MYB5-like and bHLH influence flavonoid composition in pomegranate

WRKY Transcription Factors Modulate the Flavonoid Pathway of Rhododendron chrysanthum Pall. Under UV-B Stress

The depletion of the ozone layer has resulted in elevated ultraviolet-B (UV-B) radiation levels, posing a significant risk to terrestrial plant growth. Rhododendron chrysanthum Pall. (R. chrysanthum), adapted to high-altitude and high-irradiation environments, has developed unique adaptive mechanisms. This study exposed R. chrysanthum to UV-B radiation for two days, with an 8 h daily treatment, utilizing metabolomic and transcriptomic analyses to explore the role of WRKY transcription factors in the plant's UV-B stress response and their regulation of flavonoid synthesis. UV-B stress resulted in a significant decrease in rETR and Ik and a significant increase in 1-qP. These chlorophyll fluorescence parameters indicate that UV-B stress impaired photosynthesis in R. chrysanthum. Faced with the detrimental impact of UV-B radiation, R. chrysanthum is capable of mitigating its effects by modulating its flavonoid biosynthetic pathways to adapt positively to the stress. This study revealed changes in the expression of 113 flavonoid-related metabolites and 42 associated genes, with WRKY transcription factors showing significant correlation with these alterations. WRKY transcription factors can influence the expression of key enzyme genes in the flavonoid metabolic pathway, thereby affecting metabolite production. A theoretical reference for investigating plant stress physiology is provided in this work, which also offers insights into the stress responses of alpine plants under adverse conditions.

Unveiling the power of MYB transcription factors: Master regulators of multi-stress responses and development in cotton

Plants, being immobile, are subject to environmental stresses more than other creatures, necessitating highly effective stress tolerance systems. Transcription factors (TFs) play a crucial role in the adaptation mechanism as they can be activated by diverse signals and ultimately control the expression of stress-responsive genes. One of the most prominent plant TFs family is MYB (myeloblastosis), which is involved in secondary metabolites, developmental mechanisms, biological processes, cellular architecture, metabolic pathways, and stress responses. Extensive research has been conducted on the involvement of MYB TFs in crops, while their role in cotton remains largely unexplored. We also utilized genome-wide data to discover potential 440 MYB genes and investigated their plausible roles in abiotic and biotic stress conditions, as well as in different tissues across diverse transcriptome databases. This review primarily summarized the structure and classification of MYB TFs biotic and abiotic stress tolerance and their role in secondary metabolism in different crops, especially in cotton. However, it intends to identify gaps in current knowledge and emphasize the need for further research to enhance our understanding of MYB roles in plants.

Identification of MYB Transcription Factor, a Regulator Related to Hydrolysable Tannin Synthesis in Canarium album L., and Functional Analysis of CaMYBR04

Hydrolysed tannins (HTs) are polyphenols, which are related to the astringency, flavour, colour, stability, medicinal value and other characteristics of many fruits and vegetables. The biosynthetic mechanism of the majority of HTs remains unknown, and many biosynthetic pathways of HTs are speculative conclusions that have not been confirmed. The fruit of Canarium album L. (Chinese olive), which is notable for its pharmacological and edible properties, is rich in HTs. The fruit has a distinctive bitter and astringent taste when initially consumed, which mellows to a sweet sensation upon chewing. HTs serve as the primary material basis for the formation of the Chinese olive fruit's astringent quality and pharmacological effects. In this study, the fruit of C. album Changying was utilised as the research material. The objective of this study was to provide a theoretical basis for the quality control of Chinese olive fruit and the application and development of its medicinal value. In addition, the study aimed to identify and screen related MYB transcription factors involved in the synthesis of HTs in the fruit and to clarify the mechanism of MYBs in the process of synthesis and regulation of HTs in Chinese olive fruit. The principal findings were as follows. A total of 83 differentially expressed Chinese olive MYB transcription factors (CaMYBs) were identified, including 54 1R-MYBs (MYB-related), 25 2R-MYBs (R2R3-MYBs), 3 3R-MYBs, and 1 4R-MYB. Through trend analysis and correlation analysis, it was found that CaMYBR04 (Isoform0032534) exhibited a significantly higher expression (FPKM) than the other CaMYBs. The full-length cDNA sequence of CaMYBR04 was cloned and transformed into strawberry. The results demonstrated that CaMYBR04 significantly enhanced the fruit's hydrolysable tannin content. Consequently, this study elucidated the function of CaMYBR04, a regulator of the Chinese olive fruit hydrolysable tannin synthesis pathway, and established a theoretical foundation for the synthesis and regulation of fruit HTs.

