Sucrose-specific induction of the anthocyanin biosynthetic pathway in Arabidopsis

Sugars act as signaling molecules, whose signal transduction pathways may lead to the activation or inactivation of gene expression. Whole-genome transcript profiling reveals that the flavonoid and anthocyanin biosynthetic pathways are strongly up-regulated following sucrose (Suc) treatment. Besides mRNA accumulation, Suc affects both flavonoid and anthocyanin contents. We investigated the effects of sugars (Suc, glucose, and fructose) on genes coding for flavonoid and anthocyanin biosynthetic enzymes in Arabidopsis (Arabidopsis thaliana). The results indicate that the sugar-dependent up-regulation of the anthocyanin synthesis pathway is Suc specific. An altered induction of several anthocyanin biosynthetic genes, consistent with in vivo sugar modulation of mRNA accumulation, is observed in the phosphoglucomutase Arabidopsis mutant accumulating high levels of soluble sugars.

Flavonoid biosynthesis-related genes in grape skin are differentially regulated by temperature and light conditions

Temperature and light are important environmental factors that affect flavonoid biosynthesis in grape berry skin. However, the interrelationships between temperature and light effects on flavonoid biosynthesis have not been fully elucidated at the molecular level. Here, we investigated the effects of temperature and light conditions on the biosynthesis of flavonoids (anthocyanins and flavonols) and the expression levels of related genes in an in vitro environmental experiment using detached grape berries. Sufficient anthocyanin accumulation in the grape skin was observed under a low temperature (15 °C) plus light treatment, whereas high temperature (35 °C) or dark treatment severely suppressed anthocyanin accumulation. This indicates that the accumulation of anthocyanins is dependent on both low temperature and light. qRT-PCR analysis showed that the responses of three MYB-related genes (VlMYBA1-3, VlMYBA1-2, and VlMYBA2) to temperature and light differed greatly even though the products of all three genes had the ability to regulate anthocyanin biosynthesis pathway genes. Furthermore, the expression levels of other MYB-related genes and many flavonoid biosynthesis pathway genes were regulated independently by temperature and light. We also found that temperature and light conditions affected the anthocyanin composition in the skin through the regulation of flavonoid biosynthesis pathway genes. Our results suggest that low temperature and light have a synergistic effect on the expression of genes in the flavonoid biosynthesis pathway. These findings provide new information about the relationships between environmental factors and flavonoid accumulation in grape berry skin.

Modulation of flavonoid metabolites in Arabidopsis thaliana through overexpression of the MYB75 transcription factor: role of kaempferol-3,7-dirhamnoside in resistance to the specialist insect herbivore Pieris brassicae

Anthocyanins and flavonols are secondary metabolites that can function in plant defence against herbivores. In Arabidopsis thaliana, anthocyanin and flavonol biosynthesis are regulated by MYB transcription factors. Overexpression of MYB75 (oxMYB75) in Arabidopsis results in increasing anthocyanin and flavonol levels which enhances plant resistance to generalist caterpillars. However, how these metabolites affect specialist herbivores has remained unknown. Performance of a specialist aphid (Brevicoryne brassicae) was unaffected after feeding on oxMYB75 plants, whereas a specialist caterpillar (Pieris brassicae) gained significantly higher body mass when feeding on this plant. An increase in anthocyanin and total flavonol glycoside levels correlated negatively with the body mass of caterpillars fed on oxMYB75 plants. However, a significant reduction of kaempferol-3,7-dirhamnoside (KRR) corresponded to an increased susceptibility of oxMYB75 plants to caterpillar feeding. Pieris brassicae caterpillars also grew less on an artificial diet containing KRR or on oxMYB75 plants that were exogenously treated with KRR, supporting KRR's function in direct defence against this specialist caterpillar. The results show that enhancing the activity of the anthocyanin pathway in oxMYB75 plants results in re-channelling of quercetin/kaempferol metabolites which has a negative effect on the accumulation of KRR, a novel defensive metabolite against a specialist caterpillar.

