Differential Expression of VvLOXA Diversifies C6 Volatile Profiles in Some Vitis vinifera Table Grape Cultivars

Comparative Analysis of the Evolution of Green Leaf Volatiles and Aroma in Six Vitis vinifera L. Cultivars during Berry Maturation in the Chinese Loess Plateau Region

Green leaf volatiles (GLVs) are important in giving grape a fresh and green aroma. But the changes in GLVs during the phenological development of grapevines are not well known. This study analyzed the GLVs and transcription levels of associated biosynthetic genes in six grape species from the Loess Plateau region at five stages of maturation. Thirteen GLVs were detected, showing unique patterns for each grape type at various growth phases. The primary components in six grapes were (E)-2-hexenal, (E)-2-hexen-1-ol, and hexanal. With the exception of Cabernet Franc in 2019, the overall GLV contents of the six types generally increased during growth and development, peaking or stabilizing at harvest. And Sauvignon Blanc, Cabernet Gernischt, and Cabernet Sauvignon exhibited higher total contents among the varieties. PLS-DA analysis revealed 3-hexenal's high VIP scores across two years, underscoring its critical role in grape variety classification. Correlation analysis revealed a strong positive correlation between the levels of hexanal, 1-hexanol, (E)-2-hexen-1-ol, (Z)-3-hexenyl acetate, nonanal, and (E, E)-2,6-nonadienal and the expression of VvHPL and VvAAT genes in the LOX-HPL pathway. Specifically, VvHPL emerges as a potential candidate gene responsible for species-specific differences in GLV compounds. Comprehending the changing patterns in the biosynthesis and accumulation of GLVs offers viticulturists and enologists the opportunity to devise targeted strategies for improving the aromatic profile of grapes and wines.

Analysis of aroma precursors in Jinmudan fresh tea leaves and dynamic change of fatty acid volatile during black tea processing

Aroma is an important factor affecting the quality of tea. Fatty acids are one of precursors and their derived contributes to tea aroma considerably. In this study, we analyzed the fatty acids of Jinmudan fresh tea leaves in different stalk position. It was found that with shoot maturity increased, the content of PUFAs (Polyunsaturated fatty acids) was increased while the content of SFAs (Saturated fatty acids) and MUFAs (Monounsaturated fatty acids) gradually decreased. During the processing period, totally 704 kinds of compounds were identified, among them, 27 kinds of fatty acid-derived volatile compounds were selected including 6 kinds of aldehydes, 8 kinds of alcohols, 13 kinds of esters and their dynamic change were revealed. Finally, the character of aroma during main processing stages and processed tea was concluded by using a flavor wheel. This study results provide a theoretical basis for the improvement of processing and quality in Jinmudan black tea.

The flavour of grape colour: anthocyanin content tunes aroma precursor composition by altering the berry microenvironment

Anthocyaninless (white) instead of black/red (coloured) fruits develop in grapevine cultivars without functional VviMYBA1 and VviMYBA2 genes, and this conditions the colour of wines that can be produced. To evaluate whether this genetic variation has additional consequences on fruit ripening and composition, we performed comparisons of microenvironment, transcriptomics, and metabolomics of developing grapes between near-isogenic white- and black-berried somatic variants of Garnacha and Tempranillo cultivars. Berry temperature was as much as 3.5 ºC lower in white- compared to black-berried Tempranillo. An RNA-seq study combined with targeted and untargeted metabolomics revealed that ripening fruits of white-berried variants were characterized by the up-regulation of photosynthesis-related and other light-responsive genes and by their higher accumulation of specific terpene aroma precursors, fatty acid-derived aldehyde volatiles, and phenylpropanoid precursor amino acids. MYBA1-MYBA2 function proved essential for flavonol trihydroxylation in black-berried somatic variants, which were also characterized by enhanced expression of pathogen defence genes in the berry skin and increased accumulation of C6-derived alcohol and ester volatiles and γ-aminobutyric acid. Collectively, our results indicate that anthocyanin depletion has side-effects on grape composition by altering the internal microenvironment of the berry and the partitioning of the phenylpropanoid pathway. Our findings show how fruit colour can condition other fruit features, such as flavour potential and stress homeostasis.

