The light-hyperresponsive high pigment-2dg mutation of tomato: alterations in the fruit metabolome

Genetic and Biotechnological Approaches to Improve Fruit Bioactive Content: A Focus on Eggplant and Tomato Anthocyanins

Anthocyanins are a large group of water-soluble flavonoid pigments. These specialized metabolites are ubiquitous in the plant kingdom and play an essential role not only in plant reproduction and dispersal but also in responses to biotic and abiotic stresses. Anthocyanins are recognized as important health-promoting and chronic-disease-preventing components in the human diet. Therefore, interest in developing food crops with improved levels and compositions of these important nutraceuticals is growing. This review focuses on work conducted to elucidate the genetic control of the anthocyanin pathway and modulate anthocyanin content in eggplant (Solanum melongena L.) and tomato (Solanum lycopersicum L.), two solanaceous fruit vegetables of worldwide relevance. While anthocyanin levels in eggplant fruit have always been an important quality trait, anthocyanin-based, purple-fruited tomato cultivars are currently a novelty. As detailed in this review, this difference in the anthocyanin content of the cultivated germplasm has largely influenced genetic studies as well as breeding and transgenic approaches to improve the anthocyanin content/profile of these two important solanaceous crops. The information provided should be of help to researchers and breeders in devising strategies to address the increasing consumer demand for nutraceutical foods.

Genetics and breeding of phenolic content in tomato, eggplant and pepper fruits

Phenolic acids and flavonoids are large groups of secondary metabolites ubiquitous in the plant kingdom. They are currently in the spotlight due to the numerous health benefits associated with their consumption, as well as for their vital roles in plant biological processes and in plant-environment interaction. Tomato, eggplant and pepper are in the top ten most consumed vegetables in the world, and their fruit accumulation profiles have been extensively characterized, showing substantial differences. A broad array of genetic and genomic tools has helped to identify QTLs and candidate genes associated with the fruit biosynthesis of phenolic acids and flavonoids. The aim of this review was to synthesize the available information making it easily available for researchers and breeders. The phenylpropanoid pathway is tightly regulated by structural genes, which are conserved across species, along with a complex network of regulatory elements like transcription factors, especially of MYB family, and cellular transporters. Moreover, phenolic compounds accumulate in tissue-specific and developmental-dependent ways, as different paths of the metabolic pathway are activated/deactivated along with fruit development. We retrieved 104 annotated putative orthologues encoding for key enzymes of the phenylpropanoid pathway in tomato (37), eggplant (29) and pepper (38) and compiled 267 QTLs (217 for tomato, 16 for eggplant and 34 for pepper) linked to fruit phenolic acids, flavonoids and total phenolics content. Combining molecular tools and genetic variability, through both conventional and genetic engineering strategies, is a feasible approach to improve phenolics content in tomato, eggplant and pepper. Finally, although the phenylpropanoid biosynthetic pathway has been well-studied in the Solanaceae, more research is needed on the identification of the candidate genes behind many QTLs, as well as their interactions with other QTLs and genes.

Tea GOLDEN2-LIKE genes enhance catechin biosynthesis through activating R2R3-MYB transcription factor

The biosynthesis of catechins, a major type of flavonoids accumulated in tea, is mediated by developmental cues and environmental stimuli. Light enhances but shading treatment reduces catechin accumulation in tea leaves. However, the transcription factors involved in light-mediated catechin biosynthesis remain to be identified. Two GOLDEN2 LIKE genes from tea plant (CsGLK1 and CsGLK2) were isolated and characterized in both tomato and tea plants. Transcripts of both CsGLK1 and CsGLK2 were affected by light intensity in tea plants. Overexpression of CsGLK1 and CsGLK2 promoted chloroplast development and carotenoid accumulation in tomato fruits. An integrated metabolomic and transcriptomic approach revealed that both catechin content and related biosynthetic genes were upregulated in CsGLK-overexpressing tomato leaves. Our further studies in tea plants indicated that CsGLKs directly regulate the transcription of CsMYB5b, a transcription factor involved in catechin biosynthesis. Suppression of CsGLKs in tea leaves led to the reduction of both CsMYB5b expression and catechin accumulation. Taken together, the results show that CsGLKs are involved in light-regulated catechin accumulation in tea plants by regulating expression of CsMYB5b and have great potential for enhancing the accumulation of both carotenoids and flavonoids in fruits of horticultural crops.

Pigment-Related Mutations Greatly Affect Berry Metabolome in San Marzano Tomatoes

The study describes the alterations in metabolomic profiles of four tomato fruit mutations introgressed into Solanum lycopersicum cv. San Marzano, a well-known Italian traditional variety. Three lines carrying variants affecting the content of all pigments, high pigment-1 (hp-1), hp-2, pigment diluter (pd), and a combination of Anthocyanin fruit and atroviolaceum (Aft_atv), were selected, and characterized. Biochemical analysis of 44 non-polar, 133 polar, and 65 volatile metabolites in ripe fruits revealed a wide range of differences between the variant lines and the recurrent parent San Marzano. Among non-polar compounds, many carotenoids, plastoquinones, and tocopherols increased in the fruit of high pigment lines, as well as in Aft_atv, whose β-carotene levels increased too. Interestingly, pd displayed enriched levels of xanthophylls (all-trans-neoxanthin and luteoxanthin) but, simultaneously, decreased levels of α-and β-/γ-tocopherols. Looking at the metabolites in the polar fraction, a significant decrease in sugar profile was observed in hp-1, pd, and Aft_atv. Conversely, many vitamins and organic acids increased in the hp-2 and Aft_atv lines, respectively. Overall, phenylpropanoids was the metabolic group with the highest extent of polar changes, with considerable increases of many compounds mainly in the case of Aft_atv, followed by the pd and hp-2 lines. Finally, several flavor-related compounds were found to be modified in all mutants, mostly due to increased levels in many benzenoid, lipid, and phenylalanine derivative volatiles, which are associated with sweeter taste and better aroma. Construction of metabolic maps, interaction networks, and correlation matrices gave an integrated representation of the large effect of single variants on the tomato fruit metabolome. In conclusion, the identified differences in the mutated lines might contribute to generating novel phenotypes in the traditional San Marzano type, with increased desirable nutraceutical and organoleptic properties.

