Evolution of the Toxins Muscarine and Psilocybin in a Family of Mushroom-Forming Fungi

Abstract

Mushroom-forming fungi produce a wide array of toxic alkaloids. However, evolutionary analyses aimed at exploring the evolution of muscarine, a toxin that stimulates the parasympathetic nervous system, and psilocybin, a hallucinogen, have never been performed. The known taxonomic distribution of muscarine within the Inocybaceae is limited, based only on assays of species from temperate regions of the northern hemisphere. Here, we present a review of muscarine and psilocybin assays performed on species of Inocybaceae during the last fifty years. To supplement these results, we used liquid chromatography–tandem mass spectrometry (LC–MS/MS) to determine whether muscarine was present in 30 new samples of Inocybaceae, the majority of which have not been previously assayed or that originated from either the tropics or temperate regions of the southern hemisphere. Our main objective is to test the hypothesis that the presence of muscarine is a shared ancestral feature of the Inocybaceae. In addition, we also test whether species of Inocyabceae that produce psilocybin are monophyletic. Our findings suggest otherwise. Muscarine has evolved independently on several occasions, together with several losses. We also detect at least two independent transitions of muscarine-free lineages to psilocybin-producing states. Although not ancestral for the family as a whole, muscarine is a shared derived trait for an inclusive clade containing three of the seven major lineages of Inocybaceae (the Inocybe, Nothocybe, and Pseudosperma clades), the common ancestor of which may have evolved ca. 60 million years ago. Thus, muscarine represents a conserved trait followed by several recent losses. Transitions to psilocybin from muscarine-producing ancestors occurred more recently between 10–20 million years ago after muscarine loss in two separate lineages. Statistical analyses firmly reject a single origin of muscarine-producing taxa.

Horizontal gene cluster transfer increased hallucinogenic mushroom diversity

“…Psilocybin and/or the related aeruginascin have also been identified in the lichenized agaric, Dictyonema huaorani (unconfirmed), and in the ectomycorrhizal genus Inocybe (Kosentka et al. ; Schmull et al. ).…”

“…Psilocybin neurological activity, coupled with HGT and retention in lineages that colonize dung and/or decayed wood, which are rich in both mycophagous and competitor inverte-brates (Rouland-Lefevre 2000), suggest that psilocybin may be a modulator of insect behavior. Psilocybin and/or the related aeruginascin have also been identified in the lichenized agaric, Dictyonema huaorani (unconfirmed), and in the ectomycorrhizal genus Inocybe (Kosentka et al 2013;Schmull et al 2014). PS distribution in Inocybe is complementary to that of the acetylcholine mimic, muscarine, which could suggest alternative strategies and pressures to manipulate animal behavior beyond the dung-and wood-decay niches.…”

Convergent evolution of psilocybin biosynthesis by psychedelic mushrooms

“…A search of the I. corydalina genome for alternative psilocybin biosynthetic clusters revealed a single candidate (Tables S3-7), containing all four types of biosynthetic enzyme necessary for the conversion of tryptophan to psilocybin, plus an MFS-transporter (Fig 2d). The decarboxylase has the functional annotation "Aromatic-L-amino-acid decarboxylase", and the presence of two methyltransferases is interesting, given that a closely related species (Inocybe aeruginascens) produces a trimethylated analogue of psilocybin called aeruginascin 27 .…”

Six Key Traits of Fungi: Their Evolutionary Origins and Genetic Bases

“…Nematodes and arthropods are the main predators of fungi, so it is likely that they are often the targets of SMs that affect animal neurotransmitter signaling pathways. For example, psilocin and muscarine are produced by a number of mushroom-forming basidiomycetes and bind to serotonin and acetylcholine receptors, respectively (103). Ascomycete molds also produce larvicidal compounds, and a mutant Aspergillus that produces few SMs due to deletion of a global regulator of SM pathways is preferred by fungivorous arthropods (104).…”