Comparative transcriptomic and metabolomic profiles reveal fruit peel color variation in two red pomegranate cultivars

Pomegranate (Punica granatum L.) which belongs to family Lythraceae, is one of the most important fruit crops of many tropical and subtropical regions. A high variability in fruit color is observed among different pomegranate accessions, which arises from the qualitative and quantitative differences in anthocyanins. However, the mechanism of fruit color variation is still not fully elucidated. In the present study, we investigated the red color mutation between a red-skinned pomegranate 'Hongbaoshi' and a purple-red-skinned cultivar 'Moshiliu', by using transcriptomic and metabolomic approaches. A total of 51 anthocyanins were identified from fruit peels, among which 3-glucoside and 3,5-diglucoside of cyanidin (Cy), delphinidin (Dp), and pelargonidin (Pg) were dominant. High proportion of Pg in early stages of 'Hongbaoshi' but high Dp in late stages of 'Moshiliu' were characterized. The unique high levels of Cy and Dp anthocyanins accumulating from early developmental stages accounted for the purple-red phenotype of 'Moshiliu'. Transcriptomic analysis revealed an early down-regulated and late up-regulated of anthocyanin-related structure genes in 'Moshiliu' compared with 'Hongbaoshi'. Alao, ANR was specially expressed in 'Hongbaoshi', with extremely low expression levels in 'Moshiliu'. For transcription factors R2R3-MYB, the profiles demonstrated a much higher transcription levels of three subgroup (SG) 5 MYBs and a sharp decrease in expression of SG6 MYB LOC116202527 in high-anthocyanin 'Moshiliu'. SG4 MYBs exhibited two entirely different patterns, LOC116203744 and LOC116212505 were down-regulated whereas LOC116205515 and LOC116212778 were up-regulated in 'Moshiliu' pomegranate. The results indicate that specific SG members of the MYB family might promote the peel coloration in different manners and play important roles in color mutation in pomegranate.

Genome-Wide Analysis of the bHLH Gene Family in Loropetalum chinense var. rubrum: Identification, Classification, Evolution, and Diversity of Expression Patterns under Cultivation

The basic helix-loop-helix (bHLH) transcription factor family is the second-largest transcription factor family in plants. Members of this family are involved in the processes of growth and development, secondary metabolic biosynthesis, signal transduction, and plant resistance. Loropetalum chinense var. rubrum is a critical woody plant with higher ornamental and economic values, which has been used as ornamental architecture and traditional Chinese herbal medicine plants. However, the bHLH transcription factors in Loropetalum chinense var. rubrum (L. chinense var. rubrum) have not yet been systematically demonstrated, and their role in the biosynthesis of anthocyanin is still unclear. Here, we identified 165 potential LcbHLHs genes by using two methods, and they were unequally distributed on chromosomes 1 to 12 of the genome of L. chinense var. rubrum. Based on an evolutionary comparison with proteins from Arabidopsis and Oryza sativa, these bHLH proteins were categorized into 21 subfamilies. Most LcbHLHs in a particular subfamily had similar gene structures and conserved motifs. The Gene Ontology annotation and Cis-elements predicted that LcbHLHs had many molecular functions and were involved in processes of plant growth, including the biosynthesis of flavonoids and anthocyanins. Transcriptomic analysis revealed different expression patterns among different tissues and cultivars of L. chinense var. rubrum. Many LcbHLHs were expressed in the leaves, and only a few genes were highly expressed in the flowers. Six LcbHLHs candidate genes were identified by bioinformatics analysis and expression analysis. Further Real-time quantitative PCR analysis and protein interaction network analysis showed that LcbHLH156, which is one of the candidate proteins belonging to the IIIf subfamily, could interact with proteins related to anthocyanin synthesis. Therefore, LcbHLH156 was transiently expressed in L. chinense var. rubrum to verify its function in regulating anthocyanin synthesis. Compared with the control group, red pigment accumulation appeared at the wound after injection, and the total anthocyanin content increased at the wound of leaves. These results lay a foundation for the research of the regulation mechanism of leaf colors in L. chinense var. rubrum and also provide a basis for the function of the LcbHLH family.

Designing plant flavonoids: harnessing transcriptional regulation and enzyme variation to enhance yield and diversity

Plant synthetic biology has emerged as a powerful and promising approach to enhance the production of value-added metabolites in plants. Flavonoids, a class of plant secondary metabolites, offer numerous health benefits and have attracted attention for their potential use in plant-based products. However, achieving high yields of specific flavonoids remains challenging due to the complex and diverse metabolic pathways involved in their biosynthesis. In recent years, synthetic biology approaches leveraging transcription factors and enzyme diversity have demonstrated promise in enhancing flavonoid yields and expanding their production repertoire. This review delves into the latest research progress in flavonoid metabolic engineering, encompassing the identification and manipulation of transcription factors and enzymes involved in flavonoid biosynthesis, as well as the deployment of synthetic biology tools for designing metabolic pathways. This review underscores the importance of employing carefully-selected transcription factors to boost plant flavonoid production and harnessing enzyme promiscuity to broaden flavonoid diversity or streamline the biosynthetic steps required for effective metabolic engineering. By harnessing the power of synthetic biology and a deeper understanding of flavonoid biosynthesis, future researchers can potentially transform the landscape of plant-based product development across the food and beverage, pharmaceutical, and cosmetic industries, ultimately benefiting consumers worldwide.

