Comparative transcriptome analysis reveals the genetic basis underlying the biosynthesis of polysaccharides in Hericium erinaceus

Abstract

Background: Hericium erinaceus, also known as lion's mane mushroom, is a widely distributed edible and medicinal fungus in Asian countries. H. erinaceus harbors diverse bioactive metabolites with anticancer, immunomodulating, anti-inflammatory, antimicrobial, antihypertensive, antidiabetic and neuroprotective properties. Although the chemical synthesis processes of these bioactive metabolites are known, the biosynthetic processes remain unknown.

Results: In this study, we obtained the transcriptomes of six H. erinaceus strains using next-generation RNA sequencing and investigated the characteristics of the transcriptomes and biosynthesis of bioactive compounds, especially polysaccharides. The transcriptomes ranged in size from 46.58 to 58.14 Mb, with the number of unigenes ranging from 20,902 to 37,259 across the six H. erinaceus strains. Approximately 60% of the unigenes were successfully annotated by comparing sequences against different databases, including the nonredundant (NR), Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), clusters of orthologous groups for eukaryotic complete genomes (KOG) and Swiss-Prot databases. Most of the transcripts were putatively involved in signal transduction, carbohydrate metabolism, translation, transport and catabolism, and amino acid metabolism. Genes involved in polysaccharide biosynthesis were identified, and these genes encoded phosphoglucomutase (PGM), glucose phosphate isomerase (PGI), UDP-glucose pyrophosphorylase (UGP), glycoside hydrolase family proteins, glycosyltransferase family proteins and other proteins. Moreover, the putative pathway for the intracellular polysaccharide biosynthesis of H. erinaceus was analyzed. Additionally, the open reading frames (ORFs) and simple sequence repeats (SSRs) were predicted from the transcriptome data of the six strains.

Conclusions: Overall, the present study may facilitate the discovery of polysaccharide biosynthesis processes in H. erinaceus and provide useful information for exploring the secondary metabolites in other members of the Basidiomycetes genus.

Keywords: Comparative transcriptome; Erinacines; Hericium erinaceus; Polysaccharide biosynthesis; RNA-Seq.

Fig. 1

The morphological characteristics of H. erinaceus dikaryotic mycelium on PDA medium. a H. erinaceus HT-4903, b H. erinaceus GT-06, c H. erinaceus CC-02, d H. erinaceus PZH-05, e H. erinaceus TJH-03, f H. erinaceus TD-04

Fig. 2

GO classification of unigenes in the six H. erinaceus strains

Fig. 3

KEGG pathway classification of unigenes in the six H. erinaceus strains

Fig. 4

The basic structure of typical mushroom polysaccharides (a), polysaccharide content (b) and the expression of important genes for polysaccharide biosynthesis (c). Mean polysaccharide contents are shown with standard errors bars from three repeated experiments

Fig. 5

KEGG mapping of the polysaccharide metabolism pathway identified in H. erinaceus. a KEGG map 00500, b KEGG map 00051, and c KEGG map 00052. The colorized oval in the map indicates the related genes from our data in this pathway. The number beside the oval is in accordance with the gene number in Table 5. Each color indicates different genes. The same color indicates the same genes

Fig. 6

Putative pathway for intercellular polysaccharide biosynthesis in H. erinaceus. The red stars indicate the three most important enzymes involved in polysaccharides

Fig. 7

qRT-PCR confirmation of 10 expressed genes in the six H. erinaceus strains. The expression patterns of selected genes were analyzed across six samples. Gray bars with standard errors represent the FPKM values according to RNA-Seq (left y-axis), and blue lines indicate the relative expression level determined by qRT-PCR (right y-axis)