Regulation of anthocyanin biosynthesis in UV-A-irradiated cell cultures of carrot and in organs of intact carrot plants

Lily (Lilium spp.) LhERF4 negatively affects anthocyanin biosynthesis by suppressing LhMYBSPLATTER transcription

Anthocyanins are among the main pigments involved in the colouration of Asiatic hybrid lily (Lilium spp.). Ethylene, a plant ripening hormone, plays an important role in promoting plant maturation and anthocyanin biosynthesis. However, whether and how ethylene regulates anthocyanin biosynthesis in lily tepals have not been characterized. Using yeast one-hybrid screening, we previously identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) named LhERF4 as a potential inhibitor of LhMYBSPLATTER-mediated negative regulation of anthocyanin biosynthesis in lily. Here, transcript and protein analysis of LhERF4, a transcriptional repressor, revealed that LhERF4 directly binds to the promoter of LhMYBSPLATTER. In addition, overexpression of LhERF4 in lily tepals negatively regulates the expression of key structural genes and the total anthocyanin content by suppressing the LhMYBSPLATTER gene. Moreover, the LhERF4 gene inhibits anthocyanin biosynthesis in response to ethylene, affecting anthocyanin accumulation and pigmentation in lily tepals. Collectively, our findings will advance and elucidate a novel regulatory network of anthocyanin biosynthesis in lily, and this research provides new insight into colouration regulation.

Appropriate Nitrogen form Ratio and UV-A Supplementation Increased Quality and Production in Purple Lettuce (Lactuca sativa L.)

Purple lettuce (Lactuca sativa L. cv. Zhongshu Purple Lettuce) was chosen as the trial material, and LED intelligent light control consoles were used as the light sources. The purpose was to increase the yield and quality of purple lettuce while lowering its nitrate level. By adding various ratios of NO3--N and NH4+-N to the nutrient solution and 20 µmol m-2 s-1 UV-A based on white, red, and blue light (130, 120, 30 µmol m-2 s-1), the effects of different NO3--N/NH4+-N ratios (NO3--N, NO3--N/NH4+-N = 3/1, NH4+-N) and UV-A interaction on yield, quality, photosynthetic characteristics, anthocyanins, and nitrogen assimilation of purple lettuce were studied. In order to produce purple lettuce hydroponically under controlled environmental conditions, a theoretical foundation and technological specifications were developed, taking into account an appropriate UV-A dose and NO3--N/NH4+-N ratio. Results demonstrate that adding a 20 µmol m-2 s-1 UV-A, and a NO3--N/NH4+-N treatment of 3/1, significantly reduced the nitrate level while increasing the growth, photosynthetic rate, chlorophyll, carotenoid, and anthocyanin content of purple lettuce. The purple leaf lettuce leaves have an enhanced capacity to absorb nitrogen. Furthermore, plants have an acceleration of nitrogen metabolism, which raises the concentration of free amino acids and soluble proteins and promotes biomass synthesis. Thus, based on the NO3--N/NH4+-N (3/1) treatment, adding 20 µmol m-2 s-1 UV-A will be helpful in boosting purple lettuce production and decreasing its nitrate content.

Callus Derived from Petals of the Rosa hybrida Breeding Line 15R-12-2 as New Material Useful for Fragrance Production

Rose (Rosa hybrida) is a major flower crop worldwide and has long been loved for its variety of colors and scents. Roses are mainly used for gardening or cutting flowers and are also used as raw materials for perfumes, cosmetics, and food. Essential oils, which are extracted from the flowers of plants, including roses, have various scents, and the essential oil market has been growing steadily owing to the growing awareness of the benefits of natural and organic products. Therefore, it is necessary to develop a system that stably supplies raw materials with uniform ingredients in line with the continuous increase in demand. In this study, conditions for the efficient induction of callus were established from the petals of the rose breeding line 15R-12-2, which has a strong scent developed by the National Institute of Horticultural and Herbal Science, Rural Development Administration. The highest callus induction rate (65%) was observed when the petals of the fully open flower (FOF) were placed on the SH11DP medium so that the abaxial surface was in contact with the medium. In addition, the VOCs contained in the petals of 15R-12-2 and the petal-derived callus were analyzed by HS-SPME-GC-MS. Thirty components, including esters and alcohols, were detected in the petal-derived callus. Among them, 2-ethylhexan-1-ol, which showed 59.01% relative content when extracted with hexane as a solvent, was the same component as detected in petals. Therefore, petal-derived callus is expected to be of high industrial value and can be suggested as an alternative pathway to obtaining VOCs.