Enhanced Reproductive Thermotolerance of the Tomato high pigment 2 Mutant Is Associated With Increased Accumulation of Flavonols in Pollen

Climate change has created an environment where heat stress conditions are becoming more frequent as temperatures continue to raise in crop production areas around the world. This situation leads to decreased crop production due to plant sensitivity to heat stress. Reproductive success is critically dependent on plants' ability to produce functional pollen grains, which are the most thermo-sensitive tissue. Flavonols are plant secondary metabolites known for their potent antioxidative activity, essential for male fertility in several species including tomato, and implicated in heat stress tolerance. Since flavonols are highly abundant in fruits of the tomato high pigment 2 (hp2) mutant, we tested the level of flavonols in pollen of this mutant, under the hypothesis that increased accumulation of flavonols would render pollen more tolerant to heat stress. Indeed, pollen from two alleles of the hp2 mutant was found to have flavonols levels increased by 18 and 280% compared with wild-type (WT) under moderate chronic heat stress (MCHS) conditions. This mutant produced on average 7.8-fold higher levels of viable pollen and displayed better germination competence under heat stress conditions. The percentage of fully seeded fruits and the number of seeds per fruit were maintained in the mutant under heat stress conditions while decreased in wild-type plants. Our results strongly suggest that increased concentrations of pollen flavonols enhance pollen thermotolerance and reproductive success under heat stress conditions. Thus, the high flavonols trait may help frame the model for improving crop resilience to heat stress.

Development of zeaxanthin-rich tomato fruit through genetic manipulations of carotenoid biosynthesis

The oxygenated carotenoid zeaxanthin provides numerous benefits to human health due to its antioxidant properties. Especially it is linked to protecting, together with the xanthophyll lutein, the retina in the human eye by filtering harmful blue light thus delaying the progression of age-related macular degeneration (AMD), the most prevalent cause of blindness in developed countries. Despite its high nutritional value, zeaxanthin is less available than other substantial carotenoids in our diet. To solve this shortage, we chose to develop a new food source that would contain a high concentration of natural zeaxanthin. Tomato (Solanum lycopersicum L.) was selected as the target plant since it is the second largest vegetable crop grown worldwide and its fruit characteristically synthesizes and accumulates a high concentration of carotenoids. We employed two genetic approaches in order to enhance zeaxanthin biosynthesis in tomato fruit: a transgenic metabolic engineering and classical genetic breeding. A nontransgenic tomato line, named 'Xantomato', was generated whose fruit accumulated zeaxanthin at a concentration of 39 μg/g fresh weight (or 577 μg/g dry weight), which comprised ca. 50% of total fruit carotenoids compared to zero in the wild type. This is the highest concentration of zeaxanthin reached in a primary crop. Xantomato can potentially increase zeaxanthin availability in the human diet and serve as raw material for industrial applications.

Unexplored nutritive potential of tomato to combat global malnutrition

Tomato, a widely consumed vegetable crop, offers a real potential to combat human nutritional deficiencies. Tomatoes are rich in micronutrients and other bioactive compounds (including vitamins, carotenoids, and minerals) that are known to be essential or beneficial for human health. This review highlights the current state of the art in the molecular understanding of the nutritional aspects, conventional and molecular breeding efforts, and biofortification studies undertaken to improve the nutritional content and quality of tomato. Transcriptomics and metabolomics studies, which offer a deeper understanding of the molecular regulation of the tomato's nutrients, are discussed. The potential uses of the wastes from the tomato processing industry (i.e., the peels and seed extracts) that are particularly rich in oils and proteins are also discussed. Recent advancements with CRISPR/Cas mediated gene-editing technology provide enormous opportunities to enhance the nutritional content of agricultural produces, including tomatoes. In this regard, genome editing efforts with respect to biofortification in the tomato plant are also discussed. The recent technological advancements and knowledge gaps described herein aim to help explore the unexplored nutritional potential of the tomato.

Beyond the limits of photoperception: constitutively active PHYTOCHROME B2 overexpression as a means of improving fruit nutritional quality in tomato

Photoreceptor engineering has recently emerged as a means for improving agronomically beneficial traits in crop species. Despite the central role played by the red/far-red photoreceptor phytochromes (PHYs) in controlling fruit physiology, the applicability of PHY engineering for increasing fleshy fruit nutritional content remains poorly exploited. In this study, we demonstrated that the fruit-specific overexpression of a constitutively active GAF domain Tyr252 -to-His PHYB2 mutant version (PHYB2Y252H ) significantly enhances the accumulation of multiple health-promoting antioxidants in tomato fruits, without negative collateral consequences on vegetative development. Compared with the native PHYB2 overexpression, PHYB2Y252H -overexpressing lines exhibited more extensive increments in transcript abundance of genes associated with fruit plastid development, chlorophyll biosynthesis and metabolic pathways responsible for the accumulation of antioxidant compounds. Accordingly, PHYB2Y252H -overexpressing fruits developed more chloroplasts containing voluminous grana at the green stage and overaccumulated carotenoids, tocopherols, flavonoids and ascorbate in ripe fruits compared with both wild-type and PHYB2-overexpressing lines. The impacts of PHYB2 or PHYB2Y252H overexpression on fruit primary metabolism were limited to a slight promotion in lipid biosynthesis and reduction in sugar accumulation. Altogether, these findings indicate that mutation-based adjustments in PHY properties represent a valuable photobiotechnological tool for tomato biofortification, highlighting the potential of photoreceptor engineering for improving quality traits in fleshy fruits.

Progress on Understanding Transcriptional Regulation of Chloroplast Development in Fleshy Fruit

Edible fleshy fruits are important food sources in the human diet. Their yield and nutritional quality have long been considered as breeding targets for improvement. Various developing fleshy fruits with functional chloroplasts are capable of photosynthesis and contribute to fruit photosynthate, leading to the accumulation of metabolites associated with nutritional quality in ripe fruit. Although tomato high-pigment mutants with dark-green fruits have been isolated for more than 100 years, our understanding of the mechanism of chloroplast development in fleshy fruit remain poor. During the past few years, several transcription factors that regulate chloroplast development in fleshy fruit were identified through map-based cloning. In addition, substantial progress has been made in elucidating the mechanisms that how these transcription factors regulate chloroplast development. This review provides a summary and update on this progress, with a framework for further investigations of the multifaceted and hierarchical regulation of chloroplast development in fleshy fruit.

