Blue flower color development by anthocyanins: from chemical structure to cell physiology

Metabolomic analysis combined with machine learning algorithms enables the evaluation of postharvest pecan color stability

Nut kernel color is a crucial quality indicator affecting the consumers first impression of the product. While growing evidence suggests that plant phenolics and their derivatives are linked to nut kernel color, the compounds (biomarkers) responsible for kernel color stability during storage remain elusive. Here, pathway-based metabolomics with machine learning algorithms were employed to identify key metabolites of postharvest pecan color stability. Metabolites in phenylpropanoid, flavonoid, and anthocyanin biosynthetic pathways were analyzed in the testa of nine pecan cultivars using liquid chromatography-mass spectrometry. With color measurements, different machine learning models were compared to find relevant biomarkers of pecan color phenotypes. Results revealed potential marker compounds that included flavonoid precursors and anthocyanidins as well as anthocyanins (e.g., peonidin, delphinidin-3-O-glucoside). Our findings provide a foundation for future research in the area, and will help select genes/proteins for the breeding of pecans with stable and desirable kernel color.

Anthocyanin glucosylation mediated by a glycoside hydrolase family 3 protein in purple carrot

Purple carrot accumulates anthocyanins modified with galactose, xylose, glucose, and sinapic acid. Most of the genes associated with anthocyanin biosynthesis have been identified, except for the glucosyltransferase genes involved in the step before the acylation in purple carrot. Anthocyanins are commonly glycosylated in reactions catalyzed by UDP-sugar-dependent glycosyltransferases (UGTs). Although many studies have been conducted on UGTs, the glucosylation of carrot anthocyanins remains unknown. Acyl-glucose-dependent glucosyltransferase activity modifying cyanidin 3-xylosylgalactoside was detected in the crude protein extract prepared from purple carrot cultured cells. In addition, the corresponding enzyme was purified. The cDNA encoding this glucosyltransferase was isolated based on the partial amino acid sequence of the purified protein. The recombinant protein produced in Nicotiana benthamiana leaves via agroinfiltration exhibited anthocyanin glucosyltransferase activity. This glucosyltransferase belongs to the glycoside hydrolase family 3 (GH3). The expression pattern of the gene encoding this GH3-type anthocyanin glucosyltransferase was consistent with anthocyanin accumulation in carrot tissues and cultured cells.

Incorporating ions during thermal processing tailors the microstructure and practical features of rice starch/anthocyanin binary system

Understanding the interplay among salt ions, anthocyanin and starch within food matrices under thermal conditions is important for the development of starch-based foods with demanded quality attributes. However, how salt ions presence influences the microstructure and properties of starch/anthocyanin binary system remains largely unclear. Herein, indica rice starch (IRS) and rice anthocyanin (RA) were used to construct an IRS-RA binary system, with thermal treatment under different concentrations of Na+ (10-40 mM) and types of salt ions (Na+ and Ca2+). The incorporation of salt ions induced the formation of a porous gel matrix, and destroyed the hydrogen bond between starch and anthocyanin through electrostatic interactions, reducing the storage modulus and radius of gyration of the binary system, and increasing the relative crystallinity (from 1.08 % to 1.51 % (20 mM Na+) and 1.69 % (20 mM Ca+)) of the IRS-RA binary system at 90 °C. Also, the DPPH radical scavenging ability of the binary system at 90 °C was enhanced upon incorporating salt ions (0.93 for Na+ condition and 0.94 for Ca2+ condition at 20 mM ion concentration). It is noteworthy that Ca2+ inclusion had more significant effects than the case for Na+ presence, presumably due to the increased charge density.

Chemical and biological study of flavonoid-related plant pigment: current findings and beyond

Flavonoids are polyphenolic plant constituents. Anthocyanins are flavonoid pigments found in higher plants that show a wide variety of colors ranging from red through purple to blue. The blue color of the flowers is mostly attributed to anthocyanins. However, only a few types of anthocyanidin, chromophore of anthocyanin, exist in nature, and the extracted pigments are unstable with the color fading away. Therefore, the wide range and stable nature of colors in flowers have remained a mystery for more than a century. The mechanism underlying anthocyanin-induced flower coloration was studied using an interdisciplinary method involving chemistry and biology. Furthermore, the chemical studies on flavonoid pigments in various edible plants, synthetic and biosynthetic studies on anthocyanins were conducted. The results of these studies have been outlined in this review.

Extraction and characterization of anthocyanin pigments from Iris flowers and metal complex formation

Exploring the chemical processes and factors influencing the stability of the blue color derived from anthocyanins is a crucial objective in agricultural and food chemistry research. The ability of these compounds to bind with metals could potentially stabilize anthocyanins extracted from plant-based foods or enable modifying their hues for application as natural food colorants. This study had two core objectives - first, to extract and identify the major anthocyanin pigments responsible for iris flower coloration. Second, to selectively complex purified iris anthocyanins with aluminum (Al3+) and copper (Cu2+) ions, probing the coordination chemistry underlying synthetic metalloanthocyanin formation. Fresh iris flowers were collected and anthocyanins extracted using an optimized acidic solution. After separation, anthocyanins were complexed with metals Al3+ and Cu2+ at pH 5-6 to understand better the evolution of blue and green colors in anthocyanin-metal chelates. Characterization of anthocyanins and their metal complexes utilized UV-visible spectrometry, colorimetry (L\* a\*b\* values), FTIR spectroscopy, and LC-MS. Metal complexation of anthocyanins exhibited bathochromic shifts of visible absorption maxima from 538 to 584 nm for Al-complex and 538-700 nm for Cu-complex. Color changes were accompanied by decreased lightness (L\*, from 87 to 81) and color coefficients a\* (+5.4 to -6.8) and b\* (-12.2 to -4.8). LC-MS analysis identified five major anthocyanin aglycones: cyanidin (Cyd, m/z 289), delphinidin (Dpd, m/z 305), petunidin (Ptd, m/z 229), malvidin (Mv, m/z 329) and pelargonidin (m/z 273), along with various glycosylated derivatives. This work successfully isolated key iris anthocyanin pigments and elucidated their metal chelation interactions underlying expanded floral color production, bridging knowledge gaps about this underexplored genus.

Anthocyanins as Natural Food Colorings: The Chemistry Behind and Challenges Still Ahead

Anthocyanins are polyphenolic O-glycosides widely responsible for the bright red, purple, and blue colors in the plant kingdom, including a great variety of fruits and vegetables. Hence, they have attracted considerable scientific and industrial interest as potential natural food colorings. However, individual anthocyanins are intrinsically reactive molecules combining electrophilic, nucleophilic, and electron-donating properties. This reactivity may be not only a source of color diversity with, for instance, the formation of new pigments upon winemaking and storage but also a cause of great color instability involving a combination of reversible and irreversible mechanisms (e.g., water addition, autoxidation) leading to colorless products. Hence, using anthocyanin-rich plant extracts as food colorings requires a deep understanding of these color-damaging mechanisms and, no less importantly, of the color-stabilizing mechanisms developed by plants, including π-stacking interactions (self-association, copigmentation), metal binding, and a combination of both. The potential of anthocyanins from deeply colored vegetables, typically acylated by hydroxycinnamic acid residues, will be emphasized in that respect. Moreover, food-grade biopolymers (proteins, polysaccharides) may provide suitable matrices for ready-to-use formulations of anthocyanins as food colorings. In this short review, the mechanisms of color loss and color stabilization are discussed as a function of anthocyanin structure and environment, and some challenges still ahead are outlined.