Functional expression of a P450 flavonoid hydroxylase for the biosynthesis of plant-specific hydroxylated flavonols in Escherichia coli

Flavonols are plant polyphenolic compounds that belong to the class of molecules collectively known as flavonoids. Because of their demonstrated health benefits towards a wide array of human pathological conditions, a great interest has emerged for their biosynthesis from well-characterized microbial hosts. We present the functional expression in Escherichia coli of a plant P450 flavonoid 3', 5'-hydroxylase (F3'5'H) as a fusion protein with a P450 reductase. This expression allowed metabolic engineering of E. coli to produce the flavonol kaempferol and the 3', 4' B-ring hydroxylated flavonol quercetin from the p-coumaric acid precursor by simultaneously co-expressing the fusion protein with 4-coumaroyl:CoA-ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3beta-hydroxylase (FHT) and flavonol synthase (FLS). Biosynthesis of the B-ring tri-hydroxylated flavonol myricetin from the engineered strains was accomplished when flavanones rather than phenylpropanoid acids were used as precursor molecules. Cultivation of the recombinant strains in rich medium increased the synthesis of all flavonoids with the exception of myricetin. The present work opens the possibility of the future production of several other hydroxylated flavonoid molecules in E. coli.

Molecular genetics of berry colour variation in table grape

The genetics and biochemistry of anthocyanins and flavonol biosynthesis and their role in plant organ pigmentation is well established in model species. However, the genetic basis of colour variation is species specific and understanding this variation is very relevant in many fruit and flower crop species. Among grape cultivars, there is a wide genetic variation for berry colour ranging from yellow-green ("white" cultivars) to dark blue berries. Berry colour results from the synthesis and accumulation of anthocyanins in the berry skin, which in plants is commonly regulated by transcription factors belonging to the MYB and bHLH families. In this work, we aimed to identify the major genetic determinants of berry colour variation in a large collection of table grape cultivars and somatic variants. The genetic analyses of berry colour in a few grape segregating progenies had previously identified a single locus on linkage group 2 responsible for colour variation. Furthermore, somatic variation for berry skin colour in cultivar Italia had been associated with the presence of a Gret1 retrotransposon in the promoter region of VvmybA1, a Myb gene whose expression is associated to skin colouration. The results show that VvmybA1 is the gene underlying the mapped locus controlling berry colour in grape. Additionally, the molecular analyses indicate that genetic and somatic berry colour variation can be associated to molecular variation at VvmybA1 in more than 95% of the analyzed cultivars. Thus, VvmybA1 is a major determinant of berry colour variation in table grape and its instability is the major cause of somatic variation for this trait.

Cytochrome P450 CYP78A9 is involved in Arabidopsis reproductive development

Synchronized communication between gametophytic and sporophytic tissue is crucial for successful reproduction, and hormones seem to have a prominent role in it. Here, we studied the role of the Arabidopsis (Arabidopsis thaliana) cytochrome P450 CYP78A9 enzyme during reproductive development. First, controlled pollination experiments indicate that CYP78A9 responds to fertilization. Second, while CYP78A9 overexpression can uncouple fruit development from fertilization, the cyp78a8 cyp78a9 loss-of-function mutant has reduced seed set due to outer ovule integument development arrest, leading to female sterility. Moreover, CYP78A9 has a specific expression pattern in inner integuments in early steps of ovule development as well as in the funiculus, embryo, and integuments of developing seeds. CYP78A9 overexpression did not change the response to the known hormones involved in flower development and fruit set, and it did not seem to have much effect on the major known hormonal pathways. Furthermore, according to previous predictions, perturbations in the flavonol biosynthesis pathway were detected in cyp78a9, cyp78a8 cyp78a9, and empty siliques (es1-D) mutants. However, it appeared that they do not cause the observed phenotypes. In summary, these results add new insights into the role of CYP78A9 in plant reproduction and present, to our knowledge, the first characterization of metabolite differences between mutants in this gene family.