Biochemical Characterization of a Flavone Synthase I from Daucus carota and its Application for Bioconversion of Flavanones to Flavones

In this study, we studied the biochemical characterization of flavone synthase I from Daucus carota (DcFNS I) and applied it with flavonoid 6-hydroxylase from Scutellaria baicalensis (SbCYP) to convert flavanones to flavones. The recombinant DcFNS I was expressed in the form of the glutathione-S-transferase fusion protein. Rather than taxifolin, naringenin, pinocembrin, and eriodictyol were accepted as substrates. The optimal temperature and pH for reaction in vitro were 35 °C and 7.5, respectively, and 2-oxoglutarate was essential in the assay system. Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺, and Zn²⁺ were not substitutes for Fe²⁺. EDTA and pyruvic acid inhibited the activity, except for Fe³⁺. Kinetic analysis revealed that the V_max and k_cat values of the recombinant DcFNS I against naringenin were 0.183 nmol mg^-1 s^-1 and 0.0121 s^-1, and 0.175 nmol mg^-1 s^-1 and 0.0116 s^-1 against pinocembrin. However, the recombinant DcFNS I had a higher affinity for naringenin than pinocembrin, with k_M values for each of 0.076 mM and 0.174 mM respectively. Thus, it catalyzed naringenin more efficiently than pinocembrin. Subsequently, using an Escherichia coli and Saccharomyces cerevisiae co-culture system, we successfully converted naringenin and pinocembrin to scutellarein and baicalein respectively. In a synthetic complete medium, the titers of scutellarein and baicalein reached 5.63 mg/L and 0.78 mg/L from 200 mg/L precursors.

Biosynthesis and regulation of anthocyanin pathway genes

Anthocyanins are the phenolic compounds responsible for coloring pigments in fruits and vegetables. Anthocyanins offer a wide range of health benefits to human health. Their scope has expanded dramatically in the past decade, making anthocyanin control, influx, and outflow regulation fascinating for many researchers. The main culprit is anthocyanin stability and concentration form, which demands novel ways because these are critical in the food industry. This review aims to examine anthocyanin synthesis via triggering transcription genes that code for anthocyanin-producing enzymes. The balance between production and breakdown determines anthocyanin accumulation. Thus, increasing the anthocyanin content in food requires the stability of molecules in the vacuolar lumen, the pigment fading process, and a better understanding of the mechanism. The promising option is biosynthesis by metabolically engineered microorganisms with a lot of success. This study aims to look into and evaluate the existing literature on anthocyanin production, namely the biosynthesis of anthocyanin pathway genes, production by microbial cell factories, and the regulatory factors that can modulate the production of anthocyanins. Understanding these mechanisms will provide new biotechnological approaches.Key points• Factors affecting the regulation of anthocyanins• Focus on degradation, biosynthesis pathway genes, and alternative systems for the production of anthocyanins• Microbial cell factories can be used to produce large amounts of anthocyanins.

MYB-6 and LDOX-1 regulated accretion of anthocyanin response to cold stress in purple black carrot (Daucus carota L.)

AIM

Anthocyanin, an essential ingredient of functional foods, is present in a wide range of plants, including black carrots. The current investigation was carried out to analyse the effect of cold stress on the expression of major anthocyanins and anthocyanin biosynthetic pathway genes, MYB6 and LDOX-1.