The road less taken: Dihydroflavonol 4-reductase inactivation and delphinidin anthocyanin loss underpins a natural intraspecific flower colour variation

Visual cues are of critical importance for the attraction of animal pollinators, however, little is known about the molecular mechanisms underpinning intraspecific floral colour variation. Here, we combined comparative spectral analysis, targeted metabolite profiling, multi-tissue transcriptomics, differential gene expression, sequence analysis and functional analysis to investigate a bee-pollinated orchid species, Glossodia major with common purple- and infrequent white-flowered morphs. We found uncommon and previously unreported delphinidin-based anthocyanins responsible for the conspicuous and pollinator-perceivable colour of the purple morph and three genetic changes underpinning the loss of colour in the white morph - (1) a loss-of-function (LOF; frameshift) mutation affecting dihydroflavonol 4-reductase (DFR1) coding sequence due to a unique 4-bp insertion, (2) specific downregulation of functional DFR1 expression and (3) the unexpected discovery of chimeric Gypsy transposable element (TE)-gene (DFR) transcripts with potential consequences to the genomic stability and post-transcriptional or epigenetic regulation of DFR. This is one of few known cases where regulatory changes and LOF mutation in an anthocyanin structural gene, rather than transcription factors, are important. Furthermore, if TEs prove to be a frequent source of mutation, the interplay between environmental stress-induced TE evolution and pollinator-mediated selection for adaptive colour variation may be an overlooked mechanism maintaining floral colour polymorphism in nature.

Effects of Red Sorghum-Derived Deoxyanthocyanidins and Their O-β-D-Glucosides on E-Cadherin Promoter Activity in PC-3 Prostate Cancer Cells

Although much less common than anthocyanins, 3-Deoxyanthocyanidins (3-DAs) and their glucosides can be found in cereals such as red sorghum. It is speculated that their bioavailability is higher than that of anthocyanins. Thus far, little is known regarding the therapeutic effects of 3-DAs and their O-β-D-glucosides on cancer, including prostate cancer. Thus, we evaluated their potential to decrease cell viability, to modulate the activity of transcription factors such as NFκB, CREB, and SOX, and to regulate the expression of the gene CDH1, encoding E-Cadherin. We found that 4',7-dihydroxyflavylium chloride (P7) and the natural apigeninidin can reduce cell viability, whereas 4',7-dihydroxyflavylium chloride (P7) and 4'-hydroxy-7-O-β-D-glucopyranosyloxyflavylium chloride (P3) increase the activities of NFkB, CREB, and SOX transcription factors, leading to the upregulation of CDH1 promoter activity in PC-3 prostate cancer cells. Thus, these compounds may contribute to the inhibition of the epithelial-to-mesenchymal transition in cancer cells and prevent the metastatic activity of more aggressive forms of androgen-resistant prostate cancer.

The R2R3-MYB transcription factor ZeMYB32 negatively regulates anthocyanin biosynthesis in Zinnia elegans

KEY MESSAGE

This study identified an R2R3-MYB from Zinnia elegans, ZeMYB32, which negatively regulates anthocyanin biosynthesis.

Molecular basis of ligand recognition specificity of flavone glucosyltransferases in Nemophila menziesii

Of the more than 100 families of glycosyltransferases, family 1 glycosyltransferases catalyze glycosylation using uridine diphosphate (UDP)-sugar as a sugar donor and are thus referred to as UDP-sugar:glycosyl transferases. The blue color of the Nemophila menziesii flower is derived from metalloanthocyanin, which consists of anthocyanin, flavone, and metal ions. Flavone 7-O-β-glucoside-4'-O-β-glucoside in the plant is sequentially biosynthesized from flavons by UDP-glucose:flavone 4'-O-glucosyltransferase (NmF4'GT) and UDP-glucose:flavone 4'-O-glucoside 7-O-glucosyltransferase (NmF4'G7GT). To identify the molecular mechanisms of glucosylation of flavone, the crystal structures of NmF4'G7GT in its apo form and in complex with UDP-glucose or luteolin were determined, and molecular structure prediction using AlphaFold2 was conducted for NmF4'GT. The crystal structures revealed that the size of the ligand-binding pocket and interaction environment for the glucose moiety at the pocket entrance plays a critical role in the substrate preference in NmF4'G7GT. The substrate specificity of NmF4'GT was examined by comparing its model structure with that of NmF4'G7GT. The structure of NmF4'GT may have a smaller acceptor pocket, leading to a substrate preference for non-glucosylated flavones (or flavone aglycones).

Metal-free production of natural blue colorants through anthocyanin-protein interactions

INTRODUCTION

The scarcity of naturally available sources for blue colorants has driven reliance on synthetic alternatives. Nevertheless, growing health concerns have prompted the development of naturally derived blue colorants, which remains challenging with limited success thus far. Anthocyanins (ACNs) are known for providing blue colors in plants, and metal complexation with acylated ACNs remains the primary strategy to generate stable blue hues. However, this approach can be costly and raise concerns regarding potential metal consumption risks.

OBJECTIVES

Our study aims to introduce a metal-free approach to achieve blue coloration in commonly distributed non-acylated 3-glucoside ACNs by exploring their interactions with proteins and unveiling the underlying mechanisms.

METHODS

Using human serum albumin (HSA) as a model protein, we investigated the structural influences of ACNs on their blue color generation using visible absorption spectroscopy, fluorescence quenching, and molecular simulations. Additionally, we examined the bluing effects of six proteins derived from milk and egg and identified the remarkable roles of bovine serum albumin (BSA) and lysozyme (LYS).

RESULTS

Our findings highlighted the importance of two or more hydroxyl or methoxyl substituents in the B-ring of ACNs for generating blue colors. Cyanidin-, delphinidin- and petunidin-3-glucoside, featuring two neighboring hydroxyl groups in the B-ring, exhibited blue coloration when interacting with HSA or LYS, driven primarily by favorable enthalpy changes. In contrast, malvidin-3-glucoside, with two methoxyl substituents, achieved blue coloration through interactions with HSA or BSA, where entropy change played significant roles.

CONCLUSION

Our work, for the first time, demonstrates the remarkable capability of widely distributed 3-glucoside ACNs to generate diverse blue shades through interactions with certain proteins. This offers a promising and straightforward strategy for the production of ACN-based blue colorants, stimulating further research in this field.

IbMYC2 Contributes to Salt and Drought Stress Tolerance via Modulating Anthocyanin Accumulation and ROS-Scavenging System in Sweet Potato

Basic helix-loop-helix (bHLH) transcription factors extensively affect various physiological processes in plant metabolism, growth, and abiotic stress. However, the regulation mechanism of bHLH transcription factors in balancing anthocyanin biosynthesis and abiotic stress in sweet potato (Ipomoea batata (L.) Lam.) remains unclear. Previously, transcriptome analysis revealed the genes that were differentially expressed among the purple-fleshed sweet potato cultivar 'Jingshu 6' and its anthocyanin-rich mutant 'JS6-5'. Here, we selected one of these potential genes, IbMYC2, which belongs to the bHLH transcription factor family, for subsequent analyses. The expression of IbMYC2 in the JS6-5 storage roots is almost four-fold higher than Jingshu 6 and significantly induced by hydrogen peroxide (H2O2), methyl jasmonate (MeJA), NaCl, and polyethylene glycol (PEG)6000. Overexpression of IbMYC2 significantly enhances anthocyanin production and exhibits a certain antioxidant capacity, thereby improving salt and drought tolerance. In contrast, reducing IbMYC2 expression increases its susceptibility. Our data showed that IbMYC2 could elevate the expression of anthocyanin synthesis pathway genes by binding to IbCHI and IbDFR promoters. Additionally, overexpressing IbMYC2 activates genes encoding reactive oxygen species (ROS)-scavenging and proline synthesis enzymes under salt and drought conditions. Taken together, these results demonstrate that the IbMYC2 gene exercises a significant impact on crop quality and stress resistance.

