초록
<P><B>Abstract</B><P>Background<P>Although Basidiomycota produce pharmaceutically and ecologically relevant natural products, knowledge of how they coordinate their primary and secondary metabolism is virtually non-existent. Upon transition from vegetative mycelium to carpophore formation, mushrooms of the genus <I>Psilocybe</I> use l-tryptophan to supply the biosynthesis of the psychedelic tryptamine alkaloid psilocybin with the scaffold, leading to a strongly increased demand for this particular amino acid as this alkaloid may account for up to 2% of the dry mass. Using <I>Psilocybe mexicana</I> as our model and relying on genetic, transcriptomic, and biochemical methods, this study investigated if l-tryptophan biosynthesis and degradation in <I>P. mexicana</I> correlate with natural product formation.</P></P><P>Results<P>A comparative transcriptomic approach of gene expression in <I>P. mexicana</I> psilocybin non-producing vegetative mycelium versus producing carpophores identified the upregulation of l-tryptophan biosynthesis genes. The shikimate pathway genes <I>trpE1</I>, <I>trpD</I>, and <I>trpB</I> (encoding anthranilate synthase, anthranilate phosphoribosyltransferase, and l-tryptophan synthase, respectively) were upregulated in carpophores. In contrast, genes <I>idoA</I> and <I>iasA</I>, encoding indole-2,3-dioxygenase and indole-3-acetaldehyde synthase, i.e., gateway enzymes for l-tryptophan-consuming pathways, were massively downregulated. Subsequently, IasA was heterologously produced in <I>Escherichia coli</I> and biochemically characterized in vitro. This enzyme represents the first characterized microbial l-tryptophan-preferring acetaldehyde synthase. A comparison of transcriptomic data collected in this study with prior data of <I>Psilocybe cubensis</I> showed species-specific differences in how l-tryptophan metabolism genes are regulated, despite the close taxonomic relationship.</P></P><P>Conclusions<P>The upregulated l-tryptophan biosynthesis genes and, oppositely, the concomitant downregulated genes encoding l-tryptophan-consuming enzymes reflect a well-adjusted cellular system to route this amino acid toward psilocybin production. Our study has pilot character beyond the genus <I>Psilocybe</I> and provides, for the first time, insight in the coordination of mushroom primary and secondary metabolism.</P></P></P>