The grapevine VvibZIPC22 transcription factor is involved in the regulation of flavonoid biosynthesis

In grapevine, flavonoids constitute one of the most abundant subgroups of secondary metabolites, influencing the quality, health value, and typicity of wines. Their synthesis in many plant species is mainly regulated at the transcriptional level by modulation of flavonoid pathway genes either by single regulators or by complexes of different regulators. In particular, bZIP and MYB factors interact synergistically in the recognition of light response units present in the promoter of some genes of the pathway, thus mediating light-dependent flavonoid biosynthesis. We recently identified VvibZIPC22, a member of clade C of the grapevine bZIP family, in a quantitative trait locus (QTL) specifically associated with kaemperol content in mature berries. Here, to validate the involvement of this candidate gene in the fine regulation of flavonol biosynthesis, we characterized its function by in vitro and in vivo experiments. A role for this gene in the control of flavonol biosynthesis was indeed confirmed by its highest expression at flowering and during UV light-mediated induction, paralleled by accumulation of the flavonol synthase 1 transcript and flavonol compounds. The overexpression of VvibZIPC22 in tobacco caused a significant increase in several flavonoids in the flower, via induction of general and specific genes of the pathway. In agreement with this evidence, VvibZIPC22 was able to activate the promoters of specific genes of the flavonoid pathway, alone or together with other factors, as revealed by transient reporter assays. These findings, supported by in silico indications, allowed us to propose VvibZIPC22 as a new regulator of flavonoid biosynthesis in grapevine.

Molecular Basis for Chemical Evolution of Flavones to Flavonols and Anthocyanins in Land Plants

During the course of evolution of land plants, different classes of flavonoids, including flavonols and anthocyanins, sequentially emerged, facilitating adaptation to the harsh terrestrial environment. Flavanone 3β-hydroxylase (F3H), an enzyme functioning in flavonol and anthocyanin biosynthesis and a member of the 2-oxoglutarate-dependent dioxygenase (2-ODD) family, catalyzes the hydroxylation of (2S)-flavanones to dihydroflavonols, but its origin and evolution remain elusive. Here, we demonstrate that functional flavone synthase Is (FNS Is) are widely distributed in the primitive land plants liverworts and evolutionarily connected to seed plant F3Hs. We identified and characterized a set of 2-ODD enzymes from several liverwort species and plants in various evolutionary clades of the plant kingdom. The bifunctional enzyme FNS I/F2H emerged in liverworts, and FNS I/F3H evolved in Physcomitrium (Physcomitrella) patens and Selaginella moellendorffii, suggesting that they represent the functional transition forms between canonical FNS Is and F3Hs. The functional transition from FNS Is to F3Hs provides a molecular basis for the chemical evolution of flavones to flavonols and anthocyanins, which contributes to the acquisition of a broader spectrum of flavonoids in seed plants and facilitates their adaptation to the terrestrial ecosystem.

CsMYB60 is a key regulator of flavonols and proanthocyanidans that determine the colour of fruit spines in cucumber

Spine colour is an important fruit quality trait that influences the commercial value of cucumber (Cucumis sativus). However, little is known about the metabolites and the regulatory mechanisms of their biosynthesis in black spine varieties. In this study, we determined that the pigments of black spines are flavonoids, including flavonols and proanthocyanidins (PAs). We identified CsMYB60 as the best candidate for the previously identified B (Black spine) locus. Expression levels of CsMYB60 and the key genes involved in flavonoid biosynthesis were higher in black-spine inbred lines than that in white-spine lines at different developmental stages. The insertion of a Mutator-like element (CsMULE) in the second intron of CsMYB60 decreased its expression in a white-spine line. Transient overexpression assays indicated that CsMYB60 is a key regulatory gene and Cs4CL is a key structural gene in the pigmentation of black spines. In addition, the DNA methylation level in the CsMYB60 promoter was much lower in the black-spine line compared with white-spine line. The CsMULE insert may decrease the expression level of CsMYB60, causing hindered synthesis of flavonols and PAs in cucumber fruit spines.

