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• Distinctive terpenoid accumulation profiles were observed in F1 hybrids, with notably elevated levels of monoterpenes detected in muscat grapes when contrasted with neutral grapes. • Linalool, α-terpineol, and l-α-terpineol emerged as signature aroma compounds exclusively present in muscat grapes. • Unveiling pivotal genes and transcription factors pivotal to the biosynthesis pathways of monoterpenes. • Members of the Nudix hydrolase (NUDX) family, alongside other genes in signal transduction pathways, are implicated in the modulation of monoterpene accumulation within grape skins. Monoterpenes are typical aroma components of muscat grape (Vitis vinifera L.) cultivars. However, differences in the molecular mechanism of monoterpene biosynthesis between Muscat and non-Muscat grapes remain unclear. Here, comprehensive transcriptomic and metabolomic analyses of two F1 hybrids with different aroma profiles obtained from crosses between 'Muscat Hamburg' and 'Red Globe' grapes were performed to examine the unique monoterpene accumulation pattern and related candidate genes. The concentrations of most monoterpenes differed at various times, in the hybrid progeny, increasing from the pre-veraison stage to the veraison stage, followed by a decreasing trend from veraison to maturity. Within the F1 generation, the concentrations of accumulated monoterpenes were significantly higher in Muscat grapes than in neutral grapes. Furthermore, linalool, α-terpineol, and l-α-terpineol may be important odorants affecting the floral characteristics of Muscat grapes due to their high odor activity values. Transcriptional analysis identified three VvDXS (LOC100249323, LOC100268079, and LOC100247834), 1 VvHDS (LOC100257071), one VvMVK (LOC100251148), one VvHMGR (LOC100265082), and one VvGGPPS (LOC100257234) genes encoding proteins involved in the MEP and MVA pathways. Eleven TPS genes potentially involved in monoterpene regulation were also identified. Among them, VvTPS (LOC100853562) showed consistency with the accumulation of monoterpenes and had a high expression level; MYB (LOC100255488), GATA (LOC100262474), and ERF (LOC100255943, LOC100260401) were selected as candidate genes encoding transcription factors. The findings in this study provide new insights for further functional validation and investigation of genes related to monoterpene synthesis in Muscat aroma grapes. [Display omitted] [ABSTRACT FROM AUTHOR]

UV-C irradiation increases resveratrol content in grape skins, but it reaches a maximum at a certain UV-C dose. In contrast, UV-B has a weak resveratrol-enhancing effect at low doses, but it has not been investigated at high doses. In this study, we investigated the effect of high-dose UV-B on resveratrol contents in grape skins. Irradiation of Muscat Bailey A with 290 nm UV-B LED at 22 500 and 225 000 µmol m-2 increased the resveratrol contents in the grape skins by 2.1- and 9.0-fold, respectively, without significant increases in other phenolic compounds. The effect was also confirmed for 2 other cultivars: Shine Muscat and Delaware. Transcriptome analysis of the grape skins of Muscat Bailey A immediately after irradiation with UV-B at 225 000 µmol m-2 showed that genes related to biotic and abiotic stresses were upregulated. Hence, it was suggested that high-dose UV-B irradiation induces a stress response and specifically activates resveratrol biosynthesis. [ABSTRACT FROM AUTHOR]

Two lactic acid bacteria (LAB) strains of Lactobacillus plantarum 21802 and Lactobacillus brevis 6239 were selected and combined for fermentation of grape juice. The changes of sugars, organic acids, volatiles, phenolic compounds as well as antioxidant capacity of the grape juice were characterized. Results showed that fermentation with LAB led to a slight decrease in sugar content and increased in organic acid content. The sugars were mainly consumed at the initial stage of fermentation, while the malic acid was consumed completely during the fermentation. The contents of total phenolics and flavonoids in grape juice decreased gradually during the fermentation process. As compared with the initial contents in unfermented grape juice, the contents of proanthocyanin B2, rutin, isoquercitrin, rhamnose-3-O-glucoside in the final fermented grape juice were increased by 26.83%, 249.24%, 138.48%, 139.60%, respectively, while the contents of gallic acid, proanthocyanin B1, catechin and epicatechin were decreased by 24.49%, 14.85%, 71.68%, 42.52%, respectively. The mice fed with the fermented grape juice showed higher activity of superoxide dismutase and lower level of malondialdehyde both in serum and liver tissue than those fed with the unfermented grape juice. Fermentation with LAB also enhanced the flavor profile by increasing the total number and content of volatile compounds, especially those of monoterpene alcohols, which are the main and characteristic aroma volatile compounds in Muscat aroma grapes. This research confirmed that fermentation with LAB might be a desirable option for improving the flavor and nutritional attributes of grape juice by altering the ratio of sugar to organic acid, improving the phenolic compounds, enhancing the antioxidant capacity, intensifying of the characteristic aroma and pleasant flavor of the grape juice. [ABSTRACT FROM AUTHOR]