Modulation of the Tomato Fruit Metabolome by LED Light

Metabolic profiles of tomatoes change during ripening and light can modulate the activity of relevant biochemical pathways. We investigated the effects of light directly supplied to the fruits on the metabolome of the fruit pericarp during ripening. Mature green tomatoes were exposed to well-controlled conditions with light as the only varying factor; control fruits were kept in darkness. In experiment 1 the fruits were exposed to either white light or darkness for 15 days. In experiment 2, fruits were exposed to different light spectra (blue, green, red, far-red, white) added to white background light for seven days. Changes in the global metabolome of the fruit pericarp were monitored using LCMS and GCMS (554 compounds in total). Health-beneficial compounds (carotenoids, flavonoids, tocopherols and phenolic acids) accumulated faster under white light compared to darkness, while alkaloids and chlorophylls decreased faster. Light also changed the levels of taste-related metabolites including glutamate and malate. The light spectrum treatments indicated that the addition of blue light was the most effective treatment in altering the fruit metabolome. We conclude that light during ripening of tomatoes can have various effects on the metabolome and may help with shaping the levels of key compounds involved in various fruit quality characteristics.

The rin, nor and Cnr spontaneous mutations inhibit tomato fruit ripening in additive and epistatic manners

Tomato fruit ripening is regulated by transcription factors (TFs), their downstream effector genes, and the ethylene biosynthesis and signalling pathway. Spontaneous non-ripening mutants ripening inhibitor (rin), non-ripening (nor) and Colorless non-ripening (Cnr) correspond with mutations in or near the TF-encoding genes MADS-RIN, NAC-NOR and SPL-CNR, respectively. Here, we produced heterozygous single and double mutants of rin, nor and Cnr and evaluated their functions and genetic interactions in the same genetic background. We showed how these mutations interact at the level of phenotype, individual effector gene expression, and sensory and quality aspects, in a dose-dependent manner. Rin and nor have broadly similar quantitative effects on all aspects, demonstrating their additivity in fruit ripening regulation. We also found that the Cnr allele is epistatic to rin and nor and that its pleiotropic effects on fruit size and volatile production, in contrast to the well-known dominant effect on ripening, are incompletely dominant, or recessive.

Changes in flavonoid and carotenoid profiles alter volatile organic compounds in purple and orange cherry tomatoes obtained by allele introgression

BACKGROUND

Tomatoes are an important source of human health-promoting compounds, and efforts have been made to enhance their nutritional quality through conventional plant breeding or biotechnology. This study assessed the composition of volatile compounds, phenolics and carotenoids in two allele-introgressed tomato lines, an anthocyanin-rich purple tomato and a β-carotene-rich orange tomato, as well as a red tomato.

RESULTS

The purple tomato peel accumulated a high amount of anthocyanins, mainly petunidin 3-(p-coumaroyl)-rutinoside-5-glucoside, responsible for the purple color, and other flavonoids such as rutin and kaempferol. The orange tomato did not undergo changes in the flavonoid profile but accumulated a high amount of β-carotene, with impairment on lycopene. A total of 27 volatile compounds were detected in purple tomato, 38 in orange tomato and 39 in red tomato. They comprise terpenes, carbonyls, alcohols, esters and hydrocarbons. The difference in the volatile compound profiles of ripe fruits can be related to differences in some precursor contents in the introgression lines. Orange tomato accumulates volatiles from β-carotene cleavage, not detected in the red fruits. Otherwise, volatiles from lycopene were absent in orange tomato as a result of the inhibition on lycopene accumulation. Phenolic volatiles were higher in the purple tomato, which has the highest total phenolic content.

CONCLUSION

The introgessed alleles seem to have a positive effect on the enrichment of ripe tomato in bioactive compounds such as anthocyanins and β-carotene, improving nutritional quality. However, the allele introgression resulted in marked changes in volatile compound profiles, whose impact on tomato flavor and consumer acceptability needs to be evaluated. © 2019 Society of Chemical Industry.

Empowering crop resilience to environmental multiple stress through the modulation of key response components

Crop plants have developed a multitude of defense and adaptation responses to protect themselves against invading pathogens and challenging environmental stresses, mostly operating jointly. The plant perception of overall stress induces a coordinated response mediated by complex signaling networks. Experimental evidences proved that plant response to combined biotic and abiotic stresses substantially diverge from the responses to individual stresses. Moreover, the cross-talk of signaling pathways involved in responding to biotic and abiotic stresses is pivoted on several converging elements able to simultaneously modulate the timing and amplitude of the overall plant response. Comprehensively, the interaction between biotic and abiotic stresses can dramatically changes the plant response to the individual stress and the phenotypical outcome of each stress factor. System biology and data mining can synergistically help biologists in finding out regulative mechanisms and key genes controlling the response to biotic and abiotic stresses. Deploying new genetic engineering solutions can rely on the modification of genes involved in resistance/tolerance processes and/or in the modulation of regulatory elements. Finally, a model of the engineered crop for enhanced tolerance to pressures resulting from invasive pathogens and abiotic constraints in semiarid and warm environment is discussed.

Bee glue (propolis) improves reproductive organs, sperm quality and histological changes and antioxidant parameters of testis tissues in rats exposed to excess copper

This study was designed to determine the effects of propolis on the sperm quality, antioxidant and histological parameters in the testicular tissues of male Sprague Dawley rats exposed to excessive copper (Cu). In this aim, 24 rats were randomly divided into four groups as follows: the control, Cu, Propolis and Cu+Propolis. When compared to control group, Cu administration significantly decreased sperm motility and concentration, increased total abnormal sperm rate. It caused a significant induction the malondialdehyde (MDA), and reduction the superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) in testicular tissues. Also, it caused loss, disorganisation and vacuolation of the germinal epithelium, oedema of the interstitial tissues, proliferation of the interstitial cells, spilled immature spermatogenic cells in the lumen of some seminiferous tubules. A large number of active caspase-3-positive stained apoptotic cells and a significant decrease in Johnsen's testicular score were determined. However, significant ameliorations were observed in all sperm characteristics, MDA, SOD, CAT, GSH, seminiferous tubules, number of apoptotic cells and Johnsen's testicular score in Cu+Propolis group. Our results showed that oral supplementation of propolis had curative effect on the sperm quality, antioxidant and histological parameters in the testicular tissues of male Sprague Dawley rats exposed to Cu.

