Comparison of UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene sequences between white grapes (Vitis vinifera) and their sports with red skin

Promoter replication of grape MYB transcription factor is associated with a new red flesh phenotype

KEY MESSAGE

In our study, we discovered a fragment duplication autoregulation mechanism in 'ZS-HY', which may be the reason for the phenotype of red foliage and red flesh in grapes. In grapes, MYBA1 and MYBA2 are the main genetic factors responsible for skin coloration which are located at the color loci on chromosome 2, but the exact genes responsible for color have not been identified in the flesh. We used a new teinturier grape germplasm 'ZhongShan-HongYu' (ZS-HY) which accumulate anthocyanin both in skin and flesh as experimental materials. All tissues of 'ZS-HY' contained cyanidin 3-O-(6″-p-coumaroyl glucoside), and pelargonidins were detected in skin, flesh, and tendril. Through gene expression analysis at different stage of flesh, significant differences in the expression levels of VvMYBA1 were found. Gene amplification analysis showed that the VvMYBA1 promoter is composed of two alleles, VvMYBA1a and 'VvMYBA1c-like'. An insertion of a 408 bp repetitive fragment was detected in the allele 'VvMYBA1c-like'. In this process, we found the 408 bp repetitive fragment was co-segregated with red flesh and foliage phenotype. Our results revealed that the 408 bp fragment replication insertion in promoter of 'VvMYBA1c-like' was the target of its protein, and the number of repeat fragments was related to the increase of trans-activation of VvMYBA1 protein. The activation of promoter by VvMYBA1 was enhanced by the addition of VvMYC1. In addition, VvMYBA1 interacted with VvMYC1 to promote the expression of VvGT1 and VvGST4 genes in 'ZS-HY'. The discovery of this mutation event provides new insights into the regulation of VvMYBA1 on anthocyanin accumulation in red-fleshed grape, which is of great significance for molecular breeding of red-fleshed table grapes.

The PpMYB75-PpDFR module reveals the difference between 'SR' and its bud variant 'RMHC' in peach red flesh

'Red Meat Honey Crisp (RMHC)' has been widely cultivated by growers in recent years due to its early maturity, and red meat type characteristics. As a bud variant of 'Super Red (SR)' peach, red flesh is the most distinctive characteristic of 'Red Meat Honey Crisp (RMHC)'. However, the mechanism of red flesh formation in 'RMHC' remains unclear. In this study, 79 differentially produced metabolites were identified by metabolomics analysis. The anthocyanin content in 'RMHC' was significantly higher than that in 'SR' during the same period, such as cyanidin O-syringic acid and cyanidin 3-O-glucoside. Other flavonoids also increased during the formation of red flesh, including flavonols (6-hydroxykaempferol-7-O-glucoside, hyperin), flavanols (protocatechuic acid, (+)-gallocatechin), and flavonoids (chrysoeriol 5-O-hexoside, tricetin). In addition, transcriptomic analysis and RT-qPCR showed that the expression levels of the flavonoid synthesis pathway transcription factor MYB75 and some structural genes, such as PpDFR, PpCHS, PpC4H, and PpLDOX increased significantly in 'RMHC'. Subcellular localization analysis revealed that MYB75 was localized to the nucleus. Yeast single hybridization assays showed that MYB75 bound to the cis-acting element CCGTTG of the PpDFR promoter region. The MYB75-PpDFR regulatory network was identified to be a key pathway in the reddening of 'RMHC' flesh. Moreover, this is the first study to describe the cause for red meat reddening in 'RMHC' compared to 'SR' peaches using transcriptomics, metabolomics and molecular methods. Our study identified a key transcription factor involved in the regulation of the flavonoid synthetic pathway and contributes to peach breeding-related efforts as well as the identification of genes involved in color formation in other species.

Integrated metabolomics and transcriptomics reveal molecular mechanisms of corolla coloration in Rhododendron dauricum L

Rhododendron dauricum L. is a semi-evergreen shrub of high ornamental and medicinal values in Northeast China. To study the molecular mechanisms of corolla coloration in R. dauricum, integrated metabolomics and transcriptomics were performed in R. dauricum featuring purple flowers and R. dauricum var. album featuring white flowers. Comparative metabolomics revealed 25 differential metabolites in the corolla of the two distinct colors, enriched in flavonoids that are closely related to pigmentation in the flower. Differential analysis of the transcriptomics data revealed enrichment of structural genes for flavonoid biosynthesis (99 up- and 58 down-regulated, respectively, in purple corollas compared to white ones). Significantly, CHS and CHI, key genes in the early stage of anthocyanin synthesis, as well as F3H, F3'H, F3'5'H, DFR, ANS, and UFGT that promote the accumulation of pigments in the late stage of anthocyanin synthesis, were up-regulated in R. dauricum (purple color). In R. dauricum var. album, FLS were key genes determining the accumulation of flavonols. In addition, transcriptome-metabolome correlation analysis identified 16 R2R3 MYB transcription factors (out of 83 MYBs) that are important for corolla coloration. Five negative and four positive MYBs were further identified by integrated transcriptional and metabolic network analysis, revealing a key role of MYBA and MYB12 in regulating anthocyanins and flavonols, respectively. Moreover, we validated the function of RdMYBA by creating stable transgenic plants and found that RdMYBA promotes anthocyanin biosynthesis. In summary, we systematically characterized the transcriptome and metabolome of two R. dauricum cultivars with different flower colors and identified MYBs as key factors in modulating corolla coloration.

Identification of Flavanone 3-Hydroxylase Gene Family in Strawberry and Expression Analysis of Fruit at Different Coloring Stages

The color of strawberry fruit is an important appearance quality index that affects the marketability of fruit, and the content and type of anthocyanin are two of the main reasons for the formation of fruit color. At present, the research on anthocyanin synthesis mainly focuses on the phenylpropane metabolic pathway, and the F3H gene family is an important member of this metabolic pathway. Therefore, in order to clarify the role of flavanone 3-hydroxylase (F3H) in regulating anthocyanin accumulation in strawberry, we identified F3H gene family members in strawberry and analyzed their bioinformatics and expression at different fruit color stages. The results showed that the strawberry F3H family contains 126 members, which are distributed on seven chromosomes and can be divided into six subgroups. The promoter region of strawberry F3H gene family contains light response elements, abiotic stress response elements and hormone response elements. Intraspecic collinearity analysis showed that there were six pairs of collinearity of the F3H gene. Interspecific collinearity analysis showed that there were more collinearity relationships between strawberry and apple, grape and Arabidopsis, but less collinearity between strawberry and rice. Via tissue-specific expression analysis, we found that the expression levels of FvF3H48, FvF3H120 and FvF3H74 were higher in the stages of germination, growth, flowering and fruit setting. The expression levels of FvF3H42 and FvF3H16 were higher in seeds. The expression levels of FvF3H16 and FvF3H11 were higher in the ovary wall of stage 1, stage 2, stage 3 and stage 5. FvF3H15 and FvF3H48 were highly expressed in the pericardium, anther, receptacle and anther. Real-time fluorescence quantitative PCR showed the expression changes in F3H in the fruit coloring process. The results indicate that the expression levels of most members were higher during the S3 stage, such as FvF3H7, FvF3H16, FvF3H32, FvF3H82, FvF3H89, FvF3H92 and FvF3H112. FvF3H63 and FvF3H104 exhibited particularly high expression levels during the S1 stage, with some genes also showing elevated expression during the S4 stage, including FvF3H13, FvF3H27, FvF3H66 and FvF3H103. FvF3H58, FvF3H69, FvF3H79 and FvF3H80 showed higher expression levels during the S2 stage. These findings lay the groundwork for elucidating the biological functions of the strawberry F3H gene family and the selection of related genes.

Integrated transcriptomic and metabolomic analysis revealed altitude-related regulatory mechanisms on flavonoid accumulation in potato tubers

Not least because it is adaptable to a variety of geographies and climates, potato (Solanum tuberosum L.) is grown across much of the world. Pigmented potato tubers have been found to contain large quantities of flavonoids, which have various functional roles and act as antioxidants in the human diet. However, the effect of altitude on the biosynthesis and accumulation of flavonoids in potato tubers is poorly characterized. Here we carried out an integrated metabolomic and transcriptomic study in order to evaluate how cultivation at low (800 m), moderate (1800 m), and high (3600 m) altitude affects flavonoid biosynthesis in pigmented potato tubers. Both red and purple potato tubers grown at a high altitude contained the highest flavonoid content, and the most highly pigmented flesh, followed by those grown at a low altitude. Co-expression network analysis revealed three modules containing genes which were positively correlated with altitude-responsive flavonoid accumulation. The anthocyanin repressors StMYBATV and StMYB3 exhibited a significant positive relationship with altitude-responsive flavonoid accumulation. The repressive function of StMYB3 was further verified in tobacco flowers and potato tubers. The results presented here add to the growing body of knowledge regarding the response of flavonoid biosynthesis to environmental conditions, and should aid in efforts to develop novel varieties of pigmented potatoes for use across different geographies.

Metabolome and transcriptome analyses of anthocyanin biosynthesis reveal key metabolites and candidate genes in purple wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) is continuously subjected to genetic improvement to optimize grain quality. Purple wheat has recently gained attention because of its high anthocyanin and nutrient content. In this study, we performed an integrated transcriptome and metabolome analysis of the inbred wheat lines ZM152 (white wheat line) and ZM163 (purple wheat line) to elucidate molecular networks and identify potential genes regulating anthocyanin synthesis. A total of 564 metabolites were detected, of which 47 metabolite contents differed significantly between the two lines. Twenty-five flavonoids, including four anthocyanins, were significantly higher in purple wheat. High contents of cyanidin 3-rutinoside and malvidin 3-glucoside might contribute to the purple coloration of the wheat grains. Consistently, gene ontology and pathway enrichment analyses revealed that flavonoid and anthocyanin biosynthesis were mostly enriched, and the expression of anthocyanin structural genes was specifically upregulated in purple wheat lines, while transcription factors (TFs) were mostly downregulated in purple wheat lines. Especially, the correlation analysis showed the anthocyanin synthesis-related genes CHS (TraesCS2B02G048400) and UFGT (TraesCS7A02G155400) were likely regulated negatively by the TFs MYB4 (TraesCS1A02G268800, TraesCS1B02G279400), TT8 (TraesCS1D02G094200, TraesCS1B02G113100, and TraesCS1A02G102400), which thus could be considered important regulatory genes in the anthocyanin biosynthesis pathway of purple wheat lines. In summary, these results offer new insights into anthocyanin biosynthesis and accumulation of purple wheat, and provide very useful candidate genes for future colored wheat breeding.