METHODS AND RESULTS

Five cultivated carrot genotypes belonging to the eastern group, having anthocyanin pigment, were used in the current study. The qRT-PCR analysis revealed that relative gene expression of transcription factor MYB-6 and LDOX1gene was highly expressed upon cold stress compared to non-stress samples. High-performance liquid chromatography-based quantification of Cyanidin 3-O-glucoside (Kuromanin chloride), Ferulic acid, 3,5-Dimethoxy-4-hydroxycinnamic acid (Sinapic acid), and Rutin revealed a significant increase in these major anthocyanins in response to cold stress when compared to control plants.

CONCLUSION

We conclude that MYB6 and LDOX1 gene expression increases upon cold stress, which induces accumulation of major anthocyanins in purple black carrot and suggests a possible cross-link between cold stress and anthocyanin biosynthesis in purple black carrot.

Anthocyanins, multi-functional natural products of industrial relevance: Recent biotechnological advances

Anthocyanins, the color compounds of plants, are known for their wide applications in food, nutraceuticals and cosmetic industry. The biosynthetic pathway of anthocyanins is well established with the identification of potential key regulatory genes, which makes it possible to modulate its production by biotechnological means. Various biotechnological systems, including use of in vitro plant cell or tissue cultures as well as microorganisms have been used for the production of anthocyanins under controlled conditions, however, a wide range of factors affects their production. In addition, metabolic engineering technologies have also used the heterologous production of anthocyanins in recombinant plants and microorganisms. However, these approaches have mostly been tested at the lab- and pilot-scales, while very few up-scaling studies have been undertaken. Various challenges and ways of investigation are proposed here to improve anthocyanin production by using the in vitro plant cell or tissue culture and metabolic engineering of plants and microbial culture systems. All these methods are capable of modulating the production of anthocyanins , which can be further utilized for pharmaceutical, cosmetics and food applications.

The Effects of Ultraviolet A/B Treatments on Anthocyanin Accumulation and Gene Expression in Dark-Purple Tea Cultivar 'Ziyan' (Camellia sinensis)

‘Ziyan’ is a novel anthocyanin-rich tea cultivar with dark purple young shoots. However, how its anthocyanin accumulation is affected by environmental factors, such as ultraviolet (UV), remains unclear. In this study, we observed that UV light treatments stimulated anthocyanin accumulation in ‘Ziyan’ leaves, and we further analyzed the underlying mechanisms at gene expression and enzyme activity levels. In addition, the catechins and chlorophyll contents of young shoots under different light treatments were also changed. The results showed that the contents of total anthocyanins and three major anthocyanin molecules, i.e., delphinidin, cyanidin, and pelargonidin, were significantly higher in leaves under UV-A, UV-B, and UV-AB treatments than those under white light treatment alone. However, the total catechins and chlorophyll contents in these purple tea plant leaves displayed the opposite trends. The anthocyanin content was the highest under UV-A treatment, which was higher by about 66% than control. Compared with the white light treatment alone, the enzyme activities of chalcone synthase (CHS), flavonoid 3′,5′-hydroxylase (F3′5′H), and anthocyanidin synthase (ANS) under UV treatments increased significantly, whereas the leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) activities reduced. There was no significant difference in dihydroflavonol 4-reductase (DFR) activity under all treatments. Comparative transcriptome analyses unveiled that there were 565 differentially expressed genes (DEGs) of 29,648 genes in three pair-wise comparisons (white light versus UV-A, W vs. UV-A; white light versus UV-B, W vs. UV-A; white light versus UV-AB, W vs. UV-AB). The structural genes in anthocyanin pathway such as flavanone 3-hydroxylase (F3H), F3′5′H, DFR, and ANS, and regulatory gene TT8 were upregulated under UV-A treatment; F3′5′H, DFR, ANS, and UFGT and regulatory genes EGL1 and TT2 were upregulated under UV-AB treatment. However, most structural genes involved in phenylpropanoid and flavonoid pathways were downregulated under UV-B treatment compared with control. The expression of LAR and ANR were repressed in all UV treatments. Our results indicated that UV-A and UV-B radiations can induce anthocyanin accumulation in tea plant ‘Ziyan’ by upregulating the structural and regulatory genes involved in anthocyanin biosynthesis. In addition, UV radiation repressed the expression levels of LAR, ANR, and FLS, resulting in reduced ANR activity and a metabolic flux shift toward anthocyanin biosynthesis.

