Mechanism Of Anthocyanin Biosynthesis Research Articles

The ncRNAs Involved in the Regulation of Abiotic Stress-Induced Anthocyanin Biosynthesis in Plants.

Plants have evolved complicated defense and adaptive systems to grow in various abiotic stress environments such as drought, cold, and salinity. Anthocyanins belong to the secondary metabolites of flavonoids with strong antioxidant activity in response to various abiotic stress and enhance stress tolerance. Anthocyanin accumulation often accompanies the resistance to abiotic stress in plants to scavenge reactive oxygen species (ROS). Recent research evidence showed that many regulatory pathways such as osmoregulation, antioxidant response, plant hormone response, photosynthesis, and respiration regulation are involved in plant adaption to stress. However, the molecular regulatory mechanisms involved in controlling anthocyanin biosynthesis in relation to abiotic stress response have remained obscure. Here, we summarize the current research progress of specific regulators including small RNAs, and lncRNAs involved in the molecular regulation of abiotic stress-induced anthocyanin biosynthesis. In addition, an integrated regulatory network of anthocyanin biosynthesis controlled by microRNAs (miRNAs), long non-coding RNAs (lncRNAs), transcription factors, and stress response factors is also discussed. Understanding molecular mechanisms of anthocyanin biosynthesis for ROS scavenging in various abiotic stress responses will benefit us for resistance breeding in crop plants.

Identification of HpMYB1 inducing anthocyanin accumulation in Hippeastrum Hybridum tepals by RNA-seq

BackgroundCultivated Hippeastrum × hybridum is a popular ornamental plant with large and colorful flowers, long flowering duration, and high commercial value. As its main ornamental feature, its flower color is related to the anthocyanin content in the tepals. However, the molecular regulatory mechanisms of anthocyanin biosynthesis in H. × hybridum have not yet been elucidated.ResultsIn the present study, 12 cDNA libraries of four stages of H.× hybridum ‘Royal Velvet’ tepal development were used for RNA-seq, obtaining 79.83 gigabases (GB) of clean data. The data were assembled into 148,453 unigenes, and 11,262 differentially expressed genes were identified. Forty key enzymes participating in anthocyanin biosynthesis were investigated, and the results showed that most of the anthocyanin structural genes were expressed at low levels in S1 and were markedly upregulated in S2 and S3. The expression profiles of 12 selected genes were verified by qRT-PCR. Furthermore, the R2R3-MYB transcription factor (TF), HpMYB1, involved in the regulation of anthocyanin biosynthesis was identified by sequence, expression pattern, and subcellular localization analyses. Its overexpression in tobacco significantly increased the anthocyanin levels in various tissues and activated anthocyanin-related genes.ConclusionsUsing RNA-seq technology, we successfully identified a potential R2R3-MYB gene, HpMYB1, that regulates anthocyanin biosynthesis in H.× hybridum ‘Royal Velvet’. Our findings provide basic transcript information and valuable transcriptome data for further identification of key genes involved in anthocyanin biosynthesis and can be applied in the artificial breeding of new H. × hybridum cultivars with enhanced ornamental value.

Integrated Transcriptomic and Metabolomic Analysis Reveal the Underlying Mechanism of Anthocyanin Biosynthesis in Toona sinensis Leaves.

Toona sinensis, commonly known as Chinese Toon, is a plant species that possesses noteworthy value as a tree and vegetable. Its tender young buds exhibit a diverse range of colors, primarily determined by the presence and composition of anthocyanins and flavonoids. However, the underlying mechanisms of anthocyanin biosynthesis in Toona sinensis have been rarely reported. To explore the related genes and metabolites associated with composition of leaf color, we conducted an analysis of the transcriptome and metabolome of five distinct Toona clones. The results showed that differentially expressed genes and metabolites involved in anthocyanin biosynthesis pathway were mainly enriched. A conjoint analysis of transcripts and metabolites was carried out in JFC (red) and LFC (green), resulting in the identification of 510 genes and 23 anthocyanin-related metabolites with a positive correlation coefficient greater than 0.8. Among these genes and metabolites, 23 transcription factors and phytohormone-related genes showed strong coefficients with 13 anthocyanin derivates, which mainly belonged to the stable types of delphinidin, cyanidin, peonidin. The core derivative was found to be Cyanidin-3-O-arabinoside, which was present in JFC at 520.93 times the abundance compared to LFC. Additionally, the regulatory network and relative expression levels of genes revealed that the structural genes DFR, ANS, and UFGT1 might be directly or indirectly regulated by the transcription factors SOC1 (MADS-box), CPC (MYB), and bHLH162 (bHLH) to control the accumulation of anthocyanin. The expression of these genes was significantly higher in red clones compared to green clones. Furthermore, RNA-seq results accurately reflected the true expression levels of genes. Overall, this study provides a foundation for future research aimed at manipulating anthocyanin biosynthesis to improve plant coloration or to derive human health benefits.

