Identification and Characterization of Anthocyanin Biosynthesis-Related Genes in Kohlrabi

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

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

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.

Anthocyanins, Vibrant Color Pigments, and Their Role in Skin Cancer Prevention

Until today, numerous studies evaluated the topic of anthocyanins and various types of cancer, regarding the anthocyanins' preventative and inhibitory effects, underlying molecular mechanisms, and such. However, there is no targeted review available regarding the anticarcinogenic effects of dietary anthocyanins on skin cancers. If diagnosed at the early stages, the survival rate of skin cancer is quite high. Nevertheless, the metastatic form has a short prognosis. In fact, the incidence of melanoma skin cancer, the type with high mortality, has increased exponentially over the last 30 years, causing the majority of skin cancer deaths. Malignant melanoma is considered a highly destructive type of skin cancer due to its particular capacity to grow and spread faster than any other type of cancers. Plants, in general, have been used in disease treatment for a long time, and medicinal plants are commonly a part of anticancer drugs on the market. Accordingly, this work primarily aims to emphasize the most recent improvements on the anticarcinogenic effects of anthocyanins from different plant sources, with an in-depth emphasis on melanoma skin cancer. We also briefly summarized the anthocyanin chemistry, their rich dietary sources in flowers, fruits, and vegetables, as well as their associated potential health benefits. Additionally, the importance of anthocyanins in topical applications such as their use in cosmetics is also given.

Isolation and Analysis of Anthocyanin Pathway Genes from Ribes Genus Reveals MYB Gene with Potent Anthocyanin-Inducing Capabilities

Horticultural crops of the Ribes genus are valued for their anthocyanin-rich fruits, but until now, there were no data about the genes and regulation of their flavonoid pathway. In this study, the coding sequences of flavonoid pathway enzymes and their putative regulators MYB10, bHLH3 and WD40 were isolated, and their expression analyzed in fruits with varying anthocyanin levels from different cultivars of four species belonging to the Ribes genus. Transcription levels of anthocyanin synthesis enzymes and the regulatory gene RrMYB10 correlated with fruit coloration and anthocyanin quantities of different Ribes cultivars. Regulatory genes were tested for the ability to modulate anthocyanin biosynthesis during transient expression in the leaves of two Nicotiana species and to activate Prunus avium promoters of late anthocyanin biosynthesis genes in N. tabacum. Functional tests showed a strong capability of RrMyb10 to induce anthocyanin synthesis in a heterologous system, even without the concurrent expression of any heterologous bHLH, whereas RrbHLH3 enhanced MYB-induced anthocyanin synthesis. Data obtained in this work facilitate further analysis of the anthocyanin synthesis pathway in key Ribes species, and potent anthocyanin inducer RrMyb10 can be used to manipulate anthocyanin expression in heterologous systems.

The novel gene BrMYB2, located on chromosome A07, with a short intron 1 controls the purple-head trait of Chinese cabbage (Brassica rapa L.)

Anthocyanins are important secondary metabolites in plants, but information on anthocyanin biosynthesis mechanisms in Chinese cabbage is limited. The new purple head Chinese cabbage cultivar 11S91 was analyzed, and an R2R3-MYB regulatory gene BrMYB2, located on chromosome A07, controlling the dominant purple-head trait was isolated. High expression of BrMYB2 generated a large accumulation of anthocyanins in 11S91, accompanied by highly upregulated BrTT8, BrF3'H, BrDFR1, BrANS1, BrUGTs, BrATs, and BrGSTs. 11S91 inherited the purple locus from purple trait donor 95T2-5, and they shared consensus CDSs and gDNAs with those of BrMYB2 (cBrMYB2 and gBrMYB2). Two SNPs in cBrMYB2 in 11S91 did not cause loss of function; in addition to several SNPs at both ends of intron 1, a large deletion had occurred in intron 1 of gBrMYB2 in 11S91. Genetic transformation of Arabidopsis showed that gBrMYB2 overexpression lines presented deeper purple color and higher expression than did the cBrMYB2 and cBrmyb2 lines, whereas gBrmyb2 with a long intron 1 did not cause the purple phenotype. We first show that BrMYB2 promotes anthocyanin biosynthesis under the control of the short intron 1 of gBrMYB2 in purple head Chinese cabbage, and gBrmyb2 with a long intron 1 represses anthocyanin production in white head Chinese cabbage. This evidence provides a new understanding of anthocyanin biosynthesis and purple germplasm generation in Brassica vegetables.