Two B-box proteins, PavBBX6/9, positively regulate light-induced anthocyanin accumulation in sweet cherry

Anthocyanin production in bicolored sweet cherry (Prunus avium cv. Rainier) fruit is induced by light exposure, leading to red coloration. The phytohormone abscisic acid (ABA) is essential for this process, but the regulatory relationships that link light and ABA with anthocyanin-associated coloration are currently unclear. In this study, we determined that light treatment of bicolored sweet cherry fruit increased anthocyanin accumulation and induced ABA production and that ABA participates in light-modulated anthocyanin accumulation in bicolored sweet cherry. Two B-box (BBX) genes, PavBBX6/9, were highly induced by light and ABA treatments, as was anthocyanin accumulation. The ectopic expression of PavBBX6 or PavBBX9 in Arabidopsis (Arabidopsis thaliana) increased anthocyanin biosynthesis and ABA accumulation. Overexpressing PavBBX6 or PavBBX9 in sweet cherry calli also enhanced light-induced anthocyanin biosynthesis and ABA accumulation. Additionally, transient overexpression of PavBBX6 or PavBBX9 in sweet cherry peel increased anthocyanin and ABA contents, whereas silencing either gene had the opposite effects. PavBBX6 and PavBBX9 directly bound to the G-box elements in the promoter of UDP glucose-flavonoid-3-O-glycosyltransferase (PavUFGT), a key gene for anthocyanin biosynthesis, and 9-cis-epoxycarotenoid dioxygenase 1 (PavNCED1), a key gene for ABA biosynthesis, and enhanced their activities. These results suggest that PavBBX6 and PavBBX9 positively regulate light-induced anthocyanin and ABA biosynthesis by promoting PavUFGT and PavNCED1 expression, respectively. Our study provides insights into the relationship between the light-induced ABA biosynthetic pathway and anthocyanin accumulation in bicolored sweet cherry fruit.

Comprehensive analysis of metabolome and transcriptome reveals the mechanism of color formation in different leave of Loropetalum Chinense var. Rubrum

BACKGROUND

Loropetalum chinense var. rubrum (L. chinense var. rubrum) is a precious, coloured-leaf native ornamental plant in the Hunan Province. We found an L. chinense var. rubrum tree with three different leaf colours: GL (green leaf), ML (mosaic leaf), and PL (purple leaf). The mechanism of leaf coloration in this plant is still unclear. Therefore, this study aimed to identify the metabolites and genes involved in determining the colour composition of L. chinense var. rubrum leaves, using phenotypic/anatomic observations, pigment content detection, and comparative metabolomics and transcriptomics.

RESULTS

We observed that the mesophyll cells in PL were purple, while those in GL were green and those in ML were a mix of purple-green. The contents of chlorophyll a, b, carotenoids, and total chlorophyll in PL and ML were significantly lower than those in GL. While the anthocyanin content in PL and ML was significantly higher than that in GL. The metabolomics results showed the differences in the content of cyanidin 3-O-glucoside, delphinidin 3-O-glucoside, cyanidin 3,5-O-diglucoside, pelargonidin, and petunidin 3,5-diglucoside in ML, GL, and PL were significant. Considering that the change trend of anthocyanin content change was consistent with the leaf colour difference, we speculated that these compounds might influence the colour of L. chinense var. rubrum leaves. Using transcriptomics, we finally identified nine differentially expressed structural genes (one ANR (ANR1217); four CYP75As (CYP75A1815, CYP75A2846, CYP75A2909, and CYP75A1716); four UFGTs (UFGT1876, UFGT1649, UFGT1839, and UFGT3273) and nine transcription factors (two MYBs (MYB1057 and MYB1211), one MADS-box (MADS1235), two AP2-likes (AP2-like1779 and AP2-like2234), one bZIP (bZIP3720), two WD40s (WD2173 and WD1867) and one bHLH (bHLH1631) that might be related to flavonoid biosynthesis and then impacted the appearance of colour in L. chinense var. rubrum leaves.

CONCLUSION

This study revealed potential molecular mechanisms associated with leaf coloration in L. chinense var. rubrum by analyzing differential metabolites and genes related to the anthocyanin biosynthesis pathway. It also provided a reference for research on leaf colour variation in other ornamental plants.

Biostimulants promote the accumulation of carbohydrates and biosynthesis of anthocyanins in 'Yinhongli' plum

Biostimulants play an important role in promoting crop growth and development and improving fruit yield, but their influence on fruit quality in horticulture plants is still unclear. In this study, four types of biostimulants, Ainuo (AN), Aigefu (AG), Weiguo (WG), and Guanwu Shuang (GS) were applied to the fruit surface of 'Yinhongli' plum at 60 and 75 days after anthesis to investigate their effect on carbohydrates and biosynthesis of anthocyanins, and also analyze the relationship between sugar and anthocyanin accumulation during fruit color change to ripening. Results showed that all biostimulant treatments significantly improved fruit appearance quality, and increased single fruit weight and TSS/TA. Cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside, are the most important anthocyanins in the red skin of the 'Yinhongli' plum, and no anthocyanin was detected in the green skin. In addition, WG and GS treatments significantly increased the expression of structural genes involved in anthocyanin biosynthesis compared with the control, especially chalcone synthase (CHS) and flavonoid 3-O-glucosyltransferase (UFGT) at 95-105 d after anthesis, leading to anthocyanin accumulation 10 days earlier than the control. Correlation analysis showed that there was a significant correlation between total sugar and anthocyanin content during fruit coloring and ripening.

The Anthocyanin Accumulation Related ZmBZ1, Facilitates Seedling Salinity Stress Tolerance via ROS Scavenging

Anthocyanins are a class of antioxidants that scavenge free radicals in cells and play an important role in promoting human health and preventing many diseases. Here, we characterized a maize Bronze gene (BZ1) from the purple colored W22 introgression line, which encodes an anthocyanin 3-O-glucosyltransferase, a key enzyme in the anthocyanin synthesis pathway. Mutation of ZmBZ1 showed bronze-colored seeds and reduced anthocyanins in seeds aleurone layer, seedlings coleoptile, and stem of mature plants by comparison with purple colored W22 (WT). Furthermore, we proved that maize BZ1 is an aleurone layer-specific expressed protein and sub-located in cell nucleus. Real-time tracing of the anthocyanins in developing seeds demonstrated that the pigment was visible from 16 DAP (day after pollination) in field condition, and first deposited in the crown part then spread all over the seed. Additionally, it was transferred along with the embryo cell activity during seed germination, from aleurone layer to cotyledon and coleoptile, as confirmed by microscopy and real-time qRT-PCR. Finally, we demonstrated that the ZmBZ1 contributes to stress tolerance, especially salinity. Further study proved that ZmBZ1 participates in reactive oxygen scavenging (ROS) by accumulating anthocyanins, thereby enhancing the tolerance to abiotic stress.

Clarifying the mechanisms of the light-induced color formation of apple peel under dark conditions through metabolomics and transcriptomic analyses

Many studies have demonstrated that anthocyanin synthesis in apple peel is induced by light, but the color of bagged apple peel continues to change under dark conditions after light induction has not been characterized. Here, transcriptional and metabolic changes associated with changes in apple peel coloration in the dark after different light induction treatments were studied. Apple pericarp can achieve a normal color under complete darkness followed by light induction. Metabolomics analysis indicated that the expression levels of cyanidin-3-O-galactoside and cyanidin-3-O-glucoside were high, which might be associated with the red color development of apple peel. Transcriptome analysis revealed high expression levels of MdUFGTs, MdMYBs, and MdNACs, which might play a key role in light-induced anthocyanin accumulation under dark conditions. 13 key genes related to dark coloring after light induction was screened. The results of this study provide new insights into the mechanism of anthocyanin synthesis under dark conditions.

Metabolome and Transcriptome Analyses of Anthocyanin Accumulation Mechanisms Reveal Metabolite Variations and Key Candidate Genes Involved in the Pigmentation of Prunus tomentosa Thunb. Cherry Fruit

Prunus tomentosa Thunb. has excellent nutritional, economic, and ornamental values with different fruit color. The red coloration of fruit is determined by anthocyanin pigmentation, which is an attractive trait for consumers. However, the mechanisms underlying fruit color formation in the P. tomentosa cherry are not well understood. In this research, the pigmentation patterns in red-color P. tomentosa (RP) fruit and white-color P. tomentosa (WP) were evaluated. Anthocyanin content in matured RP fruit was significantly abundant compared with WP fruit. Metabolomic profiling revealed that pelargonidin 3-O-glucoside, cyanidin 3-O-rutinoside, and pelargonidin 3-O-rutinoside were the predominant anthocyanin compounds in the RP fruit, while, WP fruit had less anthocyanin compositions and lower level. Then, integrative analyses of transcriptome and metabolome identified 285 significant differentially expressed genes (DEGs) closely related to anthocyanin differentially expressed metabolites (DEMs). Among them, nine genes were involved in anthocyanin biosynthesis, transport and degradation pathway, including four biosynthesis genes (PtPAL1, PtDFR, PtANS, and PtUFGT), two transport genes (PtGST11, PtABC10), and three degradation genes (PtPOD1, PtPOD16, PtPOD73). Transcriptome data and real-time PCR showed that the transcript levels of biosynthesis and transport genes were significantly higher in RP than in WP, especially PtANS, PtUFGT, and PtGST11, suggesting they may play key roles in red-colored fruit formation. Meanwhile, the degradation-related genes PtPOD1/16/73 took on exactly opposite trend, suggesting their potential effects on anthocyanin degradation. These results provide novel insights into color patterns formation mechanisms of cherries fruit, and the candidate key genes identified in anthocyanin biosynthesis, transport and degradation may provide a valuable resource for cherry breeding research in future.

