Transcriptome and metabolite profiling reveals that prolonged drought modulates the phenylpropanoid and terpenoid pathway in white grapes (Vitis vinifera L.)

Background: Secondary metabolism contributes to the adaptation of a plant to its environment. In wine grapes, fruit secondary metabolism largely determines wine quality. Climate change is predicted to exacerbate drought events in several viticultural areas, potentially affecting the wine quality. In red grapes, water deficit modulates flavonoid accumulation, leading to major quantitative and compositional changes in the profile of the anthocyanin pigments; in white grapes, the effect of water deficit on secondary metabolism is still largely unknown Results: In this study we investigated the impact of water deficit on the secondary metabolism of white grapes using a large scale metabolite and transcript profiling approach in a season characterized by prolonged drought. Irrigated grapevines were compared to non-irrigated grapevines that suffered from water deficit from early stages of berry development to harvest. A large effect of water deficit on fruit secondary metabolism was observed. Increased concentrations of phenylpropanoids, monoterpenes, and tocopherols were detected, while carotenoid and flavonoid accumulations were differentially modulated by water deficit according to the berry developmental stage. The RNA- sequencing analysis carried out on berries collected at three developmental stages—before, at the onset, and at late ripening—indicated that water deficit affected the expression of 4,889 genes. The Gene Ontology category secondary metabolic process was overrepresented within up-regulated genes at all the stages of fruit development considered, and within down-regulated genes before ripening. Eighteen phenylpropanoid, 16 flavonoid, 9 carotenoid, and 16 terpenoid structural genes were modulated by water deficit, indicating the transcriptional regulation of these metabolic pathways in fruit exposed to water deficit. An integrated network and promoter analyses identified a transcriptional regulatory module that encompasses terpenoid genes, transcription factors, and enriched drought- responsive elements in the promoter regions of those genes as part of the grapes response to drought Conclusion: Our study reveals that grapevine berries respond to drought by modulating several secondary metabolic pathways, and particularly, by stimulating the production of phenylpropanoids, the carotenoid zeaxanthin, and of volatile organic compounds such as monoterpenes, with potential effects on grape and wine antioxidant potential, composition, and sensory feature

Multi-Omics and Integrated Network Analyses Reveal New Insights into the Systems Relationships between Metabolites, Structural Genes, and Transcriptional Regulators in Developing Grape Berries (Vitis vinifera L.) Exposed to Water Deficit

Grapes are one of the major fruit crops and they are cultivated in many dry environments. This study comprehensively characterizes the metabolic response of grape berries exposed to water deficit at different developmental stages. Increases of proline, branched-chain amino acids, phenylpropanoids, anthocyanins, and free volatile organic compounds have been previously observed in grape berries exposed to water deficit. Integrating RNA-sequencing analysis of the transcriptome with large-scale analysis of central and specialized metabolites, we reveal that these increases occur via a coordinated regulation of key structural pathway genes. Water deficit-induced up-regulation of flavonoid genes is also coordinated with the down-regulation of many stilbene synthases and a consistent decrease in stilbenoid concentration. Water deficit activated both ABA-dependent and ABA-independent signal transduction pathways by modulating the expression of several transcription factors. Gene-gene and gene-metabolite network analyses showed that water deficit-responsive transcription factors such as bZIPs, AP2/ERFs, MYBs, and NACs are implicated in the regulation of stress-responsive metabolites. Enrichment of known and novel cis-regulatory elements in the promoters of several ripening-specific/water deficit-induced modules further affirms the involvement of a transcription factor cross-talk in the berry response to water deficit. Together, our integrated approaches show that water deficit-regulated gene modules are strongly linked to key fruit-quality metabolites and multiple signal transduction pathways may be critical to achieve a balance between the regulation of the stress-response and the berry ripening program. This study constitutes an invaluable resource for future discoveries and comparative studies, in grapes and other fruits, centered on reproductive tissue metabolism under abiotic stress.This study was funded by the European Territorial Cooperation program (Sustainable viticulture and improvement of the territorial resources of the grape and wine industry), the Fondazione Edmund Mach (GMPF Program), the COST Action FA1106 Quality Fruit, Genome British Columbia (10R21188), and the Natural Sciences and Engineering Research Council of Canada (10R23082)