Pigment variation and transcriptional response of the pigment synthesis pathway in the S2309 triple-color ornamental kale (Brassica oleracea L. var. acephala) line

Ornamental kale is popular because of its colorful leaves and few studies have investigated the mechanism of color changes. In this study, an ornamental kale line (S2309) with three leaf colors was developed. Analysis of the anthocyanin, chlorophyll, and carotenoid contents and RNA-seq were performed on the three leaf color types. There was less chlorophyll in the white leaves and purple leaves than in the green leaves, and the anthocyanin content was greatest in the purple leaves. All the downregulated DEGs related to chlorophyll metabolism were detected only in the S2309_G vs. S2309_W comparison, which indicated that the decrease in chlorophyll content was caused mainly by the inhibition of chlorophyll biosynthesis during the leaf color change from green to white. Moreover, the expression of 19 DEGs involved in the anthocyanin biosynthesis pathway was upregulated. These results provide new insight into the mechanisms underlying the three-color formation.

Grown to be Blue-Antioxidant Properties and Health Effects of Colored Vegetables. Part I: Root Vegetables

During the last few decades, the food and beverage industry faced increasing demand for the design of new functional food products free of synthetic compounds and artificial additives. Anthocyanins are widely used as natural colorants in various food products to replenish blue color losses during processing and to add blue color to colorless products, while other compounds such as carotenoids and betalains are considered as good sources of other shades. Root vegetables are well known for their broad palette of colors, and some species, such as black carrot and beet root, are already widely used as sources of natural colorants in the food and drug industry. Ongoing research aims at identifying alternative vegetable sources with diverse functional and structural features imparting beneficial effects onto human health. The current review provides a systematic description of colored root vegetables based on their belowground edible parts, and it highlights species and/or cultivars that present atypical colors, especially those containing pigment compounds responsible for hues of blue color. Finally, the main health effects and antioxidant properties associated with the presence of coloring compounds are presented, as well as the effects that processing treatments may have on chemical composition and coloring compounds in particular.

Anthocyanins: From plant pigments to health benefits at mitochondrial level

Anthocyanins are water-soluble pigments providing certain color for various plant parts, especially in edible berries. Earlier these compounds were only known as natural food colorants, the stability of which depended on pH, light, storage temperature and chemical structure. However, due to the increase of the in vitro, in vivo experimental data, as well as of the epidemiological studies, today anthocyanins and their metabolites are also regarded as potential pharmaceutical compounds providing various beneficial health effects on either human or animal cardiovascular system, brain, liver, pancreas and kidney. Many of these effects are shown to be related to the free-radical scavenging and antioxidant properties of anthocyanins, or to their ability to modulate the intracellular antioxidant systems. However, it is generally overlooked that instead of acting exclusively as antioxidants certain anthocyanins affect the activity of mitochondria that are the main source of energy in cells. Therefore, the aim of the present review is to summarize the major knowledge about the chemistry and regulation of biosynthesis of anthocyanins in plants, to overview the facts on bioavailability, and to discuss the most recent experimental findings related to the beneficial health effects emphasizing mitochondria.

Abscisic acid and ethylene biosynthesis-related genes are associated with anthocyanin accumulation in purple ornamental cabbage (Brassica oleracea var. acephala)

Purple ornamental cabbage (Brassica oleracea var. acephala) is a popular decorative plant, cultivated for its colorful leaf rosettes that persist in cool weather. It is characterized by green outer leaves and purple inner leaves, whose purple pigmentation is due to the accumulation of anthocyanin pigments. Phytohormones play important roles in anthocyanin biosynthesis in other species. Here, we identified 14 and 19 candidate genes putatively involved in abscisic acid (ABA) and ethylene (ET) biosynthesis, respectively, in B. oleracea. We determined the expression patterns of these candidate genes by reverse-transcription quantitative PCR (RT-qPCR). Among candidate ABA biosynthesis-related genes, the expressions of BoNCED2.1, BoNCED2.2, BoNCED6, BoNCED9.1, and BoAAO3.2 were significantly higher in purple compared to green leaves. Likewise, most of the ET biosynthetic genes (BoACS6, BoACS9.1, BoACS11, BoACO1.1, BoACO1.2, BoACO3.1, BoACO4, and BoACO5) had significantly higher expression in purple compared to green leaves. Among these genes, BoNCED2.1, BoNCED2.2, BoACS11, and BoACO4 showed particularly strong associations with total anthocyanin content of the purple inner leaves. Our results suggest that ABA and ET might promote the intense purple pigmentation of the inner leaves of purple ornamental cabbage.