ZC3H13-mediated N6-methyladenosine modification of PHF10 is impaired by fisetin which inhibits the DNA damage response in pancreatic cancer

DNA damage repair is a major barrier for chemotherapy efficacy of pancreatic ductal adenocarcinoma (PDAC), including the efficacy of platinum-based and gemcitabine/nab-paclitaxel treatments. N6-methyladenosine modifications (m6A) have recently been reported to play a role in homologous recombination (HR) repair of DNA double strand breaks (DSBs); however, the mechanism of action remains unknown. Our previous work indicated that fisetin may be a promising anti-tumour agent that induces DNA damage. In this study, we reported that fisetin induced DSBs and suppressed HR repair through m6A modification in PDAC cells. The m6A writer ZC3H13 and PHF10, which is a subunit of the PBAF chromatin remodelling complex, were identified as the main molecules affected by fisetin treatment. To our knowledge, it's the first time that PHF10 was found and involved in the DNA damage response. PHF10 loss-of-function resulted in elevated recruitment of γH2AX, RAD51, and 53BP1 to DSB sites and decreased HR repair efficiency. Moreover, ZC3H13 knockdown downregulated the m6A methylation of PHF10 and decreased PHF10 translation in a YTHDF1-dependent manner. In conclusion, our study demonstrates that fisetin enhanced DSBs via ZC3Hl3-mediated m6A modification of PHF10, which may provide insight into novel therapeutic approaches for PDAC.

Functional characterization of three flavonol synthase genes from Camellia sinensis: Roles in flavonol accumulation

Flavonol derivatives are a group of flavonoids benefiting human health. Their abundant presence in tea is associated with astringent taste. To date, mechanism pertaining to the biosynthesis of flavonols in tea plants remains unknown. In this study, we used bioinformatic analysis mining the tea genome and obtained three cDNAs that were annotated to encode flavonol synthases (FLS). Three cDNAs, namely CsFLSa, b, and c, were heterogenously expressed in E. coli to induce recombinant proteins, which were further used to incubate with three substrates, dihydrokampferol (DHK), dihydroquercetin (DHQ), and dihydromyricetin (DHM). The resulting data showed that three rCsFLSs preferred to catalyze (DHK). Overexpression of each cDNA in tobacco led to the increase of kampferol and the reduction of anthocyanins in flowers. Further metabolic profiling of flavan-3-ols in young tea shoots characterized that kaempferol derivatives were the most abundant, followed by quercetin and then myricetin derivatives. Taken together, these data characterized the key step committed to the biosynthesis of flavonols in tea leaves. Moreover, these data enhance understanding the metabolic accumulation relevance between flavonols and other main flavonoids such as flavan-3-ols in tea leaves.

Effects of UV-A radiation on organ-specific accumulation and gene expression of isoflavones and flavonols in soybean sprout

Organ-specific flavonoid destination in soybean sprouts following UV irradiation is still unclear although the metabolic pathway of flavonoid synthesis and UV responded flavonoid accumulation have been well investigated. We report the identification of organ-specific localization and specific gene expression of isoflavones and kaempferol glycosides in the soybean sprouts responded to UV-A irradiation. UV-A irradiation stimulated only root isoflavones, especially increase of genistein types. The daidzein types predominated in non-UV-A treated roots. Kaempferol glycosides were not increased in roots by UV-A, but distinctly increased in aerial organs, especially in the cotyledons. These results demonstrate that UV-A upregulates the naringenin pathway synthesizing genistin and kaempferol rather than the liquiritigenin pathway synthesizing daidzin and glycitin. High GmUGT9 and other gene expression related to isoflavone synthesis in roots clearly demonstrate the UV-A-induced isoflavone accumulation. Aerial organ specific increase of GmF3H, GmFLS1, and GmDFR1 expression by UV-A distinctly demonstrates the flavonol increase in aerial organs.