Metabolomic and Transcriptomic Profiling Uncover the Underlying Mechanism of Color Differentiation in Scutellaria baicalensis Georgi. Flowers

Scutellaria baicalensis Georgi. (Chinese skullcap or Huang-qin) is an extremely crucial medicinal plant in the Labiate family, and the color of its flowers naturally appears purple. However, during the long-term cultivation of S. baicalensis, very few plants of S. baicalensis also present white and purple-red flower colors under the same ecological conditions. However, the complex metabolic and transcriptional networks underlying color formation in white, purple-red, and purple flowers of S. baicalensis remain largely unclarified. To gain an insight into this issue, we conducted transcriptome and metabolomic profiling to elucidate the anthocyanin synthesis metabolic pathway in the flowers of S. baicalensis, and to identify the differentially expressed candidate genes potentially involved in the biosynthesis of anthocyanins. The results showed that 15 anthocyanins were identified, among which cyanidin 3-rutinoside and delphin chloride were the primary anthocyanins, and accumulation was significantly related to the flower color changes of S. baicalensis. Furthermore, the down-regulation of SbDFR (Sb02g31040) reduced the anthocyanin levels in the flowers of S. baicalensis. The differential expression of the Sb3GT (Sb07g04780 and Sb01g72290) gene in purple and purple-red flowers affected anthocyanin accumulation, suggesting that anthocyanin levels were closely associated with the expression of SbDFR and Sb3GT, which play important roles in regulating the anthocyanin biosynthesis process of S. baicalensis flowers. Transcriptomic analysis revealed that transcription factors WRKY, bHLH, and NAC were also highly correlated with anthocyanin accumulation, especially for NAC35, which positively regulated SbDFR (Sb02g31040) gene expression and modulated anthocyanin biosynthesis in flower color variation of S. baicalensis. Overall, this study presents the first experimental evidence for the metabolomic and transcriptomic profiles of S. baicalensis in response to flower coloration, which provides a foundation for dynamic metabolic engineering and plant breeding, and to understand floral evolution in S. baicalensis plants.

Comparative Transcriptome Analysis of Softening and Ripening-Related Genes in Kiwifruit Cultivars Treated with Ethylene

This work presents the transcriptome analysis of green ‘Hayward’ (Actinidia deliciosa) and gold ‘Haegeum’ (Actinidia chinensis) kiwifruit cultivars after treatment with ethylene for three days at 25 °C. Illumina high-throughput sequencing platform was used to sequence total mRNAs and the transcriptome gene set was constructed by de novo assembly. A total of 1287 and 1724 unigenes were differentially expressed during the comparison of ethylene treatment with control in green ‘Hayward’ and gold ‘Haegeum’, respectively. From the differentially expressed unigenes, 594 and 906 were upregulated, and 693 and 818 were downregulated in the green and gold kiwifruit cultivars, respectively, when treated with ethylene. We also identified a list of genes that were expressed commonly and exclusively in the green and gold kiwifruit cultivars treated with ethylene. Several genes were expressed differentially during the ripening of kiwifruits, and their cumulative effect brought about the softening- and ripening-related changes. This work also identified and categorized genes related to softening and other changes during ripening. Furthermore, the transcript levels of 12 selected representative genes from the differentially expressed genes (DEGs) identified in the transcriptome analysis were confirmed via quantitative real-time PCR (qRT-PCR) to validate the reliability of the expression profiles obtained from RNA-Seq. The data obtained from the present study will add to the information available on the molecular mechanisms of the effects of ethylene during the ripening of kiwifruits. This study will also provide resources for further studies of the genes related to ripening, helping kiwifruit breeders and postharvest technologists to improve ripening quality.

Gret1 retrotransposon and VvmybA1 gene sequences in somatic mutants of new table grape varieties ‘Brasil’ and –Black Star’ (Vitis vinifera L.)

Somatic mutations in grapes are relatively frequent and associated with diversity in grape skin color and berry morphology. Mutations that occur on a side branch of the ‘Benitaka’ cultivar with rosy-red berry skin color generated the ‘Brasil’ cultivar, and mutations that occurred on a side branch of ‘Brasil’ generated the ‘Black Star’ cultivar, both showing a black color in the berry skin. Therefore, genetic characterization of the Gret1 retrotransposon and the VvmybA1 gene in ‘Italia’, ‘Rubi’, ‘Benitaka’, ‘Brasil’, and ‘Black Star’ was started to find whether the altered coloration of berries in ‘Brasil’ and ‘Black Star’ is a product of different mutation patterns in the investigated sequences. Six primer combinations were used for the amplification of different sequences of the Gret1 retrotransposon and VvmybA1 gene of the five cultivars. Polymerase chain reaction (PCR) of the Gret1 retrotransposon and the VvmybA1 gene and sequencing of the amplified products using six primer combinations showed no different alleles or different nucleotide sequences in ‘Brasil’ and ‘Black Star’. The sequencing of the VvmybA1 gene in the present study showed that the mutations that occurred in the cultivar ‘Italia’ for generating the ‘Benitaka’ cultivar persisted in the ‘Brasil’ and ‘Black Star’ cultivars.

Anthocyanin Accumulation and Differential Expression of the Biosynthetic Genes Result in a Discrepancy in the Red Color of Herbaceous Peony (Paeonia lactiflora Pall.) Flowers

Herbaceous peony (Paeonia lactiflora Pall.) is an ornamental plant with huge potential in the international flower market. Similar to the flowers of most other ornamental plants, the top sellers of P. lactiflora are those with red or pink flowers. However, most studies on flower colors have focused on the novel colors and have neglected the most common red flowers. In this study, a red cultivar of P. lactiflora (‘Dafugui’) and a pink cultivar (‘Qingwen’) were selected in order to study the discrepancy in the red color of the flowers. The results demonstrate that these two cultivars have the same compositions as anthocyanins, flavones, and flavonols but different contents. ‘Dafugui’ was found to have a high accumulation of upstream substances due to the higher expression of the early genes encoding phenylalanine ammonialyase (PlPAL) and flavonoid 3′-hydroxylase (PlF3′H). Moreover, the anthocyanidin synthase gene (PlANS) and UDP-glucose flavonoid 3-O-glucosyltransferase gene (PlUF3GT) encoding enzymes catalyze these upstream substances into anthocyanins, resulting in more redness in ‘Dafugui’ than in ‘Qingwen’. Our study thus provides a better understanding of the anthocyanin accumulation and coloring mechanism of P. lactiflora and can serve as a theoretical basis for breeding more red flowers using genetic engineering techniques to cater to consumers’ preferences.

A 69 kbp Deletion at the Berry Color Locus Is Responsible for Berry Color Recovery in Vitis vinifera L. Cultivar 'Riesling Rot'

‘Riesling Weiss’ is a white grapevine variety famous worldwide for fruity wines with higher acidity. Hardly known is ‘Riesling Rot’, a red-berried variant of ‘Riesling Weiss’ that disappeared from commercial cultivation but has increased in awareness in the last decades. The question arises of which variant, white or red, is the original and, consequently, which cultivar is the true ancestor. Sequencing the berry color locus of ‘Riesling Rot’ revealed a new VvmybA gene variant in one of the two haplophases called VvmybA3/1RR. The allele displays homologous recombination of VvmybA3 and VvmybA1 with a deletion of about 69 kbp between both genes that restores VvmybA1 transcripts. Furthermore, analysis of ‘Riesling Weiss’, ‘Riesling Rot’, and the ancestor ‘Heunisch Weiss’ along chromosome 2 using SSR (simple sequence repeat) markers elucidated that the haplophase of ‘Riesling Weiss’ was inherited from the white-berried parent variety ‘Heunisch Weiss’. Since no color mutants of ‘Heunisch Weiss’ are described that could have served as allele donors, we concluded that, in contrast to the public opinion, ‘Riesling Rot’ resulted from a mutational event in ‘Riesling Weiss’ and not vice versa.

Enhancement of anthocyanin and chromatic profiles in 'Cabernet Sauvignon' (Vitis vinifera L.) by foliar nitrogen fertilizer during veraison

BACKGROUND

The influence of foliar nitrogen fertilizer during veraison (FNFV) on anthocyanin accumulation and chromatic characteristics of 'Cabernet Sauvignon' grapes over two seasons was investigated.

RESULTS

Urea and phenylalanine fertilizers (TU and TP, respectively) and a control were sprayed three times at veraison. In 2018, TU displayed a significant enhancement in total individual anthocyanin content and a* and C_ab * profiles. In 2019, FNAV significantly improved the content of total non-acylated, acylated anthocyanin and total individual anthocyanin, and the profiles of L*, a* and C_ab *, except a* in TU. The whole process from phenylalanine variation to anthocyanin accumulation in grape skins was analyzed. On the whole, after the first FNFV to harvest, the increase in phenylalanine metabolism, abscisic acid content, effects of PAL (Phenylalanine ammonia lyase), UFGT (UDP glucose-flavonoid 3-O-glucosyltransferase) and transcript concentrations of VvPAL and VvUFGT involved in anthocyanin biosynthesis were also strong evidence explaining the increased anthocyanin and chromatic profiles in 2019.

CONCLUSION

Overall, FNFV for nitrogen-deficient grapevines could significantly improve grape color, especially in the 2019 veraison with a proper climate. © 2021 Society of Chemical Industry.