Toward the 'golden' era: The status in uncovering the regulatory control of carotenoid accumulation in plants

Carotenoids are essential pigments to plants and important natural products to humans. Carotenoids as both primary and specialized metabolites fulfill multifaceted functions in plants. As such, carotenoid accumulation (a net process of biosynthesis, degradation and sequestration) is subjected to complicated regulation throughout plant life cycle in response to developmental and environmental signals. Investigation of transcriptional regulation of carotenoid metabolic genes remains the focus in understanding the regulatory control of carotenoid accumulation. While discovery of bona fide carotenoid metabolic regulators is still challenging, the recent progress of identification of various transcription factors and regulators helps us to construct hierarchical regulatory network of carotenoid accumulation. The elucidation of carotenoid regulatory mechanisms at protein level and in chromoplast provides some insights into post-translational regulation of carotenogenic enzymes and carotenoid sequestration in plastid sink. This review briefly describes the pathways and main flux-controlling steps for carotenoid accumulation in plants. It highlights our recent understanding of the regulatory mechanisms underlying carotenoid accumulation at both transcriptional and post-translational levels. It also discusses the opportunities to expand toolbox for further shedding light upon the intrinsic regulation of carotenoid accumulation in plants.

Light-Controlled Fruit Pigmentation and Flavor Volatiles in Tomato and Bell Pepper

Light is a major environmental factor affecting the regulation of secondary metabolites, such as pigments and flavor. The Solanaceae plant family has diverse patterns of fruit metabolisms that serve as suitable models to understand the molecular basis of its regulation across species. To investigate light-dependent regulation for fruit pigmentation and volatile flavors, major fruit pigments, their biosynthetic gene expression, and volatiles were analyzed in covered fruits of tomato and bell pepper. Immature covered fruits were found to be ivory in color and no chlorophyll was detected in both plants. The total carotenoid content was found to be reduced in ripe tomato and bell pepper under cover. Naringenin chalcone decreased more than 7-fold in ripe tomato and total flavonoids decreased about 10-fold in immature and ripe pepper fruit under light deficiency. Light positively impacts fruit pigmentation in tomato and bell pepper by regulating gene expression in carotenoid and flavonoid biosynthesis, especially phytoene synthase and chalcone synthase, respectively. Nineteen volatile flavors were detected, and seven of these exhibited light-dependent regulations for both ripe tomato and pepper. This study will help in improving fruit quality and aid future research works to understand the molecular mechanisms regulating the influence of light-dependency on pigments and flavor volatiles.

Tomato Fruit Development and Metabolism

Tomato (Solanum lycopersicum L.) belongs to the Solanaceae family and is the second most important fruit or vegetable crop next to potato (Solanum tuberosum L.). It is cultivated for fresh fruit and processed products. Tomatoes contain many health-promoting compounds including vitamins, carotenoids, and phenolic compounds. In addition to its economic and nutritional importance, tomatoes have become the model for the study of fleshy fruit development. Tomato is a climacteric fruit and dramatic metabolic changes occur during its fruit development. In this review, we provide an overview of our current understanding of tomato fruit metabolism. We begin by detailing the genetic and hormonal control of fruit development and ripening, after which we document the primary metabolism of tomato fruits, with a special focus on sugar, organic acid, and amino acid metabolism. Links between primary and secondary metabolic pathways are further highlighted by the importance of pigments, flavonoids, and volatiles for tomato fruit quality. Finally, as tomato plants are sensitive to several abiotic stresses, we briefly summarize the effects of adverse environmental conditions on tomato fruit metabolism and quality.

Changes in bioavailability of sour cherry (Prunus cerasus L.) phenolics and anthocyanins when consumed with dairy food matrices

In this study, it is aimed to understand the changes in sour cherry phytochemicals when their co-digestions are simulated in dairy model systems comprising skim milk, non-fat-yoghurt, probiotic yoghurt or cream. These co-digestions were analyzed for their total phenolic and anthocyanin contents, total antioxidant activity (TAA) in addition to phenolic and anthocyanin profiles, individually. Sour cherry phenolics were stable during gastric conditions (120%); 54% lost in pancreatic digestion and being available (59%) in serum available fraction (IN). Anthocyanins were lost both in gastric (30%) and pancreatic digestions (16%), being only little available (0.6%) in IN. Soymilk had inhibitory effects on TAA. Dairy food matrix components evaluated were found to have distinct effects on the measured bioavailability of individual sour cherry phenolics. This study might aid both consumers and industry on selecting the food matrices to aiding increase in bioavailability.

A tomato B-box protein SlBBX20 modulates carotenoid biosynthesis by directly activating PHYTOENE SYNTHASE 1, and is targeted for 26S proteasome-mediated degradation

Carotenoids play important roles in many biological processes, such as light harvesting, photoprotection and visual attraction in plants. However, the regulation of carotenoid biosynthesis is still not fully understood. Here, we demonstrate that SlBBX20, a B-box (BBX) zinc-finger transcription factor, is a positive regulator of carotenoid accumulation in tomato (Solanum lycopersicum). Overexpression of SlBBX20 leads to dark green fruits and leaves and higher levels of carotenoids relative to the wild-type. Interactions between SlBBX20 and DE-ETIOLATED 1 (SlDET1) lead to the ubiquitination and 26S proteasome-mediated degradation of SlBBX20. Moreover, deficiencies in the components of the CUL4-DDB1-DET1 complex enhanced the stability of the SlBBX20 protein. Thus, we conclude that SlBBX20 is a substrate of the CUL4-DDB1-DET1 E3 ligase. SlBBX20 can activate the expression of PHYTOENE SYNTHASE 1, encoding a key enzyme in carotenoid biosynthesis, by directly binding to a G-box motif in its promoter, which results in the elevated levels of carotenoids in SlBBX20 overexpression lines. We identified a key regulator of carotenoid biosynthesis and demonstrated that the stability of SlBBX20 is regulated by ubiquitination. These findings provide us a new target for the genetic improvement of the nutritional quality of tomato fruit.

Dynamic Changes in Health-Promoting Properties and Eating Quality During Off-Vine Ripening of Tomatoes

Tomato (Solanum lycopersicon L.) fruit is rich in various nutrients, vitamins and health-promoting molecules. Fresh tomatoes are an important part of the Mediterranean gastronomy, and their consumption is thought to contribute substantially to the reduced incidence of some chronic diseases in the Mediterranean populations in comparison with those of other world areas. Unfortunately, tomato fruit is highly perishable, resulting in important economic losses and posing a challenge to storage, logistic and supply management. This review summarizes the current knowledge on some important health-promoting and eating quality traits of tomato fruits after harvest and highlights the existence of substantial cultivar-to-cultivar variation in the postharvest evolution of the considered traits according to maturity stage at harvest and in response to postharvest manipulations. It also suggests the need for adapting postharvest procedures to the characteristics of each particular genotype to preserve the optimal quality of the fresh product.