Assessing Anthocyanin Biosynthesis in Solanaceae as a Model Pathway for Secondary Metabolism

Solanaceae have played an important role in elucidating how flower color is specified by the flavonoid biosynthesis pathway (FBP), which produces anthocyanins and other secondary metabolites. With well-established reverse genetics tools and rich genomic resources, Solanaceae provide a robust framework to examine the diversification of this well-studied pathway over short evolutionary timescales and to evaluate the predictability of genetic perturbation on pathway flux. Genomes of eight Solanaceae species, nine related asterids, and four rosids were mined to evaluate variation in copy number of the suite of FBP enzymes involved in anthocyanin biosynthesis. Comparison of annotation sources indicated that the NCBI annotation pipeline generated more and longer FBP annotations on average than genome-specific annotation pipelines. The pattern of diversification of each enzyme among asterids was assessed by phylogenetic analysis, showing that the CHS superfamily encompasses a large paralogous family of ancient and recent duplicates, whereas other FBP enzymes have diversified via recent duplications in particular lineages. Heterologous expression of a pansy F3′5′H gene in tobacco changed flower color from pink to dark purple, demonstrating that anthocyanin production can be predictably modified using reverse genetics. These results suggest that the Solanaceae FBP could be an ideal system to model genotype-to-phenotype interactions for secondary metabolism.

Advances in research on the carrot, an important root vegetable in the Apiaceae family

Carrots (Daucus carota L.), among the most important root vegetables in the Apiaceae family, are cultivated worldwide. The storage root is widely utilized due to its richness in carotenoids, anthocyanins, dietary fiber, vitamins and other nutrients. Carrot extracts, which serve as sources of antioxidants, have important functions in preventing many diseases. The biosynthesis, metabolism, and medicinal properties of carotenoids in carrots have been widely studied. Research on hormone regulation in the growth and development of carrots has also been widely performed. Recently, with the development of high-throughput sequencing technology, many efficient tools have been adopted in carrot research. A large amount of sequence data has been produced and applied to improve carrot breeding. A genome editing system based on CRISPR/Cas9 was also constructed for carrot research. In this review, we will briefly summarize the origins, genetic breeding, resistance breeding, genome editing, omics research, hormone regulation, and nutritional composition of carrots. Perspectives about future research work on carrots are also briefly provided.

Identification of transcription factor genes involved in anthocyanin biosynthesis in carrot (Daucus carota L.) using RNA-Seq

BACKGROUND

Anthocyanins are water-soluble colored flavonoids present in multiple organs of various plant species including flowers, fruits, leaves, stems and roots. DNA-binding R2R3-MYB transcription factors, basic helix-loop-helix (bHLH) transcription factors, and WD40 repeat proteins are known to form MYB-bHLH-WD repeat (MBW) complexes, which activates the transcription of structural genes in the anthocyanin pathway. Although black cultivars of carrots (Daucus carota L.) can accumulate large quantities of anthocyanin in their storage roots, the regulatory genes responsible for their biosynthesis are not well characterized. The current study aimed to analyze global transcription profiles based on RNA sequencing (RNA-Seq), and mine MYB, bHLH and WD40 genes that may function as positive or negative regulators in the carrot anthocyanin biosynthesis pathways.

