Construction of RNA silencing system of Penicillium brevicompactum and genetic manipulation of the regulator pbpcz in mycophenolic acid production

Penicillium brevicompactum is a critical industrial strain for the production of mycophenolic acid (MPA). However, the genetic background of Penicillium brevicompactum is unclear, and there are few tools available for genetic manipulation. To investigate its gene function, we first verified the feasibility of a pair of citrate synthase promoter (Pcit) and terminator (Tcit) from P. brevicompactum by constructing a fluorescent expression cassette. Based on this, an RNAi vector was designed and constructed with reverse promoters. This study focused on the functional investigation of the pbpcz gene in P. brevicompactum, a regulator belonging to the Zn(II) Cys family. RNAi was used to silence the pbpcz gene, providing a valuable tool for genetic studies in P. brevicompactum. After seven days, we observed differences in the number of spores between different phenotypes strains of pbpcz gene. Compared to the wild-type strain (WT), the spore yield of the pbpcz gene silencing mutant (M2) was only 51.4 %, while that of the pbpcz gene overexpressed mutant (SE4) was increased by 50 %. Expression levels of the three genes (brlA, abaA, and wetA) comprising conidia's central regulatory pathway were significantly reduced in the pbpcz gene silencing mutant, while fluorescence localization showed that PbPCZ protein was mainly distributed in spores. The results indicated that the pbpcz gene is critical for conidia and asexual development of P. brevicompactum. In addition, overexpressing the pbpcz gene resulted in a 30.3 % increase in MPA production compared to the wild type, with a final yield of 3.57 g/L. These results provide evidence that PbPCZ acts as a positive regulator in P. brevicompactum, controlling MPA production and regulating conidia and asexual development.