Evolution of green leaf volatile profile and aroma potential during the berry development in five Vitis vinifera L. Cultivars

Green leaf volatiles (GLVs), play important roles in the green and fresh aroma characteristics of grape berries. The evolution of GLV profiles regarding the varietal difference during grapevine phenological ripening is not well understood. This study generated the GLV profiles of five Vitis vinifera L. cultivars ('Cabernet Sauvignon,' 'Cabernet Franc,' 'Cabernet Gernischt,' 'Chardonnay,' and 'Sauvignon Blanc') at five ripening stages. GLVs were distinctive at different E-L stages for each grape variety. (E)-2-hexen-1-ol, 1-hexanol, and hexanal were the dominant components in all mature berries. In terms of total GLV content, all varieties reached the maximum at maturity in the 2019 vintage, and the total GLV content was higher in mature Sauvignon Blanc and Cabernet Sauvignon grapes. In the 2020 vintage, the total GLV content in Chardonnay and Sauvignon Blanc berries rapidly accumulated at veraison and peaked before harvest. The present results could help winemakers create a good balance of wine aroma.

Zinc Biofortification in Vitis vinifera: Implications for Quality and Wine Production

Nowadays, there is a growing concern about micronutrient deficits in food products, with agronomic biofortification being considered a mitigation strategy. In this context, as Zn is essential for growth and maintenance of human health, a workflow for the biofortification of grapes from the Vitis vinifera variety Fernão Pires, which contains this nutrient, was carried out considering the soil properties of the vineyard. Additionally, Zn accumulation in the tissues of the grapes and the implications for some quality parameters and on winemaking were assessed. Vines were sprayed three times with ZnO and ZnSO₄ at concentrations of 150, 450, and 900 g ha^-1 during the production cycle. Physiological data were obtained through chlorophyll a fluorescence data, to access the potential symptoms of toxicity. At harvest, treated grapes revealed significant increases of Zn concentration relative to the control, being more pronounced for ZnO and ZnSO₄ in the skin and seeds, respectively. After winemaking, an increase was also found regarding the control (i.e., 1.59-fold with ZnSO₄-450 g ha^-1). The contents of the sugars and fatty acids, as well as the colorimetric analyses, were also assessed, but significant variations were not found among treatments. In general, Zn biofortification increased with ZnO and ZnSO₄, without significantly affecting the physicochemical characteristics of grapes.

The Expression of Aroma Components and Related Genes in Merlot and Marselan Scion-Rootstock Grape and Wine

Rootstocks were bred and selected from several species in order to enhance the resistance against biotic or abiotic stresses. There are few studies on the effect of rootstocks on aroma and related gene expression. This study focused on the effects of three rootstocks, Kober 5BB (5BB), 1103 Paulsen (1103P), and Selection Oppenheim (SO4), on the aroma and volatile-related gene expression levels of Merlot and Marselan berries and wines. These three rootstocks reduced the total aroma content of Merlot wine. 5BB upregulated VvLoXA and showed increased C6 alcohols. 1103P enhanced the linalool from Merlot berry, with marked upregulation of VvLinNer1. Conversely, rootstocks increased the total aroma content of Marselan berry, verified by the related expression levels of volatile-related genes. For Marselan berry, 5BB and 1103P upregulated five VvGTs and nine genes from the LOX and MEP pathway. 1103P increased the contents of C6 alcohols, C6 aldehydes, and citronellol from Marselan berry. Compared to 5BB and SO4, rootstock 1103P provided berries of better quality and richer aroma volatiles to Merlot and Marselan, while all three of the rootstocks had a significant effect on scion–rootstocks.

Monoterpenoids Evolution and MEP Pathway Gene Expression Profiles in Seven Table Grape Varieties

This research investigated the evolution of both monoterpenoids and expression profiles of related biosynthesis genes in the MEP pathway in seven different table grape varieties from veraison to maturity stage in two seasons, and the correlation was further evaluated between monoterpenoid accumulation and expression of these genes studied in these varieties. Results showed that linalool, trans-furan linalool oxide, geraniol, and cis-furan linalool oxide were the main compounds in the five Muscat varieties two seasons. ‘Zaomeiguixiang’ had the highest contents of geraniol and β-Citronellol. ‘Xiangfei’ had the most abundant of linalool and cis-furan linalool oxide, whereas the neutral varieties of ‘Moldova’ and ‘Christmas Rose’ had the least amount. Monoterpenoid volatiles have been grouped in three evolutionary patterns in the berry development of these varieties. ‘Zaomeiguixiang’ and ‘Xiangfei’ had distinct different pattern of terpenoids evolution profiles. Pearson’s correlation analysis showed that in the MEP pathway, the first biosynthesis gene VvDXS3 was significantly correlated to the accumulation of monoterpenoids, and appeared to be an important candidate gene for synthesis of the monoterpenoids.

