Drawing Links from Transcriptome to Metabolites: The Evolution of Aroma in the Ripening Berry of Moscato Bianco (Vitis vinifera L.)

Site-Directed Mutagenesis of VvCYP76F14 (Cytochrome P450) Unveils Its Potential for Selection in Wine Grape Varieties Linked to the Development of Wine Bouquet

Bouquet is a fascinating wine characteristic that serves as an indicator of wine quality, developing during the aging process. The multifunctional monoterpenol oxidase VvCYP76F14 in wine grapes sequentially catalyzes three reactions to produce (E)-8-carboxylinalool, a crucial precursor for wine bouquet. Previous studies indicated that the activity of VvCYP76F14 derived from different wine grape varieties did not correlate with the amino acid sequence differences. In this study, 54 wine grape varieties were categorized into neutral, aromatic, and full-bodied types based on the sequence differences of VvCYP76F14, closely correlated with the content of wine lactone precursors. Computer modeling and molecular docking analysis of the full-bodied CYP76F14 revealed 17, 19, and 18 amino acid residues in the VvCYP76F14-linalool, VvCYP76F14-(E)-8-hydroxylinalool, and VvCYP76F14-(E)-8-oxolinalool complexes, respectively. Site-directed mutagenesis and in vitro enzyme activity analysis confirmed the substitutions of the key amino acid residues in neutral and aromatic varieties. Notably, the D299 mutation of VvCYP76F14 resulted in the complete loss of (E)-8-oxolinalool and (E)-8-carboxylinalool activities, aligning with the undetectable levels of (E)-8-oxolinalool and (E)-8-carboxylinalool in "Yantai 2-3-37", which harbors the D299T substitution. Favorably, VvCYP76F14 could serve as a cost-effective fingerprint marker for screening superior hybrid offspring with the desired levels of wine lactone precursors.

Metabolomic and transcriptomic integrated analysis revealed the decrease of monoterpenes accumulation in table grapes during long time low temperature storage

Low temperature is the commonly used technique for maintaining the quality of table grapes during postharvest storage. However, this technique could strongly affect the aromatic flavor of fruit. Monoterpenes are the key compounds contributing to the Muscat aromas of grapes. The detailed information and molecular mechanisms underlying the changes in monoterpenes during postharvest low temperature storage have not been thoroughly characterized. In this study, the effects of low temperature storage on the free and bound monoterpene profiles in four cultivars of table grape were determined at both the transcriptomic and metabolomic levels. A total of 27 compounds in both free and bound forms were identified in the four cultivars and showed quantitative differences between the cultivars. Hierarchical cluster and principal component analysis indicated that the free and bound monoterpene profiles were remarkably affected by the low temperature storage. The monoterpenes in the same biosynthesis pathway were clustered together and showed similar evolution trends during low temperature storage. And the content of most of free monoterpenes underwent a rapid decline during low-temperature storage at a certain stage, but the time was different in 4 grape cultivars. Transcriptomic analysis revealed that the expression of DXS, HDR, GPPS and TPS genes involved in the monoterpene synthesis pathway were consistent with the changes in the accumulation of monoterpene compounds. While the expression of HMGS, HMGR genes in MVA pathway and branch genes GGPPS and FPPS were negatively correlated with the accumulation of monoterpenes. The findings provide new insights into the underlying mechanisms of the berry aroma flavor change during low temperature storage.

Effects of ultraviolet and infrared radiation absence or presence on the aroma volatile compounds in winegrape during veraison