Metabolome and transcriptome analyses reveal the colouring mechanism of red honeysuckle (Lonicera japonica Thunb.)

Honeysuckle has been widely used as a medicinal herb and food additive in China for a long time. However, little is known about the pigment composition and colouring mechanism of red honeysuckle, which is a rare germplasm resource. This study aims to investigate the anthocyanin components and colouring mechanism of red honeysuckle, and to identify potential regulatory genes in the anthocyanin biosynthesis pathway. ‘Yujin 1’ and ‘Yujin 2’, with yellow-white and red flower buds, respectively, were selected for the study. Using a metabolomics method, we identified the anthocyanin components, while transcriptomics analysis was used to mine the structural and regulatory genes of the anthocyanin biosynthesis pathway. Additionally, protein-protein interaction analysis was employed to predict the regulation mechanism of anthocyanin biosynthesis. The results revealed that cyanidin-3,5-O-diglucoside, peonidin-3,5-O-diglucoside, and cyanidin-3-O-glucoside were the main pigment components of red honeysuckle. We also constructed a possible anthocyanin biosynthetic pathway and identified MYB and bHLH transcription factors that may play regulatory roles in this pathway. Furthermore, our findings suggest that bHLH23 may regulate anthocyanin biosynthesis by binding to the DFR gene promoter. These findings have significant implications for breeding new honeysuckle varieties and developing functional foods and medicines.

ChMYB1-ChbHLH42-ChTTG1 module regulates abscisic acid-induced anthocyanin biosynthesis in Cerasus humilis

Cerasus humilis is a kind of economic fruit tree peculiar to China, which is widely used in the food, landscape, and pharmaceutical industries. Anthocyanins are a phenolic metabolite that plays an essential role in fruit coloration. However, the regulatory network of C. humilis in anthocyanin biosynthesis is still unclear. In this study, the R2R3-MYB transcription factor ChMYB1 was isolated from the full genome of the species. Yeast one-hybrid, dual-luciferase assays, and GUS staining showed that ChMYB1 significantly increased anthocyanin contents in C. humilis fruit by promoting the expression of ChCHS and ChUFGT by binding MBS (MYB-binding elements). ChMYB1 interacted with ChbHLH42 and ChTTG1 to form the MBW complex and further enhanced the expression of ChUFGT. In addition, abscisic acid (ABA) treatment promoted the expression of ChMYB1 and anthocyanin accumulation in C. humilis fruit. Interestingly, ABA treatment enhanced the interaction between ChMYB1 and ChbHLH42. Furthermore, ChABI5 inhibited the interaction between ChMYB1 and ChbHLH42. Our data elucidated the primary molecular mechanism of anthocyanin biosynthesis in C. humilis fruit, deepening the understanding of the regulatory network affecting anthocyanin metabolism in edible fruit crops.