Transcriptome and Metabolomics Integrated Analysis Reveals Terpene Synthesis Genes Controlling Linalool Synthesis in Grape Berries

In this study, four hybrids from the cross between "Italia" and "Tamina" grapes were chosen to investigate their distinct monoterpenoids patterns and candidate genes involved. Monoterpenoid profiles and transcriptome data were generated at four berry developmental stages. Trans-rose oxide, cis-rose oxide, citronellol, neral, nerol, nerol oxide, geraniol, geranial, geranic acid, and cis-isogeraniol were the dominant compounds in R250 hybrid, while linalool, hotrienol, linalool oxide pyranoside, and cis-furan linalool oxide were the main compounds in R77 hybrid. Six TPS-g subfamily genes were found related with the contents of linalool and its related monoterpenoids by weighted gene coexpression network analysis (WGCNA) and phylogenetic analysis. Among them, TPS59 was cloned and functionally verified by transient overexpression in the leaves of Vitis quinquangularis. Meanwhile, NAC (newGene_195), C2C2-GATA (VIT_15s0021g02510), and bHLH (VIT_14s0128g00110) were selected as candidate transcription factors (TFs) that could regulate the expression of the six TPS-b genes. These data enhanced our understanding on the regulation of monoterpenoid biosynthesis in grapes.

The Dynamic Change in Fatty Acids during the Postharvest Process of Oolong Tea Production

As important factors to oolong tea quality, the accumulation and dynamic change in aroma substances attracts great attention. The volatile composition of oolong tea is closely related to the precursor contents. Fatty acids (FAs) and their derivatives are basic components of oolong tea fragrance during the postharvest process. However, information about the precursors of FAs during the postharvest process of oolong tea production is rare. To investigate the transformation of fatty acids during the process of oolong tea production, gas chromatograph−flame ionization detection (GC-FID) was conducted to analyze the composition of FAs. The results show that the content of total polyunsaturated FAs initially increased and then decreased. Specifically, the contents of α-linolenic acid, linoleic acid and other representative substances decreased after the turn-over process of oolong tea production. The results of partial least squares discrimination analysis (PLS-DA) showed that five types of FAs were obviously impacted by the processing methods of oolong tea (VIP > 1.0). LOX (Lipoxygenase, EC 1.13.11.12) is considered one of the key rate-limiting enzymes of long-chain unsaturated FAs in the LOX-HPL (hydroperoxide lyase) pathway, and the mechanical wounding occurring during the postharvest process of oolong tea production greatly elevated the activity of LOX.

The SLC27A1 Gene and Its Enriched PPAR Pathway Are Involved in the Regulation of Flavor Compound Hexanal Content in Chinese Native Chickens

The role of hexanal in flavor as an indicator of the degree of oxidation of meat products is undeniable. However, the genes and pathways of hexanal formation have not been characterized in detail. In this study, we performed differential gene expression analysis and weighted gene co-expression network analysis (WGCNA) on groups of Tiannong partridge chickens with different relative hexanal content in order to find the genes involved in the formation of hexanal and the specific pathways of hexanal formation. Then we confirmed the relationship of these candidate genes with hexanal using Jingxing Yellow chicken and Wenchang chicken. In this study, WGCNA revealed a module of co-expressed genes that were highly associated with the volatile organic compound hexanal. We also compared transcriptome gene expression data of samples from chicken groups with high and low relative contents of hexanal and identified a total of 651 differentially expressed genes (DEGs). Among them, 356 genes were up regulated, and 295 genes were downregulated. The different biological functions associated with the DEGs, hub genes and hexanal were identified by functional analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations. Among all the hub genes in the significant module identified by WGCNA, more were enriched in the PPAR signaling pathway, the proteasome pathway, etc. Additionally, we found that DEGs and hub genes, including SLC27A1, ACOX3, NR4A1, VEGFA, JUN, EGR1, CACNB1, GADD45A and DUSP1, were co-enriched in the peroxisome proliferator-activated receptor (PPAR) signaling pathway, p53 signaling pathway and mitogen-activated protein kinases (MAPK) signaling pathway, etc. Transcriptome results of the Jingxing Yellow chicken population showed that the SLC27A1 gene was significantly associated with hexanal and enriched in the PPAR pathway. Our study provides a comprehensive insight into the key genes related to hexanal content, and can be further explored by functional and molecular studies.