Light environmental factors have been identified to influence grape aromas greatly. Among them, the effect of non-visible light on grape aroma compounds has scarcely been investigated during grape growth and development. In the present study, ultraviolet (UV) or infrared (IR) radiation was eliminated in the grape bunch zone, and the grape bunches were irradiated with UV or IR light in vitro. The effect of UV and IR radiation on the grape aroma profile of the Cabernet Sauvignon variety was assessed by headspace solid phase microextraction gas chromatography mass spectrometer (HS-SPME GC-MS). A total of 16 aroma compounds were identified in the grape berries under UV radiation absence (UV-) or IR radiation absence (IR-). They were classified into aliphatic alcohols, aliphatic acids, benzenolds, aldehydes, and monoterpenes. A total of 23 aroma compounds were identified in the grape berries under UV radiation presence (UV+) or IR radiation presence (IR+), which were classified into aliphatic alcohols, aliphatic ketones, aliphatic esters, aliphatic acids, monoterpenes, aldehydes, volatile phenols, and other volatiles. Linalool and hexanal aroma compounds were the most responsive to UV- and UV+, according to OPLS-DA analysis. Hexanal was increased by UV- and decreased by UV+, thus was negatively correlated with UV radiation. Benzaldehyde and 2-decanone were also found as the main differing aroma compounds according to VIP scores in the IR- and IR+, respectively. The significant differences of aroma compounds in three UV and IR intensities were also observed by headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS). The content of acetic acid, 2-methylbutanal, and pentanal were reduced with the radiation intensity increase, and the content of 2-3-butanedione, butyl acetate, and 1-hexanol was enhanced, especially with UV radiation. This study improves our understanding of the non-visible light role in volatile aroma compound accumulation and further expands on the useful wavelength for plant growth and development. Our study provides a theoretical basis for non-visible light field management and indoor plant growth applications.

Water deficit before veraison is crucial in regulating berry VOCs concentration in Sangiovese grapevines

The impact of water deficit on volatile organic compounds (VOCs) responsible for grape aroma remains quite unclear. The aim of this study was to evaluate the effect of different timing and intensity of water deficit on berry VOCs and on their biosynthetic pathways. Fully irrigated control vines were compared with the following treatments: i) two different levels of water deficit from berry pea-size through veraison, ii) one level of water deficit during the lag-phase, and iii) two different levels of water deficit from veraison through harvest. At harvest, total VOC concentrations were higher in berries of water stressed vines from berry pea size through veraison or during the lag phase, whereas post-veraison water deficit determined similar concentrations as control. This pattern was even more pronounced for the glycosylated fraction and was also observed for single compounds, mainly monoterpenes and C₁₃-norisoprenoids. On the other hand, free VOCs were higher in berries from lag phase or post-veraison stressed vines. The significant glycosylated and free VOCs increment measured after the short water stress limited to the lag phase highlight the pivotal role played by this stage in berry aroma compound biosynthesis modulation. The severity of water stress before veraison was also important, since glycosylated VOCs showed a positive correlation with the pre-veraison daily water stress integral. The RNA-seq analysis showed a wide regulation induced by irrigation regimes on terpenes and carotenoids biosynthetic pathways. The terpene synthases and glycosyltransferases as well as genes of the network of transcription factors were upregulated, especially in berries from pre-veraison stressed vines. Since the timing and intensity of water deficit contribute to regulate berry VOCs, irrigation management can be used to achieve high-quality grapes while saving water.

Grapevine mono- and sesquiterpenes: Genetics, metabolism, and ecophysiology

Mono- and sesquiterpenes are volatile organic compounds which play crucial roles in human perception of table grape and wine flavour and aroma, and as such their biosynthesis has received significant attention. Here, the biosynthesis of mono- and sesquiterpenes in grapevine is reviewed, with a specific focus on the metabolic pathways which lead to formation of these compounds, and the characterised genetic variation underlying modulation of this metabolism. The bottlenecks for terpene precursor formation in the cytosol and plastid are understood to be the HMG-CoA reductase (HMGR) and 1-deoxy-D-xylylose-5-phosphate synthase (DXS) enzymes, respectively, and lead to the formation of prenyldiphosphate precursors. The functional plasticity of the terpene synthase enzymes which act on the prenyldiphosphate precursors allows for the massive variation in observed terpene product accumulation. This diversity is further enhanced in grapevine by significant duplication of genes coding for structurally diverse terpene synthases. Relatively minor nucleotide variations are sufficient to influence both product and substrate specificity of terpene synthase genes, with these variations impacting cultivar-specific aroma profiles. While the importance of these compounds in terms of grape quality is well documented, they also play several interesting roles in the grapevine's ecophysiological interaction with its environment. Mono- and sesquiterpenes are involved in attraction of pollinators, agents of seed dispersal and herbivores, defence against fungal infection, promotion of mutualistic rhizobacteria interaction, and are elevated in conditions of high light radiation. The ever-increasing grapevine genome sequence data will potentially allow for future breeders and biotechnologists to tailor the aroma profiles of novel grapevine cultivars through exploitation of the significant genetic variation observed in terpene synthase genes.