Integrative analyses of metabolome and transcriptome reveals metabolomic variations and candidate genes involved in sweet cherry (Prunus avium L.) fruit quality during development and ripening

Sweet cherry (Prunus avium L.), one of the most appreciated and most important commercial temperate fruits, has high sensory quality and nutritional value. Investigating its metabolic variations provides valuable information on the formation of fruit quality. In this study, widely targeted LC-MS/MS based metabolomics was used to identify and quantify metabolic changes during 'Black Pearl' sweet cherry development and ripening. A total of 263 significant differentially expressed metabolites (DEMs) were detected during the four fruit-development stages. Significant differences were observed in the composition and content of compounds in the four stages of cherry development, especially sugars, organic acids, and flavonoids. Moreover, transcriptome analysis provided a molecular basis for metabolic variations during fruit development. A total of 6724 significant differentially expressed genes (DEGs) were identified. Further correlation analysis of major DEMs and DEGs showed that 19 key DEGs were involved in sugar metabolism, 23 key DEGs in organic acid metabolism, and 13 key DEGs in flavonoid metabolism. The upregulated genes involved in the flavonoid pathway probably play an important role in regulating the rapid increase of anthocyanin content during fruit development. These comprehensive analysis data provide a better understanding to improve fruit quality traits based on molecular and metabolic levels.

Integrative Analyses of Metabolomes and Transcriptomes Provide Insights into Flavonoid Variation in Grape Berries

Flavonoids in grapes contribute the quality of the berry, but the flavonoid diversity and the regulatory networks underlying the variation require a further investigation. In this study, we integrated multi-omics data to systematically explore the global metabolic and transcriptional profiles in the skins and pulps of three grape cultivars. The results revealed large-scale differences involved in the flavonoid metabolic pathway. A total of 133 flavonoids, including flavone and flavone C-glycosides, were identified. Beyond the visible differences of anthocyanins, there was large variation in other sub-branched flavonoids, most of which were positively correlated with anthocyanins in grapes. The expressions of most flavonoid biosynthetic genes and the major regulators MYBA1 were strongly consistent with the changes in flavonoids. Integrative analysis identified two novel transcription factors (MYB24 and MADS5) and two ubiquitin proteins (RHA2) as promising regulatory candidates for flavonoid biosynthesis in grapes. Further verification in various grape accessions indicated that five major genes including flavonol 3'5'-hydroxylase (F3'5'H), UDP-glucose:flavonoid 3-O-glycosyl-transferase, anthocyanin O-methyltransferase, acyltransferase (3AT), and glutathione S-transferase (GST4) controlled flavonoid variation in grape berries. These findings provide valuable information for understanding the mechanism of flavonoid biosynthesis in grape berries and the further development of grape health products.

Ethylene Induced by Sound Stimulation Enhances Anthocyanin Accumulation in Grape Berry Skin through Direct Upregulation of UDP-Glucose: Flavonoid 3-O-Glucosyltransferase

Global warming has resulted in the loss of anthocyanin accumulation in berry skin. Sound stimulation can be used as a potential method for enhancing fruit color development since many plants recognize sound vibration as an external stimulus and alter their physiological status in response to it. Sound stimulation (sine wave sound at 1000 Hz) enhanced anthocyanin accumulation in grape cultured cells and berry skins in field-grown grapevines at the early stage of ripening. The transcription of UFGT and ACO2, which encode the key enzymes in anthocyanin and ethylene biosynthesis, respectively, was upregulated in grape cultured cells exposed to sound stimulation. In contrast, the transcription of MybA1 and NCED1, which encode a transcription factor for UFGT and a key enzyme in abscisic acid biosynthesis, respectively, was not affected by the sound stimulation. A treatment with an ethylene biosynthesis inhibitor, aminoethoxyvinyl glycine hydrochloride, revered the enhancement of anthocyanin accumulation by sound stimulation. As the promoter assay using a GUS reporter gene demonstrated that UFGT promoter was directly activated by the ethylene-releasing compound ethephon, which enhanced anthocyanin accumulation in grape cultured cells, we conclude that sound stimulation enhanced anthocyanin accumulation through the direct upregulation of UFGT by ethylene biosynthesis. Our findings suggest that sound stimulation contributes to alleviating poor coloration in berry skin as a novel and innovative practical technique in viticulture.

Transcriptomics Integrated With Widely Targeted Metabolomics Reveals the Mechanism Underlying Grain Color Formation in Wheat at the Grain-Filling Stage

Colored wheat grains have a unique nutritional value. To elucidate the color formation mechanism in wheat seeds, comprehensive metabolomic and transcriptomic analyses were conducted on purple (Dianmai 20-1), blue (Dianmai 20-8), and white (Dianmai 16) wheat at the grain-filling stage. The results showed that the flavonoid biosynthesis pathway was closely related to grain color formation. Among the 603 metabolites identified in all varieties, there were 98 flavonoids. Forty-six flavonoids were detected in purple and blue wheat, and there were fewer flavonoids in white wheat than in colored wheat. Integrated transcriptomic and metabolomic analyses showed that gene expression modulated the flavonoid composition and content, resulting in different metabolite levels of pelargonidin, cyanidin, and delphinidin, thus affecting the color formation of wheat grains. The present study clarifies the mechanism by which pigmentation develops in wheat grains and provides an empirical reference for colored wheat breeding.

Auxin Treatment Enhances Anthocyanin Production in the Non-Climacteric Sweet Cherry (Prunus avium L.)

Abscisic acid (ABA) is a key signaling molecule promoting ripening of non-climacteric fruits such as sweet cherry (Prunus avium L.). To shed light on the role of other hormones on fruit development, ripening and anthocyanin production, the synthetic auxin 1-naphthaleneacetic acid (NAA) was applied to sweet cherry trees during the straw-color stage of fruit development. NAA-treated fruits exhibited higher concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC) and ABA-glucose ester (ABA-GE), which are a precursor of ethylene and a primary storage form of ABA, respectively. Consistent with these observations, transcript levels of genes encoding ACC synthase and ACC oxidase, both involved in ethylene biosynthesis, were increased after 6 days of NAA treatment, and both ABA concentration and expression of the regulator gene of ABA biosynthesis (NCED1 encoding 9-cis-epoxycarotenoid dioxygenase) were highest during early fruit ripening. In addition, transcript levels of key anthocyanin regulatory, biosynthetic and transport genes were significantly upregulated upon fruit exposure to NAA. This was accompanied by an increased anthocyanin concentration and fruit weight whilst fruit firmness and cracking index decreased. Altogether our data suggest that NAA treatment alters ethylene production, which in turn induces ripening in sweet cherry and enhanced anthocyanin production, possibly through ABA metabolism. The results from our study highlight the potential to use a single NAA treatment for manipulation of cherry ripening.

Transcriptome and metabolome analysis reveals anthocyanin biosynthesis pathway associated with ramie (Boehmeria nivea (L.) Gaud.) leaf color formation

Background

The bast fiber crop ramie can be used as high-quality forage resources, especially in tropical or subtropical region where there is lack of high-quality protein feed. Hongxuan No.1 (HX_1) is a unique ramie variety with a light reddish brown leaf color, which is obviously different from elite cultivar, Zhongzhu No.1 (ZZ_1, green leaf). While, the regulatory mechanism of color difference or secondary metaboliates synthesis between these two varieties have not been studied.

Results

In this study, phenotypic, transcriptomic and metabolomic analysis of HX_1 and ZZ_1 were conducted to elucidate the mechanism of leaf color formation. Chromaticity value and pigment content measuring showed that anthocyanin was the main metabolites imparting the different leaf color phenotype between the two varieties. Based on LC/MS, at least 14 anthocyanins were identified in leaves of HX_1 and ZZ_1, and the HX_1 showed the higher relative content of malvidin-, pelargonidin-,and cyanidin-based anthocyanins. Transcriptome and metabolome co-analysis revealed that the up-regulated expression of flavonoids synthesis gene was positively correlated with total anthocyanins accumulation in ramie leaf, and the differentfially expression of “blue gene” (F3’5’H) and the “red gene” (F3’H) in leaves bring out HX_1 metabolic flow more input into the cyanidin branch. Furthermore, the enrichment of glycosylated modification pathway (UGT and AT) and the expression of flavonoid 3-O-glucosyl transferase (UFGT), anthocyanidin reductase (ANR), in leaves were significantly influenced the diversity of anthocyanins between HX_1 and ZZ_1.

Conclusions

Phenotypic, transcriptomic and metabolomic analysis of HX_1 and ZZ_1 indicated that the expression levels of genes related to anthocyanin metabolism contribute to the color formation of ramie variety. Anthocyanins are important plant secandary metabilates with many physiological functions, the results of this study will deepened our understanding of ramie leaf color formation, and provided basis for molecular breeding of functional forage ramie.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08007-0.

The Complexity of Modulating Anthocyanin Biosynthesis Pathway by Deficit Irrigation in Table Grapes

Deficit irrigation (DI) is an irrigation scheduling technique that is used in grapes to improve red color development; however, results are not always satisfactory in table grapes. The red color in grapes is mainly due to the plant pigment anthocyanin. In the present study, the anthocyanin biosynthesis in Scarlet Royal grapes (Vitis vinifera L.) grown in the San Joaquin and Coachella Valleys, and subjected to two different DI strategies was investigated. The objective of this study was to identify potential regulatory factors that may lead to potential treatments to improve red color in table grapes, especially under warm climate conditions. In both locations, DI induced the expression of several genes involved in three major pathways that control the red color in table grapes: anthocyanin biosynthesis, hormone biosynthesis, and antioxidant system. DI at veraison induced anthocyanin accumulation and enhanced red color in berries at harvest time. However, anthocyanin accumulation was lower at the Coachella Valley compared to the San Joaquin Valley. The lower level of anthocyanin was associated with lower expression of critical genes involved in anthocyanin biosynthesis, such as flavonoid-3-O-glucosyltransferase (UFGT), myb-related regulatory gene (R2R3-MYB) (MYBA1), basic helix-loop-helix (bHLH) (MYCA1) and the tryptophan-aspartic acid repeat (WDR or WD40) proteins (WDR1). Further, gene expression analysis revealed the association of ABA biosynthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED1), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO3), and the gibberellic acid (GA) catabolic gene GA2 oxidase (GA2ox1) in the induction of anthocyanin biosynthesis. An increase in the chalcone synthase gene (CHS2) was observed in response to DI treatments in both sites. However, CHS2 expression was higher in Coachella Valley after ending the DI treatment, suggesting the involvement of environmental stress in elevating its transcripts. This data was also supported by the lower level of antioxidant gene expression and enzyme activities in the Coachella Valley compared to the San Joaquin Valley. The present data suggested that the lack of grape red coloration could partially be due to the lower level of antioxidant activities resulting in accelerated anthocyanin degradation and impaired anthocyanin biosynthesis. It seems that under challenging warmer conditions, several factors are required to optimize anthocyanin accumulation via DI, including an active antioxidant system, proper light perception, and hormonal balance.