The PcERF5 promotes anthocyanin biosynthesis in red-fleshed pear (Pyrus communis) through both activating and interacting with PcMYB transcription factors

As there is a strong interest in red-skinned pears, the molecular mechanism of anthocyanin regulation in red-skinned pears has been widely investigated; however, little is known about the molecular mechanism of anthocyanin regulation in red-fleshed pears due to limited availability of such germplasm, primarily found in European pears (Pyrus communis). In this study, based on transcriptomic analysis in red-fleshed and white-fleshed pears, we identified an ethylene response factor (ERF) from P. communis, PcERF5, of which expression level in fruit flesh was significantly correlated with anthocyanin content. We then verified the function of PcERF5 in regulating anthocyanin accumulation by genetic transformation in both pear skin and apple calli. PcERF5 regulated anthocyanin biosynthesis by different regulatory pathways. On the one hand, PcERF5 can activate the transcription of flavonoid biosynthetic genes (PcDFR, PcANS and PcUFGT) and two key transcription factors encoding genes PcMYB10 and PcMYB114. On the other hand, PcERF5 interacted with PcMYB10 to form the ERF5-MYB10 protein complex that enhanced the transcriptional activation of PcERF5 on its target genes. Our results suggested that PcERF5 functioned as a transcriptional activator in regulating anthocyanin biosynthesis, which provides new insights into the regulatory mechanism of anthocyanin biosynthesis. This new knowledge will provide guidance for molecular breeding of red-fleshed pear.

Light-mediated anthocyanin biosynthesis in rose petals involves a balanced regulatory module comprising transcription factors RhHY5, RhMYB114a, and RhMYB3b.

Roses are significant botanical species with both ornamental and economic value, displaying diverse floral traits, particularly an extensive array of petal colors. The red pigmentation of rose petals is predominantly attributed to anthocyanin accumulation. However, the underlying regulatory mechanism of anthocyanin biosynthesis in roses remains elusive. This study presents a novel light-responsive regulatory module governing anthocyanin biosynthesis in rose petals, which involves the transcription factors RhHY5, RhMYB114a, and RhMYB3b. Under light conditions (1000-1500 μmol m-2 s-1), RhHY5 represses RhMYB3b expression and induces RhMYB114a expression, positively regulating anthocyanin biosynthesis in rose petals. Notably, activation of anthocyanin structural genes probably involves an interaction and synergy between RhHY5 and the MYB114a-bHLH3-WD40 complex. Additionally, RhMYB3b is activated by RhMYB114a to prevent excessive accumulation of anthocyanin. Conversely, under low light conditions (<10 μmol m-2 s-1), the degradation of RhHY5 leads to down-regulation of RhMYB114a and up-regulation of RhMYB3b, which in turn inhibits the expression of both RhMYB114a and anthocyanin structural genes. Additionally, RhMYB3b competes with RhMYB114a for binding to RhbHLH3 and the promoters of anthocyanin-related structural genes. Overall, our study uncovers a complex light-mediated regulatory network that governs anthocyanin biosynthesis in rose petals, providing new insights into the molecular mechanisms underlying petal color formation in rose.

A novel transcription factor PsMYBM enhances the biosynthesis of anthocyanins in response to light in tree peony

Light is a vital environmental factor that affects the biosynthesis of anthocyanin, and the ornamental and economic value of ornamental plants can be improved by properly regulating the conditions of light for their growth. Tree peony (Paeonia suffruticosa Andrews), “the king of flowers” in China, is popular in the whole country and contributes to cultivar breeding throughout the world. In the tree peony industry, light affects not only flower color and quality when the cultivation of flowers is forced but also its ornamental value in specific gardens and fields. However, the molecular mechanism on how light regulates the biosynthesis of anthocyanin is unclear. In this study, darkness was found to decrease the pigmentation of flower petals in the tree peony cultivar ‘Higurashi’. The differentially expressed genes responsible for anthocyanin biosynthesis were obtained through a comparative transcriptome analysis of flower petals under light/dark conditions. This led to the identification of an R2R3-MYB transcription factor designated PsMYBM. The transient silencing of PsMYBM reduced the biosynthesis of anthocyanins in the petals, while its overexpression promoted the formation of various colors in organs in transgenic tobacco (Nicotiana tabacum cv. Nc89) plants. In addition, it has been demonstrated that PsMYBM can directly activate the promotors of PsCHS and PsF3H. Moreover, light-responsive elements were also identified in the PsMYBM promoter, which could be directly bound by the light signal factor PsHY5. This study illuminates the mechanism of anthocyanin biosynthesis in response to light in tree peony, which could be applied to other woody ornamental plants. It also provides key gene resources to improve the flower color and germplasm innovation.