A novel R2R3-MYB transcription factor FaMYB5 positively regulates anthocyanin and proanthocyanidin biosynthesis in cultivated strawberries (Fragaria × ananassa)

Flavonoids have a major contribution to the fruit quality in cultivated strawberries and are regulated by MYB, bHLH and WD40 transcriptional factors. We reported here the identification of the FaMYB5, an R2R3-MYB transcription factor, which positively regulated the accumulation of anthocyanins and proanthocyanidins through the trans-activation of the F3'H and LAR. The strawberry FaEGL3 and FaLWD1/FaLWD1-like interact with the R2R3-FaMYB5 to form an MYB-bHLH-WD40 complex (MBW), enhancing the regulatory efficiency. The R2R3-FaMYB5 was constitutively expressed in various tissues and in fruits of different developmental stages, which was strikingly contrasting to the fruit-specific expression patterns of FaMYB10. Meanwhile, R2R3-FaMYB5 failed to promote a stable accumulation of anthocyanin glycosides in the mature fruits of the myb10 mutant, mainly due to the suppressed expression of TT19. The R2R3-FaMYB5 was regulated by an antisense long noncoding RNA lncRNA-myb5. Additionally, the R2R3-FaMYB5 protein could interact with FaBT2 and was degraded through the ubiquitin/26 S proteasome pathway. Transcriptome and metabolome data showed that R2R3-FaMYB5 enhanced the gene expression and the metabolite accumulation involved in the flavonoid, phenylpropanoid and lignin biosynthesis pathways. Collectively, we conclude that the FaMYB5 is an R2R3-MYB activator involved in the composition of MBW, which positively regulates the biosynthesis of anthocyanin and proanthocyanidin. These findings provided new insights into the molecular mechanisms that regulate flavonoids in strawberry fruits.

Novel Camellia sinensis O-Methyltransferase Regulated by CsMADSL1 Specifically Methylates EGCG in Cultivar "GZMe4"

Epigallocatechin-3-O-(4-O-methyl)gallate (EGCG4″Me) in Camellia sinensis possesses numerous beneficial biological activities. However, the germplasm rich in EGCG4″Me and the O-methyltransferase responsible for EGCG4″Me biosynthesis are poorly understood. Herein, the content of EGCG3″Me and EGCG4″Me in the shoots of 13 cultivars was analyzed to demonstrate that EGCG4″Me is characteristically accumulated in the "GZMe4" cultivar but not in the other 12 cultivars. A novel O-methyltransferase (CsOMTL1) was identified from "GZMe4" using RNA-Seq and correlation analysis. Using the recombinant enzyme, EGCG4″Me was synthesized in vitro. Overexpression of CsOMTL1 via Agrobacterium-mediated genetic transformation caused constitutive accumulation of EGCG4″Me in C. sinensis callus. Moreover, the transcription factor CsMADSL1 localized in the nucleus activated the transcription of CsOMTL1 and specifically interacted with its promoter. Hence, our study identified a novel O-methyltransferase that characteristically catalyzes the synthesis of EGCG4″Me and a positive regulator of EGCG4″Me synthesis in "GZMe4", which might provide a strategy for the breeding of a tea cultivar rich in EGCG4″Me.

Genome-Wide Characterization and Analysis of bHLH Transcription Factors Related to Anthocyanin Biosynthesis in Cinnamomum camphora ('Gantong 1')

Cinnamomum camphora is one of the most commonly used tree species in landscaping. Improving its ornamental traits, particularly bark and leaf colors, is one of the key breeding goals. The basic helix-loop-helix (bHLH) transcription factors (TFs) are crucial in controlling anthocyanin biosynthesis in many plants. However, their role in C. camphora remains largely unknown. In this study, we identified 150 bHLH TFs (CcbHLHs) using natural mutant C. camphora 'Gantong 1', which has unusual bark and leaf colors. Phylogenetic analysis revealed that 150 CcbHLHs were divided into 26 subfamilies which shared similar gene structures and conserved motifs. According to the protein homology analysis, we identified four candidate CcbHLHs that were highly conserved compared to the TT8 protein in A. thaliana. These TFs are potentially involved in anthocyanin biosynthesis in C. camphora. RNA-seq analysis revealed specific expression patterns of CcbHLHs in different tissue types. Furthermore, we verified expression patterns of seven CcbHLHs (CcbHLH001, CcbHLH015, CcbHLH017, CcbHLH022, CcbHLH101, CcbHLH118, and CcbHLH134) in various tissue types at different growth stages using qRT-PCR. This study opens a new avenue for subsequent research on anthocyanin biosynthesis regulated by CcbHLH TFs in C. camphora.

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.