Understanding the Sensitivity of Grape Terpenes to Jasmonates Using In Vitro Culture and In Vivo Vineyard Experiments

Terpene volatiles define the flavor of terpenic grape cultivars. However, grape terpene concentrations can vary 2- to 3-fold across seasons and vineyards, impacting vintage quality. The plant hormone methyl jasmonate (MeJA) stimulates grape terpene production but is expensive and can decrease berry weight and maturity. The synthetic jasmonate prohydrojasmon (PDJ) is cost-effective yet has not been evaluated on grape maturity and terpene production. Here, we performed in vitro (berry culture) and in vivo (vineyard) experiments using Gewürztraminer (Vitis vinifera L.) to evaluate the time- and concentration-dependent sensitivity of maturity parameters and terpene content to MeJA and PDJ. In vitro berry weight was reduced by high MeJA and PDJ concentration across timings. Terpenes were most sensitive to low MeJA concentration at veraison (increased 24-fold) in vitro. Moderate PDJ concentration applied at veraison doubled (increased twofold) terpene concentration in vivo without impacting berry weight or maturity. In conclusion, PDJ may provide a solution to mitigate seasonal variability in terpene production in terpenic grape cultivars.

Transcriptomic and metabolomic integration as a resource in grapevine to study fruit metabolite quality traits

Transcriptomics and metabolomics are methodologies being increasingly chosen to perform molecular studies in grapevine (Vitis vinifera L.), focusing either on plant and fruit development or on interaction with abiotic or biotic factors. Currently, the integration of these approaches has become of utmost relevance when studying key plant physiological and metabolic processes. The results from these analyses can undoubtedly be incorporated in breeding programs whereby genes associated with better fruit quality (e.g., those enhancing the accumulation of health-promoting compounds) or with stress resistance (e.g., those regulating beneficial responses to environmental transition) can be used as selection markers in crop improvement programs. Despite the vast amount of data being generated, integrative transcriptome/metabolome meta-analyses (i.e., the joint analysis of several studies) have not yet been fully accomplished in this species, mainly due to particular specificities of metabolomic studies, such as differences in data acquisition (i.e., different compounds being investigated), unappropriated and unstandardized metadata, or simply no deposition of data in public repositories. These meta-analyses require a high computational capacity for data mining a priori, but they also need appropriate tools to explore and visualize the integrated results. This perspective article explores the universe of omics studies conducted in V. vinifera, focusing on fruit-transcriptome and metabolome analyses as leading approaches to understand berry physiology, secondary metabolism, and quality. Moreover, we show how omics data can be integrated in a simple format and offered to the research community as a web resource, giving the chance to inspect potential gene-to-gene and gene-to-metabolite relationships that can later be tested in hypothesis-driven research. In the frame of the activities promoted by the COST Action CA17111 INTEGRAPE, we present the first grapevine transcriptomic and metabolomic integrated database (TransMetaDb) developed within the Vitis Visualization (VitViz) platform (https://tomsbiolab.com/vitviz). This tool also enables the user to conduct and explore meta-analyses utilizing different experiments, therefore hopefully motivating the community to generate Findable, Accessible, Interoperable and Reusable (F.A.I.R.) data to be included in the future.

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.