Re-sequencing and transcriptomic analysis reveal differential expression patterns and sequence variation in glucosyltransferase gene related to anthocyanin biosynthesis in walnut ( Juglans regia L.)

The color of walnut peel, usually green during the development stages, is one of the important appearance qualities of walnut fruit. Red walnut ‘RW-1’ with red peel is a specific germplasm resources due to anthocyanin accumulation, but the mechanism remains unclear. Here, re-sequencing and transcriptome were used to analyze the differences of anthocyanin accumulation in walnut peel with different colors. There were 2,696,620 SNPs and 495,238 InDels between ‘Zhonglin 1’ and ‘RW-1’, and the genetic relationship between them was closer than that of either and walnut reference genome ‘Chandler’. 1,156 differentially expressed genes (DEGs) with structural polymorphisms were screened by combining re-sequencing and transcriptome analysis. LOC108991235 (JrUFGT5), encoding anthocyanidin 3-O-glucosyltransferase, was identified by KEGG function enrichment. The JrUFGT5 gene base substitutions identified in the coding sequence (CDS) region resulted in amino acid variation, but did not occur in the protein domain region. The expression pattern of JrUFGT5 gene was positively correlated with the anthocyanin accumulation in different walnut peels, and the subcellular localization analysis showed JrUFGT5 was located in the cytoplasm and nucleus. Collectively, these findings revealed the differential expression patterns and sequence variation of a crucial anthocyanidin 3-O-glucosyltransferase gene in walnuts with different colors, which is of great significance to the exploration of the mechanism of anthocyanin biosynthesis in red walnut.

Identification of CaPs locus involving in purple stripe formation on unripe fruit, reveals allelic variation and alternative splicing of R2R3-MYB transcription factor in pepper (Capsicum annuum L.).

The purple color of unripe pepper fruit is attributed to the accumulation of anthocyanins. Only a few genes controlling the biosynthesis and regulation of anthocyanins have been cloned in Capsicum. In this study, we performed a bulked segregant analysis of the purple striped trait using an F2 population derived from a cross between the immature purple striped fruit line Chen12-4-1-1-1-1 and the normal green fruit line Zhongxian101-M-F9. We mapped the CaPs locus to an 841.39 kb region between markers M-CA690-Xba and MCA710-03 on chromosome 10. CA10g11690 encodes an R2R3-MYB transcription factor that is involved in the biosynthesis of anthocyanins as the best candidate gene. Overexpression and silencing in transformed tobacco (Nicotiana tabacum) lines indicated that CA10g11690 is involved in the formation of purple stripes in the exocarp. A comparison of parental sequences identified an insertion fragment of 1,926 bp in the second intron region of Chen12-4, and eight SNPs were detected between the two parents. Additionally, there were 49 single nucleotide polymorphic variations, two sequence deletions, and four sequence insertions in the promoter region. We found that CA10g11690 undergoes alternative splicing and generates different transcripts. Thus, the functional transcript of CA10g11690 appeared to be primarily involved in the development of purple phenotype in the exocarp. Our data provide new insight into the mechanism of anthocyanin biosynthesis and a theoretical basis for the future breeding of purple striped pepper varieties.

Transcriptome and metabolome analyses reveal molecular mechanisms of anthocyanin-related leaf color variation in poplar (Populus deltoides) cultivars.