Regulation of flavonol content and composition in (Syrah×Pinot Noir) mature grapes: integration of transcriptional profiling and metabolic quantitative trait locus analyses

Flavonols are a ubiquitous class of flavonoids that accumulate preferentially in flowers and mature berries. Besides their photo-protective function, they play a fundamental role during winemaking, stabilizing the colour by co-pigmentation with anthocyanins and contributing to organoleptic characteristics. Although the general flavonol pathway has been genetically and biochemically elucidated, the genetic control of flavonol content and composition at harvest is still not clear. To this purpose, the grapes of 170 segregating F1 individuals from a 'Syrah'×'Pinot Noir' population were evaluated at the mature stage for the content of six flavonol aglycons in four seasons. Metabolic data in combination with genetic data enabled the identification of 16 mQTLs (metabolic quantitative trait loci). For the first time, major genetic control by the linkage group 2 (LG 2)/MYBA region on flavonol variation, in particular of tri-hydroxylated flavonols, is demonstrated. Moreover, seven regions specifically associated with the fine control of flavonol biosynthesis are identified. Gene expression profiling of two groups of individuals significantly divergent for their skin flavonol content identified a large set of differentially modulated transcripts. Among these, the transcripts coding for MYB and bZIP transcription factors, methyltranferases, and glucosyltranferases specific for flavonols, proteins, and factors belonging to the UV-B signalling pathway and co-localizing with the QTL regions are proposed as candidate genes for the fine regulation of flavonol content and composition in mature grapes.

Elucidation of myricetin biosynthesis in Morella rubra of the Myricaceae

Flavonols are health-promoting bioactive compounds important for plant defense and human nutrition. Quercetin (Q) and kaempferol (K) biosynthesis have been studied extensively while little is known about myricetin (M) biosynthesis. The roles of flavonol synthases (FLSs) and flavonoid 3',5'-hydroxylase (F3'5'H) in M biosynthesis in Morella rubra, a member of the Myricaceae rich in M-based flavonols, were investigated. The level of MrFLS transcripts alone did not correlate well with the accumulation of M-based flavonols. However, combined transcript data for MrFLS1 and MrF3'5'H showed a good correlation with the accumulation of M-based flavonols in different tissues of M. rubra. Recombinant MrFLS1 and MrFLS2 proteins showed strong activity with dihydroquercetin (DHQ), dihydrokaempferol (DHK), and dihydromyricetin (DHM) as substrates, while recombinant MrF3'5'H protein preferred converting K to M, amongst a range of substrates. Tobacco (Nicotiana tabacum) overexpressing 35S::MrFLSs produced elevated levels of K-based and Q-based flavonols without affecting M-based flavonol levels, while tobacco overexpressing 35S::MrF3'5'H accumulated significantly higher levels of M-based flavonols. We conclude that M accumulation in M. rubra is affected by gene expression and enzyme specificity of FLS and F3'5'H as well as substrate availability. In the metabolic grid of flavonol biosynthesis, the strong activity of MrF3'5'H with K as substrate additionally promotes metabolic flux towards M in M. rubra.

Identification and Functional Analysis of a Flavonol Synthase Gene from Grape Hyacinth

Flavonols are important copigments that affect flower petal coloration. Flavonol synthase (FLS) catalyzes the conversion of dihydroflavonols to flavonols. In this study, we identified a FLS gene, MaFLS, expressed in petals of the ornamental monocot Muscari aucheri (grape hyacinth) and analyzed its spatial and temporal expression patterns. qRT-PCR analysis showed that MaFLS was predominantly expressed in the early stages of flower development. We next analyzed the in planta functions of MaFLS. Heterologous expression of MaFLS in Nicotiana tabacum (tobacco) resulted in a reduction in pigmentation in the petals, substantially inhibiting the expression of endogenous tobacco genes involved in anthocyanin biosynthesis (i.e., NtDFR, NtANS, and NtAN2) and upregulating the expression of NtFLS. The total anthocyanin content in the petals of the transformed tobacco plants was dramatically reduced, whereas the total flavonol content was increased. Our study suggests that MaFLS plays a key role in flavonol biosynthesis and flower coloration in grape hyacinth. Moreover, MaFLS may represent a new potential gene for molecular breeding of flower color modification and provide a basis for analyzing the effects of copigmentation on flower coloration in grape hyacinth.

