De Novo Sequencing and Analysis of Lemongrass Transcriptome Provide First Insights into the Essential Oil Biosynthesis of Aromatic Grasses.

Seema Meena,Varun Dwivedi,Sarma R Kumar,Ajit K Shasany,Dinesh A Nagegowda,Shubhra Rastogi,D K Venkata Rao,H B Shilpashree

doi:10.3389/fpls.2016.01129

Abstract

Aromatic grasses of the genus Cymbopogon (Poaceae family) represent unique group of plants that produce diverse composition of monoterpene rich essential oils, which have great value in flavor, fragrance, cosmetic, and aromatherapy industries. Despite the commercial importance of these natural aromatic oils, their biosynthesis at the molecular level remains unexplored. As the first step toward understanding the essential oil biosynthesis, we performed de novo transcriptome assembly and analysis of C. flexuosus (lemongrass) by employing Illumina sequencing. Mining of transcriptome data and subsequent phylogenetic analysis led to identification of terpene synthases, pyrophosphatases, alcohol dehydrogenases, aldo-keto reductases, carotenoid cleavage dioxygenases, alcohol acetyltransferases, and aldehyde dehydrogenases, which are potentially involved in essential oil biosynthesis. Comparative essential oil profiling and mRNA expression analysis in three Cymbopogon species (C. flexuosus, aldehyde type; C. martinii, alcohol type; and C. winterianus, intermediate type) with varying essential oil composition indicated the involvement of identified candidate genes in the formation of alcohols, aldehydes, and acetates. Molecular modeling and docking further supported the role of identified protein sequences in aroma formation in Cymbopogon. Also, simple sequence repeats were found in the transcriptome with many linked to terpene pathway genes including the genes potentially involved in aroma biosynthesis. This work provides the first insights into the essential oil biosynthesis of aromatic grasses, and the identified candidate genes and markers can be a great resource for biotechnological and molecular breeding approaches to modulate the essential oil composition.

Highlights

Essential oils, known as volatile or ethereal oils or essences, are the mixtures of highly fragrant compounds found in aromatic plants and flowers
We have generated a gene catalog for lemongrass (C. flexuosus) using de novo transcriptome assembly, which led to the discovery of potential genes (PPase, ADH, AKR, CCD, AAT, and ALDH) involved in essential oil biosynthesis
Biochemical and in planta functional characterization of identified candidates could unravel different steps of essential oil biosynthesis and regulation in Cymbopogon, which would be the subject of our future investigations

Summary

Introduction

Known as volatile or ethereal oils or essences, are the mixtures of highly fragrant compounds found in aromatic plants and flowers. The essential oil producing plants are distributed widely across the plant kingdom covering a large number of families including Lamiaceae (mint, basil, lavender), Rosaceae (roses), and Poaceae (aromatic grasses). Cymbopogon (aromatic grasses), the unique genus of Poaceae family known for its aromatic properties, comprises of about 180 species distributed across the world (Bertea and Maffei, 2010), of which 45 species have been reported in India (Padalia et al, 2011). These aromatic grasses are endowed with differential blend of several terpenoidal constituents and are large reserves of monoterpene rich essential oils (Devi et al, 2015). Essential oils and their individual constituents from aromatic grasses possess potent pharmacological activities like cytotoxic, antiinflammatory, antifungal, and antioxidant activities (Bayala et al, 2014)

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