RESULTS

RNA was isolated from differently colored calli, as well as tissue samples from taproots of various black carrot cultivars across the course of development, and gene expression levels of colored and non-colored tissue and callus samples were compared. The expression of 32 MYB, bHLH and WD40 genes were significantly correlated with anthocyanin content in black carrot taproot. Of those, 11 genes were consistently up- or downregulated in a purple color-specific manner across various calli and cultivar comparisons. The expression of 10 out of these 11 genes was validated using real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR).

CONCLUSIONS

The results of this study provide insights into regulatory genes that may be responsible for carrot anthocyanin biosynthesis, and suggest that future focus on them may help improve our overall understanding of the anthocyanin synthesis pathway.

Foliar-applied ethephon enhances the content of anthocyanin of black carrot roots (Daucus carota ssp. sativus var. atrorubens Alef.)

BACKGROUND

Black carrots (Daucus carota ssp. sativus var. atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants. Anthocyanins and phenolic compounds are specialised metabolites, accumulation of which often requires elicitors, which act as molecular signals in plant stress responses. In the present study, ethephon, an ethylene-generating compound was explored as enhancer of anthocyanin and phenolic contents during growth of 'Deep Purple' black carrots. The effects of ethephon on several parameters were investigated, and the expression of biosynthetic anthocyanin genes was studied during growth and anthocyanin accumulation.

RESULTS

Roots of ethephon-treated carrot plants exhibited an increase in anthocyanin content of approximately 25%, with values ranging from 2.25 to 3.10 mg g-1 fresh weight, compared with values ranging from 1.50 to 1.90 mg g-1 fresh weight in untreated roots. The most rapid accumulation rate for anthocyanins, phenolic compounds, soluble solids and dry matter was observed between 10 and 13 weeks after sowing in both untreated and ethephon-treated carrots. The differences in anthocyanin contents between untreated and treated carrots increased for several weeks after the ethephon treatment was terminated. Five cyanidin-based anthocyanin forms were identified, with variable relative abundance values detected during root growth. Overall, the expression of the anthocyanin biosynthetic genes analysed (PAL1, PAL3, F3H1, DFR1, LDOX2) increased in response to ethephon treatment, as did the expression of the MYB1 transcription factor, which is associated with activation of the phenylpropanoid pathway under stress conditions. In addition, a correlation was proposed between ethylene and sugar contents and the induction of anthocyanin synthesis.

CONCLUSIONS

This study presents a novel method for enhancing anthocyanin content in black carrots. This finding is of economic importance as increased pigment concentration per unit of biomass implies improved profitability parameters in food colour production. We provide new insight into the accumulation patterns of the different cyanidin-based anthocyanins and phenolic compounds during root growth. Moreover, we show that enhanced anthocyanin content in ethephon-treated carrots is accompanied by increased expression of anthocyanin biosynthetic genes.

UV-B-induced anthocyanin accumulation in hypocotyls of radish sprouts continues in the dark after irradiation

BACKGROUND

Raphanus sativus L. cv. Yanghua sprouts are rich in health-promoting anthocyanins; thus hypocotyls show a red color under light. In this study, effects of UV-B irradiation at 5 W m(-2) on anthocyanin biosynthesis in the hypocotyls of radish sprouts were investigated.

RESULTS

Anthocyanins began to accumulate rapidly from 24 h irradiation and increased continuously until 48 h, showing a similar pattern to phenylalanine ammonia lyase (PAL) activity, with a correlation coefficient of 0.804. The expression of DFR and ANS paralleled the upward trend in anthocyanin accumulation, while CHS, CHI and F3H were upregulated before accumulation. When sprouts were moved into the dark from UV-B, the anthocyanin accumulation did not stop immediately. By contrast, anthocyanin accumulated continuously for more than 12 h in the dark, which was further supported by the significantly higher PAL activity monitored at 24 h after irradiation. Similarly, the transcript levels of anthocyanin biosynthesis-related genes were much higher over 6 h after 12 h UV-B irradiation.