Combined transcriptomic and metabolic analyses reveal potential mechanism for fruit development and quality control of Chinese raspberry (Rubus chingii Hu)

Combined transcriptomic and metabolic analyses reveal that fruit of Rubus chingii Hu launches biosynthesis of phenolic acids and flavonols at beginning of fruit set and then coordinately accumulated or converted to their derivatives. Rubus chingii Hu (Chinese raspberry) is an important dual functional food with nutraceutical and pharmaceutical values. Comprehensively understanding the mechanisms of fruit development and bioactive components synthesis and regulation could accelerate genetic analysis and molecular breeding for the unique species. Combined transcriptomic and metabolic analyses of R. chingii fruits from different developmental stages, including big green, green-to-yellow, yellow-to-orange, and red stages, were conducted. A total of 89,188 unigenes were generated and 57,545 unigenes (64.52%) were annotated. Differential expression genes (DEGs) and differentially accumulated metabolites (DAMs) were mainly involved in the biosynthesis of secondary metabolites. The fruit launched the biosynthesis of phenolic acids and flavonols at the very beginning of fruit set and then coordinately accumulated or converted to their derivatives. This was tightly regulated by expressions of the related genes and MYB and bHLH transcription factors. The core genes products participated in the biosynthesis of ellagic acid (EA) and kaempferol-3-O-rutinoside (K-3-R), such as DAHPS, DQD/SDH, PAL, 4CL, CHS, CHI, F3H, F3'H, FLS, and UGT78D2, and their corresponding metabolites were elaborately characterized. Our research reveals the molecular and chemical mechanisms of the fruit development of R. chingii. The results provide a solid foundation for the genetic analysis, functional genes isolation, fruit quality improvement and modifiable breeding of R. chingii.

MdSCL8 as a Negative Regulator Participates in ALA-Induced FLS1 to Promote Flavonol Accumulation in Apples

Apples (Malus domestica) are rich in flavonols, and 5-aminolevulinic acid (ALA) plays an important role in the regulation of plant flavonoid metabolism. To date, the underlying mechanism of ALA promoting flavonol accumulation is unclear. Flavonol synthase (FLS) is a key enzyme in flavonol biosynthesis. In this study, we found that ALA could enhance the promoter activity of MdFLS1 in the ‘Fuji’ apple and improve its expression. With MdFLS1 as bait, we screened a novel transcription factor MdSCL8 by the Yeast One-Hybrid (Y1H) system from the apple cDNA library which we previously constructed. Using luciferase reporter assay and transient GUS activity assay, we verified that MdSCL8 inhibits the activity of MdFLS1 promoter and hinders MdFLS1 expression, thus reducing flavonol accumulation in apple. ALA significantly inhibited MdSCL8 expression. Therefore, ALA promoted the expression of MdFLS1 and the consequent flavonol accumulation probably by down-regulating MdSCL8. We also found that ALA significantly enhanced the gene expression of MdMYB22 and MdHY5, two positive regulators of MdFLS. We further demonstrated that MdMYB22 interacts with MdHY5, but neither of them interacts with MdSCL8. Taken together, our data suggest MdSCL8 as a novel regulator of MdFLS1 and provide important insights into mechanisms of ALA-induced flavonol accumulation in apples.

Genome-Wide Analysis of Artificial Mutations Induced by Ethyl Methanesulfonate in the Eggplant (Solanum melongena L.)

