The MSDIN family in amanitin-producing mushrooms and evolution of the prolyl oligopeptidase genes

The biosynthetic pathway for amanitins and related cyclic peptides in deadly ( ) mushrooms represents the first known ribosomal cyclic peptide pathway in the . Amanitins are found outside of the genus in distantly related agarics ( ) and ( ). A long-standing question in the field persists: why is this pathway present in these phylogenetically disjunct agarics? Two deadly mushrooms, and , were deep sequenced, and sequences of biosynthetic genes encoding MSDINs (cyclic peptide precursor) and prolyl oligopeptidases ( and ) were obtained. The two species yielded 29 and 18 MSDINs, respectively. In addition, two MSDIN sequences were cloned from basidiomes. The toxin MSDIN genes encoding amatoxins or phallotoxins from the three genera were compared, and a phylogenetic tree constructed. Prolyl oligopeptidase B (POPB), a key enzyme in the biosynthetic pathway, was used in phylogenetic reconstruction to infer the evolutionary history of the genes. Phylogenies of and based on both coding and amino acid sequences showed very different results: while genes clearly reflected the phylogeny of the host species, did not; strikingly, it formed a well-supported monophyletic clade, despite that the species belong to different genera in disjunct families. , a known house-keeping gene, was shown to be restricted in a branch containing only species and the phylogeny resembled that of those species. Phylogenetic analyses of MSDIN and genes showed tight coordination and disjunct distribution. A gene tree was compared with a corresponding species tree, and distances and substitution rates were compared. The result suggested genes have significant smaller distances and rates than the house-keeping , discounting massive gene loss. Under this assumption, the incongruency between the gene tree and species tree was shown with strong support. Additionally, k-mer analyses consistently cluster and genes, while is distinct. Our result suggests that horizontal gene transfer (HGT), at least between and was involved in the acquisition of genes, which may shed light on the evolution of the α-amanitin biosynthetic pathway.