The R2R3-type MYB transcription factor MdMYB90-like is responsible for the enhanced skin color of an apple bud sport mutant

The anthocyanin content in apple skin determines its red coloration, as seen in a Fuji apple mutant. Comparative RNA-seq analysis was performed to determine differentially expressed genes at different fruit development stages between the wild-type and the skin color mutant. A novel R2R3-MYB transcription factor, MdMYB90-like, was uncovered as the key regulatory gene for enhanced coloration in the mutant. The expression of MdMYB90-like was 21.3 times higher in the mutant. MdMYB90-like regulates anthocyanin biosynthesis directly through the activation of anthocyanin biosynthesis genes and indirectly through the activation of other transcription factors that activate anthocyanin biosynthesis. MdMYB90-like bound to the promoters of both structural genes (MdCHS and MdUFGT) and other transcription factor genes (MdMYB1 and MdbHLH3) in the yeast one-hybrid system, electrophoretic mobility shift assay, and dual-luciferase assay. Transgenic analysis showed that MdMYB90-like was localized in the nucleus, and its overexpression induced the expression of other anthocyanin-related genes, including MdCHS, MdCHI, MdANS, MdUFGT, MdbHLH3, and MdMYB1. The mutant had reduced levels of DNA methylation in two regions (-1183 to -988 and -2018 to -1778) of the MdMYB90-like gene promoter, which might explain the enhanced expression of the gene and the increased anthocyanin content in the mutant apple skin.

De novo transcriptome sequencing and anthocyanin metabolite analysis reveals leaf color of Acer pseudosieboldianum in autumn

Background

Leaf color is an important ornamental trait of colored-leaf plants. The change of leaf color is closely related to the synthesis and accumulation of anthocyanins in leaves. Acer pseudosieboldianum is a colored-leaf tree native to Northeastern China, however, there was less knowledge in Acer about anthocyanins biosynthesis and many steps of the pathway remain unknown to date.

Results

Anthocyanins metabolite and transcript profiling were conducted using HPLC and ESI-MS/MS system and high-throughput RNA sequencing respectively. The results demonstrated that five anthocyanins were detected in this experiment. It is worth mentioning that Peonidin O-hexoside and Cyanidin 3, 5-O-diglucoside were abundant, especially Cyanidin 3, 5-O-diglucoside displayed significant differences in content change at two periods, meaning it may be play an important role for the final color. Transcriptome identification showed that a total of 67.47 Gb of clean data were obtained from our sequencing results. Functional annotation of unigenes, including comparison with COG and GO databases, yielded 35,316 unigene annotations. 16,521 differentially expressed genes were identified from a statistical analysis of differentially gene expression. The genes related to leaf color formation including PAL, ANS, DFR, F3H were selected. Also, we screened out the regulatory genes such as MYB, bHLH and WD40. Combined with the detection of metabolites, the gene pathways related to anthocyanin synthesis were analyzed.

Conclusions

Cyanidin 3, 5-O-diglucoside played an important role for the final color. The genes related to leaf color formation including PAL, ANS, DFR, F3H and regulatory genes such as MYB, bHLH and WD40 were selected. This study enriched the available transcriptome information for A. pseudosieboldianum and identified a series of differentially expressed genes related to leaf color, which provides valuable information for further study on the genetic mechanism of leaf color expression in A. pseudosieboldianum.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07715-x.

Differences in Anthocyanin Accumulation Profiles between Teinturier and Non-Teinturier Cultivars during Ripening

Anthocyanins are vital components of plant secondary metabolites, and are also the most important coloring substances in wine. Teinturier cultivars are rich in anthocyanins. However, the differences in anthocyanin accumulation and profiles between teinturier and non-teinturier cultivars have not been reported. In this study, Yan 73 and Dunkelfelder were selected as the experimental materials, and three non-teinturier cultivars were used for comparison. LC-MS and qRT-PCR were used to determine the individual anthocyanin contents and the relative gene expression. The results show that the total anthocyanin content of the teinturier cultivars was considerably higher than that in non-teinturier cultivars, and the levels of individual anthocyanins increased gradually during ripening. Lower ratios of modified anthocyanins were found in the teinturier cultivars, which was not only due to the high expression level of VvUFGT and VvGST4, but also due to the relatively low expression of VvOMT in these cultivars. Cluster analysis of gene expression and anthocyanin accumulation showed that VvUFGT is related to anthocyanin accumulation, and that AM1 is related to the synthesis and transport of methylated anthocyanins. Our results will be useful for further clarifying the pathways of anthocyanin synthesis, modification, and transport in teinturier cultivars.

Transcriptome Analysis of Pre-Storage 1-MCP and High CO2-Treated 'Madoka' Peach Fruit Explains the Reduction in Chilling Injury and Improvement of Storage Period by Delaying Ripening

Cold storage of peach fruit at low temperatures may induce chilling injury (CI). Pre-storage 1-MCP and high CO₂ treatments were reported among the methods to ameliorate CI and reduce softening of peach fruit. However, molecular data indicating the changes associated with pre-storage 1-MCP and high CO₂ treatments during cold storage of peach fruit are insufficient. In this study, a comparative analysis of the difference in gene expression and physico-chemical properties of fruit at commercial harvest vs. stored fruit for 12 days at 0 °C (cold-stored (CS), pre-storage 1-MCP+CS, and pre-storage high CO₂+CS) were used to evaluate the variation among treatments. Several genes were differentially expressed in 1-MCP+CS- and CO₂+CS-treated fruits as compared to CS. Moreover, the physico-chemical and sensory data indicated that 1-MCP+CS and CO₂+CS suppressed CI and delayed ripening than the CS, which could lead to a longer storage period. We also identified the list of genes that were expressed commonly and exclusively in the fruit treated by 1-MCP+CS and CO₂+CS and compared them to the fruit quality parameters. An attempt was also made to identify and categorize genes related to softening, physiological changes, and other ripening-related changes. Furthermore, the transcript levels of 12 selected representative genes from the differentially expressed genes (DEGs) in the transcriptome analysis were confirmed via quantitative real-time PCR (qRT-PCR). These results add information on the molecular mechanisms of the pre-storage treatments during cold storage of peach fruit. Understanding the genetic response of susceptible cultivars such as ‘Madoka’ to CI-reducing pre-storage treatments would help breeders release CI-resistant cultivars and could help postharvest technologists to develop more CI-reducing technologies.

Transcriptomic dynamics changes related to anthocyanin accumulation in the fleshy roots of carmine radish (Raphanus sativus L.) characterized using RNA-Seq

Carmine radish is famous for containing a natural red pigment (red radish pigment). However, the expression of anthocyanin biosynthesis-related genes during the dynamic development stages of the fleshy roots in carmine radish has not been fully investigated. Here, based on HPLC quantification of anthocyanin levels from our previous study, young fleshy roots of the carmine radish “Hongxin 1” obtained at the dynamic development stages of fleshy roots (seedling stage (SS), initial expansion (IE), full expansion (FE), bolting stage (BS), initial flowering stage (IFS), full bloom stage (FBS) and podding stage (PS)) were used for RNA-Seq. Approximately 126 comodulated DEGs related to anthocyanin biosynthesis (common DEGs in the dynamic growth stages of fleshy roots in carmine radish) were identified, from which most DEGs appeared to be likely to participate in anthocyanin biosynthesis, including two transcription factors, RsMYB and RsRZFP. In addition, some related proteins, e.g., RsCHS, RsDFR, RsANS, RsF′3H, RsF3GGT1, Rs3AT1, RsGSTF12, RsUFGT78D2 and RsUDGT-75C1, were found as candidate contributors to the regulatory mechanism of anthocyanin synthesis in the fleshy roots of carmine radish. In addition, 11 putative DEGs related to anthocyanin synthesis were evaluated by qRT-PCR via the (2-ΔΔCT) method; the Pearson correlation analysis indicated excellent concordance between the RNA-Seq and qRT-PCR results. Furthermore, GO enrichment analysis showed that “anthocyanin-containing compound biosynthetic process” and “anthocyanin-containing compound metabolic process” were commonly overrepresented in the dynamic growth stages of fleshy roots after the initial expansion stage. Moreover, five significantly enriched pathways were identified among the DEGs in the dynamic growth stages of fleshy roots in carmine radish, namely, flavonoid biosynthesis, flavone and flavonol biosynthesis, diterpenoid biosynthesis, anthocyanin biosynthesis, and benzoxazinoid biosynthesis. In conclusion, these results will expand our understanding of the complex molecular mechanisms of anthocyanin biosynthesis in the fleshy roots of carmine radish and the putative candidate genes involved in this process.

Preharvest long-term exposure to UV-B radiation promotes fruit ripening and modifies stage-specific anthocyanin metabolism in highbush blueberry

Ultraviolet-B (UV-B) light (280-315 nm) is an important environmental signal that regulates plant development and photomorphogenesis, while also affecting the flavonoid pathway, including anthocyanin biosynthesis. Regarding the effects of UV-B radiation on fruits, the effects of a short-term or postharvest irradiation on fruit quality have been well-documented, but the effects of a long-term preharvest UV-B irradiation on fruit growth and coloration remain unclear. Thus, in this study, we investigated the effects of a long-term treatment involving an environmentally relevant UV-B dose on highbush blueberry (Vaccinium corymbosum) fruit. The preharvest UV-B treatment quickly promoted fruit growth and sugar accumulation, which is not commonly observed in other fruit tree species. The UV-B exposure also accelerated fruit ripening and coloration. The dual-luciferase assay proved that in blueberries, expression of VcUFGT encoding anthocyanin biosynthesis key enzyme, is positively and negatively regulated by VcMYBA1 and VcMYBC2, respectively. Throughout the fruit development stage, the UV-B treatment up-regulated VcMYBPA1 expression, which increased VcUFGT expression via VcMYBA1. In the green fruit stage, the UV-B treatment increased HY5 encoding UV receptor, which up-regulates VcMYBPA1 and down-regulates VcMYBC2, thereby promotes the accumulation of anthocyanins. On the other hand, excessive anthocyanin synthesis was inhibited by increased VcMYBC2 levels in mature fruits when exposed to UV-B light through HY5-independent pathway. In conclusion, anthocyanin-related MYB activators and repressor may coordinately balance the accumulation of anthocyanins in blueberry fruits, with UV-B treatments possibly influencing their effects in a stage-specific manner. The potential utility of preharvest UV-B treatments for improving blueberry fruit quality is discussed herein.