Metabolite and Transcriptome Profiles of Proanthocyanidin Biosynthesis in the Development of Litchi Fruit

The fruit of Litchi chinensis contains high levels of proanthocyanidins (PAs) in the pericarp. These substances can serve as substrates of laccase-mediated rapid pericarp browning after the fruit is harvested. In this study, we found that the major PAs in litchi pericarp were (-)-epicatechin (EC) and several procyanidins (PCs), primarily PC A2, B2, and B1, and the EC and the PC content decreased with the development of the fruit. RNA-seq analysis showed that 43 early and late structure genes related to flavonoid/PA biosynthesis were expressed in the pericarp, including five ANTHOCYANIDIN REDUCTASE (ANR), two LEUCOANTHOCYANIDIN REDUCTASE (LAR), and two ANTHOCYANIDIN SYNTHASE (ANS) genes functioning in the PA biosynthesis branch of the flavonoid pathway. Among these nine PA biosynthesis-related genes, ANR1a, LAR1/2, and ANS1 were highly positively correlated with changes in the EC/PC content, suggesting that they are the key PA biosynthesis-related genes. Several transcription factor (TF) genes, including MYB, bHLH, WRKY, and AP2 family members, were found to be highly correlated with ANR1a, LAR1/2, and ANS1, and their relevant binding elements were detected in the promoters of these target genes, strongly suggesting that these TF genes may play regulatory roles in PA biosynthesis. In summary, this study identified the candidate key structure and regulatory genes in PA biosynthesis in litchi pericarp, which will assist in understanding the accumulation of high levels of browning-related PA substances in the pericarp.

Anti-glycation, antiplatelet and antioxidant effects of different pomegranate parts

BACKGROUND

Platelet aggregation and advanced glycation end products (AGEs) and oxidative stress are known as key factors for the development of cardiovascular diseases and diabetic complications. In this context, fruit and vegetable consumption, good sources of antioxidant compounds have been largely reported as an effective way of preventing human against these diseases. The current study focuses on the evaluation of antioxidant, antiplatelet and anti-glycation activities of pomegranate (Punica granatum L.) flowers (PF), leaves (PL), peel (PP) juice (PJ) and seeds oil (PSO).

METHODS

Antioxidant activities was measured against ABTS radical and lipid peroxidation. Antiglycation activity was determined using the formation of AGE fluorescence intensity in the BSA/ribose system. Antiplatelet activity was measured in platelet rich plasma (PRP) against adenosine diphosphate (ADP), Collagen and arachidonic acid (AA).

RESULTS

PF extract displayed the highest antioxidant activity against ABTS and lipid peroxidation with IC₅₀ values of 0.7 mg/mL and 0.63 mg/mL respectively. For anti-glycation activity, PP, PF and PL inhibited moderately the pentosidine-like AGEs formation compared to positive controls with AGE-IC₅₀ value of 0.4 mg/mL. PJ and PSO haven't any anti-AGE effect. All the extracts selectively inhibited platelet aggregation caused by one, two or three inducers in dose dependent manner. PF was the most potent inhibitor caused by all three inducers, with inhibitory effects ranging from 35.6 to 66.6%. PP and PJ exhibited antiplatelet effect against both ADP and collagen and PL and PSO only against AA.

CONCLUSIONS

These results suggest that some pomegranate extracts exert potential in vitro anti-glycative and antiplatelet activities.

Biosynthetic regulatory network of flavonoid metabolites in stems and leaves of Salvia miltiorrhiza

Flavonoid secondary metabolites can treat and prevent many diseases, but systematic studies on regulation of the biosynthesis of such metabolites in aboveground parts of Salvia miltiorrhiza are lacking. In this study, metabonomic and transcriptomic analyses of different S. miltiorrhiza phenotypes were conducted to explore pathways of synthesis, catalysis, accumulation, and transport of the main flavonoid secondary metabolites regulating pigment accumulation. Tissue localization and quantitative analysis of flavonoid secondary metabolites were conducted by laser scanning confocal microscopy (LSCM). A total 3090 differentially expressed genes were obtained from 114,431 full-length unigenes in purple and green phenotypes, and 108 functional genes were involved in flavonoid biosynthesis. Five key phenylpropane structural genes (PAL, 4CL, ANS, 3AT, HCT) were highly differentially expressed, and four transcription factor genes (MYB, WRKY, bHLH, bZiP) were identified. In addition, six GST genes, nine ABC transporters, 22 MATE genes, and three SNARE genes were detected with key roles in flavonoid transport. According to LSCM, flavonoids were mainly distributed in epidermis, cortex, and collenchyma. Thus, comprehensive and systematic analyses were used to determine biosynthesis, accumulation, and transport of flavonoids in stems and leaves of different S. miltiorrhiza phenotypes. The findings will provide a reference for flavonoid production and cultivar selection.

