Although the mechanisms of regulating secondary metabolism by LaeA remains unclear, the synthesis of many secondary metabolites (SMs) in Aspergilli could be activated by LaeA mutation. In our previous sutdy, RNA-seq data has showed that the transcriptional level of many SM backbone genes could be upregulated by overexpressing LaeA. Herein, we analyzed the chemical profile of activated secondary metabolites in the variant of A. niger FGSC A1279 by overexpressing LaeA (OElaeA). 14 compounds were activated in A. niger FGSC A1279 OElaeA variant in the WATM medium. Chemical workup of organic extracts of the culture broth from the A. niger OElaeA mutant identified three pure compounds, flaviolin, orlandin and kotanin. The structures of these compounds were confirmed by HR-ESIMS, 1D/2D NMR, and computer assisted structure elucidation (CASE). Based on homologous alignment and comparison of literatures, the biosynthetic gene cluster (fla) of flaviolin was identified. The in vivo function of the backbone gene, flaA, encoding a multidomain non-reducing polyketide synthase (SAT-KS-AT-PT-ACP), was verified via gene knockout and chemical analysis. Finally, a biosynthetic model for fungal flaviolin was proposed.
Bibliographical noteAcknowledgements: This work was financially supported by the National Natural Science Foundation of China (grant number 31870024 and 31871736), the Natural Science Foundation of Guangdong Province (grant number 2019A1515010065), R&D projects in key areas of Guangdong Province (grant number 2020B020226007), the Fundamental Research Funds for the Central Universities (grant number 2019MS092), and the Science and Technology Planning Project of Guangzhou City (grant number 202002030207).
- LaeA factor
- Secondary metabolites
- A. niger
- Flaviolin biosynthetic pathway