Abstract
The conspicuous bright golden to orange-reddish coloration of species of the basidiomycete genus Laetiporus is a hallmark feature of their fruiting bodies, known among mushroom hunters as the “chicken of the woods”. This report describes the identification of an eight-domain mono-modular highly reducing polyketide synthase as sole enzyme necessary for laetiporic acid biosynthesis. Heterologous pathway reconstitution in both Aspergillus nidulans and Aspergillus niger verified that LpaA functions as a multi-chain length polyene synthase, which produces a cocktail of laetiporic acids with a methyl-branched C26–C32 main chain. Laetiporic acids show a marked antifungal activity on Aspergillus protoplasts. Given the multiple products of a single biosynthesis enzyme, our work underscores the diversity-oriented character of basidiomycete natural product biosynthesis.
Highlights
Non-terpenoid polyenes are a remarkable class of biologically active basidiomycete natural products
Identification of highly reducing polyketide synthase (HR-PKS) genes in L. sulphureus double bond system, i.e., the double bonds are positioned within the formal acetate units
We used the sequence of PPS1, the only known basidiomycete polyene synthase, as query to browse the published genome of L. sulphureus [10]
Summary
Non-terpenoid polyenes are a remarkable class of biologically active basidiomycete natural products. These compounds with up to ten conjugated carbon–carbon double bonds have been attributed to chemical defense: piptoporic acid (Fig. 1), a polyene from Piptoporus australiensis with seven double bonds in conjugation deters fungivorous larvae from feeding on the fruiting bodies [1, 2]. The intense, conspicuous orange color is the signature feature of specimens of the Laetiporus sulphureus species complex, i.e., the “chicken of the woods” fungi. These are brown-rotting bracket mushrooms that have a European and North American distribution and which are commonly found on oak, eucalypt, or willow trees. The same authors detected even longer putative polyene products, laetiporic acids B and C (with C28 and C30 main chains, respectively) by liquid chromatography and mass spectrometry
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