EFFETTO DELLA CIMATURA TARDIVA E DEL DEFICIT IDRICO SULLA QUALIT\uc0 DELL\u2019UVA MERLOT

The effect of leaf area reduction in Merlot grapevines was tested in well irrigated vines and in vines under water deficit. The effect was monitored over two consecutive seasons. In full irrigation regime (I) vines were irrigated weekly to maintain midday stem water potential (\u3a8stem) between 120.3 and 120.6 MPa. In water deficit (D) condition, irrigation was managed in order to maintain \u3a8stem between 121.0 and 121.4 MPa from fruit set to harvest. Within each irrigation regime two different levels of canopy height were imposed: high canopy (110 cm) and short canopy (60 cm). Canopy reduction under full irrigation and water deficit conditions produced different results. Brix degrees were reduced only under well irrigated conditions, while under water deficit no effects of canopy reduction were observed. The reduction of leaf area did not influence the anthocyanin and tannin concentrations

EFFECT OF DEFICIT IRRIGATION AND LEAF AREA REDUCTION IN \u2018MERLOT\u2019 GRAPEVINES AND WINEGRAPES

Two agronomic techniques, water deficit and severe leaf area reduction, applied with the objective of obtaining grapes with low sugar content without altering (or increasing) the polyphenol content. For this purpose, during the years 2011, 2012, and 2013, a Merlot experimental vineyard was set up in the experimental farm of the University of Udine. In the present communication we present the results of the 2013 season. The experiment design was a full 2x2 factorial design with two levels of irrigation imposed at berry set as the first factor (I- Irrigated vines and stem water potential maintained between -0.3 and -0.6 MPa; and D-water deficit vines, with stem water potential maintained between -0.8 and -1.4 MPa). The vineyard was sheltered by a tunnel covered by EVA film and water was supplied by a sub-surface drip irrigation system. Two levels of summer trimming (applied at the end of veraison, that is when at least 80% of all berries had changed color) was the second factor. Trimmed (T) vines were manually topped above the 6th node. Non-Trimmed vines (NT) were topped at the 12th node (normal viticultural practice). Leaf area at veraison and harvest, berry composition during ripening, and non-structural carbohydrates reserves at the beginning of the trials and after were observed. Microvinification was performed for all treatments. Results indicate that there is no interaction effect between irrigation and trimming, leading to no synergic effect on the reduction of sugars and enhancement of polyphenols. Both, water deficit and leaf area reduction heavily modified total leaf area per vine and the leaf area to fruit ratio but with different consequences in terms of grape and wine quality

Effect of Post-Veraison Canopy Reduction and Deficit Irrigation on \u2018Merlot\u2019 grape Composition