Adaptation insights from comparative transcriptome analysis of two Opisthopappus species in the Taihang mountains

Opisthopappus is a major wild source of Asteraceae with resistance to cold and drought. Two species of this genus (Opisthopappus taihangensis and O. longilobus) have been employed as model systems to address the evolutionary history of perennial herb biomes in the Taihang Mountains of China. However, further studies on the adaptive divergence processes of these two species are currently impeded by the lack of genomic resources. To elucidate the molecular mechanisms involved, a comparative analysis of these two species was conducted. Among the identified transcription factors, the bHLH members were most prevalent, which exhibited significantly different expression levels in the terpenoid metabolic pathway. O. longilobus showed higher level of expression than did O. taihangensis in terms of terpenes biosynthesis and metabolism, particularly monoterpenoids and diterpenoids. Analyses of the positive selection genes (PSGs) identified from O. taihangensis and O. longilobus revealed that 1203 genes were related to adaptative divergence, which were under rapid evolution and/or have signs of positive selection. Differential expressions of PSG occurred primarily in the mitochondrial electron transport, starch degradation, secondary metabolism, as well as nucleotide synthesis and S-metabolism pathway processes. Several PSGs were obviously differentially expressed in terpenes biosynthesis that might result in the fragrances divergence between O. longilobus and O. taihangensis, which would provide insights into adaptation of the two species to different environments that characterized by sub-humid warm temperate and temperate continental monsoon climates. The comparative analysis for these two species in Opisthopappus not only revealed how the divergence occurred from molecular perspective, but also provided novel insights into how differential adaptations occurred in Taihang Mountains.

Comparative metabolomic and transcriptomic analyses revealed the differential accumulation of secondary metabolites during the ripening process of acerola cherry (Malpighia emarginata) fruit

BACKGROUND

Acerola cherry is a famous functional fruit containing plentiful antioxidants and other nutrients. However, studies on the variations among nutrients during the ripening process of acerola fruit are scare.

RESULTS

Comparative metabolomic and transcriptomic analyses were performed and identified 31 331 unigenes and 1896 annotated metabolite features in acerola cherry fruit. K Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that several antioxidant and nutrient-related metabolic pathways, such as the flavonoids, vitamins, carotenoids, amino acids, and fatty acids metabolic pathways, were significantly changed during the ripening process. The metabolites related to the vitamin, carotenoid, and fatty acid metabolic pathways were downregulated during the ripening process. Several flavonoid biosynthesis-related genes (including dihydroflavonol 4-reductase, chalcone synthase, flavanone 3-hydroxylase, and anthocyanidin synthase), were significantly upregulated, suggesting their essential functions in the accumulation of flavonoids in mature fruit.

CONCLUSION

Most of the vitamin and carotenoid metabolism-related metabolites significantly accumulated in immature fruit, suggesting that immature acerola fruit is a good material for the extraction of vitamins and carotenoids. For macronutrients, most of the amino acids accumulated in mature fruit and most of the fatty acids greatly accumulated in immature fruit. Our data revealed the differential accumulation of antioxidants and nutrients during the ripening process of acerola cherry fruit. © 2021 Society of Chemical Industry.

Transcriptomics Integrated with Metabolomics Reveals the Effect of Cluster Thinning on Monoterpene Biosynthesis in 'Muscat Hamburg' Grape

Monoterpenes are crucial to floral and fruit aromas in grapes and wines. Cluster thinning is a common practice for improving grape quality. Using Vitis vinifera cv. Muscat Hamburg, the effects of three cluster-thinning regimes on the biosynthesis and accumulation of monoterpenes from véraison to harvest were investigated at the transcriptomics and targeted metabolomics levels. It was observed that more intense thinning produced higher concentrations of total monoterpenes, particularly in their bound forms. The numbers of differentially expressed genes among the three treatments were 193, 200, and 238 at the three developmental stages. In total, 10 modules were identified from a weighted gene correlation network analysis, and one module including 492 unigenes was associated with monoterpene metabolism. These findings provide new insights into the molecular basis of the relationship between cluster thinning and monoterpene biosynthesis in Muscat Hamburg grape. Cluster thinning could be carefully considered for its application in production.