CONCLUSION

UV-B-induced anthocyanin accumulation continues in the dark after irradiation, which was supported by unfading PAL activity and high levels of biosynthesis-related genes. This will provide evidence to produce high-quality sprouts with more anthocyanins but less energy wastage in practice.

Reactive oxygen species produced via plasma membrane NADPH oxidase regulate anthocyanin synthesis in apple peel

Solar ultraviolet irradiation regulates anthocyanin synthesis in apple peel by modulating the production of reactive oxygen species via plasma membrane NADPH oxidase instead of other pathways. The synthesis of anthocyanin in apple peels is dependent upon solar irradiation. Using 3-mm commercial glass to attenuate solar UV-A and UV-B light, we confirmed that solar UV irradiation regulated anthocyanin synthesis in apple peels after exposing previously bagged fruit to sunlight. During sunlight exposure, UV attenuation did not affect the expression of MdHY5, MdCOP1, or MdCRY2, but significantly lowered plasma membrane NADPH oxidase activity and superoxide anion concentrations. UV attenuation also reduced the expression levels of MdMYB10, MdPAL, MdCHS, MdF3H, MdDFR, MdANS and MdUFGT1, UDP-glycose:flavonoid 3-O-glycosyltransferase (UFGT) activity, and local concentrations of anthocyanin and quercetin-3-glycoside. In contrast, exogenous application of hydrogen peroxide could enhance anthocyanin and quercetin-3-glycoside synthesis. Xanthophyll cycle pool size on a chlorophyll basis was higher but its de-epoxidation was lower under direct sunlight irradiation than that under UV-attenuating conditions. This suggests that reactive oxygen species (ROS) produced in chloroplast are not major contributors to anthocyanin synthesis regulation. Inhibition of plasma membrane NADPH oxidase activity lowered the production of ROS through this mechanism, significantly inhibited the synthesis of anthocyanin, and increased the total production of ROS in apple peel under direct sunlight irradiation, suggesting that ROS produced via plasma membrane NADPH oxidase regulates anthocyanin synthesis. In summary, solar UV irradiation regulated anthocyanin synthesis in apple peels by modulating the production of ROS via plasma membrane NADPH oxidase.

Transcript profiling of structural genes involved in cyanidin-based anthocyanin biosynthesis between purple and non-purple carrot (Daucus carota L.) cultivars reveals distinct patterns

BACKGROUND

Carrots (Daucus carota L.) are among the 10 most economically important vegetable crops grown worldwide. Purple carrot cultivars accumulate rich cyanidin-based anthocyanins in a light-independent manner in their taproots whereas other carrot color types do not. Anthocyanins are important secondary metabolites in plants, protecting them from damage caused by strong light, heavy metals, and pathogens. Furthermore, they are important nutrients for human health. Molecular mechanisms underlying anthocyanin accumulation in purple carrot cultivars and loss of anthocyanin production in non-purple carrot cultivars remain unknown.

RESULTS

The taproots of the three purple carrot cultivars were rich in anthocyanin, and levels increased during development. Conversely, the six non-purple carrot cultivars failed to accumulate anthocyanins in the underground part of taproots. Six novel structural genes, CA4H1, CA4H2, 4CL1, 4CL2, CHI1, and F3'H1, were isolated from purple carrots. The expression profiles of these genes, together with other structural genes known to be involved in anthocyanin biosynthesis, were analyzed in three purple and six non-purple carrot cultivars at the 60-day-old stage. PAL3/PAL4, CA4H1, and 4CL1 expression levels were higher in purple than in non-purple carrot cultivars. Expression of CHS1, CHI1, F3H1, F3'H1, DFR1, and LDOX1/LDOX2 was highly correlated with the presence of anthocyanin as these genes were highly expressed in purple carrot taproots but not or scarcely expressed in non-purple carrot taproots.