Exploring the molecular mechanism of coloration differences in two Meconopsis wilsonii subspecies: australis and orientalis

Flower color diversity is a key taxonomic trait in Meconopsis species, enhancing their appeal as ornamental flowers. However, knowledge of the molecular mechanisms of flower color formation in Meconopsis species is still limited. M. wilsonii subsp. australis (Australis) and M. wilsonii subsp. orientalis (Orientalis) have a developmental stage presenting red-purple flowers, while Orientalis also presents blue coloration at the full-bloom period, making them an important model for exploring the mechanism of blue flower formation in M. wilsonii. In this study, we collected petals from Australis and Orientalis at different developmental stages to compare the coloration differences between the two species and detect the molecular mechanisms of blue color in Orientalis. We identified that cyanidin was the main anthocyanin in the flowers of both species, and the blue color in Orientalis primarily arises from anthocyanins (Cyanidin-3-O-sambubioside). RNA sequencing analysis was performed to detect the gene expression in the anthocyanin biosynthesis pathway, and the results suggested that gene regulation for anthocyanin biosynthesis may not be the direct reason for blue color formation in Orientalis. In addition, the growth solid of Orientalis was rich in Fe and Mg ions, and a large amount of Fe and Mg ions accumulated in the petals of Orientalis. Combined with the gene functional enrichment results, we found that the purple and red-purple colors of these two species were presented by different glycosylation levels of cyanidin, while the violet color of Orientalis might be the results of metalloanthocyanins by Fe and Mg ions, which also relieved the toxicity caused by the high content of Fe and Mg ions in its cells. The environmental adaptation-related genes were highly expressed of in both species, such as adaptation to desiccation, water deprivation, freezing, etc. Our results revealed the coloration differences between Australis and Orientalis and described the molecular mechanisms of blue coloration in Orientalis. The data in our analysis could enrich the genetic resources for M. wilsonii for further studies.

Theoretical Study on the Multiple Free Radical Scavenging Reactions of Pyranoanthocyanins

The free radical trapping capacities of multiple pyranoanthocyanins in wine storage and ageing were theoretically explored by density functional theory (DFT) methods. Intramolecular hydrogen bonds were detected in all pyranoanthocyanins, and the planarity of the compounds worsened with an increasing dielectric constant in the environment. Solvents significantly influenced the reaction enthalpies; thus, the preferred thermodynamic mechanisms of the free radical scavenging reactions were modified in different phases. This study incorporates hydrogen atom transfer (HAT), proton loss (PL), electron transfer (ET) reactions, and demethylation (De) of methoxy group mechanisms. The three pyranoanthocyanins have the capacity to capture n1+1 free radicals, where n1 represents the number of methoxy groups. In the gas phase, they prefer employing the n1-De-HAT mechanism on the guaiacyl moiety of the B ring, resulting in the formation of a stable quinone or a quinone radical to scavenge free radicals. In the benzene phase, pyranoanthocyanins trap free radicals via a PL-n1-De-HAT mechanism. In the water phase, the targeted pyranoanthocyanins may dissociate in the form of carboxylate and tend to utilize the n2-PL-n1-De-ET mechanism, where n2 and n1 represent the number of phenolic groups and methoxy groups, respectively, facilitating multiple H+/e- reactions.

Association Analysis of Transcriptome and Targeted Metabolites Identifies Key Genes Involved in Iris germanica Anthocyanin Biosynthesis

The anthocyanin biosynthetic pathway is the main pathway regulating floral coloration in Iris germanica, a well-known ornamental plant. We investigated the transcriptome profiles and targeted metabolites to elucidate the relationship between genes and metabolites in anthocyanin biosynthesis in the bitone flower cultivar 'Clarence', which has a deep blue outer perianth and nearly white inner perianth. In this study, delphinidin-, pelargonidin-, and cyanidin-based anthocyanins were detected in the flowers. The content of delphinidin-based anthocyanins increased with the development of the flower. At full bloom (stage 3), delphinidin-based anthocyanins accounted for most of the total anthocyanin metabolites, whereas the content of pelargonidin- and cyanidin-based anthocyanins was relatively low. Based on functional annotations, a number of novel genes in the anthocyanin pathway were identified, which included early biosynthetic genes IgCHS, IgCHI, and IgF3H and late biosynthetic genes Ig F3'5'H, IgANS, and IgDFR. The expression of key structural genes encoding enzymes, such as IgF3H, Ig F3'5'H, IgANS, and IgDFR, was significantly upregulated in the outer perianth compared to the inner perianth. In addition, most structural genes exhibited their highest expression at the half-color stage rather than at the full-bloom stage, which indicates that these genes function ahead of anthocyanins synthesis. Moreover, transcription factors (TFs) of plant R2R3-myeloblastosis (R2R3-MYB) related to the regulation of anthocyanin biosynthesis were identified. Among 56 R2R3-MYB genes, 2 members belonged to subgroup 4, with them regulating the expression of late biosynthetic genes in the anthocyanin biosynthetic pathway, and 4 members belonged to subgroup 7, with them regulating the expression of early biosynthetic genes in the anthocyanin biosynthetic pathway. Quantitative real-time PCR (qRT-PCR) analysis was used to validate the data of RNA sequencing (RNA-Seq). The relative expression profiles of most candidate genes were consistent with the FPKM of RNA-seq. This study identified the key structural genes encoding enzymes and TFs that affect anthocyanin biosynthesis, which provides a basis and reference for the regulation of plant anthocyanin biosynthesis in I. germanica.

Systematic identification of reference genes for qRT-PCR of Ardisia kteniophylla A. DC under different experimental conditions and for anthocyanin-related genes studies

Ardisia kteniophylla A. DC, widely known as folk medicinal herb and ornamental plant, has been extensively investigated due to its unique leaf color, anti-cancer and other pharmacological activities. The quantitative real-time PCR (qRT-PCR) was an excellent tool for the analysis of gene expression with its high sensitivity and quantitative properties. Normalizing gene expression with stable reference genes was essential for qRT-PCR accuracy. In addition, no studies have yet been performed on the selection, verification and stability of internal reference genes suitable for A. kteniophylla, which has greatly hindered the biomolecular researches of this species. In this study, 29 candidate genes were successfully screened according to stable expression patterns of large-scale RNA seq data that from a variety of tissues and the roots of different growth stages in A. kteniophylla. The candidates were then further determined via qRT-PCR in various experimental samples, including MeJA, ABA, SA, NaCl, CuSO4, AgNO3, MnSO4, CoCl2, drought, low temperature, heat, waterlogging, wounding and oxidative stress. To assess the stability of the candidates, five commonly used strategies were employed: delta-CT, geNorm, BestKeeper, NormFinder, and the comprehensive tool RefFinder. In summary, UBC2 and UBA1 were found to be effective in accurately normalizing target gene expression in A. kteniophella regardless of experimental conditions, while PP2A-2 had the lowest stability. Additionally, to verify the reliability of the recommended reference genes under different colored leaf samples, we examined the expression patterns of six genes associated with anthocyanin synthesis and regulation. Our findings suggested that PAP1 and ANS3 may be involved in leaf color change in A. kteniphella. This study successfully identified the ideal reference gene for qRT-PCR analysis in A. kteniphella, providing a foundation for future research on gene function, particularly in the biosynthesis of anthocyanins.

Heterologous Expression of Platycodon grandiflorus PgF3'5'H Modifies Flower Color Pigmentation in Tobacco

Flavonoid-3',5'-hydroxylase (F3'5'H) is the key enzyme for the biosynthesis of delphinidin-based anthocyanins, which are generally required for purple or blue flowers. Previously, we isolated a full-length cDNA of PgF3'5'H from Platycodon grandiflorus, which shared the highest homology with Campanula medium F3'5'H. In this study, PgF3'5'H was subcloned into a plant over-expression vector and transformed into tobacco via Agrobacterium tumefaciens to investigate its catalytic function. Positive transgenic tobacco T0 plants were obtained by hygromycin resistance screening and PCR detection. PgF3'5'H showed a higher expression level in all PgF3'5'H transgenic tobacco plants than in control plants. Under the drive of the cauliflower mosaic virus (CaMV) 35S promoter, the over-expressed PgF3'5'H produced dihydromyricetin (DHM) and some new anthocyanin pigments (including delphinidin, petunidin, peonidin, and malvidin derivatives), and increased dihydrokaempferol (DHK), taxifolin, tridactyl, cyanidin derivatives, and pelargonidin derivatives in PgF3'5'H transgenic tobacco plants by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis, resulting in a dramatic color alteration from light pink to magenta. These results indicate that PgF3'5'H products have F3'5'H enzyme activity. In addition, PgF3'5'H transfer alters flavonoid pigment synthesis and accumulation in tobacco. Thus, PgF3'5'H may be considered a candidate gene for gene engineering to enhance anthocyanin accumulation and the molecular breeding project for blue flowers.