Effects of Berry Thinning on the Physicochemical, Aromatic, and Sensory Properties of Shine Muscat Grapes

The effects of the level of berry thinning (30% and 50% berry removal) on the quality and sensory properties of Shine Muscat grapes were investigated. As berry thinning increased, the total soluble solids content increased and titratable acidity decreased. Berry thinning increased berry size and cluster weight but caused no change in individual berry weight. Phenolic concentrations as measured by total phenolic, proanthocyanidin, and polymeric tannin concentrations tended to increase with an increase in berry thinning. Gas chromatographic analysis indicated that C6-compounds were the significant constituents of volatile alcohols and aldehydes; linalool was the most abundant monoterpene. Odor activity analysis indicated that (E)-2-hexen-1-ol, (E)-2-hexenal, 1-hexanal, (Z)-3-hexenal, (E)-β-damascenone, linalool, and (E)-linalool oxide were active odorants. Berry thinning increased the accumulation of linalool contributing to high sensory flavor scores in thinned berries. Furthermore, its oxidized derivative-linalool oxide-contributed to enhancing the Muscat flavor. In conclusion, berry thinning induced compositional changes in Shine Muscat grape berries by accelerating the ripening rate, contribution to improved sensory properties.

Metabolic Flow of C6 Volatile Compounds From LOX-HPL Pathway Based on Airflow During the Post-harvest Process of Oolong Tea

Aroma is an essential quality indicator of oolong tea, a tea derived from the Camellia sinensis L. plant. Carboxylic 6 (C6) acids and their derivative esters are important components of fatty acid (FA)-derived volatiles in oolong tea. However, the formation and regulation mechanism of C6 acid during postharvest processing of oolong tea remains unclear. To gain better insight into the molecular and biochemical mechanisms of C6 compounds in oolong tea, a combined analysis of alcohol dehydrogenase (ADH) activity, CsADH2 key gene expression, and the FA-derived metabolome during postharvest processing of oolong tea was performed for the first time, complemented by CsHIP (hypoxia-induced protein conserved region) gene expression analysis. Volatile fatty acid derivative (VFAD)-targeted metabolomics analysis using headspace solid-phase microextraction-gas chromatography time-of-flight mass spectrometry (HS-SPEM-GC-TOF-MS) showed that the (Z)-3-hexen-1-ol content increased after each turnover, while the hexanoic acid content showed the opposite trend. The results further showed that both the ADH activity and CsADH gene expression level in oxygen-deficit-turnover tea leaves (ODT) were higher than those of oxygen-turnover tea leaves (OT). The C6-alcohol-derived ester content of OT was significantly higher than that of ODT, while C6-acid-derived ester content showed the opposite trend. Furthermore, the HIP gene family was screened and analyzed, showing that ODT treatment significantly promoted the upregulation of CsHIG4 and CsHIG6 gene expression. These results showed that the formation mechanism of oolong tea aroma quality is mediated by airflow in the lipoxygenase-hydroperoxide lyase (LOX-HPL) pathway, which provided a theoretical reference for future quality control in the postharvest processing of oolong tea.

Influence of cluster positions in the canopy and row orientation on the flavonoid and volatile compound profiles in Vitis vinifera L. Cabernet franc and Chardonnay berries

Sunlight conditions around grape clusters vary with their positions, and can have a significant effect on grape berry compounds. This study investigated the influence of cluster positions in the canopy (interior and two exterior canopy sides) and vineyard row orientation (north-south and east-west) on flavonoid and volatile compound profiles of Vitis vinifera L. cvs 'Cabernet franc' (CF) and 'Chardonnay' (CH) berries in two consecutive years. The experimental vineyard was located in Jiaodong Peninsula of China, which is characterized by a temperate monsoon-type climate and relatively short sunlight duration. Clusters located in the interior of the canopy received less sunlight irradiation than the exterior positions, and the average temperature around clusters located in different positions differed slightly. The results showed that over two years, the positions of clusters in the canopy had no consistent impact on cluster weight, berry weight, juice total soluble solids or titratable acidity for either cultivar. For both cultivars, the interior clusters had lower total flavonol concentrations than the exterior clusters, while the position of clusters in the canopy had no major impacts on the composition of anthocyanins and flavan-3-ols. The volatile compounds were somewhat influenced by the positions of clusters in the canopy, while some bound norisoprenoids and terpenoids had lower levels in interior clusters than in exterior clusters. These results will help winegrowers make decisions regarding harvest strategies.

Construction of a High-Density Genetic Map and Mapping of Firmness in Grapes (Vitis vinifera L.) Based on Whole-Genome Resequencing

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.