Functional relationship of vegetable colors and bioactive compounds: Implications in human health

Vegetables are essential protective diet ingredients that supply ample amounts of minerals, vitamins, carbohydrates, proteins, dietary fiber, and various nutraceutical compounds for protection against various disease conditions. Color is the most important quality parameter for the farmers to access the harvest maturity while for the consumer's reliable indices to define acceptability or rejection. The colored vegetables contain functional compounds like chlorophylls, carotenoids, betalains, anthocyanins, etc. well recognized for their antioxidant, antimicrobial, hypolipidemic, neuroprotective, antiaging, diuretic, and antidiabetic properties. Recently, there has been a shift in food consumption patterns from processed to semi-processed or fresh fruits and vegetables to ensure a healthy disease-free life. This shifted the focus of agriculture scientists and food processors from food security to nutrition security. This has resulted in recent improvements to existing crops like blue tomato, orange cauliflower, colored and/or black carrots, with improved color, and thus enriched bioactive compounds. Exhaustive laboratory trials though are required to document and establish their minimum effective concentrations, bioavailability, and specific health benefits. Efforts should also be directed to breed color-rich cultivars or to improve the existing varieties through conventional and molecular breeding approaches. The present review has been devoted to a better understanding of vegetable colors with specific health benefits and to provide in-hand information about the effect of specific pigment on body organs, the effect of processing on their bioavailability, and recent improvements in colors to ensure a healthy lifestyle.

Insights into long non-coding RNA regulation of anthocyanin carrot root pigmentation

Carrot (Daucus carota L.) is one of the most cultivated vegetable in the world and of great importance in the human diet. Its storage organs can accumulate large quantities of anthocyanins, metabolites that confer the purple pigmentation to carrot tissues and whose biosynthesis is well characterized. Long non-coding RNAs (lncRNAs) play critical roles in regulating gene expression of various biological processes in plants. In this study, we used a high throughput stranded RNA-seq to identify and analyze the expression profiles of lncRNAs in phloem and xylem root samples using two genotypes with a strong difference in anthocyanin production. We discovered and annotated 8484 new genes, including 2095 new protein-coding and 6373 non-coding transcripts. Moreover, we identified 639 differentially expressed lncRNAs between the phenotypically contrasted genotypes, including certain only detected in a particular tissue. We then established correlations between lncRNAs and anthocyanin biosynthesis genes in order to identify a molecular framework for the differential expression of the pathway between genotypes. A specific natural antisense transcript linked to the DcMYB7 key anthocyanin biosynthetic transcription factor suggested how the regulation of this pathway may have evolved between genotypes.

Comparative transcriptomic analysis between 'Summer Black' and its bud sport 'Nantaihutezao' during developmental stages

4-coumarate-CoA ligase (VIT_02s0109g00250) and copper amine oxidase (VIT_17s0000g09100) played essential roles in contributing to the total soluble solid and total anthocyanin variations induced by bud sport in grape berries. Taste and color, which are important organoleptic qualities of grape berry, undergo rapid and substantial changes during development and ripening. In this study, we used two cultivars 'Summer Black' and its bud sport 'Nantaihutezao' to explore and identify differentially expressed genes associated with total soluble solid and anthocyanin during developmental stages using RNA-Seq. Overall, substantial differences in expression were observed across berry development between the two cultivars. 5388 genes were detected by weighted gene co-expression network analysis (WGCNA) associated with the total soluble solid (TSS) and anthocyanin contents variations. Several of these genes were significantly enriched in the phenylalanine metabolism pathway; two hub genes 4-coumarate-CoA ligase (VIT_02s0109g00250) and copper amine oxidase (VIT_17s0000g09100) played the most essential roles in relating to the total soluble solid and total anthocyanin variations induced by bud sport through Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment and co-expression network analysis. These findings provide insights into the molecular mechanism responsible for the bud sport phenotype.

High temperature at veraison inhibits anthocyanin biosynthesis in berry skins during ripening in 'Kyoho' grapevines

We examined the effects of high temperature (HT) at veraison (the onset of ripening) on coloration and anthocyanin biosynthesis in berry skins of 'Kyoho' grapevines (Vitis labruscana L.). The vines were subjected to control, HT (6 °C higher than the control for 10 days), and intermittent HT (IHT; 6 °C higher than the control for 4 days followed by control temperature for 3 days and then 6 °C higher than the control for another 3 days) conditions from 50 to 60 days after full bloom (DAFB) in temperature-controlled rooms. Under control conditions, berry skins were tinted purple from 55 DAFB and turned to reddish-purple thereafter until 80 DAFB, concurrently with the anthocyanin accumulation. The HT and IHT treatments greatly inhibited the coloration and anthocyanin accumulation, with greater inhibition by the HT treatment. The HT and IHT treatments significantly inhibited the expressions of early (EBGs) and late anthocyanin biosynthetic genes (LBGs), and the transcription factor gene VlMYBA2. Abscisic acid (ABA) contents in the control berry skins increased from 50 DAFB, peaked at 55 DAFB, and decreased thereafter. The HT and IHT treatments reduced the increase in ABA contents, with no significant difference between HT- and IHT-treated vines. Gibberellin (GA) contents decreased during veraison in the berry skins of control and IHT-treated vines, but remained unchanged in those of HT-treated vines. These results suggest that the coloration and anthocyanin biosynthesis in berry skins are associated with changes in the ABA/GA ratio.

Comparative phenotypic and transcriptomic analysis of Victoria and flame seedless grape cultivars during berry ripening

Grape berry development is a highly coordinated and intricate process. Herein, we analyzed the phenotypic and transcriptomic patterns of Victoria (VT) and Flame Seedless (FS) grape varieties during berry development. Physiological analysis and transcriptomic sequencing were performed at four berry developmental phases. VT berry size was comparatively larger to the FS variety. At maturity, 80 days postanthesis (DPA), the FS soluble solids were 61.8% higher than VT. Further, 4889 and 2802 differentially expressed genes were identified from VT and FS 40 DPA to 80 DPA development stages, respectively. VvSWEET15, VvHXK, and MYB44 genes were up‐regulated during the postanthesis period, while bHLH14, linked to glucose metabolism, was gradually down‐regulated during berry development. These genes may have significant roles in berry development, ripening, and sugar accumulation.

A combination of linkage mapping and GWAS brings new elements on the genetic basis of yield-related traits in maize across multiple environments

Using GWAS and QTL mapping identified 100 QTL and 138 SNPs, which control yield-related traits in maize. The candidate gene GRMZM2G098557 was further validated to regulate ear row number by using a segregation population. Understanding the genetic basis of yield-related traits contributes to the improvement of grain yield in maize. This study used an inter-mated B73 × Mo17 (IBM) Syn10 doubled-haploid (DH) population and an association panel to identify the genetic loci responsible for nine yield-related traits in maize. Using quantitative trait loci (QTL) mapping, 100 QTL influencing these traits were detected across different environments in the IBM Syn10 DH population, with 25 co-detected in multiple environments. Using a genome-wide association study (GWAS), 138 single-nucleotide polymorphisms (SNPs) were identified as correlated with these traits (P < 2.04E-06) in the association panel. Twenty-one pleiotropic QTL/SNPs were identified to control different traits in both populations. A combination of QTL mapping and GWAS uncovered eight significant SNPs (PZE-101097575, PZE-103169263, ZM011204-0763, PZE-104044017, PZE-104123110, SYN8062, PZE-108060911, and PZE-102043341) that were co-located within seven QTL confidence intervals. According to the eight co-localized SNPs by the two populations, 52 candidate genes were identified, among which the ear row number (ERN)-associated SNP SYN8062 was closely linked to SBP-transcription factor 7 (GRMZM2G098557). Several SBP-transcription factors were previously demonstrated to modulate maize ERN. We then validated the phenotypic effects of SYN8062 in the IBM Syn10 DH population, indicating that the ERN of the lines with the A-allele in SYN8062 was significantly (P < 0.05) larger than that of the lines with the G-allele in SYN8062 in each environment. These findings provide valuable information for understanding the genetic mechanisms of maize grain yield formation and for improving molecular marker-assisted selection for the high-yield breeding of maize.

Fine mapping of the Ca3GT gene controlling anthocyanin biosynthesis in mature unripe fruit of Capsicum annuum L

The anthocyanin biosynthesis gene Ca3GT was fine-mapped in a 110.5-kb region through a map-based cloning strategy. Gene expression and promoter analyses confirmed the strong candidate gene Capana10g001978. Pepper (Capsicum annum L.) fruit can be dark green, green, light green, purple, yellow, or ivory at the juvenile stage. Anthocyanins are responsible for fruit color formation in mature unripe pepper fruit, and transient accumulation of anthocyanins is the main problem in breeding pepper plants with mature purple fruit. Only a few genes controlling this trait have been cloned. The present study aimed to map and identify an anthocyanin biosynthesis gene from pepper using an F₂ population derived from a cross between line '17C3808' (purple mature unripe fruit) and line '17C3807' (green mature unripe fruit). The trait was mapped on a 110.5-kb interval between markers SSR18213 and SSR18228 on chromosome 10. There were three open reading frames in this region; Capana10g001978 was predicted in this region as markers CAPS-78-708 and InDel146 co-segregated with it. Capana10g001978 is a structural gene encoding the GTB transcription factor involved in the biosynthesis of anthocyanins. Comparing parental sequences, two base mutations were identified in the exon of Capana10g001978, at positions + 528 bp and + 708 bp, which resulted in changes in the 176th and 236th amino acid residues, from glutamine (CAA) to histidine (CAC), causing a nonsense mutation (from CAG to CAA). Additionally, Capana10g001978 was highly expressed in the pericarp of mature, unripe pepper fruit. There were four single nucleotide polymorphisms, three sequence deletions, and one sequence insertion in the promoter region of purple, mature, and unripe pepper fruit, leading to the formation of a W-box and a GT1-motif. Thus, Capana10g001978 is a strong candidate gene of Ca3GT involved in anthocyanin biosynthesis in mature unripe pepper fruit. These results provide important information regarding the isolation and characterization of Ca3GT, and they are the starting point for studying the regulatory pathway responsible for anthocyanin biosynthesis in pepper.