Analysis of Terpenoid Indole Alkaloids, Carotenoids, Phytosterols, and NMR-Based Metabolomics for Catharanthus roseus Cell Suspension Cultures

The plant Catharanthus roseus is a rich source of terpenoid indole alkaloids (TIA). Some of the TIA are important as antihypertensive (ajmalicine) and anticancer (vinblastine and vincristine) drugs. However, production of the latter is very low in the plant. Therefore, in vitro plant cell cultures have been considered as a potential supply of these chemicals or their precursors. Some monomeric alkaloids can be produced by plant cell cultures, but not on a level feasible for commercialization, despite extensive studies on this plant that deepened the understanding of the TIA biosynthesis and its regulation. In order to analyze the metabolites in C. roseus cell cultures, this chapter presents the method of TIA, carotenoids, and phytosterols analyses. Furthermore, an NMR-based metabolomics approach to study C. roseus cell culture is described.

Influence of controlled deficit irrigation on tomato functional value

The effect of controlled deficit irrigation (CDI) on the accumulation of carotenoids, polyphenols and l-ascorbic acid was studied in conventional and high lycopene tomato cultivars. Plants were initially irrigated to cover 100%ET_c and after the fruit set phase, the dose was reduced to 75% or 50% of ET_c. CDI had no significant effect on the accumulation of carotenoids, while it increased the levels of the hydroxycinnamic acids chlorogenic and ferulic acids, the flavonoid rutin and l-ascorbic acid. Nevertheless, there were important interactions and this effect was highly dependent on the year and site of cultivation. Certain growing areas would be more favorable to supply high quality markets, and, fortunately, CDI would maximize polyphenol (100-75%ET_c) and l-ascorbic acid (100-50%ET_c) in these areas. A combination of the best genotype and growing area with CDI would offer high quality products, preserving a scarce resource: water.

Transcriptome Profiling of Tomato Uncovers an Involvement of Cytochrome P450s and Peroxidases in Stigma Color Formation

Stigma is a crucial structure of female reproductive organ in plants. Stigma color is usually regarded as an important trait in variety identification in some species, but the molecular mechanism of stigma color formation remains elusive. Here, we characterized a tomato mutant, yellow stigma (ys), that shows yellow rather than typical green color in the stigma. Analysis of pigment contents revealed that the level of flavonoid naringenin chalcone was increased in the ys stigma, possibly as a result of higher accumulation of p-coumaric acid, suggesting that naringenin chalcone might play a vital role in yellow color control in tomato stigma. To understand the genes and gene networks that regulate tomato stigma color, RNA-sequencing (RNA-Seq) analyses were performed to compare the transcriptomes of stigmas between ys mutant and wild-type (WT). We obtained 507 differentially expressed genes, in which, 84 and 423 genes were significantly up-regulated and down-regulated in the ys mutant, respectively. Two cytochrome P450 genes, SlC3H1 and SlC3H2 which encode p-coumarate 3-hydroxylases, and six peroxidase genes were identified to be dramatically inhibited in the yellow stigma. Further bioinformatic and biochemical analyses implied that the repression of the two SlC3Hs and six PODs may indirectly lead to higher naringenin chalcone level through inhibiting lignin biosynthesis, thereby contributing to yellow coloration in tomato stigma. Thus, our data suggest that two SlC3Hs and six PODs are involved in yellow stigma formation. This study provides valuable information for dissecting the molecular mechanism of stigma color control in tomato. Statement: This study reveals that two cytochrome P450s (SlC3H1 and SlC3H2) and six peroxidases potentially regulate the yellow stigma formation by indirectly enhancing biosynthesis of yellow-colored naringenin chalcone in the stigma of tomato.

Use of Natural Diversity and Biotechnology to Increase the Quality and Nutritional Content of Tomato and Grape

Improving fruit quality has become a major goal in plant breeding. Direct approaches to tackling fruit quality traits specifically linked to consumer preferences and environmental friendliness, such as improved flavor, nutraceutical compounds, and sustainability, have slowly been added to a breeder priority list that already includes traits like productivity, efficiency, and, especially, pest and disease control. Breeders already use molecular genetic tools to improve fruit quality although most advances have been made in producer and industrial quality standards. Furthermore, progress has largely been limited to simple agronomic traits easy-to-observe, whereas the vast majority of quality attributes, specifically those relating to flavor and nutrition, are complex and have mostly been neglected. Fortunately, wild germplasm, which is used for resistance against/tolerance of environmental stresses (including pathogens), is still available and harbors significant genetic variation for taste and health-promoting traits. Similarly, heirloom/traditional varieties could be used to identify which genes contribute to flavor and health quality and, at the same time, serve as a good source of the best alleles for organoleptic quality improvement. Grape (Vitis vinifera L.) and tomato (Solanum lycopersicum L.) produce fleshy, berry-type fruits, among the most consumed in the world. Both have undergone important domestication and selection processes, that have dramatically reduced their genetic variability, and strongly standardized fruit traits. Moreover, more and more consumers are asking for sustainable production, incompatible with the wide range of chemical inputs. In the present paper, we review the genetic resources available to tomato/grape breeders, and the recent technological progresses that facilitate the identification of genes/alleles of interest within the natural or generated variability gene pool. These technologies include omics, high-throughput phenotyping/phenomics, and biotech approaches. Our review also covers a range of technologies used to transfer to tomato and grape those alleles considered of interest for fruit quality. These include traditional breeding, TILLING (Targeting Induced Local Lesions in Genomes), genetic engineering, or NPBT (New Plant Breeding Technologies). Altogether, the combined exploitation of genetic variability and innovative biotechnological tools may facilitate breeders to improve fruit quality tacking more into account the consumer standards and the needs to move forward into more sustainable farming practices.