Whole-genome sequences of four EMS (ethyl methanesulfonate)-induced eggplant mutants were analyzed to identify genome-wide mutations. In total, 173.01 GB of paired-end reads were obtained for four EMS-induced mutants and (WT) wild type and 1,076,010 SNPs (single nucleotide polymorphisms) and 183,421 indels were identified. The most common mutation type was C/G to T/A transitions followed by A/T to G/C transitions. The mean densities were one SNP per 1.3 to 2.6 Mb. The effect of mutations on gene function was annotated and only 7.2% were determined to be deleterious. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed 10 and 11 genes, which were nonsynonymous mutation or frameshift deletion in 48-5 and L6-5 involved in the anthocyanin biosynthesis or flavone and flavonol biosynthesis. QRT-PCR results showed that only the Sme2.5_06210.1_g00004.1, which was annotated as UFGT (Flavonoid galactosidase transferase), expression significantly decreased in the L6-5 mutant compared with the WT. Also, the Sme2.5_06210.1_g00004.1 expression was lower in the colorless eggplant compared with colorful eggplant in the natural eggplant cultivar. These results suggest that Sme2.5_06210.1_g00004.1 may play a key role in eggplant anthocyanin synthesis.

Quantitative trait loci analysis of seed-specialized metabolites reveals seed-specific flavonols and differential regulation of glycoalkaloid content in tomato

Given the potential health benefits (and adverse effects), of polyphenolic and steroidal glycoalkaloids in the diet there is a growing interest in fully elucidating the genetic control of their levels in foodstuffs. Here we carried out profiling of the specialized metabolites in the seeds of the Solanum pennellii introgression lines identifying 338 putative metabolite quantitative trait loci (mQTL) for flavonoids, steroidal glycoalkaloids and further specialized metabolites. Two putative mQTL for flavonols and one for steroidal glycoalkaloids were cross-validated by evaluation of the metabolite content of recombinants harboring smaller introgression in the corresponding QTL interval or by analysis of lines from an independently derived backcross inbred line population. The steroidal glycoalkaloid mQTL was localized to a chromosomal region spanning 14 genes, including a previously defined steroidal glycoalkaloid gene cluster. The flavonoid mQTL was further validated via the use of transient and stable overexpression of the Solyc12g098600 and Solyc12g096870 genes, which encode seed-specific uridine 5'-diphosphate-glycosyltransferases. The results are discussed in the context of our understanding of the accumulation of polyphenols and steroidal glycoalkaloids, and how this knowledge may be incorporated into breeding strategies aimed at improving nutritional aspects of plants as well as in fortifying them against abiotic stress.

Annotation of genes involved in high level of dihydromyricetin production in vine tea (Ampelopsis grossedentata) by transcriptome analysis

BACKGROUND

Leaves of the medicinal plant Ampelopsis grossedentata, which is commonly known as vine tea, are used widely in the traditional Chinese beverage in southwest China. The leaves contain a large amount of dihydromyricetin, a compound with various biological activities. However, the transcript profiles involved in its biosynthetic pathway in this plant are unknown.

RESULTS

We conducted a transcriptome analysis of both young and old leaves of the vine tea plant using Illumina sequencing. Of the transcriptome datasets, a total of 52.47 million and 47.25 million clean reads were obtained from young and old leaves, respectively. Among 471,658 transcripts and 177,422 genes generated, 7768 differentially expressed genes were identified in leaves at these two stages of development. The phenylpropanoid biosynthetic pathway of vine tea was investigated according to the transcriptome profiling analysis. Most of the genes encoding phenylpropanoid biosynthesis enzymes were identified and found to be differentially expressed in different tissues and leaf stages of vine tea and also greatly contributed to the biosynthesis of dihydromyricetin in vine tea.

CONCLUSIONS

To the best of our knowledge, this is the first formal study to explore the transcriptome of A. grossedentata. The study provides an insight into the expression patterns and differential distribution of genes related to dihydromyricetin biosynthesis in vine tea. The information may pave the way to metabolically engineering plants with higher flavonoid content.