Effects of methyl jasmonate on the monoterpenes of Muscat Hamburg grapes and wine

BACKGROUND

The importance of monoterpenes in grape and wine aroma has compelled researchers to focus on developing methods to increase their abundance. Recent research has revealed that exogenous elicitors can increase the contents of these compounds. This study determined the effects of methyl jasmonate (MeJA) preharvest treatments on the monoterpene profiles of Muscat Hamburg grapes and wine.

RESULTS

A total of 27 monoterpenes were identified for Muscat Hamburg grapes and wine. The contents of most of the monoterpenes (free and glycosylated forms) in the grapes and wine increased in response to MeJA. An analysis of the expression of the genes in the terpenoid biosynthesis pathway indicated that the related biosynthetic pathways were activated by MeJA. The transcript levels of some genes were consistent with monoterpene production, including VviCSLinNer, VviGwbOciF, VviPNRLin, VviGT14 and VviUGT85A1L1. The developmental expression patterns of the VviPP2B1 and VviMYB24 transcription factor genes were positively correlated with monoterpene accumulation in ripening grapes.

CONCLUSIONS

Our results suggest that MeJA may be useful for improving the aroma quality of grapes and wines.

Transcriptomic and Metabolic Analyses Provide New Insights into the Effects of Exogenous Sucrose on Monoterpene Synthesis in "Muscat Hamburg" Grapes

Monoterpenes provide strong floral and fruit aromas to grapes and wines. In the present study, the effects of exogenous sucrose on the monoterpenes metabolites were studied at the metabolomic and transcriptomic levels in "Muscat Hamburg" grape berries. 6% sucrose aqueous solution was used as treatment, applied at the berry color change stage and 8 days after the first application. Transcriptomics analysis was carried out on berries collected at three phenological stages (berries with intermediate Brix values, E-L 36; berries not quite ripe, E-L 37; and berries harvest-ripe, E-L 38). Our results showed that the sucrose application induced the accumulation of monoterpenes at harvest, especially geraniol and geranic acid. The summary of the number of differentially expressed genes between the control and treatment was 3465, 977, and 2843 at E-L 36, E-L 37, and E-L 38, respectively. Weighted gene correlation network analysis was constructed based on the RNA-seq data, and the MElightyellow module was probably correlated with monoterpene metabolism, comprising 131 unigenes. Quantitative real-time polymerase chain expression analysis of five key differentially expressed genes in terpenoid pathways validated the RNA-seq-derived expression profiles (R² = 0.8143). Our findings provided new insights into the regulation of monoterpene biosynthesis in grape berries under exogenous sucrose.

Grape Berry Secondary Metabolites and Their Modulation by Abiotic Factors in a Climate Change Scenario-A Review

Temperature, water, solar radiation, and atmospheric CO₂ concentration are the main abiotic factors that are changing in the course of global warming. These abiotic factors govern the synthesis and degradation of primary (sugars, amino acids, organic acids, etc.) and secondary (phenolic and volatile flavor compounds and their precursors) metabolites directly, via the regulation of their biosynthetic pathways, or indirectly, via their effects on vine physiology and phenology. Several hundred secondary metabolites have been identified in the grape berry. Their biosynthesis and degradation have been characterized and have been shown to occur during different developmental stages of the berry. The understanding of how the different abiotic factors modulate secondary metabolism and thus berry quality is of crucial importance for breeders and growers to develop plant material and viticultural practices to maintain high-quality fruit and wine production in the context of global warming. Here, we review the main secondary metabolites of the grape berry, their biosynthesis, and how their accumulation and degradation is influenced by abiotic factors. The first part of the review provides an update on structure, biosynthesis, and degradation of phenolic compounds (flavonoids and non-flavonoids) and major aroma compounds (terpenes, thiols, methoxypyrazines, and C13 norisoprenoids). The second part gives an update on the influence of abiotic factors, such as water availability, temperature, radiation, and CO₂ concentration, on berry secondary metabolism. At the end of the paper, we raise some critical questions regarding intracluster berry heterogeneity and dilution effects and how the sampling strategy can impact the outcome of studies on the grapevine berry response to abiotic factors.

