A RsrC-RsrA-RsrB transcriptional circuit positively regulates polysaccharide-degrading enzyme biosynthesis and development in Penicillium oxalicum

Abstract

Abstract Filamentous fungi produce polysaccharide-degrading enzymes governing tolerance to changing environments, and this is controlled by a poorly understood transcriptional circuit. Here, genome-wide screening and genetic analyses reveal a novel regulatory circuit comprising RsrC-RsrA-RsrB that positively regulates the production of raw starch-degrading enzymes (RSDEs) in Penicillium oxalicum. Transcription factor (TF) RsrA is essential for biosynthesis of RSDEs. Two novel TFs, RsrB and RsrC, containing Zn2Cys6 and C2H2 zinc finger domains, respectively, act downstream and upstream of RsrA. RsrA activates transcription of rsrB, and three nucleotides (G-286, G-287 and G-292) are required for RsrA binding to rsrB. Polypeptide RsrB165-271 binds the conserved DNA sequence 5’-KBKWYSNRKNDVVBS-3’ in the promoters of genes encoding major amylases. RsrC specifically binds rsrA promoter via bases -850 to -825, but not the promoters of amylase genes. This regulatory circuit influences mycelial growth and conidia production. The findings expand the complex regulatory network of fungal RSDE biosynthesis and development.