Molecular and functional evolution of the fungal diterpene synthase genes

Abstract

Background: Terpenes represent one of the largest and most diversified families of natural compounds and are used in numerous industrial applications. Terpene synthase (TPS) genes originated in bacteria as diterpene synthase (di-TPS) genes. They are also found in plant and fungal genomes. The recent availability of a large number of fungal genomes represents an opportunity to investigate how genes involved in diterpene synthesis were acquired by fungi, and to assess the consequences of this process on the fungal metabolism.

Results: In order to investigate the origin of fungal di-TPS, we implemented a search for potential fungal di-TPS genes and identified their presence in several unrelated Ascomycota and Basidiomycota species. The fungal di-TPS phylogenetic tree is function-related but is not associated with the phylogeny based on housekeeping genes. The lack of agreement between fungal and di-TPS-based phylogenies suggests the presence of Horizontal Gene Transfer (HGTs) events. Further evidence for HGT was provided by conservation of synteny of di-TPS and neighbouring genes in distantly related fungi.

Conclusions: The results obtained here suggest that fungal di-TPSs originated from an ancient HGT event of a single di-TPS gene from a plant to a fungus in Ascomycota. In fungi, these di-TPSs allowed for the formation of clusters consisting in di-TPS, GGPPS and P450 genes to create functional clusters that were transferred between fungal species, producing diterpenes acting as hormones or toxins, thus affecting fungal development and pathogenicity.

Fig. 1

Fungal phylogenetic tree showing genera with genome information. Genera with putative di-TPS genes are indicated in red. For every di-TPS gene accession, the systematic classification found on the genome web page was used for the fungal phylogenetic tree

Fig. 2

Phylogenetic tree generated from inferred amino acid sequences of fungal and plant di-TPSs. The fungal and plant di-TPS used are listed in Additional file 1. For species possessing multiple di-TPS genes, “_a”,” _b” and “_c” are added to the species designation. The colours used for the species refer to their phylogenetic positions and the oblongs refer to their life style, as described in the legend. The tree is rooted at the level of the plant clade and branch values correspond to aLRT results (only values ≥ 0.95 are shown). The proposed HGT cases are highlighted by yellow squares

Fig. 3

Comparison of gene content and organization in putative diterpene biosynthetic gene clusters, assumed to have undergone HGT between fungi for A. niger_a and T. reesei_a, P. strigosozonata_a and S. lacrymans_a, A. nidulans_a and C. globosum_a, R. rufulum_b and G. lozoyensis_a. The direction and relative size of genes are indicated by arrows; the upper scale indicates the cluster size in bp. The function of putative syntenic genes is: ABH (Alpha/beta hydrolase), di-TPS (diterpene synthase), GGPPS (geranylgeranyl diphosphate synthase), GST (glutathione S-transferase), MSF (major facilitator superfamily transporter), PHT11 (integral membrane protein PTH11-like protein), P450 (Cytochrome P450), UMTAM (S-adenosylmethionine-dependent methyltransferase)

Fig. 4

Phylogenetic tree performed on GGPPS. The fungal and plant GGPPS used are listed in Additional file 8. GGPPS not in di-TPS clusters are black in colour. GGPPS in di-TPS clusters are in red for Basidiomycota, blue for Eurotiomycetes, green for Dothideomycetes and purple for Sordariomycetes. The tree is rooted at the level of the plant clade and sequences belonging to the same monophyletic group are clustered together. The branch lengths that had to be reduced for the readability of the figure are striped. The entire phylogenetic tree is described in Additional file 9