Annotation of genes involved in high level of dihydromyricetin production in vine tea (Ampelopsis grossedentata) by transcriptome analysis

BACKGROUND

Leaves of the medicinal plant Ampelopsis grossedentata, which is commonly known as vine tea, are used widely in the traditional Chinese beverage in southwest China. The leaves contain a large amount of dihydromyricetin, a compound with various biological activities. However, the transcript profiles involved in its biosynthetic pathway in this plant are unknown.

RESULTS

We conducted a transcriptome analysis of both young and old leaves of the vine tea plant using Illumina sequencing. Of the transcriptome datasets, a total of 52.47 million and 47.25 million clean reads were obtained from young and old leaves, respectively. Among 471,658 transcripts and 177,422 genes generated, 7768 differentially expressed genes were identified in leaves at these two stages of development. The phenylpropanoid biosynthetic pathway of vine tea was investigated according to the transcriptome profiling analysis. Most of the genes encoding phenylpropanoid biosynthesis enzymes were identified and found to be differentially expressed in different tissues and leaf stages of vine tea and also greatly contributed to the biosynthesis of dihydromyricetin in vine tea.

CONCLUSIONS

To the best of our knowledge, this is the first formal study to explore the transcriptome of A. grossedentata. The study provides an insight into the expression patterns and differential distribution of genes related to dihydromyricetin biosynthesis in vine tea. The information may pave the way to metabolically engineering plants with higher flavonoid content.

Effect of cluster zone leaf removal on monoterpene profiles of Sauvignon Blanc grapes and wines

Monoterpenes contribute to the varietal aromas of grapes and wines. We determined the effects of cluster zone leaf removal on the monoterpene profiles of Sauvignon Blanc grape berries and wines, and on the expression of key genes in the terpenoid pathway. Leaf removal at two intensities (half basic, 50%; full basic, 100%) was conducted at two weeks before veraison, veraison, and two weeks after veraison. Half basic leaf removal increased the pH and decreased the tartaric acid content in grapes and wines. The concentrations of most free- and bound-form monoterpenes in grapes were increased by early leaf removal. The total monoterpene contents were increased in wines in the defoliation treatments, but were significantly lower in wines from the full basic leaf removal treatments than in wines from the half basic leaf removal treatments. The defoliation treatments resulted in increased transcript levels of some key genes in terpene biosynthesis (VvPNLinNer1, VvPNLinNer2, VvPNLNGl1, VvPNLNGl2, and VvUGT88A1L1).

Transcriptome profiles of three Muscat table grape cultivars to dissect the mechanism of terpene biosynthesis

Vitis vinifera is widely grown worldwide for making wine and for use as table grapes. Of the existing cultivars, some have a floral and fruity flavour, referred to as a Muscat flavour. It is well-documented that this flavour originates from a series of terpene compounds, but the mechanism of terpene content differences among the Muscat-type cultivars remains unclear. Transcript and terpene metabolite profiles were integrated to elucidate the molecular mechanism of this phenomenon. In this research, three genotypes with different aromatic strengths were investigated by RNA sequencing. A total of 27 fruit samples from three biological replicates were sequenced on Illumina HiSeq2000 at three stages, corresponding to the veraison; berries had intermediate Brix value and were harvest-ripe. After quality assessment and data clearance, a total of 254.18 Gb of data with more than 97% Q20 bases were obtained, approximately 9.41 Gb data were generated per sample. These results will provide a valuable dataset for the discovery of the mechanism of terpene biosynthesis.

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.

