A biosynthesis gene cluster is a group of genes that sit together in a genome and code for the enzymes of one chemical pathway. For psilocybin, those enzymes are PsiD, PsiK, PsiM and PsiH, characterized in 2017 (Fricke et al., 2017).
The cluster changed how researchers ask which mushrooms make psilocybin. A 2018 study sequenced three distantly related species, Psilocybe cyanescens, Gymnopilus dilepis and Panaeolus cyanescens, found the same cluster in each, and argued that it had moved between fungal lineages by horizontal gene transfer (Reynolds et al., 2018).
A 2024 study of the genus concludes that psilocybin synthesis first arose in Psilocybe, with four or five possible transfers to other mushrooms between 40 and 9 million years ago. Before that work, the cluster had been described in only five of about 165 Psilocybe species (Bradshaw et al., 2024). Most species have never been sequenced, so the picture may change. The cluster’s presence says nothing about how much psilocybin a given mushroom holds.
Sources
- Fricke et al., 2017, Angewandte Chemie: psilocybin biosynthesis
- Reynolds et al., 2018, Evolution Letters: horizontal gene cluster transfer
- Bradshaw et al., 2024, PNAS: Psilocybe phylogenomics
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