Full-Length Transcriptome Sequencing Provides Insights into Flavonoid Biosynthesis in Camellia nitidissima Petals

Flavonoids are the main medicinal ingredients in Camellia nitidissima, but the regulatory mechanism of flavonoid biosynthesis in flowers is unclear; therefore, the flavonoids in C. nitidissima have not been effectively used. The present study performed full-length transcriptome sequencing of C. nitidissima flower. Furthermore, the reported RNA-sequencing data of C. nitidissima petals were reanalyzed using the full-length transcriptome as a reference, and the regulatory mechanism of flavonoid synthesis in petals was elucidated. The analysis identified 43,350 isoforms annotated in non-redundant protein (Nr), Kyoto Encyclopedia of Genes and Genomes (KEGG), EuKaryotic Orthologous Groups (KOG), and Swiss-Prot databases, among which 34,602 aligned to Camellia sinensis genes. A total of 11,857 differentially expressed genes (DEGs), including 112 related to flavonoid synthesis, were identified by pairwise comparison. Subsequently, analysis of the phylogeny and the conserved motifs of R2R3-MYB using the proteins sequences identified three R2R3-MYB transcription factors that regulated flavonoid biosynthesis. Weighted gene co-expression network analysis (WGCNA) identified phenylalanine ammonia-lyase (PAL) and 4-coumarate: CoA ligase(4CL) as the hub genes and showed that bHLH79 interacted with PAL. Finally, validated the expression of seven DEGs involved in flavonoid biosynthesis using real-time quantitative PCR (qRT-PCR). Thus, the present study generated and used the full-length transcriptome as the reference to analyze the transcriptome of petals and proposed a possible regulatory mechanism of flavonoid synthesis in C. nitidissima. The study's findings unravel the genetic mechanisms underlying flavonoid synthesis and suggest candidate genes for the genetic improvement of C. nitidissima.

Integrated Metabolomic and Transcriptomic Analysis Reveals Differential Flavonoid Accumulation and Its Underlying Mechanism in Fruits of Distinct Canarium album Cultivars

Canarium album fruit has great potential to be consumed as a raw material not only for food but also medicine. The diverse active metabolites composition and content of C. album fruits greatly affect their pharmacological effects. However, up to now, there has been no report on the global metabolome differences among fruits from distinct C. album cultivars. In our present study, by using non-targeted metabolomics techniques, we identified 87 DAMs (differentially accumulated metabolites) including 17 types of flavonoids from fruits of four different C. album cultivars. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis revealed that the flavone and flavonol biosynthesis- and flavonoid biosynthesis-related DAMs were major factors determining their metabolome differences. Comparative transcriptomic analysis revealed that 15 KEGG pathways were significantly enriched by genes of the identified 3655 DEGs (differentially expressed genes) among different C. album cultivars. Consistent with the metabolome data, flavonoid biosynthesis-related DEGs, including eight key structural genes (such as FLS, CCoAOMT, CHI, C4H, DFR, LAR, and C3′H, etc.) and several regulatory transcription factor (TF) genes (including 32 MYBs and 34 bHLHs, etc.), were found to be significantly enriched (p < 0.01). Our study indicated that the differential expression of flavonoid biosynthesis-related genes and accumulation of flavonoids played dominant roles in the various metabolome compositions of fruits from different C. album cultivars.

Transcriptome Analysis and HPLC Profiling of Flavonoid Biosynthesis in Citrus aurantium L. during Its Key Developmental Stages

Citrus aurantium L. (sour orange) is a significant Chinese medicinal and fruit crop rich in flavonoids. However, the pathways and genes involved in flavonoid biosynthesis at the key developmental stages of Citrus aurantium L. are not fully understood. This study found that the total flavonoid concentration gradually decreased as the fruit developed. Additionally, it showed that neohesperidin was the main flavonoid in the early stages of sour orange fruit development. However, as the development stage progressed, naringin content increased rapidly and emerged as the main flavonoid component. From 27 cDNA libraries, RNA sequencing yielded 16.64 billion clean bases, including 8989 differentially expressed genes. We identified 74 flavonoid related unigenes mapped to the phenylalanine, tyrosine, and phenylpropanoid biosynthesis pathways. A total of 152 UDP-glucuronosyltransferase genes (UGTs) were identified from C. aurantium L. transcriptome database, in which 22 key flavonoid-correlated UGTs were divided into five main AtGT groups: E, G, I, L, M. We observed that the ethylene responsive factors (ERF) and myeloblastosis (MYB) family mainly regulated the key genes involved in flavonoid biosynthesis. Overall, our study generated extensive and detailed transcriptome data on the development of C. aurantium L. and characterized the flavonoid biosynthesis pattern during its fruit developmental stages. These results will benefit genetic modification or selection to increase the flavonoid content in sour oranges.

Identification of microRNAs and their target genes related to the accumulation of anthocyanin in purple potato tubers (Solanum tuberosum)