Research Progress on Anthocyanin-Mediated Regulation of 'Black' Phenotypes of Plant Organs

The color pattern is one of the most important characteristics of plants. Black stands out among the vibrant colors due to its rare and distinctive nature. While some plant organs appear black, they are, in fact, dark purple. Anthocyanins are the key compounds responsible for the diverse hues in plant organs. Cyanidin plays an important role in the deposition of black pigments in various plant organs, such as flower, leaf, and fruit. A number of structural genes and transcription factors are involved in the metabolism of anthocyanins in black organs. It has been shown that the high expression of R2R3-MYB transcription factors, such as PeMYB7, PeMYB11, and CsMYB90, regulates black pigmentation in plants. This review provides a comprehensive overview of the anthocyanin pathways that are involved in the regulation of black pigments in plant organs, including flower, leaf, and fruit. It is a great starting point for further investigation into the molecular regulation mechanism of plant color and the development of novel cultivars with black plant organs.

Transcription and Metabolic Profiling Analysis of Three Discolorations in a Day of Hibiscus mutabilis

In this study, we used combined transcriptomics and metabolomics to analyze the H. mutabilis cultivar's genetic and physiological mechanisms during three flower color transition periods (from white to pink, then from pink to red) within the span of one day. As a result, 186 genes were found to be significantly increased with the deepening of the H. mutabilis flower color; these genes were mainly involved in the expression of peroxidase 30, zinc finger protein, phosphate transporter PHO1, etc. In contrast, 298 genes were significantly downregulated with the deepening of H. mutabilis flower color, including those involved in the expression of probable O-methyltransferase 3, copper binding protein 9, and heat stress transcription factor A-6b. Some genes showed differential expression strategies as the flower color gradually darkened. We further detected 19 metabolites that gradually increased with the deepening of the H. mutabilis flower color, including L-isoleucine, palmitic acid, L-methionine, and (+)-7-isonitrobenzene. The content of the metabolite hexadecanedioate decreased with the deepening of the H. mutabilis flower color. Combined transcriptomics and metabolomics revealed that the metabolic pathways, including those related to anthocyanin biosynthesis, cysteine and methionine metabolism, and sulfur metabolism, appear to be closely related to H. mutabilis flower color transition. This study served as the first report on the genetic and physiological mechanisms of short-term H. mutabilis flower color transition and will promote the molecular breeding of ornamental cultivars of H. mutabilis.

A Review of the Chemistry and Biological Activities of Natural Colorants, Dyes, and Pigments: Challenges, and Opportunities for Food, Cosmetics, and Pharmaceutical Application

Natural pigments are important sources for the screening of bioactive lead compounds. This article reviewed the chemistry and therapeutic potentials of over 570 colored molecules from plants, fungi, bacteria, insects, algae, and marine sources. Moreover, related biological activities, advanced extraction, and identification approaches were reviewed. A variety of biological activities, including cytotoxicity against cancer cells, antioxidant, anti-inflammatory, wound healing, anti-microbial, antiviral, and anti-protozoal activities, have been reported for different pigments. Considering their structural backbone, they were classified as naphthoquinones, carotenoids, flavonoids, xanthones, anthocyanins, benzotropolones, alkaloids, terpenoids, isoprenoids, and non-isoprenoids. Alkaloid pigments were mostly isolated from bacteria and marine sources, while flavonoids were mostly found in plants and mushrooms. Colored quinones and xanthones were mostly extracted from plants and fungi, while colored polyketides and terpenoids are often found in marine sources and fungi. Carotenoids are mostly distributed among bacteria, followed by fungi and plants. The pigments isolated from insects have different structures, but among them, carotenoids and quinone/xanthone are the most important. Considering good manufacturing practices, the current permitted natural colorants are: Carotenoids (canthaxanthin, β-carotene, β-apo-8'-carotenal, annatto, astaxanthin) and their sources, lycopene, anthocyanins, betanin, chlorophyllins, spirulina extract, carmine and cochineal extract, henna, riboflavin, pyrogallol, logwood extract, guaiazulene, turmeric, and soy leghemoglobin.

Progress on molecular modification and functional applications of anthocyanins

Anthocyanins have attracted a lot of attention in the fields of natural pigments, food packaging, and functional foods due to their color, antioxidant, and nutraceutical properties. However, the poor chemical stability and low bioavailability of anthocyanins currently limit their application in the food industry. Various methods can be used to modify the structure of anthocyanins and thus improve their stability and bioavailability characteristics under food processing, storage, and gastrointestinal conditions. This paper aims to review in vitro modification methods for altering the molecular structure of anthocyanins, as well as their resulting improved properties such as color, stability, solubility, and antioxidant properties, and functional applications as pigments, sensors and functional foods. In industrial production, by mixing co-pigments with anthocyanins in food systems, the color and stability of anthocyanins can be improved by using non-covalent co-pigmentation. By acylation of fatty acids and aromatic acids with anthocyanins before incorporation into food systems, the surface activity of anthocyanins can be activated and their antioxidant and bioactivity can be improved. Various other chemical modification methods, such as methylation, glycosylation, and the formation of pyranoanthocyanins, can also be utilized to tailor the molecular properties of anthocyanins expanding their range of applications in the food industry.

Interactions of Natural Flavones with Iron Are Affected by 7-O-Glycosylation, but Not by Additional 6″-O-Acylation

In iron-fortified bouillon, reactivity of the iron ion with (acylated) flavone glycosides from herbs can affect product color and bioavailability of iron. This study investigates the influence of 7-O-glycosylation and additional 6″-O-acetylation or 6″-O-malonylation of flavones on their interaction with iron. Nine (6″-O-acylated) flavone 7-O-apiosylglucosides were purified from celery (Apium graveolens), and their structures were elucidated by mass spectrometry (MS) and nuclear magnetic resonance (NMR). In the presence of iron, a bathochromic shift and darker color were observed for the 7-O-apiosylglucosides compared to the aglycon of flavones that only possess the 4-5 site. Thus, the ability of iron to coordinate to the flavone 4-5 site is increased by 7-O-glycosylation. For flavones with an additional 3'-4' site, less discoloration was observed for the 7-O-apiosylglucoside compared to the aglycon. Additional 6″-O-acylation did not affect the color. These findings indicate that model systems used to study discoloration in iron-fortified foods should also comprise (acylated) glycosides of flavonoids.

An Update on the Use of Natural Pigments and Pigment Nanoparticle Adducts for Metal Detection Based on Colour Response

Natural pigments occur in plants as secondary metabolites and have been used as safe colourants in food. Studies have reported that their unstable colour intensity might be related to metal ion interaction, which leads to the formation of metal-pigment complexes. This underlines the need for further investigations on the use of natural pigments in metal detection using colorimetric methods, since metals are important elements and can be hazardous when present in large amounts. This review aimed to discuss the use of natural pigments (mainly betalains, anthocyanins, curcuminoids, carotenoids, and chlorophyll) as reagents for portable metal detection based on their limits of detection, to determine which pigment is best for certain metals. Colorimetric-related articles over the last decade were gathered, including those involving methodological modifications, sensor developments, and a general overview. When considering sensitivity and portability, the results revealed that betalains are best applied for copper, using a smartphone-assisted sensor; curcuminoids are best applied for lead, using a curcumin nanofiber; and anthocyanin is best applied for mercury, using anthocyanin hydrogel. This provides a new perspective on the use of colour instability for the detection of metals with modern sensor developments. In addition, a coloured sheet representing metal concentrations may be useful as a standard to support on-site detection with trials on masking agents to improve selectivity.