R2R3-MYB Transcription Factors Regulate Anthocyanin Biosynthesis in Grapevine Vegetative Tissues

Anthocyanins with important physiological functions mainly accumulate in grape berry, but teinturier grape cultivars can accumulate anthocyanins in both reproductive and vegetative tissues. The molecular regulatory mechanisms of anthocyanin biosynthesis in grapevine reproductive and vegetative tissues are different. Therefore, teinturier grapevine cultivar provides opportunities to investigate transcriptional regulation of vegetative anthocyanins, and to compare with mechanisms that regulate grape berry anthocyanins. Yan73 is a teinturier Vitis vinifera variety with vegetative tissues able to accumulate anthocyanins, but the anthocyanin pattern and the molecular mechanism regulating anthocyanin biosynthesis in these tissues remain uncharacterized. We analyzed the anthocyanin metabolic and transcriptome profiles of the vegetative tissues of Yan73 and its male parent with HPLC-ESI-MS/MS and RNA-sequencing technologies. Yan73 vegetative tissues had relatively high 3'-OH, acylated, and methoxylated anthocyanins. Furthermore, peonidin-3-O-(trans-6-coumaryl)-glucoside is the most abundant anthocyanin in Yan73 grapevine vegetative tissues. A total of 30,17 and 10 anthocyanin biosynthesis genes showed up-regulated expression in Yan73 leaf, stem and tendril, respectively, indicating anthocyanin biosynthesis in Yan73 vegetative tissues is regulated by transcription factors. The up-regulated expression of VvMYBA1 on chromosome 2 and VvMYBA5, VvMYBA6, and VvMYBA7 on chromosome 14 are responsible for the anthocyanin patterns of Yan73 vegetative tissues. The expression of a set of R2R3-MYB C2 repressor genes is activated and may negatively regulate anthocyanin biosynthesis in Yan73 vegetative tissues. These findings enhance our understanding of anthocyanin biosynthesis in grapevine.

Transcriptomics analysis of Psidium cattleyanum Sabine (Myrtaceae) unveil potential genes involved in fruit pigmentation

Psidium cattleyanum Sabine is an Atlantic Forest native species that presents some populations with red fruits and others with yellow fruits. This variation in fruit pigmentation in this species is an intriguing character that could be related to species evolution but still needs to be further explored. Our goal was to provide genomic information for these morphotypes to understand the molecular mechanisms of differences in fruit colour in this species. In this study, we performed a comparative transcriptome analysis of red and yellow morphotypes of P. cattleyanum, considering two stages of fruit ripening. The transcriptomic analysis performed encompassing leaves, unripe and ripe fruits, in triplicate for each morphotype. The transcriptome consensus from each morphotype showed 301,058 and 298,310 contigs from plants with yellow and red fruits, respectively. The differential expression revealed important genes that were involved in anthocyanins biosynthesis, such as the anthocyanidin synthase (ANS) and UDP-glucose:flavonoid-o-glucosyltransferase (UFGT) that were differentially regulated during fruit ripening. This study reveals stimulating data for the understanding of the pathways and mechanisms involved in the maturation and colouring of P. cattleyanum fruits and suggests that the ANS and UFGT genes are key factors involved in the synthase and pigmentation accumulation in red fruits.

Transcriptomic analysis of flower color variation in the ornamental crabapple (Malus spp.) half-sib family through Illumina and PacBio Sequel sequencing

Ornamental crabapple is an important woody ornamental plant with flower colors ranging from white to pink to red, and the degree of redness is directly related to the anthocyanin content. To explore the molecular mechanism leading to the variation in flower color in ornamental crabapple, transcriptome sequencing using the Illumina and PacBio Sequel platforms revealed the difference in gene expression between the petals of plants with white and red flowers in the half-sib family. In total, the analysis identified 603 differentially expressed genes (DEGs), including 449 upregulated and 154 downregulated genes. GO and KEGG enrichment analyses of the DEGs showed that the oxidation-reduction process and catalytic activity were more active in red petals, and most of the DEGs were involved in secondary metabolite synthesis and plant hormone signaling. Among the 603 DEGs, 10 were enriched as structural genes. Transcription factors related to anthocyanin synthesis and five genes related to anthocyanin transport and degradation were highly expressed in red petals. In addition, this study found that five AUX gene signals were differentially expressed in the two petal types. The discovery of these DEGs indicates that plant endogenous hormones also exert a regulatory effect on flower color.

Hybrid de novo transcriptome assembly of poinsettia (Euphorbia pulcherrima Willd. Ex Klotsch) bracts

BACKGROUND

Poinsettia is a popular and important ornamental crop, mostly during the Christmas season. Its bract coloration ranges from pink/red to creamy/white shades. Despite its ornamental value, there is a lack of knowledge about the genetics and molecular biology of poinsettia, especially on the mechanisms of color formation. We performed an RNA-Seq analysis in order to shed light on the transcriptome of poinsettia bracts. Moreover, we analyzed the transcriptome differences of red- and white-bracted poinsettia varieties during bract development and coloration. For the assembly of a bract transcriptome, two paired-end cDNA libraries from a red and white poinsettia pair were sequenced with the Illumina technology, and one library from a red-bracted variety was used for PacBio sequencing. Both short and long reads were assembled using a hybrid de novo strategy. Samples of red- and white-bracted poinsettias were sequenced and comparatively analyzed in three color developmental stages in order to understand the mechanisms of color formation and accumulation in the species.

RESULTS

The final transcriptome contains 288,524 contigs, with 33% showing confident protein annotation against the TAIR10 database. The BUSCO pipeline, which is based on near-universal orthologous gene groups, was applied to assess the transcriptome completeness. From a total of 1440 BUSCO groups searched, 77% were categorized as complete (41% as single-copy and 36% as duplicated), 10% as fragmented and 13% as missing BUSCOs. The gene expression comparison between red and white varieties of poinsettia showed a differential regulation of the flavonoid biosynthesis pathway only at particular stages of bract development. An initial impairment of the flavonoid pathway early in the color accumulation process for the white poinsettia variety was observed, but these differences were no longer present in the subsequent stages of bract development. Nonetheless, GSTF11 and UGT79B10 showed a lower expression in the last stage of bract development for the white variety and, therefore, are potential candidates for further studies on poinsettia coloration.

CONCLUSIONS

In summary, this transcriptome analysis provides a valuable foundation for further studies on poinsettia, such as plant breeding and genetics, and highlights crucial information on the molecular mechanism of color formation.

De novo transcriptome sequencing of radish (Raphanus sativus L.) fleshy roots: analysis of major genes involved in the anthocyanin synthesis pathway

Background

The HongXin radish (Raphanus sativus L.), which contains the natural red pigment (red radish pigment), is grown in the Fuling district of Chongqing City. However, the molecular mechanisms underlying anthocyanin synthesis for the formation of natural red pigment in the fleshy roots of HongXin radish are not well studied.

Results

De novo transcriptome of HX-1 radish, as well as that of the advanced inbred lines HX-2 and HX-3 were characterized using next generation sequencing (NGS) technology. In total, approximately 66.22 million paired-end reads comprising 34, 927 unigenes (N50 = 1, 621 bp) were obtained. Based on sequence similarity search with known proteins, total of 30, 127 (about 86.26%) unigenes were identified. Additionally, functional annotation and classification of these unigenes indicated that most of the unigenes were predominantly enriched in the metabolic process-related terms, especially for the biosynthetic pathways of secondary metabolites. Moreover, majority of the anthocyanin biosynthesis-related genes (ABRGs) involved in the regulation of anthocyanin biosynthesis were identified by targeted search for their annotation. Subsequently, the expression of 15 putative ABRGs involved in the anthocyanin synthesis-related pathways were validated using quantitative real-time polymerase chain reaction (qRT-PCR). Of those, RsPAL2, RsCHS-B2, RsDFR1, RsDFR2, RsFLS, RsMT3 and RsUFGT73B2-like were identified significantly associated with anthocyanin biosynthesis. Especially for RsDFR1, RsDFR2 and RsFLS, of those, RsDFR1 and RsDFR2 were highest enriched in the HX-3 and WG-3, but RsFLS were down-regulated in HX-3 and WG-3. We proposed that the transcripts of RsDFR1, RsDFR2 and RsFLS might be act as key regulators in anthocyanin biosynthesis pathway.

Conclusions

The assembled radish transcript sequences were analysed to identify the key ABRGs involved in the regulation of anthocyanin biosynthesis. Additionally, the expression patterns of candidate ABRGs involved in the anthocyanin biosynthetic pathway were validated by qRT-PCR. We proposed that the transcripts of RsDFR1, RsDFR2 and RsFLS might be acted as key regulators in anthocyanin biosynthesis pathway. This study will enhance our understanding of the biosynthesis and metabolism of anthocyanin in radish.