MicroRNAs (miRNAs) are types of endogenous non-coding small RNAs found in eukaryotes that are 18-25 nucleotides long. miRNAs are considered to be key regulatory factors of the expression of target mRNA. The roles of miRNAs involved in the regulation of anthocyanin accumulation in pigmented potatoes have not been systematically reported. In this study, the differentially expressed miRNAs and their target genes involved in the accumulation of anthocyanin during different developmental stages in purple potato (Solanum tuberosum L.) were identified using small RNA (sRNA) and degradome sequencing. A total of 275 differentially expressed miRNAs were identified in the sRNA libraries. A total of 69,387,200 raw reads were obtained from three degradome libraries. The anthocyanin responsive miRNA-mRNA modules were analyzed, and 37 miRNAs and 23 target genes were obtained. Different miRNAs regulate the key enzymes of anthocyanin synthesis in purple potato. The structural genes included phenylalanine ammonia lyase, chalcone isomerase, flavanone 3-hydroxylase, and anthocyanidin 3-O-glucosyltransferase. The regulatory genes included WD40, MYB, and SPL9. stu-miR172e-5p_L-1R-1, stu-miR828a, stu-miR29b-4-5p, stu-miR8019-5p_L-4R-3, stu-miR396b-5p, stu-miR5303f_L-7R + 2, stu-miR7997a_L-3, stu-miR7997b_L-3, stu-miR7997c_L + 3R-5_2ss2TA3AG, stu-miR156f-5p_L + 1, stu-miR156a, stu-miR156a_R-1, stu-miR156e, stu-miR858, stu-miR5021, stu-miR828 and their target genes were validated by qRT-PCR. They play important roles in the coloration and accumulation of purple potatoes. These results provide new insights into the biosynthesis of anthocyanins in pigmented potatoes.

Metabolome and Transcriptome Profiling Unveil the Mechanisms of Polyphenol Synthesis in the Developing Endopleura of Walnut (Juglans regia L.)

Walnut (Juglans regia L.) is an important woody nut tree species, and its endopleura (the inner coating of a seed) is rich in many polyphenols. Thus far, the pathways and essential genes involved in polyphenol biosynthesis in developing walnut endopleura remain largely unclear. We compared metabolite differences between endopleura and embryo in mature walnuts, and analyzed the changes of metabolites in endopleura at 35, 63, 91, 119, and 147 days after pollination (DAP). A total of 760 metabolites were detected in the metabolome, and the polyphenol contents in endopleura were higher than those in embryos. A total of 15 types of procyanidins, 10 types of kaempferol glycosides, and 21 types of quercetin glycosides that accumulated during endopleura development were identified. The analysis of the phenylpropane metabolic pathway showed that phenylalanine was gradually transformed into proanthocyanidins and other secondary metabolites with the development of endopleura. A total of 49 unigenes related to polyphenol synthesis were identified by transcriptome analysis of endopleura. The expression patterns of PAL, C4H, 4CL, CHS, CHI, F3H, LDOX, and ANR were similar, and their expression levels were highest in endopleura at maturity. Transcriptome and metabolome analysis showed that endopleura rapidly synthesized and accumulated polyphenols during maturation. Moreover, the transcription factor MYB111 played an important role in synthesizing polyphenols in endopleura, and its expression pattern was positively correlated with the accumulation pattern of quercetin, kaempferol, and proanthocyanidins. MYB111 was co-expressed with NAP, NAC, ATR1, and other genes related to cell senescence and abiotic stress response. Our study analyzed the composition and molecular synthesis mechanism of polyphenols in walnut endopleura, and provided new perspectives and insights regarding the nutritional research of walnut nuts.

Cloning and expression analysis of HY5 transcription factor gene of safflower in response to light signal

The flower of the safflower (Carthamus tinctorius L.) is a traditional Chinese medicine that can improve cerebral blood flow due to its enrichment in flavonoids. Light is one of the main environmental factors that affects safflower growth and flavonoid synthesis. Elongated hypocotyl 5 (HY5) plays an important role in plants' light signal transduction. However, no study of HY5 in safflower has been conducted. In this study, a 462-bp sequence of CtHY5 was successfully cloned. The expression pattern of CtHY5 in different safflower tissues and the expression patterns of CtHY5 and CtCHS1 in full-blooming flowers that were treated under different light intensities were studied. The subcellular localization and the overexpression of CtHY5 were carried out as well. CtHY5 has a DNA-binding region belonging to the basic leucine zipper transcription factor family. CtHY5 was specifically expressed in flowers. The expression level of CtHY5 first increased and then decreased with increasing light intensity, which was similar to the expression pattern of CtCHS1. The subcellular localization study was implemented in safflower protoplasts and the YFP fluorescence was observed in nucleus. The overexpression analysis initially verified the promotion effect of CtHY5 to the expression of CtCHS1 and the content of flavonoids.

Genome-wide identification and characterization of PdbHLH transcription factors related to anthocyanin biosynthesis in colored-leaf poplar (Populus deltoids)

Basic helix-loop-helix (bHLH) proteins are transcription factors (TFs) that have been shown to regulate anthocyanin biosynthesis in many plant species. However, the bHLH gene family in Populus deltoids has not yet been reported. In this study, 185 PdbHLH genes were identified in the Populus deltoids genome and were classified into 15 groups based on their sequence similarity and phylogenetic relationships. Analysis of the gene structure, chromosome location and conserved motif of the PdbHLH genes were performed by bioinformatic methods. Gene duplication analyses revealed that 114 PdbHLH were expanded and retained after WGD/segmental and proximal duplication. Investigation of cis-regulatory elements of PdbHLH genes indicated that many PdbHLH genes are involved in the regulation of anthocyanin biosynthesis. The expression patterns of PdbHLHs were obtained from previous data in two colored-leaf poplar (QHP and JHP) and green leaf poplar (L2025). Further analysis revealed that 12 candidate genes, including 3 genes (PdbHLH57, PdbHLH143, and PdbHLH173) from the subgroup III(f) and 9 gene from other groups, were positively associated with anthocyanin biosynthesis. In addition, 4 genes (PdbHLH4, PdbHLH1, PdbHLH18, and PdbHLH164) may be involved in negatively regulating the anthocyanin biosynthesis. These results provide a basis for the functional characterization of bHLH genes and investigations on the molecular mechanisms of anthocyanin biosynthesis in colored-leaf poplar.