In several winegrowing regions of the world, climate change has determined an acceleration of the ripening process, resulting in increased sugar concentration at harvest and in wines characterized by high alcohol levels, low acidity and reduced varietal aroma. The limitation of photosynthetic carbon availability by drastically reducing canopy size, has been proposed as a strategy to reduce berry sugar at harvest. However, in some cases, this strategy has negatively impacted other fruit composition parameters (e.g. anthocyanins). Our research investigated the effect of canopy manipulation on sugars and phenolic accumulation in the berries of grapevines subjected to different irrigation regimes. The trial was conducted at the experimental station of the University of Udine (Udine, Italy) on 28-years-old \u2018Merlot\u2019 grapevines grafted on SO4 in 2011 and 2012. We tested the effect of a severe post-veraison canopy reduction (-50% of total leaf area) in combination with deficit irrigation to reduce sugar concentration and enhance phenolic concentration in the berries at harvest. Four treatments were tested: 1) Canopy reduction under deficit irrigation (CR-WD), 2) Canopy reduction under full irrigation (CR-I), 3) No canopy reduction under deficit irrigation (C-WD), and 4) No canopy reduction under full irrigation (C-I). In 2011, CR-WD treatment resulted in berries with lower sugar concentration and higher anthocyanin concentration than the other treatments. Canopy reduction was also efficient in reducing sugar without altering anthocyanin concentration under well-watered conditions. In 2012, however, canopy reduction did not reduce sugar concentration at harvest. Our data suggests that modifying the source-sink balance via canopy reduction is a viable practice for modulating sugar accumulation only when the leaf area/crop weight ratio is a limiting factor. Seasonal weather variability may overcome the targeted ratio by compensating fruit size and/or yield and canopy reduction should be managed accordingly

From grape berries to wines: drought impacts on key secondary metabolites

Aim: We aimed to study the impact of water deficit on the concentration of key flavour and phenolic secondary metabolites of wines. Methods and results: A drought-stress field trial was conducted on Vitis vinifera cv. Merlot and Tocai Friulano for two seasons. Fully irrigated (C) and deficit irrigated (D) grapes were microvinified and the resulting wines were analysed to determine the concentrations of anthocyanins, tannins, and free and glycosidically-bound Volatile Organic Compounds (VOCs). A descriptive sensory test was undertaken on the same wines. Water stressed grapes produced wines with higher concentrations of anthocyanins in Merlot and of free and glycosidically-bound monoterpenes in Tocai Friulano. Both cultivars displayed higher amounts of glycosidically-bound C13-norisoprenoids. Conclusions: Previously observed drought-induced compositional changes to the grapes were transfered to the wines, with an increase in polyphenols and VOCs. However, the timing and the duration of the water stress in the field only heavily impacted the final wine composition with major metabolic modification when the severe water deficit started early (at approximately 40 days after anthesis) and lasted over the entire season until harvest. Significance and impact of the study: This study highlights the positive role of a controlled water deficit on the composition of the wines in terms of secondary metabolites

Multi-omics and integrated network analyses reveal new insights into the systems relationships between metabolites, structural genes, and transcriptional regulators in developing grape berries (Vitis vinifera L.) exposed to water deficit

Grapes are one of the major fruit crops and they are cultivated in many dry environments. This study comprehensively characterizes the metabolic response of grape berries exposed to water deficit at different developmental stages. Increases of proline, branched-chain amino acids, phenylpropanoids, anthocyanins, and free volatile organic compounds have been previously observed in grape berries exposed to water deficit. Integrating RNA-sequencing analysis of the transcriptome with large-scale analysis of central and specialized metabolites, we reveal that these increases occur via a coordinated regulation of key structural pathway genes. Water deficit-induced up-regulation of flavonoid genes is also coordinated with the down-regulation of many stilbene synthases and a consistent decrease in stilbenoid concentration. Water deficit activated both ABA-dependent and ABA-independent signal transduction pathways by modulating the expression of several transcription factors. Gene-gene and gene metabolite network analyses showed that water deficit-responsive transcription factors such as bZIPs, AP2/ERFs, MYBs, and NACs are implicated in the regulation of stress responsive metabolites. Enrichment of known and novel cis-regulatory elements in the promoters of several ripening-specific/water deficit-induced modules further affirms the involvement of a transcription factor cross-talk in the berry response to water deficit. Together, our integrated approaches show that water deficit-regulated gene modules are strongly linked to key fruit-quality metabolites and multiple signal transduction pathways may be critical to achieve a balance between the regulation of the stress response and the berry ripening program. This study constitutes an invaluable resource for future discoveries and comparative studies, in grapes and other fruits, centered on reproductive tissue metabolism under abiotic stress