Transcriptional Analysis in the Arabidopsis Roots Reveals New Regulators that Link rac-GR24 Treatment with Changes in Flavonol Accumulation, Root Hair Elongation and Lateral Root Density

The synthetic strigolactone (SL) analog, rac-GR24, has been instrumental in studying the role of SLs as well as karrikins because it activates the receptors DWARF14 (D14) and KARRIKIN INSENSITIVE 2 (KAI2) of their signaling pathways, respectively. Treatment with rac-GR24 modifies the root architecture at different levels, such as decreasing the lateral root density (LRD), while promoting root hair elongation or flavonol accumulation. Previously, we have shown that the flavonol biosynthesis is transcriptionally activated in the root by rac-GR24 treatment, but, thus far, the molecular players involved in that response have remained unknown. To get an in-depth insight into the changes that occur after the compound is perceived by the roots, we compared the root transcriptomes of the wild type and the more axillary growth2 (max2) mutant, affected in both SL and karrikin signaling pathways, with and without rac-GR24 treatment. Quantitative reverse transcription (qRT)-PCR, reporter line analysis and mutant phenotyping indicated that the flavonol response and the root hair elongation are controlled by the ELONGATED HYPOCOTYL 5 (HY5) and MYB12 transcription factors, but HY5, in contrast to MYB12, affects the LRD as well. Furthermore, we identified the transcription factors TARGET OF MONOPTEROS 5 (TMO5) and TMO5 LIKE1 as negative and the Mediator complex as positive regulators of the rac-GR24 effect on LRD. Altogether, hereby, we get closer toward understanding the molecular mechanisms that underlay the rac-GR24 responses in the root.

Soil sustainable utilization technology: mechanism of flavonols in resistance process of heavy metal

The soil ecosystem is critical for agricultural production, affecting many aspects of human health. Soil has more unknown biodiversity and edaphic parameters than any other ecosystem especially when polluted. Metagenomics and metatranscriptomics were applied to research on toxicological characteristics of Pb and resistance mechanism of flavonols. Rhizosphere microorganisms-plants system, a unified system closely related to soil environment was taken as research object. Results emphasize gene expression changes in different test groups. Gene ontology enrichment and eggNOG showed that Pb has a toxic effect on gene and protein function which concentrated on ATPase and ATP-dependent activity. Differentially expressed genes in the flavonols group indicated that flavonols regulate amino acid transport and other transportation process related to Pb stress. Kegg analysis represents that Pb interferences energy production process via not only the upstream like glycolysis and tricarboxylic acid (TCA) circle but also oxidative phosphorylation process, which can also produce reactive oxygen species and impact the eliminating process. Flavonols have shown the ability in alleviating toxic effect of Pb and improving the resistance of plants. Flavonols can recover the electronic transmission and other process in TCA and oxidative phosphorylation via ascorbic acid-glutathione metabolism. Flavonols activated antioxidative process and non-specific immunity via vitamins B₂-B₆ metabolism.

Sucrose-specific induction of the anthocyanin biosynthetic pathway in Arabidopsis

Sugars act as signaling molecules, whose signal transduction pathways may lead to the activation or inactivation of gene expression. Whole-genome transcript profiling reveals that the flavonoid and anthocyanin biosynthetic pathways are strongly up-regulated following sucrose (Suc) treatment. Besides mRNA accumulation, Suc affects both flavonoid and anthocyanin contents. We investigated the effects of sugars (Suc, glucose, and fructose) on genes coding for flavonoid and anthocyanin biosynthetic enzymes in Arabidopsis (Arabidopsis thaliana). The results indicate that the sugar-dependent up-regulation of the anthocyanin synthesis pathway is Suc specific. An altered induction of several anthocyanin biosynthetic genes, consistent with in vivo sugar modulation of mRNA accumulation, is observed in the phosphoglucomutase Arabidopsis mutant accumulating high levels of soluble sugars.