrysogenum

Fungal morphogenesis and secondary metabolism are frequently associated; however, the molecular determinants connecting both processes remain largely undefined. Here we demonstrate that CPCR1 (cephalosporin C regulator 1 from Acremonium chrysogenum), a member of the winged helix/regulator factor X (RFX) transcription factor family that regulates cephalosporin C biosynthesis, also controls morphological development in the beta-lactam producer A. chrysogenum. The use of a disruption strain, multicopy strains as well as several recombinant control strains revealed that CPCR1 is required for hyphal fragmentation, and thus the formation of arthrospores. In a Delta cpcR1 disruption strain that exhibits only hyphal growth, the wild-type cpcR1 gene was able to restore arthrospore formation; a phenomenon not observed for Delta cpcR1 derivatives or non-related genes. The intracellular expression of cpcR1, and control genes (pcbC, egfp) was determined by in vivo monitoring of fluorescent protein fusions. Further, the role of the forkhead transcription factor AcFKH1, which directly interacts with CPCR1, was studied by generating an Acfkh1 knockout strain. In contrast to CPCR1, AcFKH1 is not directly involved in the fragmentation of hyphae. Instead, the presence of AcFKH1 seems to be necessary for CPCR1 function in A. chrysogenum morphogenesis, as overexpression of a functional cpcR1 gene in a Delta Acfkh1 background has no effect on arthrospore formation. Moreover, strains lacking Acfkh1 exhibit defects in cell separation, indicating an involvement of the forkhead transcription factor in mycelial growth of A. chrysogenum. Our data offer the potential to control fungal growth in biotechnical processes that require defined morphological stages for optimal production yields.