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Genetic origin of homopyrones, a rare type of hybrid phenylpropanoid- and polyketide-derived yellow pigments from Aspergillus homomorphus

  • Genomics, Transcriptomics, Proteomics
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Abstract

In recent years, there has been an increasing demand for the replacement of synthetic food colorants with naturally derived alternatives. Filamentous fungi are prolific producers of secondary metabolites including polyketide-derived pigments, many of which have not been fully characterized yet. During our ongoing investigations of black aspergilli, we noticed that Aspergillus homomorphus turned yellow when cultivated on malt extract agar plates. Chemical discovery guided by UV and MS led to the isolation of two novel yellow natural products, and their structures were elucidated as aromatic α-pyrones homopyrones A (1) and B (2) by HRMS and NMR. Combined investigations including retro-biosynthesis, genome mining, and gene deletions successfully linked both compounds to their related biosynthetic gene clusters. This demonstrated that homopyrones are biosynthesized by using cinnamoyl-CoA as the starter unit, followed by extension with three malonyl-CoA units, and lactonization to give the core hybrid backbone structure. The polyketide synthase AhpA includes a C-methylation domain, which however seems to be promiscuous since only 2 is C-methylated. Altogether, the homopyrones represent a rare case of hybrid phenylpropanoid- and polyketide-derived natural products in filamentous fungi.

Key points

• Homopyrones represent a rare type of fungal polyketides synthesized from cinnamic-CoA.

• CRISPR/Cas9 technology has been firstly applied in Aspergillus homomorphus.

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All data generated or analyzed during this study are included in this published article (and its supplementary information files).

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Acknowledgements

We thank Professor Jens C. Frisvad for sharing his expertise on metabolites of Aspergillus homomorphus and A. indologenus. Y.G. was a scholarship recipient (201709110107) from the China Scholarship Council. The authors thank the Novo Nordisk Foundation for their grant support (NNF15OC0016610). We thank Sara Bastrup Kreutz Nielsen and Astrid Zedlitz Johansen for their valuable assistance in making the pyrG mutation in A. homomorphus.

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Contributions

U.H.M, C.H.G. and T.O.L. planned and designed the study. Material preparation, experiment conduction, data collection and analysis, and manuscript drafting were performed by M.E.F., Y.G., C.H., and J.B.H. All authors commented on the manuscript. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Uffe H. Mortensen or Thomas O. Larsen.

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This article does not contain any studies with human participants or animals.

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The authors declare no competing interests.

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Futyma, M.E., Guo, Y., Hoeck, C. et al. Genetic origin of homopyrones, a rare type of hybrid phenylpropanoid- and polyketide-derived yellow pigments from Aspergillus homomorphus. Appl Microbiol Biotechnol 105, 5113–5121 (2021). https://doi.org/10.1007/s00253-021-11379-8

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  • DOI: https://doi.org/10.1007/s00253-021-11379-8

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