Anthocyanin metabolic engineering of Euphorbia pulcherrima: advances and perspectives

The range of floral colors is determined by the type of plant pigment accumulated by the plant. Anthocyanins are the most common flavonoid pigments in angiosperms; they provide a wide range of visible colors from red-magenta to blue-purple, products of cyanidin and delphinidin biosynthesis, respectively. For the floriculture industry, floral color is one of the most important ornamental characteristics for the development of new commercial varieties; however, most plant species are restricted to a certain color spectrum, limited by their own genetics. In fact, many ornamental crops lack bluish varieties due to the lack of activity of essential biosynthetic enzymes for the accumulation of delphinidin. An example is the poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch), the ornamental plant symbol of Christmas and native to Mexico. Its popularity is the result of the variety of colors displayed by its bracts, a kind of modified leaves that accumulate reddish pigments based mainly on cyanidin and, to a lesser extent, on pelargonidin. The commercial success of this plant lies in the development of new varieties and, although consumers like the typical red color, they are also looking for poinsettias with new and innovative colors. Previous research has demonstrated the possibility of manipulating flower color through metabolic engineering of the anthocyanin biosynthesis pathway and plant tissue culture in different ornamental plant species. For example, transgenic cultivars of flowers such as roses, carnations or chrysanthemums owe their attractive bluish colors to a high and exclusive accumulation of delphinidin. Here, we discuss the possibilities of genetic engineering of the anthocyanin biosynthetic pathway in E. pulcherrima through the introduction of one or more foreign delphinidin biosynthetic genes under the transcriptional control of a pathway-specific promoter, and the genome editing possibilities as an alternative tool to modify the color of the bracts. In addition, some other approaches such as the appropriate selection of the cultivars that presented the most suitable intracellular conditions to accumulate delphinidin, as well as the incorporation of genes encoding anthocyanin-modifying enzymes or transcription factors to favor the bluish pigmentation of the flowers are also revised.

Genome-wide identification and bioinformatics analysis of the WRKY transcription factors and screening of candidate genes for anthocyanin biosynthesis in azalea (Rhododendron simsii)

WRKY transcription factors have been demonstrated to influence the anthocyanin biosynthesis in many plant species. However, there is limited knowledge about the structure and function of WRKY genes in the major ornamental plant azalea (Rhododendron simsii). In this study, we identified 57 RsWRKY genes in the R. simsii genome and classified them into three main groups and several subgroups based on their structural and phylogenetic characteristics. Comparative genomic analysis suggested WRKY gene family has significantly expanded during plant evolution from lower to higher species. Gene duplication analysis indicated that the expansion of the RsWRKY gene family was primarily due to whole-genome duplication (WGD). Additionally, selective pressure analysis (Ka/Ks) suggested that all RsWRKY duplication gene pairs underwent purifying selection. Synteny analysis indicated that 63 and 24 pairs of RsWRKY genes were orthologous to Arabidopsis thaliana and Oryza sativa, respectively. Furthermore, RNA-seq data was used to investigate the expression patterns of RsWRKYs, revealing that 17 and 9 candidate genes may be associated with anthocyanin synthesis at the bud and full bloom stages, respectively. These findings provide valuable insights into the molecular mechanisms underlying anthocyanin biosynthesis in Rhododendron species and lay the foundation for future functional studies of WRKY genes.

Flavonoid Synthesis-Related Genes Determine the Color of Flower Petals in Brassica napus L

The color of rapeseed (Brassica napus L.) petal is usually yellow but can be milky-white to orange or pink. Thus, the petal color is a popular target in rapeseed breeding programs. In his study, metabolites and RNA were extracted from the yellow (Y), yellow/purple (YP), light purple (LP), and purple (P) rapeseed petals. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), RNA-Seq, and quantitative real-time (qRT-PCR) analyses were performed to analyze the expression correlation of differential metabolites and differential genes. A total of 223 metabolites were identified in the petals of the three purple and yellow rapeseed varieties by UPLC-MS/MS. A total of 20511 differentially expressed genes (DEGs) between P, LP, YP, versus Y plant petals were detected. This study focused on the co-regulation of 4898 differential genes in the three comparison groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional annotation and quantitative RT-PCR analysis showed that the expression of BnaA10g23330D (BnF3H) affects the synthesis of downstream peonidin and delphinidin and is a key gene regulating the purple color of petals in B. napus. L. The gene may play a key role in regulating rapeseed flower color; however, further studies are needed to verify this. These results deepen our understanding of the molecular mechanisms underlying petal color and provide the theoretical and practical basis for flower breeding targeting petal color.

Integrating Multi-Omics Analysis Reveals the Regulatory Mechanisms of White-Violet Mutant Flowers in Grape Hyacinth (Muscari latifolium)

Grape hyacinth (Muscari spp.) is a famous bulbous blue flower; however, few bicolor varieties are available in the market. Therefore, the discovery of bicolor varieties and understanding of their mechanisms are crucial to the breeding of new varieties. In this study, we report a significant bicolor mutant with white upper and violet lower portions, with both parts belonging to a single raceme. Ionomics showed that pH and metal element contents were not responsible for the bicolor formation. Targeted metabolomics illustrated that the content of the 24 color-related compounds was significantly lower in the upper part than that in the lower part. Moreover, full-length transcriptomics combined with second-generation transcriptomics revealed 12,237 differentially expressed genes in which anthocyanin synthesis gene expression of the upper part was noted to be significantly lower than that of the lower part. Transcription factor differential expression analysis was used to describe the presence of a pair of MaMYB113a/b sequences, with low levels of expression in the upper part and high expression in the lower part. Furthermore, tobacco transformation confirmed that overexpression of MaMYB113a/b can promote anthocyanin accumulation in tobacco leaves. Accordingly, the differential expression of MaMYB113a/b contributes the formation of a bicolor mutant in Muscari latifolium.

The Na+/H+ Exchanger NHX1 Controls H+ Accumulation in the Vacuole to Influence Sepal Color in Hydrangea macrophylla

Hydrangea macrophylla is popular for its unique physiological characteristics and changeable colors. Previous studies have shown that the pH of the vacuoles of the sepal cells of hydrangea affects the color of the sepals. Located on the vacuolar membrane, NHX1 is an important H+ proton pump that drives the exchange of metal ions. This proton pump affects the physiological environment by controlling the accumulation of H+ in the vacuole. In hydrangea, the HmNHX1 gene has an open reading frame of 1626 bp and encodes a total of 541 amino acids. Bioinformatic analysis showed that HmNHX1, which encodes a Na+/H+ exchanger, is located on the vacuolar membrane. Tissue-specific expression analysis showed that the expression of this gene in the treatment group was higher than that in the control group. The ion flux in the vacuoles of colored hydrangea in the treatment group and the control group were measured, and the results showed that HmNHX1 was indeed a Na+/H+ exchanger. When the results of the HmNHX1 expression analysis and ion flux measurements are combined, it can be seen that HmNHX1 regulates the accumulation of H+ in the vacuole, ultimately affecting the color of the plant.

Color, Antioxidant Capacity and Flavonoid Composition in Hibiscus rosa-sinensis Cultivars

Hibiscus rosa-sinensis plants are mainly cultivated as ornamental plants, but they also have food and medicinal uses. In this work, 16 H. rosa-sinensis cultivars were studied to measure their colorimetric parameters and the chemical composition of hydroethanolic extracts obtained from their petals. These extracts were characterized using UHPLC-ESI⁺-Obitrap-MS, and their antioxidant activity was evaluated using the ORAC assay. The identified flavonoids included anthocyanins derived from cyanidin, glycosylated flavonols derived from quercetin and kaempferol, and flavan-3-ols such as catechin and epicatechin. Cyanidin-sophoroside was the anthocyanin present in extracts of lilac, pink, orange, and red flowers, but was not detected in extracts of white or yellow flowers. The total flavonol concentration in the flower extracts was inversely proportional to the total anthocyanin content. The flavonol concentration varied according to the cultivar in the following order: red < pink < orange < yellow ≈ white, with the extract from the red flower presenting the lowest flavonol concentration and the highest anthocyanin concentration. The antioxidant activity increased in proportion to the anthocyanin concentration, from 1580 µmol Trolox^®/g sample (white cultivar) to 3840 µmol Trolox^®/g sample (red cultivar).