Dynamics of ADH and related genes responsible for the transformation of C6-aldehydes to C6-alcohols during the postharvest process of oolong tea

Aroma is an important index of tea quality. The volatile C6-compounds formed from linoleic and linolenic acids in tea leaf lipids are essential components of tea. C6-compounds are formed and transformed during the postharvest process of tea leaves. However, the metabolic flux of these C6-compounds, the activities of related enzymes, and the transcription of related genes during the postharvest process of oolong tea remain unclear. In this study, the chemical profiles of C6-aldehydes and C6-alcohols, the pattern of ADH enzyme activity, and the level of CsADH gene expression during the postharvest process of oolong tea were investigated. We found that the turnover process had a positive effect on the accumulation of C6-alcohols and simultaneously induced ADH activity, especially during the withering stage. The expression of CsADH peaked during the turnover stage. The relative expression level of CSA019598 typically increased during the postharvest process. Correlation analysis demonstrated that CSA019598 expression increased as ADH activity increased. This finding suggests that CSA019598 may play a prominent role in regulating ADH. These results advance our understanding of C6-compound formation during the postharvest process of oolong tea. We aim to evaluate how green leaf volatiles affect the enzymatic formation and genetic transcription of aromatic compounds in oolong tea in future studies.

Metabolomic and transcriptomic changes underlying cold and anaerobic stresses after storage of table grapes

The currently accepted paradigm is that fruits and vegetables should be consumed fresh and that their quality deteriorates during storage; however, there are indications that some metabolic properties can, in fact, be improved. We examined the effects of low temperature and high-CO₂ conditions on table grapes, Vitis vinifera L. cv. 'Superior Seedless'. Berries were sampled at harvest (T0) and after low-temperature storage for 6 weeks under either normal atmosphere conditions (TC) or under an O₂ level of 5 kPa and elevated CO₂ levels of 5, 10 or 15 kPa (T5, T10, T15). Accumulation of 10 stilbenes, including E-ε-viniferin, E-miyabenol C and piceatannol, significantly increased under TC treatment as compared to T0 or T15. Sensory analysis demonstrated that elevated CO₂ elicited dose-dependent off-flavor accumulation. These changes were accompanied by an accumulation of 12 volatile metabolites, e.g., ethyl acetate and diacetyl, that imparted disagreeable flavors to fresh fruit. Transcriptome analysis revealed enrichment of genes involved in pyruvate metabolism and the phenylpropanoid pathway. One of the transcription factors induced at low temperature but not under high CO₂ was VvMYB14, which regulates stilbene biosynthesis. Our findings reveal the potential to alter the levels of targeted metabolites in stored produce through understanding the effects of postharvest treatments.

Functional Insights into the Roles of Hormones in the Dendrobium officinale-Tulasnella sp. Germinated Seed Symbiotic Association

Dendrobium is one of the largest genera in the Orchidaceae, and D. officinale is used in traditional medicine, particularly in China. D. officinale seeds are minute and contain limited energy reserves, and colonization by a compatible fungus is essential for germination under natural conditions. When the orchid mycorrhizal fungi (OMF) initiates symbiotic interactions with germination-driven orchid seeds, phytohormones from the orchid or the fungus play key roles, but the details of the possible biochemical pathways are still poorly understood. In the present study, we established a symbiotic system between D. officinale and Tulasnella sp. for seed germination. RNA-Seq was used to construct libraries of symbiotic-germinated seeds (DoTc), asymbiotic-germinated seeds (Do), and free-living OMF (Tc) to investigate the expression profiles of biosynthesis and metabolism pathway genes for three classes of endogenous hormones: JA (jasmonic acid), ABA (abscisic acid) and SLs (strigolactones), in D. officinale seeds and OMF under symbiotic and asymbiotic conditions. Low concentrations of endogenous JA, ABA, or SLs were detected in the D. officinale-Tulasnella symbiont compared with the asymbiotic tissues. Gene annotation results suggest that the expression of DEGs (differentially expressed genes) related to JA and ABA biosynthesis from D. officinale were down-regulated, while most of the key DEGs related to SL biosynthesis from D. officinale were up-regulated in the symbiotic germinated seeds compared with the asymbiotic germinated seeds. Moreover, in the OMF, we found a significantly up-regulated differential expression of the JA and ABA biosynthesis-related genes in the symbiotic interaction, with the opposite expression trends to those found in Dendrobium. This indicates that Dendrobium seed symbiotic germination may be stimulated by the apparent involvement of the OMF in the production of hormones, and relatively low concentrations of endogenous JA, ABA, or SLs might be maintained to promote the growth of the D. officinale-Tulasnella symbiotic protocorm-like body. These results will increase our understanding of the possible roles played by endogenous hormones in the regulation of the orchid-fungus symbiosis.