CONCLUSIONS

This study isolated six novel structural genes involved in anthocyanin biosynthesis in carrots. Among the 13 analyzed structural genes, PAL3/PAL4, CA4H1, 4CL1, CHS1, CHI1, F3H1, F3'H1, DFR1, and LDOX1/LDOX2 may participate in anthocyanin biosynthesis in the taproots of purple carrot cultivars. CHS1, CHI1, F3H1, F3'H1, DFR1, and LDOX1/LDOX2 may lead to loss of light-independent anthocyanin production in orange and yellow carrots. These results suggest that numerous structural genes are involved in anthocyanin production in the taproots of purple carrot cultivars and in the loss of anthocyanin production in non-purple carrots. Unexpressed or scarcely expressed genes in the taproots of non-purple carrot cultivars may be caused by the inactivation of regulator genes. Our results provide new insights into anthocyanin biosynthesis at the molecular level in carrots and for other root vegetables.

Expression and mapping of anthocyanin biosynthesis genes in carrot

Anthocyanin gene expression has been extensively studied in leaves, fruits and flowers of numerous plants. Little, however, is known about anthocyanin accumulation in roots of carrots or other species. We quantified expression of six anthocyanin biosynthetic genes [phenylalanine ammonia-lyase (PAL3), chalcone synthase (CHS1), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR1), leucoanthocyanidin dioxygenase (LDOX2), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT)] in three carrot inbreds with contrasting root color: solid purple (phloem and xylem); purple outer phloem/orange xylem; and orange phloem and xylem. Transcripts for five of these genes (CHS1, DFR1, F3H, LDOX2, PAL3) accumulated at high levels in solid purple carrots, less in purple-orange carrot, and low or no transcript in orange carrots. Gene expression coincided with anthocyanin accumulation. In contrast, UFGT expression was comparable in purple and orange carrots and relatively unchanged during root development. In addition, five anthocyanin biosynthesis genes [FLS1 (flavonol synthase), F3H, LDOX2, PAL3, and UFGT] and three anthocyanin transcription factors (DcEFR1, DcMYB3 and DcMYB5) were mapped in a population segregating for the P 1 locus that conditions purple root color. P 1 mapped to chromosome 3 and of the eight anthocyanin biosynthesis genes, only F3H and FLS1 were linked to P 1. The gene expression and mapping data suggest a coordinated regulatory control of anthocyanin expression in carrot root and establish a framework for studying the anthocyanin pathway in carrots, and they also suggest that none of the genes evaluated is a candidate for P 1.

Three types of ultraviolet irradiation differentially promote expression of shikimate pathway genes and production of anthocyanins in grape berries

Modulation of flavonoid biosynthesis in grape berries has always aroused great attention among researchers. However, little study has been made on the shikimate pathway that guides photo-assimilate flow into flavonoid metabolism. The present study indicated that the treatments of three ultraviolet (UV) wavelengths differentially up-regulated transcriptional expression of some structural genes in the shikimate pathway and post-chorismate pathway of grape berries and this up-regulation was developmental stage-dependent and not synchronous. Of these genes, VvDAHPS-1 and VvDAHPS-2 encoding the entry enzymes of the shikimate pathway showed most significant UV-response and their transcription was strongly promoted by UV-A stimuli in the 3-week grapes and by UV-B and UV-C in the 7-week and 11-week grapes. The elevation of VvAS expression by UV induction appeared in the 3-week grapes and VvCM-1 was expressed relatively more concomitantly with berry mature. Correspondently, UV-B and UV-C irradiation increased the content of various anthocyanins in the 11-week grapes, but UV-A did not. These data suggest that UV-responsive production of anthocyanins is in part a consequence of the increase in carbon supply via promoting the shikimate pathway and the Phe/Trp specific pathway.