Colored-leaf plants are increasingly popular for their aesthetic, ecological, and social value, which are important materials for research on the regulation of plant pigments. However, anthocyanin components and the molecular mechanisms of anthocyanin biosynthesis in colored-leaf poplar remain unclear. Consequently, an integrative analysis of transcriptome and metabolome is performed to identify the key metabolic pathways and key genes, which could contribute to the molecular mechanism of anthocyanin biosynthesis in the colored-leaf cultivars poplar. In this study, integrated metabolite and transcriptome analysis was performed to explore the anthocyanin composition and the specific regulatory network of anthocyanin biosynthesis in the purple leaves of the cultivars 'Quanhong' (QHP) and 'Zhongshanyuan' (ZSY). Correlation analysis between RNA-seq data and metabolite profiles were also performed to explore the candidate genes associated with anthocyanin biosynthesis. R2R3-MYB and bHLH TFs with differential expression levels were used to perform a correlation analysis with differentially accumulated anthocyanins. A total of 39 anthocyanin compounds were detected by LC-MS/MS analysis. Twelve cyanidins, seven pelargonidins, five delphinidins, and five procyanidins were identified as the major anthocyanin compounds, which were differentially accumulated in purple leaves of QHP and ZSY. The major genes associated with anthocyanin biosynthesis, including structural genes and transcription factors, were differentially expressed in purple leaves of QHP and ZSY through RNA-sequencing (RNA-seq) data analysis, which was consistent with quantitative real-time PCR analysis results. Correlation analysis between RNA-seq data and metabolite profiles showed that the expression patterns of certain differentially expressed genes in the anthocyanin biosynthesis pathway were strongly correlated with the differential accumulation of anthocyanins. One R2R3-MYB subfamily member in the SG5 subgroup, Podel.04G021100, showed a similar expression pattern to some structural genes. This gene was strongly correlated with 16 anthocyanin compounds, indicating that Podel.04G021100 might be involved in the regulation of anthocyanin biosynthesis. These results contribute to a systematic and comprehensive understanding of anthocyanin accumulation and to the molecular mechanisms of anthocyanin biosynthesis in QHP and ZSY.

ETHYLENE RESPONSE FACTORS 4.1/4.2 with an EAR motif repress anthocyanin biosynthesis in red-skinned pears.

Red-skinned pears (Pyrus L.) are preferred to consumers for their attractive color and abundant anthocyanins. Pyrus ETHYLENE RESPONSE FACTOR 3 (PyERF3) positively regulates anthocyanin biosynthesis through interacting with Pyrus myeloblastosis family 114 (PyMYB114) and Pyrus basic helix-loop-helix 3 (PybHLH3) in red-skinned pears. However, the role of APETALA2/ethylene response factors (AP2/ERFs), which negatively regulate anthocyanin biosynthesis, remains unclear in red-skinned pears. Here, we validated that 2 AP2/ERFs, PyERF4.1 and PyERF4.2, screened from the transcriptome data of 'Starkrimson' pear (Pyrus communis L.) and its green mutant, inhibit anthocyanin biosynthesis in transgenic pear calli, as well as in overexpression and gene-edited tomato (Solanum lycopersicum) fruits. Meanwhile, the co-transformation of PyERF4.1/PyERF4.2 with PyERF3-PyMYB114-PybHLH3 inhibited anthocyanin biosynthesis in pear fruits and strawberry (Fragaria vesca) receptacles. Further assays showed that PyMYB114 activated the transcription of PyERF4.1/PyERF4.2; PyERF4.1/PyERF4.2 then interacted with PyERF3 to affect the stability of the PyERF3-PyMYB114-PybHLH3 complex, thereby inhibiting the transcription of the anthocyanin biosynthesis gene Pyrus anthocyanidin synthase (PyANS). Furthermore, deletion of the ERF-associated-amphiphilic repression (EAR) motif eliminated the inhibitory effect of PyERF4.1/PyERF4.2 on anthocyanin biosynthesis, and a mutation of the PyERF4.2-EAR motif (LxLxM to LxLxL) strengthened the inhibitory effect, demonstrating that the EAR motif is indispensable for the inhibitory effect of PyERF4.1/PyERF4.2 on anthocyanin biosynthesis in pears. Our study has shed light on a feedback regulatory loop mechanism that balances the excessive accumulation of anthocyanins in red-skinned pears, providing insights into the regulatory mechanism of anthocyanin biosynthesis and the regulatory network of coloration in red-skinned pears.

