Abstract
Xenovulene A is a complex fungal meroterpenoid, produced by the organism hitherto known as Acremonium strictum IMI 501407, for which limited biosynthetic evidence exists. Here, we generate a draft genome and show that the producing organism is previously unknown and should be renamed as Sarocladium schorii. A biosynthetic gene cluster is discovered which bears resemblance to those involved in the biosynthesis of fungal tropolones, with additional genes of unknown function. Heterologous reconstruction of the entire pathway in Aspergillus oryzae allows the chemical steps of biosynthesis to be dissected. The pathway shows very limited similarity to the biosynthesis of other fungal meroterpenoids. The pathway features: the initial formation of tropolone intermediates; the likely involvement of a hetero Diels–Alder enzyme; a terpene cyclase with no significant sequence homology to any known terpene cyclase and two enzymes catalysing oxidative-ring contractions.
Highlights
Xenovulene A is a complex fungal meroterpenoid, produced by the organism hitherto known as Acremonium strictum IMI 501407, for which limited biosynthetic evidence exists
We showed that fungi produce tropolones such as stipitatic acid 3 via oxidative-ring expansion of methylorcinaldehyde 4 using a two-step process in which a Xenovulene A 1
A. strictum IMI 501407 was obtained from the Centre for Agriculture and Bioscience International (CABI), and under literature fermentation conditions, the production of a compound corresponding to 1 was observed by liquid chromatography mass spectrometry (LCMS)
Summary
Xenovulene A is a complex fungal meroterpenoid, produced by the organism hitherto known as Acremonium strictum IMI 501407, for which limited biosynthetic evidence exists. In an early attempt to gain molecular information on xenovulene biosynthesis, we previously obtained a short genomic fragment of A. strictum IMI 501407 containing a partial biosynthetic gene cluster (BGC) from which one gene (aspks1) was shown to encode an iterative non-reducing polyketide synthase (nr-PKS) which produces 3-methylorcinaldehyde 4 when expressed in Aspergillus oryzae[7]. We report the results of genome sequencing of A. strictum IMI 501407, the discovery of xenovulene A 1 BGC, heterologous expression experiments to probe the biosynthetic steps and the discovery of three previously unreported types of biosynthetic enzymes, including a putative hetero-Diels Alderase, two enzymes that catalyse oxidative-ring contractions and a class of terpene cyclase unrelated to other known terpene cyclases
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