De novo transcriptome sequencing of Rhododendron molle and identification of genes involved in the biosynthesis of secondary metabolites

Guo-Lin Zhou,Ping Zhu

doi:10.1186/s12870-020-02586-y

Abstract

BackgroundRhododendron molle (Ericaceae) is a traditional Chinese medicinal plant, its flower and root have been widely used to treat rheumatism and relieve pain for thousands of years in China. Chemical studies have revealed that R. molle contains abundant secondary metabolites such as terpenoinds, flavonoids and lignans, some of which have exhibited various bioactivities including antioxidant, hypotension and analgesic activity. In spite of immense pharmaceutical importance, the mechanism underlying the biosynthesis of secondary metabolites remains unknown and the genomic information is unavailable.ResultsTo gain molecular insight into this plant, especially on the information of pharmaceutically important secondary metabolites including grayanane diterpenoids, we conducted deep transcriptome sequencing for R. molle flower and root using the Illumina Hiseq platform. In total, 100,603 unigenes were generated through de novo assembly with mean length of 778 bp, 57.1% of these unigenes were annotated in public databases and 17,906 of those unigenes showed significant match in the KEGG database. Unigenes involved in the biosynthesis of secondary metabolites were annotated, including the TPSs and CYPs that were potentially responsible for the biosynthesis of grayanoids. Moreover, 3376 transcription factors and 10,828 simple sequence repeats (SSRs) were also identified. Additionally, we further performed differential gene expression (DEG) analysis of the flower and root transcriptome libraries and identified numerous genes that were specifically expressed or up-regulated in flower.ConclusionsTo the best of our knowledge, this is the first time to generate and thoroughly analyze the transcriptome data of both R. molle flower and root. This study provided an important genetic resource which will shed light on elucidating various secondary metabolite biosynthetic pathways in R. molle, especially for those with medicinal value and allow for drug development in this plant.

Highlights

Rhododendron molle (Ericaceae) is a traditional Chinese medicinal plant, its flower and root have been widely used to treat rheumatism and relieve pain for thousands of years in China
We further explore the unigenes related to secondary metabolism, a total of 11 pathways including 437 unigenes were found to participate in “biosynthesis of other secondary metabolites”, among which the most unigenes were enriched in the beta-Alanine metabolism (118 unigenes) (Fig. 2b), followed by‘Phenylalanine biosynthesis’ (100 unigenes) and ‘flavonoid biosynthesis (53 unigenes)
We focused on searching for candidate genes involved in grayanoids biosynthesis, out of 17,906 unigenes, 102 unigenes were involved in terpenoid backbone biosynthesis

Summary

Introduction

Rhododendron molle (Ericaceae) is a traditional Chinese medicinal plant, its flower and root have been widely used to treat rheumatism and relieve pain for thousands of years in China. Modern chemical studies have demonstrated that R. molle produces abundant secondary metabolites, mainly including terpenoids, flavonoids and lignans [6,7,8,9], among these compounds, the grayanane diterpenoids are the most important characteristic constituents in this plant, which account for the plant’s most significant bioactivities namely, analgesia, anti-nociceptive effects [7, 10], and hypotensive activity [11]. Our transcriptome data provided a valuable resource for the discovery of functional genes involved in various metabolic pathways, especially for the putative genes related to the biosynthetic pathways of the medicinally important secondary metabolites and will pave the way towards enhanced biosynthesis of secondary metabolites with medicinal properties through synthetic biology approach

Methods

Results

Discussion

Conclusion