• The difference in the content and composition of anthocyanins in three grape was investigated. • 70 DAB was determined as a turning point for the epidermis color change. • CHS, F3'H, ANS and UFGT were proposed as candidate genes for anthocyanin synthesis. • The expression levels of anthocyanins biosynthetic genes in grape were measured. In this study, Shine Muscat (YG), Gaoqiansui (GQS) and Moldova (ME) were used to study the changes of anthocyanin and related genes expression in grape skin during fruit growth and development. CHS, F3'H, ANS and UFGT were the main genes with relatively high expression levels. Significant differences were observed in the expressions of CHS, F3'H, ANS , and UFGT among YG, GQS, ME in most fruit developmental stages. Large differences were discovered in the anthocyanin contents and components among three grape cultivars. During fruit development YG only contained trace anthocyanins. Peonidin, malvidin and cyanidin derivates are the main components in GQS, while the main components of ME are malvidin, petunidin, and delphinidin. Almost all the genes tested were positively correlated with anthocyanins between GQS and ME but irrelevant in YG during fruit development. High expression of CHS, F3'H, ANS, and UFGT and other genes probably promote the synthesis of anthocyanins. Overall CHS, F3'H, ANS, and UFGT were proposed as prominent candidate genes for anthocyanin synthesis in grape skin. This study provides reference for further understanding the physiological and biochemical mechanisms of anthocyanin synthesis in grape fruits which could be better for breeding programs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preharvest MeJA application upregulates terpene biosynthesis in postharvest grapes. • Preharvest MeJA application upregulates phenolics biosynthesis in postharvest grapes. • The effect of preharvest MeJA application on the quality of postharvest grapes is dose-dependent. Methyl jasmonate (MeJA) is an important phytohormone that regulates the development of grape, but the effect and underpin mechanism of its preharvest application on secondary metabolites accumulation in postharvest grape berries are still unclear. In this study, the transcriptome profiles combined with metabolic components analysis were used to determine the effect of preharvest MeJA application on the quality formation of postharvest rose-flavor table grape Shine Muscat. The results indicated that preharvest MeJA treatment had no significant effect on TSS content, but had a down-regulation effect on the accumulation of reducing sugar and titratable acid in the berries. The content of chlorophylls and carotenoids in treated berries was significantly higher than that of the control. Many phenolic components, such as trans -ferulic acid, resveratrol, quercetin, and kaempferol, were sensitive to MeJA and their contents were also significantly higher than that of the control under MeJA treatments during the shelf life. Compared with other volatile aroma components, terpenoid components were more sensitive to preharvest MeJA signals, the content of which presented an overall upward trend with increasing MeJA concentration and prolonging storage time. Furthermore, most of the differentially expressed genes in the general phenylpropanoid pathway and terpenoid biosynthesis pathway were up-regulated responding to MeJA signals. The most upregulated regulatory factors, such as VvWRKY72 , VvMYB24 , and VvWRI1 , may be involved in MeJA signal transduction and regulation. Preharvest MeJA may be an effective technique for enhancing the quality of postharvest Shine Muscat grape berries, with its positive effect on enhancing the characteristic aroma and nutritional components. [ABSTRACT FROM AUTHOR]

Polyphenol oxidases (PPOs) are important enzymes that are widely found in both prokaryotes and eukaryotes including grapes. Studies of grape PPO to date have mostly relied on enzymes extracted and purified from plants. In this work, we describe the production of the mature form of Shine Muscat grape PPO by using an Escherichia coli expression system. We have optimised the purification procedure to obtain pure and active recombinant enzymes and characterised the catalytic efficiency of the recombinant grape PPO by using ultraviolet/visible (UV/Vis) spectrophotometry. Our work provides a simple protocol of obtaining pure and active recombinant grape PPO that will enable further studies about the catalytic mechanism and inhibition of this enzyme. • Mature grape polyphenol oxidase was produced in Escherichia coli. • Purification protocol was optimised to produce active enzymes. • First report of active, mature polyphenol oxidase from a eukaryotic source produced in E. coli. [ABSTRACT FROM AUTHOR]

