Transcriptome analysis and targeted metabolic profiling for pathway elucidation and identification of a geraniol synthase involved in iridoid biosynthesis from Gardenia jasminoides

• Published in: Industrial crops and products 2019-06, Vol.132, p.48-58
• Main Authors: Ye, Peng, Liang, Shuangcheng, Wang, Xiaomin, Duan, Lixin, Jiang-Yan, Fengyang, Yang, Jinfen, Zhan, Ruoting, Ma, Dongming
• Format: Article
• Language: English
• Subjects: Gardenia jasminoides Ellis; Geniposide; Iridoids; Metabolic profiling; Transcriptome
• ISSN: 0926-6690; 1872-633X
• DOI: 10.1016/j.indcrop.2019.02.002

[Display omitted] •Twelve Transcriptomes from four different tissues screened candidate genes involved in iridoid metabolism of Gardenia jasminoides.•A geraniol synthase (GES), the first enzyme in iridoid pathway displayed the conversions of GPP to geraniol.•Seven iridoid or iridoid glycosides were highly accumulated in fruits used for medicine.•The iridoid and iridoid glycosides biosynthesis pathway was proposed.•The study will be beneficial for metabolic engineering to produce pharmaceutical ingredients. Iridoid compounds have been reported to be accumulated in the dried fruits of Gardenia jasminoides (Rubiaceae), which are used in traditional Chinese medicine. These compounds exhibit obvious pharmacological activities, including effective protective effects on the liver and therapeutic efficacy for cardiovascular diseases. However, the biosynthetic pathway of iridoid remains uninvestigated. In this study, 12 transcriptomes from four tissues (lower leaves, top leaves, flowers, and fruits) were analyzed to characterize the accumulation of active constituents and to identify the corresponding genes involved in iridoid biosynthesis. Almost all genes in the mevalonate (MVA) pathway and the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway were found in our transcriptome database; these pathways comprise upstream pathways of iridoid compounds (monoterpene derivatives), most of which are abundant in flowers and fruits. Geraniol synthase (GES), which is involved in the first branch step in the iridoid biosynthetic pathway, was cloned, and quantitative real-time PCR (qRT-PCR) revealed that GjGES showed a similar expression pattern to that in the transcriptome in terms of reads per kilobase per million (RPKM) mapped reads. The recombinant GjGES protein efficiently converted geranyl diphosphate (GPP) to geraniol. Subsequently, the metabolic profiling of seven iridoids and iridoid glycosides, namely geniposide, gardenoside, genipin, geniposidic acid, genipin-1-β-gentiobioside, shanzhiside, and shanzhiside methyl ester, revealed that these compounds were highly accumulated in fruits. Consequently, the metabolites and speculated unigenes involved in iridoid metabolic pathways enabled the identification of glucosyltransferase, hydroxylase, and O-methyltransferase candidate genes responsible for the biosynthesis of iridoid and iridoid glycosides. The results of the present study can serve as a reference for the functional characterization of enzyme-coding genes and are