Identification of a WRKY transcriptional activator from Camellia sinensis that regulates methylated EGCG biosynthesis

Naturally occurring methylated catechins, especially methylated EGCG in tea leaves are known to have many health benefits. Although the genes involved in methylated EGCG biosynthesis have been studied extensively, the transcriptional factors controlling methylated EGCG biosynthesis are still poorly understood. In the present study, a WRKY domain-containing protein termed CsWRKY57like was identified, which belongs to group IIc of the WRKY family, and contains one conserved WRKY motif. CsWRKY57like was found to localize in the nucleus, function as a transcriptional activator, and its expression positively correlated with methylated EGCG level. In addition, CsWRKY57like activated the transcription of three genes related to methylated EGCG biosynthesis, including CCoAOMT, CsLAR, and CsDFR by specifically interacting with their promoters via binding to the cis-acting element (C/T)TGAC(T/C). Further assays revealed that CsWRKY57like physically interacts with CsVQ4, and participates in the metabolic regulation of O-methylated catechin biosynthesis. Collectively, we conclude that CsWRKY57like may positively impact the biosynthesis of methylated EGCG in the tea plant, which comprehensively enriches the regulatory network of WRKY TFs associated with methylated EGCG and provide a potential strategy for the breeding of specific tea plant cultivars with high methylated EGCG .

Nutraceutical Content and Genetic Diversity Share a Common Pattern in New Pomegranate Genotypes

The nutraceutical value of pomegranate in the treatment of many diseases is well-documented and is linked to its richness in phenolic compounds. This study aims to evaluate the nutraceutical and genetic diversity of novel pomegranate genotypes (G1-G5) in comparison to leading commercial pomegranate varieties, i.e., 'Wonderful', 'Primosole', 'Dente di Cavallo' and 'Valenciana'. Morphometric measurements were carried out on fruits, accompanied by chemical characterization (total phenolic content, antioxidant activity, carbohydrates and minerals) and the development of four new polymorphic SSR markers involved in the flavonoid pathway. The cultivars displayed a marked variability in the weight and shape of the fruits, as well as in the weight of the arils and juice yield. The highest level of total phenolic content and antioxidant activity was found in 'Wonderful' and G4, while the lowest was in 'Dente di Cavallo'. Furthermore, the results showed that pomegranate juice is an excellent source of minerals, especially potassium, which plays a key role in organ functioning. The new flavonoid-related markers effectively differentiated the cultivars with the same diversity pattern as morpho-chemical characterization, so the SSRs developed in the present study can be used as a rapid tool for the identification of pomegranate cultivars with relevant nutraceutical traits, such as the new genotypes investigated.

Anthocyanins from Pomegranate (Punica granatum L. ) and Their Role in Antioxidant Capacities in Vitro

As phytochemicals, anthocyanins are not only responsible for the diverse colors in nature, but are associated with broad-spectrum health-promoting effects for human beings. Pomegranate is abundant in anthocyanins which possess high antioxidant capacities. However, the pomegranate anthocyanins profile and their contributions to antioxidant capacities are not fully depicted. The purpose of this paper is to review anthocyanins from pomegranate as important antioxidants. Total anthocyanin content (TAC) and six major components vary greatly with intrinsic and extrinsic factors. In pomegranate, anthocyanins mainly acted as primary antioxidants, while their action as secondary antioxidants were not conclusive. The antioxidant potentials of anthocyanins were significantly affected by factors especially chemical structure and detection assays in vitro. The current knowledge may provide insights into potential applications for pomegranate anthocyanins based on their antioxidant activities.

Comparative transcriptome analysis of Alpinia oxyphylla Miq. reveals tissue-specific expression of flavonoid biosynthesis genes

BACKGROUND

Alpinia oxyphylla Miq. is an important edible and medicinal herb, and its dried fruits are widely used in traditional herbal medicine. Flavonoids are one of the main chemical compounds in A. oxyphylla; however, the genetic and molecular mechanisms of flavonoid biosynthesis are not well understood. We performed transcriptome analysis in the fruit, root, and leaf tissues of A. oxyphylla to delineate tissue-specific gene expression and metabolic pathways in this medicinal plant.

