Integrated metabolome and transcriptome analysis of Magnolia champaca identifies biosynthetic pathways for floral volatile organic compounds

Abstract

Background Magnolia champaca, commonly known as champak is a well-known tree due to its highly fragrant flowers. Champak floral scent is attributed to a complex mix of volatile organic compounds (VOCs). These aromatic flowers are widely used in flavors and fragrances industry. Despite its commercial importance, the VOC biosynthesis pathways in these flowers are largely unknown. Here, we combine metabolite and RNA sequencing (RNA-seq) analyses of fully opened champak flowers to discover the active VOC biosynthesis pathways as well as floral scent-related genes.ResultsVolatile collection by headspace method and analysis by gas chromatography-mass spectrometry (GC-MS) identified a total of 43 VOCs from fully opened champak flowers, of which 46.9% were terpenoids, 38.9% were volatile esters and 5.2% belonged to phenylpropanoids/benzenoids. Sequencing and de novo assembly of champak flower transcriptome yielded 47,688 non-redundant unigenes. Transcriptome assembly was validated using standard polymerase chain reaction (PCR) based approach for randomly selected unigenes. The detailed profiles of VOCs led to the discovery of pathways and genes involved in floral scent biosynthesis from RNA-seq data. Analysis of expression levels of many floral-scent biosynthesis-related unigenes in flowers and leaves showed that most of them were expressed higher in flowers than in leaf tissues. Moreover, our metabolite-guided transcriptomics, in vitro and in vivo enzyme assays and transgenic studies identified (R)-linalool synthase that is essential for the production of major VOCs of champak flowers, (R)-linalool and linalool oxides.ConclusionAs our study is the first report on transcriptome analysis of Magnolia champaca, this transcriptome dataset that serves as an important public information for functional genomics will not only facilitate better understanding of ecological functions of champak floral VOCs, but also provide biotechnological targets for sustainable production of champak floral scent.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3846-8) contains supplementary material, which is available to authorized users.

Composition and Biosynthesis of Scent Compounds from Sterile Flowers of an Ornamental Plant Clematis florida cv. ‘Kaiser’

“…The proteins they encode are 554 (CfTPS1), 586 (CfTPS2), and 591 (CfTPS3) amino acids in length. A sequence alignment revealed that all of the CfTPS proteins contained the conserved 'DD XX D' and 'NSE/DTE' motifs that are essential for the binding of the co-factors Mg 2+ or Mn 2+ to catalyze terpene biosynthesis [19].…”

“…The general biochemical pathways leading to the different classes of volatiles are relatively well understood, and several key protein families such as the terpene synthase (TPS) family, BAHD acyltransferase family, and small molecule methyltransferase families have been described to play important roles in the formation of floral volatiles [14][15][16][17]. In many of these studies, the successful identification of scent-producing genes was based on the integration of metabolomic and transcriptomic data [18][19][20]. TPSs involved in the biosynthesis of floral volatile terpenes, particularly monoterpenes (C 10 ) and sesquiterpenes (C 15 ), belong to TPS-a, TPS-b, and TPS-g subfamilies [18][19][20][21][22][23].…”

“…In many of these studies, the successful identification of scent-producing genes was based on the integration of metabolomic and transcriptomic data [18][19][20]. TPSs involved in the biosynthesis of floral volatile terpenes, particularly monoterpenes (C 10 ) and sesquiterpenes (C 15 ), belong to TPS-a, TPS-b, and TPS-g subfamilies [18][19][20][21][22][23]. Floral volatiles emitted from angiosperm plants possess multifaceted functions particularly for attracting pollinators and defending against florivores [11].…”

Experimental Design and Sample Preparation in Forest Tree Metabolomics

“…In addition to the direct economic benefits provided by tree species, i.e., timber and non-timber products, gaming and tourism, forests have an immensurable ecological value, being the major determinants for water, oxygen, carbon, and energy balance and can be seen as a major opportunity to mitigate climate change effects [12], i.e., continued drought, increased soil and water salinization and acidification, and intensification of extreme temperatures [13]. In forest tree metabolomics research, most biological questions are indeed related to the responses towards the acclimation and adaptation to a permanently changing environment [14][15][16][17][18][19][20][21][22][23][24][25][26] as well as to the identification of potentially active components in tree species of pharmacological, agricultural, environmental, or industrial importance [27][28][29][30][31][32][33].…”

Transcriptomic and proteomic approaches to explore the differences in monoterpene and benzenoid biosynthesis between scented and unscented genotypes of wintersweet

“…However, the genetic improvement of floral scent falls behind breeding research aimed at improving flower shapes and colors (Dudareva and Pichersky ). Nonetheless, because of increasing consumer demand, more studies are beginning to focus on scent traits (Jin et al , Yue et al , Dhandapani et al , Hu et al , Zhao et al ).…”