Monoterpenes are the most important contributors to the floral and fruity flavor of Muscat grapes. However, loss of Muscat flavor and decreased quality during shelf life often affect the commercial value of grapes. Light radiation can be an effective tool to maintain postharvest quality. In the present study, the effect of different wavelengths of light (white, red, blue, red–blue, UV-A and UV-B) on the quality of 'Shine Muscat' (Vitis labrusca × vinifera) during the shelf life was carried out. Grapes irradiated with white, red, blue and red‒blue light showed degraded chlorophyll and accumulated carotenoids in the skin compared to grapes under dark conditions. Blue and red‒blue light were more effective than other wavelengths of light in maintaining and increasing the levels of monoterpenes, such as linalool, limonene, and geraniol. Blue light exhibited the best maintenance and promotion effects on overall quality based on principal component analysis, and promoted the expression of some key genes involved in monoterpene synthesis, such as VvPNLinNer 1, VvPNLinNer 2, VvTPS60 and VvPNLNGL4. The transient over-expression experiment revealed that VvTPS60 may be primarily responsible for catalyzing the linalool synthesis. Results suggest that exposing postharvest grapes to different wavelengths of light is a promising technology to improve fruit quality. [Display omitted] • Blue and red–blue lights increased the content of most monoterpens in grapes. • Postharvest light could up-regulate the expression of monoterpene biosynthetic genes. • Bule light had the best maintenance and promotion effects on overall grape quality. • VvTPS60 may be primarily responsible for catalyzing the linalool biosynthesis. [ABSTRACT FROM AUTHOR]

Volatile compounds are considered to be essential for the flavor and aroma quality of grapes. Thidiazuron (TDZ) is a commonly used growth regulator in grape cultivation that stimulates larger berries and prevents fruit drop. This study was conducted to investigate the effect of TDZ on the production of aroma volatiles and to identify the key genes involved in the terpene biosynthesis pathways that are affected by this compound. Treatment with TDZ had a negative effect on the concentration of volatile compounds, especially on monoterpenes, which likely impacts the sensory characteristics of the fruit. The expression analysis of genes related to the monoterpenoid biosynthesis pathways confirmed that treatment with TDZ negatively regulated the key genes DXS1, DXS3, DXR, HDR, VvPNGer and VvPNlinNer1. Specifically, the expression levels of the aforementioned genes were down-regulated in almost all berry development stages in the TDZ-treated samples. The novel results from the present study can be used to aid in the development of food products which maintain the flavor quality and sensory characteristics of grape. Furthermore, these findings can provide the theoretical basis that can help to optimize the utilization of TDZ for the field production of grapes at a commercial scale. [ABSTRACT FROM AUTHOR]

Berry firmness is one of the most important quality traits in table grapes. The underlying molecular and genetic mechanisms for berry firmness remain unclear. We constructed a high-density genetic map based on whole-genome resequencing to identify loci associated with berry firmness. The genetic map had 19 linkage groups, including 1662 bin markers (26,039 SNPs), covering 1463.38 cM, and the average inter-marker distance was 0.88 cM. An analysis of berry firmness in the F1 population and both parents for three consecutive years revealed continuous variability in F1, with a distribution close to the normal distribution. Based on the genetic map and phenotypic data, three potentially significant quantitative trait loci (QTLs) related to berry firmness were identified by composite interval mapping. The contribution rate of each QTL ranged from 21.5% to 28.6%. We identified four candidate genes associated with grape firmness, which are related to endoglucanase, abscisic acid (ABA), and transcription factors. A qRT-PCR analysis revealed that the expression of abscisic-aldehyde oxidase-like gene (VIT_18s0041g02410) and endoglucanase 3 gene (VIT_18s0089g00210) in Muscat Hamburg was higher than in Crimson Seedless at the veraison stage, which was consistent with that of parent berry firmness. These results confirmed that VIT_18s0041g02410 and VIT_18s0089g00210 are candidate genes associated with berry firmness. [ABSTRACT FROM AUTHOR]