Genome editing as a tool to achieve the crop ideotype and de novo domestication of wild relatives: Case study in tomato

The ideotype is a theoretical model of an archetypal cultivated plant. Recent progress in genome editing is aiding the pursuit of this ideal in crop breeding. Breeding is relatively straightforward when the traits in question are monogenic in nature and show Mendelian inheritance. Conversely, traits with a diffuse, polygenic basis such as abiotic stress resistance are more difficult to harness. In recent years, many genes have been identified that are important for plant domestication and act by increasing yield, grain or fruit size or altering plant architecture. Here, we propose that (a) key monogenic traits whose physiology has been unveiled can be molecularly tailored to achieve the ideotype; and (b) wild relatives of crops harboring polygenic stress resistance genes or other traits of interest could be de novo domesticated by manipulating monogenic yield-related traits through state-of-the-art gene editing techniques. An overview of the genomic and physiological challenges in the world's main staple crops is provided. We focus on tomato and its wild Solanum (section Lycopersicon) relatives as a suitable model for molecular design in the pursuit of the ideotype for elite cultivars and to test de novo domestication of wild relatives.

Silencing of the SlNAP7 gene influences plastid development and lycopene accumulation in tomato

Ripening is an important stage of fruit development. To screen the genes associated with pigment formation in tomato fruit, a suppression subtractive hybridization (SSH) cDNA library was constructed by using tomato fruit in the green ripe and break ripe stages, and 129 differential genes were obtained. Using redness as a screening marker, virus-induced gene silencing (VIGS) of the differential genes was performed with a sprout vacuum-infiltration system (SVI). The results showed that silencing the SlNAP7 gene affected the chloroplast development of tomato leaves, manifesting as a photo-bleaching phenotype, and silenced fruit significantly affected the accumulation of lycopene, manifested as a yellow phenotype. In our study, we found that silencing the SlNAP7 gene downregulates the expression of the POR and PORA genes and destroys the normal development of the chloroplast. The expression of related genes included in the lycopene biosynthesis pathway was not significantly changed, but lycopene accumulation was significantly reduced in tomato fruit. Perhaps it was caused by the destruction of the chromoplast, which leads to the oxidation of lycopene. The results show that the SlNAP7 gene influences chloroplast development and lycopene accumulation in tomato.

Phytochrome Interacting Factors (PIFs) in Solanum lycopersicum: Diversity, Evolutionary History and Expression Profiling during Different Developmental Processes

Although the importance of light for tomato plant yield and edible fruit quality is well known, the PHYTOCHROME INTERACTING FACTORS (PIFs), main components of phytochrome-mediated light signal transduction, have been studied almost exclusively in Arabidopsis thaliana. Here, the diversity, evolution and expression profile of PIF gene subfamily in Solanum lycopersicum was characterized. Eight tomato PIF loci were identified, named SlPIF1a, SlPIF1b, SlPIF3, SlPIF4, SlPIF7a, SlPIF7b, SlPIF8a and SlPIF8b. The duplication of SlPIF1, SlPIF7 and SlPIF8 genes were dated and temporally coincided with the whole-genome triplication event that preceded tomato and potato divergence. Different patterns of mRNA accumulation in response to light treatments were observed during seedling deetiolation, dark-induced senescence, diel cycle and fruit ripening. SlPIF4 showed similar expression profile as that reported for A. thaliana homologs, indicating an evolutionary conserved function of PIF4 clade. A comprehensive analysis of the evolutionary and transcriptional data allowed proposing that duplicated SlPIFs have undergone sub- and neofunctionalization at mRNA level, pinpointing the importance of transcriptional regulation for the maintenance of duplicated genes. Altogether, the results indicate that genome polyploidization and functional divergence have played a major role in diversification of the Solanum PIF gene subfamily.

Tomato as a Source of Carotenoids and Polyphenols Targeted to Cancer Prevention

A diet rich in vegetables has been associated with a reduced risk of many diseases related to aging and modern lifestyle. Over the past several decades, many researches have pointed out the direct relation between the intake of bioactive compounds present in tomato and a reduced risk of suffering different types of cancer. These bioactive constituents comprise phytochemicals such as carotenoids and polyphenols. The direct intake of these chemoprotective molecules seems to show higher efficiencies when they are ingested in its natural biological matrix than when they are ingested isolated or in dietary supplements. Consequently, there is a growing trend for improvement of the contents of these bioactive compounds in foods. The control of growing environment and processing conditions can ensure the maximum potential accumulation or moderate the loss of bioactive compounds, but the best results are obtained developing new varieties via plant breeding. The modification of single steps of metabolic pathways or their regulation via conventional breeding or genetic engineering has offered excellent results in crops such as tomato. In this review, we analyse the potential of tomato as source of the bioactive constituents with cancer-preventive properties and the result of modern breeding programs as a strategy to increase the levels of these compounds in the diet.

Suppression of tomato SlNAC1 transcription factor delays fruit ripening

Fruit ripening is a complex process involving many physiological and biochemical changes, including those for ethylene, carotenoid, and cell wall metabolism. Tomato (Solanum lycopersicum) serves as a research model for fruit development and ripening because it possesses numerous favorable genetic features. In this study, SlNAC1 was cloned. An antisense (AS) vector was constructed and transferred to tomato to further explore the function of SlNAC1. The results showed that AS fruits exhibited delayed ripening and a deeper red appearance when these fruits were fully ripened. Fully ripened AS fruits also produced higher total carotenoid and lycopene contents than those of the wild-type (WT) line. Ethylene production of AS fruits was delayed but occurred to a higher extent than that of WT fruits. The softening of AS fruits was slower than that of WT fruits. Endogenous abscisic acid (ABA) level in AS-4 fruits was lower than that in WT fruits. Exogenous ABA accelerated the softening of AS fruits. Furthermore, AS fruits demonstrated up-regulated expression of genes related to lycopene and ethylene biosynthesis but down-regulated expression of genes related to cell wall metabolism and ABA synthesis. Therefore, SlNAC1 is likely implicated in fruit ripening.

Identification of Loci Affecting Accumulation of Secondary Metabolites in Tomato Fruit of a Solanum lycopersicum × Solanum chmielewskii Introgression Line Population

Semi-polar metabolites such as flavonoids, phenolic acids, and alkaloids are very important health-related compounds in tomato. As a first step to identify genes responsible for the synthesis of semi-polar metabolites, quantitative trait loci (QTLs) that influence the semi-polar metabolite content in red-ripe tomato fruit were identified, by characterizing fruits of a population of introgression lines (ILs) derived from a cross between the cultivated tomato Solanum lycopersicum and the wild species Solanum chmielewskii. By analyzing fruits of plants grown at two different locations, we were able to identify robust metabolite QTLs for changes in phenylpropanoid glycoconjugation on chromosome 9, for accumulation of flavonol glycosides on chromosome 5, and for alkaloids on chromosome 7. To further characterize the QTLs we used a combination of genome sequencing, transcriptomics and targeted metabolomics to identify candidate key genes underlying the observed metabolic variation.

