Transcription Factor NsdD Regulates the Expression of Genes Involved in Plant Biomass-Degrading Enzymes, Conidiation, and Pigment Biosynthesis in Penicillium oxalicum

Soil fungi produce a wide range of chemical compounds and enzymes with potential for applications in medicine and biotechnology. Cellular processes in soil fungi are highly dependent on the regulation under environmentally-induced stress, but most of the underlying mechanisms remain unclear. Previous work identified a key GATA-type transcription factor PoxNsdD (POX08415) that regulates the expression of cellulase and xylanase genes in Penicillium oxalicum . PoxNsdD shares 57-64% identity with the key activator NsdD involved in asexual development in Aspergillus . In the present study, the regulatory roles of PoxNsdD in P. oxalicum were further explored. Comparative transcriptomic profiling revealed that PoxNsdD regulated major genes involved in starch, cellulose and hemicellulose degradation, as well as conidiation and pigment biosynthesis. Subsequent experiments confirmed that the Δ PoxNsdD lost 43.9–78.8% of starch-digesting enzyme activity when grown on soluble corn starch, and produced 54.9–146.0% more conidia than the parental strain Δ PoxKu70 . During cultivation, Δ PoxNsdD cultures changed color from pale-orange to brick-red, while the Δ PoxKu70 remained bluish-white. Real-time quantitative reverse-transcription PCR displayed that PoxNsdD dynamically regulated the expression of a glucoamylase gene POX01356 / Amy15A , a α-amylase gene POX09352 / Amy13A , and the regulatory gene POX03890 / amyR , as well as a polyketide synthase gene POX01430 / alb1 / wA for the yellow pigment biosynthesis and a conidiation-regulated gene POX06534 / brlA . Moreover, in vitro binding experiments showed that PoxNsdD bound the promoter regions of the above described genes. This work provides novel insights into the regulatory mechanisms of fungal cellular processes, and may assist genetic engineering of P. oxalicum for potential industrial and medical applications. Importance Most filamentous fungi produce a vast number of extracellular enzymes used commercially for biorefineries of plant biomass to produce biofuels and value-added chemicals, which might promote the transition to a more environment-friendly economy. The expression of these extracellular enzyme genes is tightly controlled at the transcriptional level, which limits their yields. Hitherto our understanding on regulation of expression of plant biomass-degrading enzyme genes in filamentous fungi is rather limited. Here, regulatory roles of a key regulator PoxNsdD were further explored in soil fungus Penicillium oxalicum , which contributes to the understanding of gene regulation in filamentous fungi, and exploiting the biotechnological potential of P. oxalicum via genetic engineering.