Abstract
Monoterpenes confer typical floral notes to “Muscat” grapevine varieties and, to a lesser extent, to other aromatic non-Muscat varieties. Previous studies have led to the identification and functional characterization of some enzymes and genes in this pathway. However, the underlying genetic map is still far from being complete. For example, the specific steps of monoterpene metabolism and its regulation are largely unknown. With the aim of identifying new candidates for the missing links, we applied an integrative functional genomics approach based on the targeted metabolic and genome-wide transcript profiling of Moscato Bianco ripening berries. In particular, gas chromatography-mass spectrometry analysis of free and bound terpenoid compounds was combined with microarray analysis in the skins of berries collected at five developmental stages from pre-veraison to over-ripening. Differentially expressed metabolites and probes were identified in the pairwise comparison between time points by using the early stage as a reference. Metabolic and transcriptomic data were integrated through pairwise correlation and clustering approaches to discover genes linked with particular metabolites or groups of metabolites. These candidate transcripts were further checked for co-localization with quantitative trait loci (QTLs) affecting aromatic compounds. Our findings provide insights into the biological networks of grapevine secondary metabolism, both at the catalytic and regulatory levels. Examples include a nudix hydrolase as component of a terpene synthase-independent pathway for monoterpene biosynthesis, genes potentially involved in monoterpene metabolism (cytochrome P450 hydroxylases, epoxide hydrolases, glucosyltransferases), transport (vesicle-associated proteins, ABCG transporters, glutathione S-transferases, amino acid permeases), and transcriptional control (transcription factors of the ERF, MYB and NAC families, intermediates in light- and circadian cycle-mediated regulation with supporting evidence from the literature and additional regulatory genes with a previously unreported association to monoterpene accumulation).
Highlights
A great deal of the consumer interest in wine derives from its aroma characteristics
Systems biology has been successfully applied to the discovery of regulatory and biosynthetic genes involved in the control of metabolite production (Yuan et al, 2008; Liberman et al, 2012), including examples from grape (Zamboni et al, 2010; Fortes et al, 2011; Agudelo-Romero et al, 2013; Costantini et al, 2015; Malacarne et al, 2015; Suzuki et al, 2015; Wen et al, 2015; Savoi et al, 2016)
The present work provides a temporal profiling of aromatic compounds in the Moscato Bianco ripening berry
Summary
A great deal of the consumer interest in wine derives from its aroma characteristics. Several lines of evidence (Battilana et al, 2009, 2011; Duchêne et al, 2009; Emanuelli et al, 2010; Martin et al, 2012; Wen et al, 2015) support the existence of at least two rate-limiting enzymes in the grapevine MEP pathway, namely the first (1-deoxy-Dxylulose 5-phosphate synthase, VvDXS1) and the last (4-hydroxy3-methylbut-2-enyl diphosphate reductase, VvHDR) Both IPP and DMAPP are substrates for short-chain prenyltransferases, which produce prenyl diphosphate precursors for the large family of terpene synthases (TPSs). Once a terpenoid alcohol skeleton has been produced, extensive modifications determine the final monoterpene composition of grapes and wines (Ribéreau-Gayon et al, 1975; Williams et al, 1989; Luan et al, 2004, 2005, 2006a,b; Mathieu et al, 2009) These secondary transformations are (at least in part) catalyzed by enzymes (Luan et al, 2006a; D’Onofrio et al, 2016) that in most cases have not been identified. Limiting the reactions responsible for the depletion of key odorants (e.g., through the selection of genotypes with low monoterpene glycosyltransferase or oxygenase activities in breeding programs) could be an alternative approach for the improvement of grape/wine flavor (Bönisch et al, 2014a; Hjelmeland and Ebeler, 2015)
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