Fractionate analysis of the phytochemical composition and antioxidant activities in advanced breeding lines of high-lycopene tomatoes

The results of the first study characterizing new high-lycopene tomato advanced breeding lines, to determine the phytochemical content as well asin vitroantioxidant activities of peel, pulp and seed fractions are presented.

Multidimensional analytical approach based on UHPLC-UV-ion mobility-MS for the screening of natural pigments

Here, we propose a novel strategy that combines a typical ultra high performance liquid chromatography (UHPLC), data-independent mass spectrometry (MS(E)) workflow with traveling wave ion mobility (TWIM) and UV detection, to improve the characterization of carotenoids and chlorophylls in complex biological matrices. UV detection selectively highlighted pigments absorbing at specific wavelengths, while TWIM coupled to MS was used to maximize the peak capacity. We applied this approach for the analysis of pigments in different microalgae samples, including Chlorella vulgaris, Dunaliella salina, and Phaeodactylum tricornutum. Using UHPLC-UV-MS(E) information (retention time, absorbance at 450 nm, and accurate masses of precursors and product ions), we tentatively identified 26 different pigments (carotenes, chlorophylls, and xanthophylls). By adding TWIM information (collision cross sections), we further resolved 5 isobaric pigments, not resolved by UHPLC-UV-MS(E) alone. The characterization of the molecular phenotypes allowed us to differentiate the microalgae species. Our results demonstrate that a combination of TWIM and UV detection with traditional analytical approaches increases the selectivity and specificity of analysis, providing a new tool to characterize pigments in biological samples. We anticipate that such an analytical approach will be extended to other lipidomics and metabolomics applications.

Overexpression of tomato SlNAC1 transcription factor alters fruit pigmentation and softening

BACKGROUND

Fruit maturation and ripening are genetically regulated processes that involve a complex interplay of plant hormones, growth regulators and multiple biological and environmental factors. Tomato (Solanum lycopersicum) has been used as a model of biological and genetic studies on the regulation of specific ripening pathways, including ethylene, carotenoid and cell wall metabolism. This model has also been used to investigate the functions of upstream signalling and transcriptional regulators. Thus far, many ripening-associated transcription factors that influence fruit development and ripening have been reported. NAC transcription factors are plant specific and play important roles in many stages of plant growth and development, such as lateral root formation, secondary cell wall synthesis, and embryo, floral organ, vegetative organ and fruit development.

RESULTS

Tissue-specific analysis by quantitative real-time PCR showed that SlNAC1 was highly accumulated in immature green fruits; the expression of SlNAC1 increased with fruit ripening till to the highest level at 7 d after the breaker stage. The overexpression of SlNAC1 resulted in reduced carotenoids by altering carotenoid pathway flux and decreasing ethylene synthesis mediated mainly by the reduced expression of ethylene biosynthetic genes of system-2, thus led to yellow or orange mature fruits. The results of yeast one-hybrid experiment demonstrated that SlNAC1 can interact with the regulatory regions of genes related lycopene and ethylene synthesis. These results also indicated that SlNAC1 inhibited fruit ripening by affecting ethylene synthesis and carotenoid accumulation in SlNAC1 overexpression lines. In addition, the overexpression of SlNAC1 reduced the firmness of the fruits and the thickness of the pericarp and produced more abscisic acid, resulting in the early softening of fruits. Hence, in SlNAC1 overexpression lines, both ethylene-dependent and abscisic acid-dependent pathways are regulated by SlNAC1 in fruit ripening regulatory network.

CONCLUSIONS

SlNAC1 had a broad influence on tomato fruit ripening and regulated SlNAC1 overexpression tomato fruit ripening through both ethylene-dependent and abscisic acid-dependent pathways. Thus, this study provided new insights into the current model of tomato fruit ripening regulatory network.

An O-methyltransferase modifies accumulation of methylated anthocyanins in seedlings of tomato

Anthocyanins contribute to the appearance of fruit by conferring to them a red, blue or purple colour. In a food context, they have also been suggested to promote consumer health. In purple tomato tissues, such as hypocotyls, stems and purple fruits, various anthocyanins accumulate. These molecules have characteristic patterns of modification, including hydroxylations, methylations, glycosylations and acylations. The genetic basis for many of these modifications has not been fully elucidated, and nor has their role in the functioning of anthocyanins. In this paper, AnthOMT, an O-methyltransferase (OMT) mediating the methylation of anthocyanins, has been identified and functionally characterized using a combined metabolomics and transcriptomics approach. Gene candidates were selected from the draft tomato genome, and their expression was subsequently monitored in a tomato seedling system comprising three tissues and involving several time points. In addition, we also followed gene expression in wild-type red and purple transgenic tomato fruits expressing Rosea1 and Delila transcription factors. Of the 57 candidates identified, only a single OMT gene showed patterns strongly correlating with both accumulation of anthocyanins and expression of anthocyanin biosynthesis genes. This candidate (AnthOMT) was compared to a closely related caffeoyl CoA OMT by recombinant expression in Escherichia coli, and then tested for substrate specificity. AnthOMT showed a strong affinity for glycosylated anthocyanins, while other flavonoid glycosides and aglycones were much less preferred. Gene silencing experiments with AnthOMT resulted in reduced levels of the predominant methylated anthocyanins. This confirms the role of this enzyme in the diversification of tomato anthocyanins.

Recent Advances in the Application of Metabolomics to Studies of Biogenic Volatile Organic Compounds (BVOC) Produced by Plant

In many plants, biogenic volatile organic compounds (BVOCs) are produced as specialized metabolites that contribute to the characteristics of each plant. The varieties and composition of BVOCs are chemically diverse by plant species and the circumstances in which the plants grow, and also influenced by herbivory damage and pathogen infection. Plant-produced BVOCs are receptive to many organisms, from microorganisms to human, as both airborne attractants and repellants. In addition, it is known that some BVOCs act as signals to prime a plant for the defense response in plant-to-plant communications. The compositional profiles of BVOCs can, thus, have profound influences in the physiological and ecological aspects of living organisms. Apart from that, some of them are commercially valuable as aroma/flavor compounds for human. Metabolomic technologies have recently revealed new insights in biological systems through metabolic dynamics. Here, the recent advances in metabolomics technologies focusing on plant-produced BVOC analyses are overviewed. Their application markedly improves our knowledge of the role of BVOCs in chemosystematics, ecological influences, and aroma research, as well as being useful to prove the biosynthetic mechanisms of BVOCs.

