Next generation sequencing unravels the biosynthetic ability of spearmint (Mentha spicata) peltate glandular trichomes through comparative transcriptomics.

Jingjing Jin,Jun Liu,In-Cheol Jang,Rajani Sarojam,Qian Wang,Deepa Panicker,Jun-Lin Yin,Mi Jung Kim,Nam-Hai Chua,Limsoon Wong

doi:10.1186/s12870-014-0292-5

Abstract

BackgroundPlant glandular trichomes are chemical factories with specialized metabolic capabilities to produce diverse compounds. Aromatic mint plants produce valuable essential oil in specialised glandular trichomes known as peltate glandular trichomes (PGT). Here, we performed next generation transcriptome sequencing of different tissues of Mentha spicata (spearmint) to identify differentially expressed transcripts specific to PGT. Our results provide a comprehensive overview of PGT’s dynamic metabolic activities which will help towards pathway engineering.ResultsSpearmint RNAs from 3 different tissues: PGT, leaf and leaf stripped of PGTs (leaf-PGT) were sequenced by Illumina paired end sequencing. The sequences were assembled de novo into 40,587 non-redundant unigenes; spanning a total of 101 Mb. Functions could be assigned to 27,025 (67%) unigenes and among these 3,919 unigenes were differentially expressed in PGT relative to leaf - PGT. Lack of photosynthetic transcripts in PGT transcriptome indicated the high levels of purity of isolated PGT, as mint PGT are non-photosynthetic. A significant number of these unigenes remained unannotated or encoded hypothetical proteins. We found 16 terpene synthases (TPS), 18 cytochrome P450s, 5 lipid transfer proteins and several transcription factors that were preferentially expressed in PGT. Among the 16 TPSs, two were characterized biochemically and found to be sesquiterpene synthases.ConclusionsThe extensive transcriptome data set renders a complete description of genes differentially expressed in spearmint PGT. This will facilitate the metabolic engineering of mint terpene pathway to increase yield and also enable the development of strategies for sustainable production of novel or altered valuable compounds in mint.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0292-5) contains supplementary material, which is available to authorized users.

Highlights

Plant glandular trichomes are chemical factories with specialized metabolic capabilities to produce diverse compounds
Spearmint peltate glandular trichomes (PGT) and their development Spearmint leaves produce three different types of trichomes on their surfaces: non-glandular multicellular hair like, capitate glandular trichomes with a single secretory head cell and PGTs whose secretory head is composed of eight-cells with a single stalk and basal cell (Figure 1A)
These PGT glands possess a large subcuticular storage space that is formed by the separation of the cuticle from the apical cells and the essential oil is secreted into this cavity [12] (Figure 1B)

Summary

Introduction

Plant glandular trichomes are chemical factories with specialized metabolic capabilities to produce diverse compounds. Plants produce an enormous variety of specialised metabolites among which terpenes are the largest and most structurally diverse class of natural products. They are the main components of plant essential oils. Many of these terpenes are produced and stored in specialised secretory structures called glandular trichomes [1,2]. These terpenes provide protection for plants against a variety of herbivores and pathogens [3] and are commercially quite valuable. Our knowledge about the development of secretory glandular trichomes and terpene production and its regulation is very limited making it difficult to engineer these metabolic pathways [4,5]

Methods

Results

Conclusion