Biosynthesis and genetic regulation of proanthocyanidins in plants

Proanthocyanidins (PAs), also known as condensed tannins, are a group of polyphenolic secondary metabolites synthesized in plants as oligomers or polymers of flavan-3-ol units via the flavonoid pathway. Due to their structural complexity and varied composition, only in the recent years has the study on the biosynthesis and regulation of PAs in plants taken off, although some details of the synthetic mechanism remain unclear. This paper aims to summarize the status of research on the structures of PAs in plants, the genes encoding key enzymes of biosynthetic pathway, the transport factors, the transcriptional regulation of PA biosynthesis and the genetic manipulation of PAs. The problems of this field were also discussed, including the nature of the final "enzyme" which catalyzes the polymerization reaction of PAs and the possible mechanism of how the elementary units of flavanols are assembled in vivo.

Modifying the acylation of flavonols in Petunia hybrida

The potential for chemically-regulating the acylation of natural products in whole plants has been determined by treating petunia leaves with phenylpropanoid acyl donors supplied as the respective methyl esters. Treatment with derivatives of the naturally-occurring acylating species caffeic acid resulted in a general increase in flavonol derivatives, notably caffeoylated quercetin-3-O-diglucoside (QDG) and kaempferol-3-O-diglucoside (KDG). Similarly, methyl ferulate increased the content of feruloylated KDG 40-fold. Treatment with methyl coumarate resulted in the appearance of a coumaroylated derivative of quercetin-3-O-glucuronyl-glucoside (QGGA). When the feeding studies were repeated with the equivalent phenylpropanoid isosubstituted with fluorine groups a semi-synthetic 4-fluorocinnamoyl ester of QGGA was observed. Our results demonstrate the potential to regulate the acylation of flavonols and potentially other natural products by treating whole plants with methyl esters of natural and unnatural acyl donors.

Molecular evolution of flavonoid dioxygenases in the family Apiaceae

Plant species of the family Apiaceae are known to accumulate flavonoids mainly in the form of flavones and flavonols. Three 2-oxoglutarate-dependent dioxygenases, flavone synthase or flavanone 3 beta-hydroxylase and flavonol synthase are involved in the biosynthesis of these secondary metabolites. The corresponding genes were cloned recently from parsley (Petroselinum crispum) leaves. Flavone synthase I appears to be confined to the Apiaceae, and the unique occurrence as well as its high sequence similarity to flavanone 3beta-hydroxylase laid the basis for evolutionary studies. In order to examine the relationship of these two enzymes throughout the Apiaceae, RT-PCR based cloning and functional identification of flavone synthases I or flavanone 3beta-hydroxylases were accomplished from Ammi majus, Anethum graveolens, Apium graveolens, Pimpinella anisum, Conium maculatum and Daucus carota, yielding three additional synthase and three additional hydroxylase cDNAs. Molecular and phylogenetic analyses of these sequences were compatible with the phylogeny based on morphological characteristics and suggested that flavone synthase I most likely resulted from gene duplication of flavanone 3beta-hydroxylase, and functional diversification at some point during the development of the apiaceae subfamilies. Furthermore, the genomic sequences from Petroselinum crispum and Daucus carota revealed two introns in each of the synthases and a lack of introns in the hydroxylases. These results might be explained by intron losses from the hydroxylases occurring at a later stage of evolution.

Anthocyanins and Human Health: An In Vitro Investigative Approach

Anthocyanin pigments and associated flavonoids have demonstrated ability to protect against a myriad of human diseases, yet they have been notoriously difficult to study with regard to human health. Anthocyanins frequently interact with other phytochemicals to potentiate biological effects, thus contributions from individual components are difficult to decipher. The complex, multicomponent structure of compounds in a bioactive mixture and the degradation of flavonoids during harsh extraction procedures obscure the precise assignment of bioactivity to individual pigments. Extensive metabolic breakdown after ingestion complicates tracking of anthocyanins to assess absorption, bioavailability, and accumulation in various organs. Anthocyanin pigments and other flavonoids that are uniformly, predictably produced in rigorously controlled plant cell culture systems can be a great advantage for health and nutrition research because they are quickly, easily isolated, lack interferences found in whole fruits, can be elicited to provoke rapid and prolific accumulation, and are amenable to biolabeling so that metabolic fate can be investigated after ingestion.