RESULTS

In all, 8.85, 10.10, 8.68, 6.89, and 8.51 Gb clean data were obtained for early-, middle-, and late-stage fruits, leaves, and roots, respectively. Furthermore, 50,401 unigenes were grouped into functional categories based on four databases, namely Nr (47,745 unigenes), Uniprot (49,685 unigenes), KOG (20,153 unigenes), and KEGG (27,285 unigenes). A total of 3110 differentially expressed genes (DEGs) and five distinct clusters with similar expression patterns were obtained, in which 27 unigenes encoded 13 key enzymes associated with flavonoid biosynthesis. In particular, 9 DEGs were significantly up-regulated in fruits, whereas expression of 11 DEGs were highly up-regulated in roots, compared with those in leaves.

CONCLUSION

The DEGs and metabolic pathway related to flavonoids biosynthesis were identified in root, leaf, and different stages of fruits from A. oxyphylla. These results provide insights into the molecular mechanism of flavonoid biosynthesis in A. oxyphylla and application of genetically engineered varieties of A. oxyphylla.

Transcriptome-based metabolic profiling of flavonoids in Agave lechuguilla waste biomass

Agave lechuguilla is one of the most abundant species in arid and semiarid regions of Mexico, and is used to extract fiber. However, 85 % of the harvested plant material is discarded. Previous bioprospecting studies of the waste biomass suggest the presence of bioactive compounds, although the extraction process limited metabolite characterization. This work achieved flavonoid profiling of A. lechuguilla in both processed and non-processed leaf tissues using transcriptomic analysis. Functional annotation of the first de novo transcriptome of A. lechuguilla (255.7 Mbp) allowed identifying genes coding for 33 enzymes and 8 transcription factors involved in flavonoid biosynthesis. The flavonoid metabolic pathway was mostly elucidated by HPLC-MS/MS screening of alcoholic extracts. Key genes of flavonoid synthesis were higher expressed in processed leaf tissues than in non-processed leaves, suggesting a high content of flavonoids and glycoside derivatives in the waste biomass. Targeted HPLC-UV-MS analyses confirmed the concentration of isorhamnetin (1251.96 μg), flavanone (291.51 μg), hesperidin (34.23 μg), delphinidin (24.23 μg), quercetin (15.57 μg), kaempferol (13.71 μg), cyanidin (12.32 μg), apigenin (9.70 μg) and catechin (7.91 μg) per gram of dry residue. Transcriptomic and biochemical profiling concur in the potential of lechuguilla by-products with a wide range of applications in agriculture, feed, food, cosmetics, and pharmaceutical industries.

Transcriptome Analysis of Ginkgo biloba L. Leaves across Late Developmental Stages Based on RNA-Seq and Co-Expression Network

The final size of plant leaves is strictly controlled by environmental and genetic factors, which coordinate cell expansion and cell cycle activity in space and time; however, the regulatory mechanisms of leaf growth are still poorly understood. Ginkgo biloba is a dioecious species native to China with medicinally and phylogenetically important characteristics, and its fan-shaped leaves are unique in gymnosperms, while the mechanism of G. biloba leaf development remains unclear. In this study we studied the transcriptome of G. biloba leaves at three developmental stages using high-throughput RNA-seq technology. Approximately 4167 differentially expressed genes (DEGs) were obtained, and a total of 12,137 genes were structure optimized together with 732 new genes identified. More than 50 growth-related factors and gene modules were identified based on DEG and Weighted Gene Co-expression Network Analysis. These results could remarkably expand the existing transcriptome resources of G. biloba, and provide references for subsequent analysis of ginkgo leaf development.

Fine Mapping of the "black" Peel Color in Pomegranate (Punica granatum L.) Strongly Suggests That a Mutation in the Anthocyanidin Reductase (ANR) Gene Is Responsible for the Trait

Anthocyanins are important dietary and health-promoting substances present in high quantities in the peel and arils of the pomegranate (Punica granatum L.) fruit. Yet, there is a high variation in the content of anthocyanin among different pomegranate varieties. The 'Black' pomegranate variety (P.G.127-28) found in Israel contains exceptionally high levels of anthocyanins in its fruit peel which can reach up to two orders of magnitude higher content as compared to that of other pomegranate varieties' peel anthocyanins. Biochemical analysis reveals that delphinidin is highly abundant in the peel of 'Black' variety. The pattern of anthocyanin accumulation in the fruit peel during fruit development of 'Black' variety differs from that of other pomegranates. High anthocyanin levels are maintained during all developmental stages. Moreover, the accumulation of anthocyanin in the fruit peel of 'Black' variety is not dependent on light. Genetic analysis of an F₂ population segregating for the "black" phenotype reveals that it is determined by a single recessive gene. Genetic mapping of the F₂ population using single nucleotide polymorphism (SNP) markers identified few markers tightly linked to the "black" phenotype. Recombination analysis of the F₂ population and F₃ populations narrowed the "black" trait to an area of 178.5 kb on the draft genome sequence of pomegranate cv. 'Dabenzi.' A putative anthocyanidin reductase (ANR) gene is located in this area. Only pomegranate varieties displaying the "black" trait carry a base pair deletion toward the end of the gene, causing a frame shift resulting in a shorter protein. We propose that this mutation in the ANR gene is responsible for the different anthocyanin composition and high anthocyanin levels of the "black" trait in pomegranate.