Increasing tomato fruit quality by enhancing fruit chloroplast function. A double-edged sword?

Fruits are generally regarded as photosynthate sinks as they rely on energy provided by sugars transported from leaves to carry out the highly demanding processes of development and ripening; eventually these imported photosynthates also contribute to the fruit organoleptic properties. Three recent reports have revealed, however, that transcriptional factors enhancing chloroplast development in fruit may result in higher contents not only of tomato fruit-specialized metabolites but also of sugars. In addition to suggesting new ways to improve fruit quality by fortifying fruit chloroplasts and plastids, these results prompted us to re-evaluate the importance of the contribution of chloroplasts/photosynthesis to fruit development and ripening.

The role of abscisic acid in fruit ripening and responses to abiotic stress

The phytohormone abscisic acid (ABA) plays a crucial role not only in fruit development and ripening, but also in adaptive responses to biotic and abiotic stresses. In these processes, the actions of ABA are under the control of complex regulatory mechanisms involving ABA metabolism, signal transduction, and transport. The endogenous ABA content is determined by the dynamic balance between biosynthesis and catabolism, processes which are regulated by 9-cis-epoxycarotenoid dioxygenase (NCED) and ABA 8'-hydroxylase (CYP707A), respectively. ABA conjugation by cytosolic UDP-glucosyltransferases, or release by β-glucosidases, is also important for maintaining ABA homeostasis. Recently, multiple putative ABA receptors localized at different subcellular sites have been reported. Among these is a major breakthrough in the field of ABA signalling-the identification of a signalling cascade involving the PYR/PYL/RCAR protein family, the type 2C protein phosphatases (PP2Cs), and subfamily 2 of the SNF1-related kinases (SnRK2s). With regard to transport, two ATP-binding cassette (ABC) proteins and two ABA transporters in the nitrate transporter 1/peptide transporter (NRT1/PTR) family have been identified. In this review, we summarize recent research progress on the role of ABA in fruit ripening, stress response, and transcriptional regulation, and also the functional verification of both ABA-responsive and ripening-related genes. In addition, we suggest possible commercial applications of genetic manipulation of ABA signalling to improve fruit quality and yields.

Plant systems biology: insights, advances and challenges

Plants dwelling at the base of biological food chain are of fundamental significance in providing solutions to some of the most daunting ecological and environmental problems faced by our planet. The reductionist views of molecular biology provide only a partial understanding to the phenotypic knowledge of plants. Systems biology offers a comprehensive view of plant systems, by employing a holistic approach integrating the molecular data at various hierarchical levels. In this review, we discuss the basics of systems biology including the various 'omics' approaches and their integration, the modeling aspects and the tools needed for the plant systems research. A particular emphasis is given to the recent analytical advances, updated published examples of plant systems biology studies and the future trends.

Whole transcriptome sequencing reveals genes involved in plastid/chloroplast division and development are regulated by the HP1/DDB1 at an early stage of tomato fruit development

The phenotype of tomato high pigment-1 (hp1) mutant is characterized by overproduction of pigments including chlorophyll and carotenoids during fruit development and ripening. Although the increased plastid compartment size has been thought to largely attribute to the enhanced pigmentation, the molecular aspects of how the HP1/DDB1 gene manipulates plastid biogenesis and development are largely unknown. In the present study, we compared transcriptome profiles of immature fruit pericarp tissue between tomato cv. Ailsa Craig (WT) and its isogenic hp1 mutant. Over 20 million sequence reads, representing > 1.6 Gb sequence data per sample, were generated and assembled into 21,972 and 22,167 gene models in WT and hp1, respectively, accounting for over 60 % official gene models in both samples. Subsequent analyses revealed that 8,322 and 7,989 alternative splicing events, 8833 or 8510 extended 5'-UTRs, 8,263 or 8,939 extended 3'-UTRs, and 1,136 and 1,133 novel transcripts, exist in WT and hp1, respectively. Significant differences in expression level of 880 genes were detected between the WT and hp1, many of which are involved in signaling transduction, transcription regulation and biotic and abiotic stresses response. Distinctly, RNA-seq datasets, quantitative RT-PCR analyses demonstrate that, in hp1 mutant pericarp tissue at early developmental stage, an apparent expression alteration was found in several regulators directly involved in plastid division and development. These results provide a useful reference for a more accurate and more detailed characterization of the molecular process in the development and pigmentation of tomato fruits.

Interaction analysis of grapevine MIKC(c)-type MADS transcription factors and heterologous expression of putative véraison regulators in tomato

MIKC(c)-type MADS-domain transcription factors include important regulators of floral development that interact in protein complexes to control the development of floral organs, as described by the ABC model. Members of the SEPALLATA (SEP) and AGAMOUS (AG) MADS clades include proteins involved in stamen and carpel specification and certain members of these families, such as tomato (Solanum lycopersicon) SlRIN and SlTAGL1, have been shown to regulate fruit development and ripening initiation. A number of expression studies have shown that several floral homeotic MADS genes are expressed during grapevine (Vitis vinifera) berry development, including potential homologues of these characterized ripening regulators. To gain insight into the regulation of berry development and ripening in grapevine, we studied the interactions and functions of grapevine floral homeotic MADS genes. Using the yeast 2- and 3-hybrid systems, we determined that the complexes formed during fruit development and ripening may involve several classes of floral homeotic MADS proteins. We found that a heterologously expressed grapevine SEP gene, VviSEP4, is capable of partially complementing the non-ripening phenotype of the tomato rin mutant, indicating that a role for this gene in ripening regulation may be conserved in fleshy fruit ripening. We also found that ectopic expression of a grapevine AG clade gene, VviAG1, in tomato results in the development of fleshy sepals with the chemical characteristics of tomato fruit pericarp. Additionally, we performed 2-hybrid screens on a library prepared from Pinot noir véraison-stage berry and identified proteins that may interact with the MADS factors that are expressed during berry development and that may represent regulatory functions in grape berry development.