Functional characterization of the sterigmatocystin secondary metabolite gene cluster in the filamentous fungus Podospora anserina: involvement in oxidative stress response, sexual development, pigmentation and interspecific competitions

Abstract

Summary Filamentous fungi are known as prolific untapped reservoirs of diverse secondary metabolites, where genes required for their synthesis are organized in clusters. The bioactive properties of these compounds are closely related to their functions in fungal biology, which are not well understood. In this study, we focused on the Podospora anserina gene cluster responsible for the biosynthesis of sterigmatocystin (ST). Deletion of the PaStcA gene encoding the polyketide synthase and overexpression (OE) of the PaAflR gene encoding the ST‐specific transcription factor in P. anserina were performed. We showed that growth of PaStcAΔ was inhibited in the presence of methylglyoxal, while OE‐PaAflR showed a little inhibition, indicating that ST production may enhance oxidative stress tolerance in P. anserina. We also showed that the OE‐PaAflR strain displayed an overpigmented thallus mediated by the melanin pathway. Overexpression of PaAflR also led to sterility. Interspecific confrontation assays showed that ST‐overexpressed strains produced a high level of peroxides and possessed a higher competitiveness against other fungi. Comparative metabolite profiling demonstrated that PaStcAΔ strain was unable to produce ST, while OE‐PaAflR displayed a ST overproduction. This study contributes to a better understanding of ST in P. anserina, especially with regard to its involvement in fungal physiology.

Involvement of PaSNF1 in Fungal Development, Sterigmatocystin Biosynthesis, and Lignocellulosic Degradation in the Filamentous Fungus Podospora anserina

“…Correspondingly, the deletion of PaSNF1 led to a defect in perithecium production and ascospore formation. Moreover, OE-PaAflR displayed overproduction of ST, and overexpression of PaAflR also led to sterility (Shen et al, 2019). These results indicated that ST was closely related to the development of fungi and spore formation.…”

“…Recent studies have shown that ABR1 was involved in biosynthesis of DHN melanin, which colored ascospores; and knockout of ABR1 led to decreased ascospore pigmentation accompanied by lowered ascospore germination rate (Xie et al, 2018). Shen et al (2019) reported that PaStcA and PaAflR were key genes necessary for the biosynthesis of ST in P. anserina, deletion of PaStcA that blocked the ST pathway, and overexpression of PaAflR that resulted in the excessive accumulation of ST, thus leading to a female sterility phenotype. In this study, to identify the metabolites regulated by PaSNF1, the large-scale fermentation of the PaSNF1 mutant was performed, and the structures of metabolites with unique peaks were characterized.…”

“…The ST biosynthetic gene cluster was regulated by the cluster-specific AflR transcription factor, which functioned downstream of glucose sensing (Fernandes et al, 1998). Overexpression of PaAflR led to a ST overproduction and a female sterility phenotype in P. anserina (Shen et al, 2019). Additionally, LaeA also regulated the ST biosynthetic gene cluster in an AflR-dependent manner.…”

Azaphilones biosynthesis complements the defence mechanism of Trichoderma guizhouense against oxidative stress

“…Thereby, oxidative stress seems to have been a key player in the evolution of fungal secondary metabolism (Roze et al ., 2011; Montibus et al ., 2015). In fact, stimulation of SMs formation by oxidative stress and ROS formation has recently been reported in several fungi, such as aflatoxin production by A. parasiticus , ochratoxin A formation by A. ochraceus , deoxynivalenol formation by F. graminearum and sterigmatocystin formation in Podospora anserina (Jayashree and Subramanyam, 2000; Reverberi et al ., 2012; Chen et al ., 2019; Shen et al ., 2019). In P. anserina , SMs were considered to function as a supplemental source of antioxidant protection, which enhance stress tolerance along with antioxidant enzyme gene expression (Shen et al ., 2019).…”

Functional Characterization of the GATA-Type Transcription Factor PaNsdD in the Filamentous Fungus Podospora anserina and Its Interplay with the Sterigmatocystin Pathway

“…Notably, mining of the P. anserina genome revealed a large number of putative biosynthetic gene clusters (BGCs) for secondary metabolites ( 11 ). However, to date, only very few products that exhibited antibacterial, antifungal, and larvicidal activities have been characterized in this species during past decades ( 12 – 14 ), probably because most BGCs are silent under standard culture conditions ( 10 , 15 ). Genomics-driven BGC detection and preliminary chemical investigations so far imply that P. anserina is a prolific, as-yet unexploited natural product reservoir.…”