Identification of a Monosomic Alien Chromosome Addition Line Responsible for the Purple Color Trait in Heading Chinese Cabbage

Purple heading Chinese cabbage has become popular in recent years due to its attractive color and health benefits. However, purple varieties remain rare, and the regulation mechanism of anthocyanin accumulation in Chinese cabbage is still largely unknown. By introducing the purple color trait from Brassica juncea, a new purple heading Chinese cabbage cultivar (18M-245) was generated with deep purple leaves at both the seedling and adult stages. Anthocyanin accumulation in 18M-245 increased when grown at low temperatures. FISH and genotyping results showed that the purple trait was caused by an alien chromosome addition line derived from the Brassica B genome. The LDOX coding gene BjuB014115 from the addition line was highly expressed in 18M-245, consistent with the results of anthocyanin accumulation. Meanwhile, several MYB and bHLH transcriptional factors from the Brassica A genome were found to directly bind to the promoter of BjuB014115, suggesting that interactions between the Brassica A and B genomes are involved in the regulatory network of anthocyanin biosynthesis in Chinese cabbage. Our results provide new insights into the regulation mechanism of anthocyanin biosynthesis in purple heading Chinese cabbage.

Anthocyanins in Plant Food: Current Status, Genetic Modification, and Future Perspectives.

Anthocyanins are naturally occurring polyphenolic pigments that give food varied colors. Because of their high antioxidant activities, the consumption of anthocyanins has been associated with the benefit of preventing various chronic diseases. However, due to natural evolution or human selection, anthocyanins are found only in certain species. Additionally, the insufficient levels of anthocyanins in the most common foods also limit the optimal benefits. To solve this problem, considerable work has been done on germplasm improvement of common species using novel gene editing or transgenic techniques. This review summarized the recent advances in the molecular mechanism of anthocyanin biosynthesis and focused on the progress in using the CRISPR/Cas gene editing or multigene overexpression methods to improve plant food anthocyanins content. In response to the concerns of genome modified food, the future trends in developing anthocyanin-enriched plant food by using novel transgene or marker-free genome modified technologies are discussed. We hope to provide new insights and ideas for better using natural products like anthocyanins to promote human health.

Transcription and Metabolism Pathways of Anthocyanin in Purple Shamrock (Oxalis triangularis A.St.-Hil.).

Anthocyanins are water-soluble pigments that can impart various colors to plants. Purple shamrock (Oxalis triangularis) possesses unique ornamental value due to its purple leaves. In this study, three anthocyanins, including malvidin 3-O-(4-O-(6-O-malonyl-glucopyranoside)-rhamnopyranosyl)-5-O-(6-O-malonyl-glucopyranoside), delphinidin-3-O-rutinoside and malvidin-3,5-di-O-glucoside, were characterized with ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) in purple shamrock. To investigate the molecular mechanism of anthocyanin biosynthesis in green shamrock (Oxalis corymbosa) and purple shamrock, RNA-seq and qRT-PCR were performed, and the results showed that most of the anthocyanin biosynthetic and regulatory genes were up-regulated in purple shamrock. Then, dark treatment and low temperature treatment experiments in purple shamrock showed that both light and low temperature can induce the biosynthesis of anthocyanins.

Integrated transcriptome and metabolome analysis reveals the anthocyanin biosynthesis mechanisms in blueberry (Vaccinium corymbosum L.) leaves under different light qualities.

Blueberry (Vaccinium corymbosum L.) is a popular fruit with an abundance of anthocyanins in its leaves and fruits. Light is one of the pivotal environmental elements that affects plant growth and development, but the regulatory mechanism between light quality and anthocyanin formation is poorly understood. An integrated transcriptome and metabolome analysis was performed to investigate the effects of white (control), blue (B), red (R), and red/blue (60R/40B) light on blueberry growth and reveal the potential pathway controlling anthocyanin biosynthesis in blueberry leaves. The anthocyanin content was significantly improved by the blue and red/blue light when compared with white light, whereas there was a significant reduction in the photosynthesis under the blue light, showing an inverse trend to that of anthocyanin accumulation. Transcriptomic analysis resulted in the assembly of 134,709 unigenes. Of these, 22 were differentially expressed genes (DEGs) that participate in the anthocyanin biosynthesis pathway, with the majority being significantly up-regulated under the blue light. Most of the photosynthesis-related genes that were down-regulated were expressed during anthocyanin accumulation. Targeted metabolome profiling identified 44 metabolites associated with anthocyanin biosynthesis. The contents of most of these metabolites were higher under blue light than the other light conditions, which was consistent with the transcriptome results. The integrated transcriptome and metabolome analysis suggested that, under blue light, leucoanthocyanidin dioxygenase (LDOX), O-methyltransferase (OMT), and UDP-glucose flavonoid glucosyltransferase (UFGT) were the most significantly expressed, and they promoted the synthesis of cyanidin (Cy), malvidin (Mv), and pelargonidin (Pg) anthocyanidins, respectively. The expression levels of dihydroflavonol 4-reductase (DFR) and OMT, as well as the accumulation of delphinidin (Dp), peonidin (Pn), and petunidin (Pt), were significantly increased by the red/blue light. The blue and red/blue lights promoted anthocyanin biosynthesis via inducing the expression of key structural genes and accumulation of metabolites involved in anthocyanin synthesis pathway. Moreover, there was a possible feedback regulating correlation between anthocyanin biosynthesis and photosynthesis under different light qualities in blueberry leaves. This study would provide a theoretical basis for elucidating the underlying regulatory mechanism of anthocyanin biosynthesis of V. corymbosum.