Molecular analysis of anthocyanin biosynthesis-related genes reveal BoTT8 associated with purple hypocotyl of broccoli (Brassica oleracea var. italica L.)

Broccoli (Brassica oleracea var. italica L.) is a highly nutritious vegetable that typically forms pure green or purple florets. However, green broccoli florets sometimes accumulate slight purplish pigmentation in response environmental factors, decreasing their market value. In the present study, we aimed to develop molecular markers to distinguish broccoli genotypes as pure green or purplish floret color at the early seedling stage. Anthocyanins are known to be involved in the purple pigmentation in plants. The purplish broccoli lines were shown to accumulate purple pigmentation in the hypocotyls of very young seedlings; therefore, the expression profiles of the structural and regulatory genes of anthocyanin biosynthesis were analyzed in the hypocotyls using qRT-PCR. BoPAL, BoDFR, BoMYB114, BoTT8, BoMYC1.1, BoMYC1.2, and BoTTG1 were identified as putative candidate genes responsible for the purple hypocotyl color. BoTT8 was much more highly expressed in the purple than green hypocotyls; therefore, it was cloned and sequenced from various broccoli lines, revealing SNP and InDel variations between these genotypes. We tested four SNPs (G > A; A > T; G > C; T > G) in the first three exons and a 14-bp InDel (ATATTTATATATAT) in the BoTT8 promoter in 51 broccoli genotypes, and we found these genetic variations could distinguish the green lines, purple lines, and F₁ hybrids. These novel molecular markers could be useful in broccoli breeding programs to develop a true green or purple broccoli cultivar.

Expression profiles of organogenesis-related genes over the time course of one-step de novo shoot organogenesis from intact seedlings of kohlrabi

Kohlrabi (Brassica oleracea var. gongylodes) is an important vegetable crop that is able to undergo shoot regeneration in culture from intact seedlings in a single-step regeneration process, using cytokinin as the only plant growth regulator. In this work, we present the expression profiles of seven organogenesis-related genes over the time course of shoot regeneration from intact seedlings of kohlrabi cv. Vienna Purple on shoot regeneration media containing trans-zeatin, cis-zeatin, benzyl adenine or thidiazuron. Two auxin transporter genes - PIN3 and PIN4, a cytokinin response regulator - ARR5, two shoot apical meristem-related transcription factors - CUC1 and RGD3, and two cell cycle-related genes - CDKB2;1 and CYCB2;4 - displayed bimodal expression patterns on most cytokinin-containing media when their expression levels were normalized against control plants grown on hormone-free media. The first expression peak corresponded to direct upregulation by cytokinin from the growth media, and the second one reflected transcriptional events related to callus formation and/or acquisition of organogenic competence, corresponding to the shoot regeneration phases that have already been characterized in Arabidopsis thaliana. We demonstrate that the genes involved in the two-step shoot regeneration of Arabidopsis display their expected expression profiles during the single-step shoot regeneration of its close phylogenetic relative kohlrabi confirming the universality of their roles in the distinct phases of the regeneration process in Brassicaceae. The results presented here represent a first step towards genetic characterization of the morphogenetic processes in this important crop species.

Transcriptome profiling of two contrasting ornamental cabbage (Brassica oleracea var. acephala) lines provides insights into purple and white inner leaf pigmentation

Background

Ornamental cabbage (Brassica oleracea var. acephala) is an attractive landscape plant that remains colorful at low temperatures during winter. Its key feature is its inner leaf coloration, which can include red, pink, lavender, blue, violet and white. Some ornamental cabbages exhibit variation in leaf color pattern linked to leaf developmental stage. However, little is known about the molecular mechanism underlying changes in leaf pigmentation pattern between developmental stages.