Annotation, classification, genomic organization and expression of the Vitis vinifera CYPome

Cytochromes P450 are enzymes that participate in a wide range of functions in plants, from hormonal signaling and biosynthesis of structural polymers, to defense or communication with other organisms. They represent one of the largest gene/protein families in the plant kingdom. The manual annotation of cytochrome P450 genes in the genome of Vitis vinifera PN40024 revealed 579 P450 sequences, including 279 complete genes. Most of the P450 sequences in grapevine genome are organized in physical clusters, resulting from tandem or segmental duplications. Although most of these clusters are small (2 to 35, median = 3), some P450 families, such as CYP76 and CYP82, underwent multiple duplications and form large clusters of homologous sequences. Analysis of gene expression revealed highly specific expression patterns, which are often the same within the genes in large physical clusters. Some of these genes are induced upon biotic stress, which points to their role in plant defense, whereas others are specifically activated during grape berry ripening and might be responsible for the production of berry-specific metabolites, such as aroma compounds. Our work provides an exhaustive and robust annotation including clear identification, structural organization, evolutionary dynamics and expression patterns for the grapevine cytochrome P450 families, paving the way to efficient functional characterization of genes involved in grapevine defense pathways and aroma biosynthesis.

Induction of Terpene Biosynthesis in Berries of Microvine Transformed with VvDXS1 Alleles

Terpenoids, especially monoterpenes, are major aroma-impact compounds in grape and wine. Previous studies highlighted a key regulatory role for grapevine 1-deoxy-D-xylulose 5-phosphate synthase 1 (VvDXS1), the first enzyme of the methylerythritol phosphate pathway for isoprenoid precursor biosynthesis. Here, the parallel analysis of VvDXS1 genotype and terpene concentration in a germplasm collection demonstrated that VvDXS1 sequence has a very high predictive value for the accumulation of monoterpenes and also has an influence on sesquiterpene levels. A metabolic engineering approach was applied by expressing distinct VvDXS1 alleles in the grapevine model system "microvine" and assessing the effects on downstream pathways at transcriptional and metabolic level in different organs and fruit developmental stages. The underlying goal was to investigate two potential perturbation mechanisms, the former based on a significant over-expression of the wild-type (neutral) VvDXS1 allele and the latter on the ex-novo expression of an enzyme with increased catalytic efficiency from the mutated (muscat) VvDXS1 allele. The integration of the two VvDXS1 alleles in distinct microvine lines was found to alter the expression of several terpenoid biosynthetic genes, as assayed through an ad hoc developed TaqMan array based on cDNA libraries of four aromatic cultivars. In particular, enhanced transcription of monoterpene, sesquiterpene and carotenoid pathway genes was observed. The accumulation of monoterpenes in ripe berries was higher in the transformed microvines compared to control plants. This effect is predominantly attributed to the improved activity of the VvDXS1 enzyme coded by the muscat allele, whereas the up-regulation of VvDXS1 plays a secondary role in the increase of monoterpenes.

Diurnal regulation of the floral scent emission by light and circadian rhythm in the Phalaenopsis orchids

BACKGROUND

Phalaenopsis bellina and its closely related species, P. violacea, emit linalool, geraniol and their derivatives as the predominant monoterpenes at the full-bloom stages. Geranyl diphosphate synthase (PbGDPS) is the key enzyme that converts precursors for monoterpene biosynthesis. Besides the monoterpenes being synthesized in concert with floral development stages, we noticed that the scent emission of P. bellina and P. violacea was detected mainly in the daytime.

RESULTS

The monoterpenes of P. violacea flowers displayed a diurnal emission pattern, which was regulated by an internal oscillator in the treatment of constant light. In contrast, constant dark diminished the scent emission levels, indicating that light also affects monoterpene emission in P. violacea. Further treating P. violacea with various light wavelengths showed that the monoterpene emission was greatest in white light condition. Other Phalaenopsis hybrids, including P. I-Hsin Venus 'KHM2212' and P. Meidarland Bellina Age 'LM128', responded differently to various light wavelengths but most of them still showed the highest scent emission under the whole spectra of light. A great number of light-responsive, HY5-interacting, and circadian-responsive elements was enriched on the promoters of both structural genes and transcription factors for monoterpene biosynthesis. Furthermore, several putative genes encoding components involved in light and circadian signaling pathways were also identified in the transcriptome of P. bellina flowers at consecutive stages (from the anthesis day to day 7 post anthesis).

CONCLUSIONS

Taken together, both circadian clock and light factors had positive effects on orchid floral scent emission, and the regulation resided on the control of both structural genes and transcription factors for monoterpene biosynthesis.