An R3-MYB repressor, BnCPC forms a feedback regulation with MBW complex to modulate anthocyanin biosynthesis in Brassica napus

BackgroundAnthocyanins are metabolites of phenylpropanoid pathway, and involves in diverse processes of plant development and adaptation, which are regulated by the MYB-bHLH-WD40 (MBW) protein complexes. Many R2R3-MYB activators have been well characterized, but the MYB repressors in anthocyanin biosynthesis were recognized recently, which are also important in modulating phenylpropanoid metabolism in plants. The regulatory mechanism of anthocyanin biosynthesis in oil crop Brassica napus remains to be revealed.ResultsIn this study, we identified an anthocyanin repressor BnCPC in B. napus. BnCPC encoded a typical R3-MYB protein containing a conserved [D/E]Lx2[R/K]x3Lx6Lx3R motif for interaction with bHLH proteins. Overexpression of BnCPC in B. napus inhibited anthocyanin accumulation, especially under anthocyanin inducible conditions. Protein–protein interaction and dual-luciferase assays confirmed that BnCPC could compete with BnPAP1 to interact with bHLHs (BnTT8 and BnEGL3), and repress the expression of anthocyanin biosynthetic genes (e.g., BnDFR) that activated by MBW complexes. Moreover, we found BnCPC inhibited the MBW complex-induced BnCPC activity.ConclusionsOverall, this research demonstrated that BnCPC repressed anthocyanin biosynthesis by affecting the formation of MBW complex, and formed a feedback loop to regulate anthocyanin accumulation in B. napus.

Integrative metabolome and transcriptome analyses reveals the black fruit coloring mechanism of Crataegus maximowiczii C. K. Schneid

Crataegus is an economically important plant due to its medicinal and health-promoting properties. Flavonoids are the main functional components of Crataegus fruit. Fruits of naturally pollinated Crataegus maximowiczii possess an extraordinary black skin and are rich in anthocyanins and other flavonoids. However, the composition of anthocyanins and the overall molecular mechanism of anthocyanin biosynthesis in C. maximowiczii fruits have not been fully elucidated. In this study, the metabolome and transcriptome of C. maximowiczii fruits with black and red skin were analyzed. The results revealed that the differential metabolites and genes were enriched in the anthocyanin biosynthesis pathways in C. maximowiczii fruits. In total, 52 differentially accumulated flavonoid metabolites, 12 differentially accumulated anthocyanins and 22 differentially expressed genes were identified. After weighted gene coexpression network analysis, two modules were found to be highly interrelated with the accumulation of anthocyanin components. The coexpression networks of these two modules were used to identify key candidate transcription factors associated with anthocyanin biosynthesis, such as MYB5, MYB113, bHLH60, ERF105, bZIP44, NAC082, and WRKY11. The results revealed that cyanidin-based anthocyanins were the main pigments responsible for the black coloration of C. maximowiczii fruits. Based on these differentially accumulated anthocyanins and key genes, genetic and metabolic regulatory networks of anthocyanin biosynthesis were also proposed. Overall, this study elucidates the molecular basis of the formation of black color in C. maximowiczii fruits, and provides an intensive study on anthocyanin biosynthesis in C. maximowiczii for comprehensive utilization.

