Abstract
Pelargonium genus contains about 280 species among which at least 30 species are odorant. Aromas produced by scented species are remarkably diverse such as rose, mint, lemon, nutmeg, ginger and many others scents. Amongst odorant species, rose-scented pelargoniums, also named pelargonium rosat, are the most famous hybrids for their production of essential oil (EO), widely used by perfume and cosmetic industries. Although EO composition has been extensively studied, the underlying biosynthetic pathways and their regulation, most notably of terpenes, are largely unknown. To gain a better understanding of the terpene metabolic pathways in pelargonium rosat, we generated a transcriptome dataset of pelargonium leaf and used a candidate gene approach to functionally characterise four terpene synthases (TPSs), including a geraniol synthase, a key enzyme responsible for the biosynthesis of the main rose-scented terpenes. We also report for the first time the characterisation of a novel sesquiterpene synthase catalysing the biosynthesis of 10-epi-γ-eudesmol. We found a strong correlation between expression of the four genes encoding the respective TPSs and accumulation of the corresponding products in several pelargonium cultivars and species. Finally, using publically available RNA-Seq data and de novo transcriptome assemblies, we inferred a maximum likelihood phylogeny from 270 pelargonium TPSs, including the four newly discovered enzymes, providing clues about TPS evolution in the Pelargonium genus. Notably, we show that, by contrast to other TPSs, geraniol synthases from the TPS-g subfamily conserved their molecular function throughout evolution.
Highlights
The Pelargonium genus belongs to the Geraniaceae family and contains about 280 species exhibiting a wild range of variation in leaf and floral morphology, as well as body plan organisation (Bakker et al, 2004; Jones et al, 2009; Roeschenbleck et al, 2014; Blerot et al, 2015)
We report the identification and functional characterisation of a geraniol synthase (PhGES) and an eudesmol synthase (PhEDS), two major terpene synthases (TPSs) controlling essential oil (EO) composition in pelargonium rosat cultivars, as well as a cineole and a myrcene synthase (PhCINS and PhMYRS, respectively) using a 454 transcriptome of P. × hybridum cv. rosat ‘Grasse.’ We show a strong correlation between expression of the genes encoding these enzymes and presence of their respective products in several pelargonium cultivars and species
Known sequences of GES, limonene synthase and EDS were used to search for homologous sequences in the transcriptome and four TPSs were identified as good candidates based on their percentage of similarity
Summary
The Pelargonium genus belongs to the Geraniaceae family and contains about 280 species exhibiting a wild range of variation in leaf and floral morphology, as well as body plan organisation (Bakker et al, 2004; Jones et al, 2009; Roeschenbleck et al, 2014; Blerot et al, 2015). Aromas of odorant species are remarkably diverse such as rose, mint, lemon, nutmeg, ginger and many other scents, underlying a richness of scented compounds produced in Pelargonium (Demarne and Van der Walt, 1992; Lis-Balchin, 2003; Lalli et al, 2006). × hybridum cultivars, named pelargonium rosat, are the most emblematic cultivars and are often used to replace the expensive Rosa damascena essential oil (EO). Among the scented Pelargonium hybrids, the rose scented P. These hybrids descend from several crossings between P. graveolens or P. radens in one hand and P. capitatum in the other hand. Characterisation of flavones and antioxidants in the hydrolate phase obtained during EO extraction opened new areas for valorisation of by-products (Rao et al, 2002; Sangwan and Singh, 2015)
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