Resonance Raman and Visible Micro-Spectroscopy for the In-Vivo and In-Vitro Characterization of Anthocyanin-Based Pigments in Blue and Violet Flowers: A Comparison with HPLC-ESI- MS Analysis of the Extracts

Microanalysis techniques based on resonance Raman and reflection visible spectroscopy have been applied to the characterization of pigments responsible for the blue or violet coloration in flowers; in particular of Lobelia erinus, Campanula portenschlagiana, Cineraria, Viola tricolor, Anemone coronaria, Agapanthus, Platycodon, Salvia farinacea, Plumbago capensis, Ceratostigma plumbaginoides, Commelina communis and Salvia patens. The spectroscopic methods were applied both in vivo on the flower petals and in vitro on extracts obtained through a procedure based on SPE (solid-phase extraction) optimized for minimal quantities of vegetable raw material. Different patterns obtained for the Raman spectra have been correlated, also on the basis of density functional theory (DFT) calculations, with different schemes of substitution of the benzopyrilium nucleus of the anthocyanins and with various possible forms of copigmentation responsible for the stabilization of the blue color. The results obtained were verified by comparison with the analysis of the extracts by HPLC-ESI-MS (liquid chromatography-electrospray ionization-mass spectrometry).

Novel insight into anthocyanin metabolism and molecular characterization of its key regulators in Camellia sasanqua

Flower color is a trait that affects the ornamental value of a plant. Camellia sasanqua is a horticultural plant with rich flower color, but little is known about the regulatory mechanism of color diversity in this plant. Here, the anthocyanin profile of 20 C. sasanqua cultivars revealed and quantified 11 anthocyanin derivatives (five delphinidin-based and six cyanidin-based anthocyanins) for the first time. Cyanidin-3-O-(6-O-(E)-p-coumaroyl)-glucoside was the main contributor to flower base color, and the accumulation of cyanidin and delphinidin derivatives differed in the petals. To further explore the molecular mechanism of color divergence, a transcriptome analysis was performed using C. sasanqua cultivars 'YingYueYe', 'WanXia', 'XueYueHua', and'XiaoMeiGui'. The co-expression network related to differences in delphinidin and cyanidin derivatives accumulation was identified. Eleven candidate genes encoding key enzymes (e.g., F3H, F3'H, and ANS) were involved in anthocyanin biosynthesis. Moreover, 27 transcription factors were screened as regulators of the two types of accumulating anthocyanins. The association was suggested by correlation analysis between the expression levels of the candidate genes and the different camellia cultivars. We concluded that cyanidin and delphinidin derivatives are the major drivers of color diversity in C. sasanqua. This finding provides valuable resources for the study of flower color in C. sasanqua and lays a foundation for genetic modification of anthocyanin biosynthesis.

Delphinidin-3-rutinoside from Blackcurrant Berries (Ribes nigrum): In Vitro Antiproliferative Activity and Interactions with Other Phenolic Compounds

Blackcurrant berries (Rigrum L.) are of great interest for food scientists/technologists as a source of delphinidin-3-rutinoside (D3R). This is an uncommon phenolic compound in diets that unveils potent antiproliferative activity besides its colour. Other phenolic compounds, such as chlorogenic acid (CA) and epicatechin (EC), also known by their antiproliferative effects, are abundant in foods and beverages. To design smart food/supplements combinations containing blackcurrant and improved anticancer properties at the gastrointestinal level, there is the need for more data concerning the combined effects of those molecules. In this work, synergistic, additive, or antagonistic effects against gastric and intestinal cancers of D3R, CA, and EC were assessed in vitro. The antiproliferative activity of D3R, CA, and EC, alone and in binary combinations (D3R+CA, D3R+EC, and CA+EC) on NCI-N87 (gastric) and Caco-2 (intestinal) cells, was assessed following the Chou-Talalay theorem at equipotent contributions (i.e., (IC₅₀)₁/(IC₅₀)₂). D3R presented the strongest antiproliferative activity of the single molecules tested, with IC₅₀ values of 24.9 µM and 102.5 µM on NCI-N87 and Caco-2 cells, respectively. The combinations D3R+CA and CA+EC were synergic against NCI-N87 until IC₅₀ and IC₇₅, respectively, while D3R+EC shifted from slight antagonism to synergism at higher doses. On Caco-2 cells, antagonism at low doses and synergism at high doses was observed. Therefore, the synergisms observed on the gastric cancer model at low doses occurred on the colon model only at high doses. Data herein described is vital to the targeted smart design of foods and supplements, as it is foreseen that the same combination of phenolic compounds causes different interactions/effects depending on the dose and gastrointestinal compartment.

CmHY5 functions in apigenin biosynthesis by regulating flavone synthase II expression in chrysanthemum flowers

The predominant flavones in the ray florets of chrysanthemum flowers are apigenin and its derivatives. CmHY5 participates in apigenin biosynthesis by directly regulating the expression of FNSII-1 in chrysanthemum. Chrysanthemum (Chrysanthemum morifolium) flowers have been used for centuries as functional food and in herbal tea and traditional medicine. The chrysanthemum flower contains significant amounts of the biologically active compound flavones, which has medicinal properties. However, the mechanism regulating flavones biosynthesis in chrysanthemum flowers organs is still unclear. Here, we compared the transcriptomes and metabolomes of different floral organs between two cultivars with contrasting flavone levels in their flowers. We identified 186 flavonoids by metabolome analysis. The predominant flavones in the ray florets of chrysanthemum flowers are apigenin and its derivatives, of which the contents are highly correlated with the expression of flavones synthase II gene CmFNSII-1. We also determined that CmHY5 is a direct upstream regulator of CmFNSII-1 transcription. We showed that CmHY5 RNAi interference lines in chrysanthemum have lower contents of apigenin compared to wild-type chrysanthemum. Our results demonstrated that CmHY5 participates in flavone biosynthesis by directly regulating the expression of FNSII-1 in chrysanthemum.

Behind the Scenes of Anthocyanins-From the Health Benefits to Potential Applications in Food, Pharmaceutical and Cosmetic Fields

Anthocyanins are widespread and biologically active water-soluble phenolic pigments responsible for a wide range of vivid colours, from red (acidic conditions) to purplish blue (basic conditions), present in fruits, vegetables, and coloured grains. The pigments' stability and colours are influenced mainly by pH but also by structure, temperature, and light. The colour-stabilizing mechanisms of plants are determined by inter- and intramolecular co-pigmentation and metal complexation, driven by van der Waals, π-π stacking, hydrogen bonding, and metal-ligand interactions. This group of flavonoids is well-known to have potent anti-inflammatory and antioxidant effects, which explains the biological effects associated with them. Therefore, this review provides an overview of the role of anthocyanins as natural colorants, showing they are less harmful than conventional colorants, with several technological potential applications in different industrial fields, namely in the textile and food industries, as well as in the development of photosensitizers for dye-sensitized solar cells, as new photosensitizers in photodynamic therapy, pharmaceuticals, and in the cosmetic industry, mainly on the formulation of skin care formulations, sunscreen filters, nail colorants, skin & hair cleansing products, amongst others. In addition, we will unveil some of the latest studies about the health benefits of anthocyanins, mainly focusing on the protection against the most prevalent human diseases mediated by oxidative stress, namely cardiovascular and neurodegenerative diseases, cancer, and diabetes. The contribution of anthocyanins to visual health is also very relevant and will be briefly explored.