Integrated metabolomic and transcriptomic analysis of the anthocyanin and proanthocyanidin regulatory networks in red walnut natural hybrid progeny leaves.

BackgroundWalnuts are among the most important dry fruit crops worldwide, typically exhibiting green leaves and yellow–brown or gray–yellow seed coats. A specific walnut accession with red leaves and seed coats, ‘RW-1’, was selected for study because of its high anthocyanin and proanthocyanidin (PA) contents. Anthocyanins and PAs are important secondary metabolites and play key roles in plant responses to biotic and abiotic stresses. However, few studies have focused on the molecular mechanism of anthocyanin biosynthesis in walnuts.MethodsIn this study, we determined the anthocyanin and PA components and their contents in different color leaves of ‘RW-1’ natural hybrid progenies at various developmental stages. Integrated transcriptome and metabolome analyses were used to identify the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs). We also performed conjoint analyses on DEGs and DAMs to ascertain the degree pathways, and explore the regulation of anthocyanin and PA biosynthesis.ResultsThe results of widely targeted metabolome profiling and anthocyanin detection revealed 395 substances, including four PAs and 26 anthocyanins, in red (SR) and green leaves (SG) of ‘RW-1’ natural hybrid progenies. From the research, the contents of all anthocyanin components in SR were higher than that in SG. Among them, the contents of delphinidin 3-O-galactoside, cyanidin 3-O-galactoside, delphinidin 3-O-arabinoside and cyanidin 3-O-glucoside were significantly higher than others, and they were considered as the main types of anthocyanins. However, nine anthocyanins were detected only in SR. For PAs, the content of procyanidin C1 was higher in SR compared with SG, while procyanidin B1 and procyanidin B3 were higher in SR-1 and SR-3 but downregulated in SR-2 compared with the controls. Furthermore, transcriptome analysis revealed that the expressions of structural genes (C4H, F3H, F3′5′H, UFGT, LAR and ANR), three MYBs predicted as the activators of anthocyanin and PA biosynthesis, two MYBs predicted as the repressors of anthocyanin biosynthesis, and five WD40s in the anthocyanin and PA biosynthetic pathways were significantly higher in the SR walnuts. Gene-metabolite correlation analyses revealed a core set of 31 genes that were strongly correlated with four anthocyanins and one PA metabolites. The alteration of gene coding sequence altered the binding or regulation of regulatory factors to structural genes in different color leaves, resulting in the effective increase of anthocyanins and PAs accumulation in red walnut.ConclusionsThis study provides valuable information on anthocyanin and PA metabolites and candidate genes for anthocyanin and PA biosynthesis, yielding new insights into anthocyanin and PA biosynthesis in walnuts.

Methylation level of potato gene OMT30376 regulates tuber anthocyanin transformations.

After anthocyanin synthesis, a variety of anthocyanin compounds are produced through further methylation, glycosylation, and acylation. However, the effect of the potato methylase gene on anthocyanin biosynthesis has not been reported. Red and purple mutation types appear in tubers of the potato cultivar ‘Purple Viking’ with chimeric skin phenotypes. In this study, transcriptome and anthocyanin metabolome analyses were performed on skin of Purple Viking tubers and associated mutants. According to the metabolome analysis, the transformation of delphinidin into malvidin-3-O-glucoside and petunidin 3-O-glucoside and that of cyanidin into rosinidin O-hexoside and peonidin-3-O-glucoside were hindered in red tubers. Expression of methyltransferase gene OMT30376 was significantly lower in red tubers than in purple ones, whereas the methylation level of OMT30376 was significantly higher in red tubers. In addition, red skin appeared in tubers from purple tuber plants treated with S-adenosylmethionine (SAM), indicating the difference between purple and red was caused by the methylation degree of the gene OMT30376. Thus, the results of the study suggest that the OMT30376 gene is involved in the transformation of anthocyanins in potato tubers. The results also provide an important reference to reveal the regulatory mechanisms of anthocyanin biosynthesis and transformation.