Molecular cloning and functional characterization of AcGST1, an anthocyanin-related glutathione S-transferase gene in kiwifruit (Actinidia chinensis)

AcGST1, an anthocyanin-related GST, may functions as a carrier to transport anthocyanins from ER to tonoplast in kiwifruit. It was positively regulated by AcMYBF110 through directly binding to its promoter. Anthocyanins are synthesized in the cytoplasmic surface of the endoplasmic reticulum but accumulate predominantly in the vacuole. Previous studies in model and ornamental plants have suggested that a member of the glutathione S-transferase (GST) gene family is involved in sequestration of anthocyanins into the vacuole. However, little is known about anthocyanin-related GST protein in kiwifruit. Here, four putative AcGSTs were identified from the genome of the red-fleshed Actinidia chinensis cv 'Hongyang'. Expression analyses reveal only the expression of AcGST1 was highly consistent with anthocyanin accumulation. Molecular complementation of Arabidopsis tt19 demonstrates AcGST1 can complement the anthocyanin-less phenotype of tt19. Transient expression in Actinidia arguta fruits further confirms that AcGST1 is functional in anthocyanin accumulation in kiwifruit. In vitro assays show the recombinant AcGST1 increases the water solubility of cyanidin-3-O-galactoside (C3Gal) and cyanidin-3-O-xylo-galactoside (C3XG). We further show that AcGST1 protein is localized not only in the ER but also on the tonoplast, indicating AcGST1 (like AtTT19) may functions as a carrier protein to transport anthocyanins to the tonoplast in kiwifruit. Moreover, the promoter of AcGST1 can be activated by AcMYBF110, based on results from transient dual-luciferase assays and yeast one-hybrid assays. EMSAs show that AcMYBF110 binds directly to CAGTTG and CCGTTG motifs in the AcGST1 promoter. These results indicate that AcMYBF110 plays an important role in transcriptional regulation of AcGST1 and, therefore, in controlling accumulation of anthocyanins in kiwifruit.

Differential color development and response to light deprivation of fig (Ficus carica L.) syconia peel and female flower tissues: transcriptome elucidation

BACKGROUND

Color directly affects fruit quality and consumer preference. In fig syconia, the female flower tissue is contained in a receptacle. Anthocyanin pigmentation of this tissue and the peel differs temporally and spatially. A transcriptome study was carried out to elucidate key genes and transcription factors regulating differences in fig coloring.

RESULTS

Anthocyanins in the female flower tissue were identified mainly as pelargonidin-3-glucoside and cyanidin-3-rutinoside; in the peel, the major anthocyanins were cyanidin 3-O-glucoside and cyanidin-3-rutinoside. Anthocyanin content was significantly higher in the female flower tissue vs. peel before fig ripening, whereas at ripening, the anthocyanin content in the peel was 5.39 times higher than that in the female flower tissue. Light-deprivation treatment strongly inhibited peel, but not female flower tissue, anthocyanin pigmentation. RNA-Seq revealed 522 differentially expressed genes (recruited with criteria log₂ ≥ 2 and P < 0.05) at fig ripening, with 50 upregulated and 472 downregulated genes in the female flower tissue. Light deprivation upregulated 1180 and downregulated 856 genes in the peel, and upregulated 909 and downregulated 817 genes in the female flower tissue. KEGG enrichment revealed significantly changed expression in the phenylpropanoid-biosynthesis and flavonoid-biosynthesis pathways in the peel, but not in the female flower tissue, with significant repression of FcCHS, FcCHI, FcF3H, FcF3'H, FcDFR and FcUFGT transcripts. Light deprivation led to differential expression of 71 and 80 transcription factor genes in the peel and female flower tissue, respectively. Yeast one-hybrid screen revealed that FcHY5 and FcMYB114 bind the promoter regions of FcCHS and FcDFR, respectively in the flavonoid-biosynthesis pathway.

CONCLUSIONS

Phenylpropanoid- and flavonoid-biosynthesis pathways were differentially expressed spatially and temporally in the peel and female flower tissue of fig syconia; pathway expression in the peel was strongly regulated by light signal. Differentially expressed transcription factors were recruited as candidates to screen important expression regulators in the light-dependent and light-independent anthocyanin-synthesis pathway. Our study lays the groundwork for further elucidation of crucial players in fig pigmentation.

Differences among the Anthocyanin Accumulation Patterns and Related Gene Expression Levels in Red Pears

Differences in coloration exist among red pear cultivars. Here, we selected six red pear cultivars with different genetic backgrounds to elucidate the characteristics of fruit pigmentation. We detected anthocyanin contents and the expression levels of anthocyanin synthesis-related genes in these cultivars at different stages of fruit development. The anthocyanin contents of all six cultivars showed a rise-drop tendency. Principal component and hierarchical cluster analyses were used to distinguish the types of cultivars and the genes crucial to each anthocyanin accumulation pattern. The six cultivars were divided into three groups. Red Zaosu were clustered into one group, Red Sichou and Starkrimson into another group, and Palacer, Red Bartlett, and 5 Hao clustered into a third group. The expression levels of F3H, UFGT2, MYB10, and bHLH3 were similar among the differential coloration patterns of the six cultivars, suggesting a critical and coordinated mechanism for anthocyanin synthesis. Anthocyanin transporters (GST) and light-responsive genes, such as COP1, PIF3.1, and PIF3.2 played limited roles in the regulation of anthocyanin accumulation. This study provides novel insights into the regulation of anthocyanins synthesis and accumulation in red pears.

RrGT1, a key gene associated with anthocyanin biosynthesis, was isolated from Rosa rugosa and identified via overexpression and VIGS

At present, research on the flower color of Rosa rugosa requires very innovative and practical studies. Glycosylation plays an important role in increasing the stability and solubility of anthocyanins in plants. In this study, a gene with a full-length cDNA of 1161 bp encoding 386 amino acids, designated RrGT1 (MK034140), was isolated from the flowers of R. rugosa 'Zizhi' and then functionally characterized. Sequence alignment revealed that the coding regions of RrGT1 were highly specific among different species but still contained typical conserved amino acid residues that are crucial for RrGT1 enzyme activity. RrGT1 transcripts were detected in various tissues of R. rugosa 'Zizhi' and Rosa davurica, and their expression patterns corresponded with the accumulation of anthocyanins. Additionally, the in vivo function of RrGT1 was investigated via its overexpression in Arabidopsis thaliana. Transgenic Arabidopsis plants expressing RrGT1 regained red color pigmentation of their leaves and flower stems, indicating that RrGT1 could encode a functional glycosyltransferase (GT) protein for anthocyanin biosynthesis and could function in other species. The functional verification of RrGT1 for anthocyanin biosynthesis in R. rugosa was performed via virus-induced gene silencing (VIGS). This was the first time that a VIGS system was developed for use with perennial Rosa plants grown naturally in the field as experimental materials to study a key color-controlling gene in Rosa. When the RrGT1 gene was silenced, the Rosa plants displayed a pale petal color phenotype. The detection results showed that the expression of the endogenous RrGT1 gene was significantly downregulated while the six key structural genes in its upstream were normally expressed, and the contents of all anthocyanins also decreased significantly. Therefore, we speculated that glycosylation of RrGT1 plays a crucial role in anthocyanin biosynthesis in R. rugosa.

Anthocyanin accumulation and biosynthesis are modulated by regulated deficit irrigation in Cabernet Sauvignon (Vitis Vinifera L.) grapes and wines

Anthocyanins contents and compositions play an important role in grape berries and wines. Grapevines are widely cultivated in arid and semi-arid areas, and water shortage restricts the development of wine industry. The aim of this work was to gain insight on the effect of regulated deficit irrigation (RDI) on the accumulation and biosynthesis of anthocyanins in Cabernet Sauvignon (Vitis Vinifera L.) grapes and wines. High-performance liquid chromatography (HPLC) was used for anthocyanins profiles analyses and real-time quantitative PCR (qRT-PCR) was used for the genes expressions measurement. The grapevines were treated with 60% (RDI-1), 70% (RDI-2), 80% (RDI-3), 100% (CK, traditional drip irrigation) of their estimated evapotranspiration (ETc) respectively. RDI treatments significantly reduced titration acid and increased pH with higher total soluble solids. RDI-1 treatment increased total anthocyanins contents in berries and wines in both two vintages. RDI-1 and RDI-2 treatments significantly increased the contents of acylated anthocyanins in berries and wines, especially Malvidin-3-acetly-glucoside. RDI treatments significantly increased non-acylated anthocyanins contents in wines, such as Delphinidin-3-gliucoside and Malvidin-3-glucoside. RDI treatments upregulated the expressions of VvPAL, VvC4H, VvCHS, VvF3'H, VvF3'5'H, VvLDOX, and VvOMT in both two vintages. Correlation analysis showed the accumulation of anthocyanins was closely related to the key genes expressions, including VvPAL, VvF3'H, VvF3'5'H etc. The present results provided direct evidence and detailed data to explain that RDI treatments regulated the accumulation of anthocyanins by regulating genes expressions in the anthocyanin synthesis pathway.

RrGT2, A Key Gene Associated with Anthocyanin Biosynthesis in Rosa rugosa, Was Identified Via Virus-Induced Gene Silencing and Overexpression

In this study, a gene with a full-length cDNA of 1422 bp encoding 473 amino acids, designated RrGT2, was isolated from R. rugosa 'Zizhi' and then functionally characterized. RrGT2 transcripts were detected in various tissues and were proved that their expression patterns corresponded with anthocyanins accumulation. Functional verification of RrGT2 in R. rugosa was performed via VIGS. When RrGT2 was silenced, the Rosa plants displayed a pale petal color phenotype. The detection results showed that the expression of RrGT2 was significantly downregulated, which was consistent with the decrease of all anthocyanins; while the expression of six key upstream structural genes was normal. Additionally, the in vivo function of RrGT2 was investigated via its overexpression in tobacco. In transgenic tobacco plants expressing RrGT2, anthocyanin accumulation was induced in the flowers, indicating that RrGT2 could encode a functional GT protein for anthocyanin biosynthesis and could function in other species. The application of VIGS in transgenic tobacco resulted in the treated tobacco plants presenting flowers whose phenotypes were lighter in color than those of normal plants. These results also validated and affirmed previous conclusions. Therefore, we speculated that glycosylation of RrGT2 plays a crucial role in anthocyanin biosynthesis in R. rugosa.