New insights into the influence of NHX-type Cation/H+ antiporter on flower color in Phalaenopsis orchids

Vacuolar sodium/proton Na⁺(K⁺)/H⁺ exchanger (NHX) influence color formation because of their effects on cellular pH and Na⁺/K⁺ homeostasis. Research regarding NHXs has mainly focused on the vacuolar NHX family members. However, the NHX functions related to Phalaenopsis flower coloration remain relatively uncharacterized. In this study, we cloned and characterized PeNHX1, a vacuolar cation/H⁺ antiporter-encoding gene that is highly expressed in the Phalaenopsis equestris (orchid) flower lip. Phylogenetic and sequence analyses showed that PeNHX1 is a vacuolar NHX protein family member that is similar to other known vacuolar antiporters. The PeNHX1-GFP fusion protein was clearly localized to the vacuolar membrane in a transient transfection assay. A quantitative real-time PCR analysis revealed the increased expression of PeNHX1 in different flower developmental stages. Moreover, it was more highly expressed in the lip than in the other flower organs. On the basis of virus-induced gene silencing, we determined that decreased PeNHX1 expression significantly reduces P. equestris petal coloration. Furthermore, the overexpression of PeNHX1 in Phalaenopsis Big Chili caused the pH to increase and the petal color to change from red to blue. The results indicate that NHX1 may mediates the Na ⁺ or K⁺/H⁺ exchange, thereby regulating the vacuolar pH to promote blue coloration. This research provides a theoretical basis for the development of orchid varieties with blue flowers.

Diverse Physiological Roles of Flavonoids in Plant Environmental Stress Responses and Tolerance

Flavonoids are characterized as the low molecular weight polyphenolic compounds universally distributed in planta. They are a chemically varied group of secondary metabolites with a broad range of biological activity. The increasing amount of evidence has demonstrated the various physiological functions of flavonoids in stress response. In this paper, we provide a brief introduction to flavonoids' biochemistry and biosynthesis. Then, we review the recent findings on the alternation of flavonoid content under different stress conditions to come up with an overall picture of the mechanism of involvement of flavonoids in plants' response to various abiotic stresses. The participation of flavonoids in antioxidant systems, flavonoid-mediated response to different abiotic stresses, the involvement of flavonoids in stress signaling networks, and the physiological response of plants under stress conditions are discussed in this review. Moreover, molecular and genetic approaches to tailoring flavonoid biosynthesis and regulation under abiotic stress are addressed in this review.

Evolution and function of red pigmentation in land plants

BACKGROUND

Land plants commonly produce red pigmentation as a response to environmental stressors, both abiotic and biotic. The type of pigment produced varies among different land plant lineages. In the majority of species they are flavonoids, a large branch of the phenylpropanoid pathway. Flavonoids that can confer red colours include 3-hydroxyanthocyanins, 3-deoxyanthocyanins, sphagnorubins and auronidins, which are the predominant red pigments in flowering plants, ferns, mosses and liverworts, respectively. However, some flowering plants have lost the capacity for anthocyanin biosynthesis and produce nitrogen-containing betalain pigments instead. Some terrestrial algal species also produce red pigmentation as an abiotic stress response, and these include both carotenoid and phenolic pigments.

SCOPE

In this review, we examine: which environmental triggers induce red pigmentation in non-reproductive tissues; theories on the functions of stress-induced pigmentation; the evolution of the biosynthetic pathways; and structure-function aspects of different pigment types. We also compare data on stress-induced pigmentation in land plants with those for terrestrial algae, and discuss possible explanations for the lack of red pigmentation in the hornwort lineage of land plants.

CONCLUSIONS

The evidence suggests that pigment biosynthetic pathways have evolved numerous times in land plants to provide compounds that have red colour to screen damaging photosynthetically active radiation but that also have secondary functions that provide specific benefits to the particular land plant lineage.

Evidence-Based Anti-Diabetic Properties of Plant from the Occitan Valleys of the Piedmont Alps

Data on urban and rural diabetes prevalence ratios show a significantly lower presence of diabetes in rural areas. Several bioactive compounds of plant origin are known to exert anti-diabetic properties. Interestingly, most of them naturally occur in different plants present in mountainous areas and are linked to traditions of herbal use. This review will aim to evaluate the last 10 years of evidence-based data on the potential anti-diabetic properties of 9 plants used in the Piedmont Alps (North-Western Italy) and identified through an ethnobotanical approach, based on the Occitan language minority of the Cuneo province (Sambucus nigra L., Achillea millefolium L., Cornus mas L., Vaccinium myrtillus L., Fragaria vesca L., Rosa canina L., Rubus idaeus L., Rubus fruticosus/ulmifolius L., Urtica dioica L.), where there is a long history of herbal remedies. The mechanism underlying the anti-hyperglycemic effects and the clinical evidence available are discussed. Overall, this review points to the possible use of these plants as preventive or add-on therapy in treating diabetes. However, studies of a single variety grown in the geographical area, with strict standardization and titration of all the active ingredients, are warranted before applying the WHO strategy 2014-2023.

Genetic and multi-omics analyses reveal BnaA07.PAP2In-184-317 as the key gene conferring anthocyanin-based color in Brassica napus flowers

The molecular mechanisms underlying anthocyanin-based flower coloration remain unknown in Brassica napus. To identify the key genes and metabolites associated with apricot and pink flower colors, metabolome, BSA-seq, and RNA-seq analyses were conducted on apricot-, pink-, yellow-, and white-flowered F2B. napus. Yellow carotenoids and red anthocyanins were abundant in apricot petals, while colorless carotenoids and red anthocyanins accumulated in pink petals. Most carotenoid genes were not differentially regulated between apricot and yellow or between pink and white petals. Three regulator genes, BnaMYBL2, BnaA07.PAP2, and BnaTT8, and structural genes in anthocyanin biosynthesis were dramatically enhanced in apricot and pink petals in comparison with yellow and white petals. Map-based cloning revealed that BnaA07.PAP2 is responsible for anthocyanin-based flower color and encodes a nucleus-localized protein predominantly expressed in apricot and pink flowers. Two insertions in the promoter region are responsible for the transcriptional activation of BnaA07.PAP2 in flowers. Introducing the BnaA07.PAP2In-184-317 allele broadly activated the expression of anthocyanin-related genes and promoted anthocyanin accumulation in flowers, yielding color change from yellow to apricot. These findings illustrate the genetic basis of anthocyanin-based flower coloration and provide a valuable genetic resource for breeding varieties with novel flower colors in B. napus.

Functionalization of 7-Hydroxy-pyranoflavylium: Synthesis of New Dyes with Extended Chromatic Stability

This work reports the functionalization of pyranoflavyliums pigment using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride coupling chemistry. Four cinnamic acids were used to establish an ester bond with the hydroxyl group of the pyranoflavylium, namely 4-dimethylamino-, 4-amino-, 4-bromo-, and trans-cinnamic acids. The experimental condition, namely the molar ratios, solvent, and reaction time, were adjusted to obtain higher reaction yields in a reduced period. Excellent reaction yields of 68%, 85%, 94%, and 99% were achieved for 4-amino, trans-, 4-bromo, and 4-dimethylamino pyranoflavylium cinnamates, respectively. The structure of the functionalized pigments was fully clarified using one-dimensional (1H) and two-dimensional (COSY, HSQC, and HMBC) NMR experiments and HRSM analysis. Regardless of the type of functionalization, the UV-Visible spectrum showed a bathochromic shift (red region) on the maximum absorption wavelength and the absence of acid-base reactions throughout a broad pH range in comparison to the pyranoflavylium precursor. This work offers a valuable environmentally friendly, quick, and straightforward alternative to flavylium compounds' challenging and labor-intensive functionalization, resulting in novel dyes with higher stability and dissimilar chromatic features.

Metallophenolomics: A Novel Integrated Approach to Study Complexation of Plant Phenolics with Metal/Metalloid Ions

Plant adaptive strategies have been shaped during evolutionary development in the constant interaction with a plethora of environmental factors, including the presence of metals/metalloids in the environment. Among adaptive reactions against either the excess of trace elements or toxic doses of non-essential elements, their complexation with molecular endogenous ligands, including phenolics, has received increasing attention. Currently, the complexation of phenolics with metal(loid)s is a topic of intensive studies in different scientific fields. In spite of the numerous studies on their chelating capacity, the systemic analysis of phenolics as plant ligands has not been performed yet. Such a systematizing can be performed based on the modern approach of metallomics as an integral biometal science, which in turn has been differentiated into subgroups according to the nature of the bioligands. In this regard, the present review summarizes phenolics–metal(loid)s’ interactions using the metallomic approach. Experimental results on the chelating activity of representative compounds from different phenolic subgroups in vitro and in vivo are systematized. General properties of phenolic ligands and specific properties of anthocyanins are revealed. The novel concept of metallophenolomics is proposed, as a ligand-oriented subgroup of metallomics, which is an integrated approach to study phenolics–metal(loid)s’ complexations. The research subjects of metallophenolomics are outlined according to the methodology of metallomic studies, including mission-oriented biometal sciences (environmental sciences, food sciences and nutrition, medicine, cosmetology, coloration technologies, chemical sciences, material sciences, solar cell sciences). Metallophenolomics opens new prospects to unite multidisciplinary investigations of phenolic–metal(loid) interactions.