Results

The transcriptomes of six ornamental cabbage leaf samples were obtained using Illumina sequencing technology. A total of 339.75 million high-quality clean reads were assembled into 46,744 transcripts and 46,744 unigenes. Furthermore, 12,771 genes differentially expressed across the different lines and stages were identified by pairwise comparison. We identified 74 and 13 unigenes as differentially expressed genes related to the anthocyanin biosynthetic pathway and chlorophyll metabolism, respectively. Among them, three unigenes (BoC4H2, BoUGT9, and BoGST21) and six unigenes (BoHEMA1, BoCRD1, BoPORC1, BoPORC2, BoCAO, and BoCLH1) were found as candidates for the genes encoding enzymes in the anthocyanin biosynthetic pathway and chlorophyll metabolism, respectively. In addition, two unigenes (BoRAX3 and BoTRB1) as MYB candidates, two unigenes (BoMUTE1, and BHLH168-like) as bHLH candidates were identified for purple pigmentation in ornamental cabbage.

Conclusion

Our results indicate that the purple inner leaves of purple ornamental cabbage result from a high level of anthocyanin biosynthesis, a high level of chlorophyll degradation and an extremely low level of chlorophyll biosynthesis, whereas the bicolor (purple/green) outer leaves are due to a moderate level of anthocyanin biosynthesis, a high level of chlorophyll degradation and a very low level of chlorophyll biosynthesis. In white ornamental cabbage, the white inner leaves are due to an extremely low level or absence of anthocyanin biosynthesis, a high level of chlorophyll degradation and a very low level of chlorophyll biosynthesis, whereas the bicolor (white/green) leaves are due to a high level of chlorophyll degradation and a low level of chlorophyll biosynthesis and absence of anthocyanin biosynthesis. These results provide insight into the molecular mechanisms underlying inner and bicolor leaf pigmentation in ornamental cabbage and offer a platform for assessing related ornamental species.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5199-3) contains supplementary material, which is available to authorized users.

Understanding the genetic regulation of anthocyanin biosynthesis in plants - Tools for breeding purple varieties of fruits and vegetables

Anthocyanins are naturally occurring flavonoids derived from the phenylpropanoid pathway. There is increasing evidence of the preventative and protective roles of anthocyanins against a broad range of pathologies, including different cancer types and metabolic diseases. However, most of the fresh produce available to consumers typically contains only small amounts of anthocyanins, mostly limited to the epidermis of plant organs. Therefore, transgenic and non-transgenic approaches have been proposed to enhance the levels of this phytonutrient in vegetables, fruits, and cereals. Here, were review the current literature on the anthocyanin biosynthesis pathway in model and crop species, including the structural and regulatory genes involved in the differential pigmentation patterns of plant structures. Furthermore, we explore the genetic regulation of anthocyanin biosynthesis and the reasons why it is strongly repressed in specific cell types, in order to create more efficient breeding strategies to boost the biosynthesis and accumulation of anthocyanins in fresh fruits and vegetables.

Molecular analysis of anthocyanin-related genes in ornamental cabbage

Ornamental cabbage (Brassica oleracea var. acephala) is a winter-grown and important decorative plant of the family Brassicaceae, which displays an exceptional coloration in the central leaves of the rosette. Anthocyanins are the key determinant of the red, purple, and blue colors of vegetative and reproductive parts of many plant species including ornamental cabbage. Total anthocyanin content was measured spectrophotometrically, and the highest anthocyanin content was detected in the red followed by light-red and white ornamental cabbage lines. Anthocyanin biosynthesis is controlled by members of three different transcription factor (TF) families, such as MYB, basic helix-loop-helix (bHLH), and WD40 repeats (WDR), which function as a MBW complex. We identified three MYB, six bHLH, and one WDR TFs that regulate anthocyanin biosynthesis in ornamental cabbage. The expression of the regulatory and biosynthetic genes for anthocyanin synthesis was determined by qPCR. The tested structural genes of the anthocyanin pathway were shown to be up-regulated in the red followed by light-red ornamental cabbage lines; however, the expression levels of the late biosynthetic genes were barely detected in the white ornamental cabbage lines. Among the regulatory genes, BoPAP2 (MYB), BoTT8, BoEGL3.1, and BoMYC1.2 (bHLH), and BoTTG1 (WDR) were identified as candidates for the regulation of anthocyanin biosynthesis. This work could be useful for the breeding of novel colorful ornamental cabbage cultivars.