Transcriptome and chemical analyses revealed the mechanism of flower color formation in Rosa rugosa

Rosa rugosa is a famous Chinese traditional flower with high ornamental value and well environmental adapt ability. The cultivation of new colorful germplasms to improve monotonous flower color could promote its landscape application. However, the mechanism of flower color formation in R. rugosa remains unclear. In this study, combined analyses of the chemical and transcriptome were performed in the R. rugosa germplasms with representative flower colors. Among the identified anthocyanins, cyanidin 3,5-O-diglucoside (Cy3G5G) and peonidin 3,5-O-diglucoside (Pn3G5G) were the two dominant anthocyanins in the petals of R. rugosa. The sum content of Cy3G5G and Pn3G5G was responsible for the petal color intensity, such as pink or purple, light- or dark- red. The ratio of Cy3G5G to Pn3G5G was contributed to the petal color hue, that is, red or pink/purple. Maintaining both high relative and high absolute content of Cy3G5G may be the precondition for forming red-colored petals in R. rugosa. Cyanidin biosynthesis shunt was the dominant pathway for anthocyanin accumulation in R. rugosa, which may be the key reason for the presence of monotonous petal color in R. rugosa, mainly pink/purple. In the upstream pathway of cyanidin biosynthesis, 35 differentially expressed structural genes encoding 12 enzymes co-expressed to regulate the sum contents of Cy3G5G and Pn3G5G, and then determined the color intensity of petals. RrAOMT, involved in the downstream pathway of cyanidin biosynthesis, regulated the ratio of Cy3G5G to Pn3G5G via methylation and then determined the color hue of petals. It was worth mentioning that significantly higher delphinidin-3,5-O-diglucoside content and RrF3'5'H expression were detected from deep purple-red-flowered 8-16 germplasm with somewhat unique and visible blue hue. Three candidate key transcription factors identified by correlation analysis, RrMYB108, RrC1, and RrMYB114, might play critical roles in the control of petal color by regulating the expression of both RrAOMT and other multiple structural genes. These results provided novel insights into anthocyanin accumulation and flower coloration mechanism in R. rugosa, and the candidate key genes involved in anthocyanin biosynthesis could be valuable resources for the breeding of ornamental plants in future.

Improved Stability of Blue Colour of Anthocyanins from Lycium ruthenicum Murr. Based on Copigmentation

Natural blue food colourant is rare. The aim of this work was to screen compounds from the common copigments that could improve the blue tones of anthocyanins (ACNs) and to investigate the effect of different copigments on the colour stability of anthocyanins in neutral species. International Commission on Illumination (CIE) colour space, UV, IR, NMR, atomic force microscopy (AFM) and computational chemistry methods were utilised to evaluate ACNs from Lycium ruthenicum Murr. (LR), which is complexed with food additives and biological agents. The results indicate that Pro-Xylane (PX), Ectoin (ECT) and dipotassium glycyrrhizinate (DG) enhance the blue colour of the ACNs. ACNs-PX presents a colour close to Oxford Blue and has a surface height of 2.13 ± 0.14 nm and slightly improved stability. The half-life of ACNs-DG is improved 24.5-fold and had the highest complexation energy (-50.63/49.15) kcal/mol, indicating hydrogen bonds and π-π stacking forces enhance stability. These findings offer a new perspective for anthocyanin utilisation as a blue colourant and contribute to the large-scale application of LR.

Blue flower coloration of Salvia macrophylla by the metalloanthocyanin, protodelphin

A survey of a metalloanthocyanin by in vivo visible spectrum and circular dichroism suggested that blue petals of Salvia macrophylla contain metalloanthocyanins. Chemical analysis of the purified blue pigment proved that the pigment in the petals is protodelphin which is the same pigment present in the blue petals of Salvia patens composed of malonylawobanin, apigenin 7,4'-diglucosides and Mg2+.

Lilac (Syringa oblata) genome provides insights into its evolution and molecular mechanism of petal color change

Color change during flower opening is common; however, little is understood on the biochemical and molecular basis related. Lilac (Syringa oblata), a well-known woody ornamental plant with obvious petal color changes, is an ideal model. Here, we presented chromosome-scale genome assembly for lilac, resolved the flavonoids metabolism, and identified key genes and potential regulatory networks related to petal color change. The genome assembly is 1.05 Gb anchored onto 23 chromosomes, with a BUSCO score of 96.6%. Whole-genome duplication (WGD) event shared within Oleaceae was revealed. Metabolome quantification identified delphinidin-3-O-rutinoside (Dp3Ru) and cyanidin-3-O-rutinoside (Cy3Ru) as the major pigments; gene co-expression networks indicated WRKY an essential regulation factor at the early flowering stage, ERF more important in the color transition period (from violet to light nearly white), while the MBW complex participated in the entire process. Our results provide a foundation for functional study and molecular breeding in lilac.

Dietary polyglycosylated anthocyanins, the smart option? A comprehensive review on their health benefits and technological applications

Over the years, anthocyanins have emerged as one of the most enthralling groups of natural phenolic compounds and more than 700 distinct structures have already been identified, illustrating the exceptional variety spread in nature. The interest raised around anthocyanins goes way beyond their visually appealing colors and their acknowledged structural and biological properties have fueled intensive research toward their application in different contexts. However, the high susceptibility of monoglycosylated anthocyanins to degradation under certain external conditions might compromise their application. In that regard, polyglycosylated anthocyanins (PGA) might offer an alternative to overcome this issue, owing to their peculiar structure and consequent less predisposition to degradation. The most recent scientific and technological findings concerning PGA and their food sources are thoroughly described and discussed in this comprehensive review. Different issues, including their physical-chemical characteristics, consumption, bioavailability, and biological relevance in the context of different pathologies, are covered in detail, along with the most relevant prospective technological applications. Due to their complex structure and acyl groups, most of the PGA exhibit an overall higher stability than the monoglycosylated ones. Their versatility allows them to act in a wide range of pathologies, either by acting directly in molecular pathways or by modulating the disease environment attributing an added value to their food sources. Their recent usage for technological applications has also been particularly successful in different industry fields including food and smart packaging or in solar energy production systems. Altogether, this review aims to put into perspective the current state and future research on PGA and their food sources.

Anthocyanic Vacuolar Inclusions: From Biosynthesis to Storage and Possible Applications

The ability of plants to accumulate specific metabolites in concentrations beyond their solubility in both aqueous and lipid environments remains a key question in plant biology. Natural Deep Eutectic Solvents (NADES) are mixtures of natural compounds in specific molar ratios, which interact through hydrogen bonding. This results in a viscous liquid that can solubilize high amounts of natural products while maintaining a negligible vapor pressure to prevent release of volatile compounds. While all the components are presents in plant cells, identifying experimental evidence for the occurrence of NADES phases remains a challenging quest. Accumulation of anthocyanin flavonoids in highly concentrated inclusions have been speculated to involve NADES as an inert solvent. The inherent pigment properties of anthocyanins provide an ideal system for studying the formation of NADES in a cellular environment. In this mini-review we discuss the biosynthesis of modified anthocyanins that facilitate their organization in condensates, their transport and storage as a specific type of phase separated inclusions in the vacuole, and the presence of NADES constituents as a natural solution for storing high amounts of flavonoids and other natural products. Finally, we highlight how the knowledge gathered from studying the discussed processes could be used for specific applications within synthetic biology to utilize NADES derived compartments for the production of valuable compounds where the production is challenged by poor solubility, toxic intermediates or unstable and volatile products.