Expression of chimeric P450 genes encoding flavonoid-3', 5'-hydroxylase in transgenic tobacco and petunia plants(1)

Reduction of flavonoid content in honeysuckle via Erysiphe lonicerae-mediated inhibition of three essential genes in flavonoid biosynthesis pathways

Honeysuckle, valued for its wide-ranging uses in medicine, cuisine, and aesthetics, faces a significant challenge in cultivation due to powdery mildew, primarily caused by the Erysiphe lonicerae pathogen. The interaction between honeysuckle and E. lonicerae, especially concerning disease progression, remains insufficiently understood. Our study, conducted in three different locations, found that honeysuckle naturally infected with E. lonicerae showed notable decreases in total flavonoid content, with reductions of 34.7%, 53.5%, and 53.8% observed in each respective site. Controlled experiments supported these findings, indicating that artificial inoculation with E. lonicerae led to a 20.9% reduction in flavonoid levels over 21 days, worsening to a 54.8% decrease by day 42. Additionally, there was a significant drop in the plant's total antioxidant capacity, reaching an 81.7% reduction 56 days after inoculation. Metabolomic analysis also revealed substantial reductions in essential medicinal components such as chlorogenic acid, luteolin, quercetin, isoquercetin, and rutin. Investigating gene expression revealed a marked decrease in the relative expression of the LjPAL1 gene, starting as early as day 7 post-inoculation and falling to a minimal level (fold change = 0.29) by day 35. This trend was mirrored by a consistent reduction in phenylalanine ammonia-lyase activity in honeysuckle through the entire process, which decreased by 72.3% by day 56. Further analysis showed significant and sustained repression of downstream genes LjFNHO1 and LjFNGT1, closely linked to LjPAL1. We identified the mechanism by which E. lonicerae inhibits this pathway and suggest that E. lonicerae may strategically weaken the honeysuckle's disease resistance by targeting key biosynthetic pathways, thereby facilitating further pathogen invasion. Based on our findings, we recommend two primary strategies: first, monitoring medicinal constituent levels in honeysuckle from E. lonicerae-affected areas to ensure its therapeutic effectiveness; and second, emphasizing early prevention and control measures against honeysuckle powdery mildew due to the persistent decline in crucial active compounds.

Heterologous Expression of Platycodon grandiflorus PgF3'5'H Modifies Flower Color Pigmentation in Tobacco

Flavonoid-3',5'-hydroxylase (F3'5'H) is the key enzyme for the biosynthesis of delphinidin-based anthocyanins, which are generally required for purple or blue flowers. Previously, we isolated a full-length cDNA of PgF3'5'H from Platycodon grandiflorus, which shared the highest homology with Campanula medium F3'5'H. In this study, PgF3'5'H was subcloned into a plant over-expression vector and transformed into tobacco via Agrobacterium tumefaciens to investigate its catalytic function. Positive transgenic tobacco T0 plants were obtained by hygromycin resistance screening and PCR detection. PgF3'5'H showed a higher expression level in all PgF3'5'H transgenic tobacco plants than in control plants. Under the drive of the cauliflower mosaic virus (CaMV) 35S promoter, the over-expressed PgF3'5'H produced dihydromyricetin (DHM) and some new anthocyanin pigments (including delphinidin, petunidin, peonidin, and malvidin derivatives), and increased dihydrokaempferol (DHK), taxifolin, tridactyl, cyanidin derivatives, and pelargonidin derivatives in PgF3'5'H transgenic tobacco plants by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis, resulting in a dramatic color alteration from light pink to magenta. These results indicate that PgF3'5'H products have F3'5'H enzyme activity. In addition, PgF3'5'H transfer alters flavonoid pigment synthesis and accumulation in tobacco. Thus, PgF3'5'H may be considered a candidate gene for gene engineering to enhance anthocyanin accumulation and the molecular breeding project for blue flowers.

Metabolic profiling and expression analysis of key genetic factors in the biosynthetic pathways of antioxidant metabolites in mungbean sprouts

Mungbeans (Vigna radiata L.), a major legume crop in Asia, contain higher amounts of functional substances than other legumes, such as catechin, chlorogenic acid, and vitexin. Germination can improve the nutritional value of legume seeds. Here, 20 functional substances were profiled in germinated mungbeans and the expression levels of the transcripts of key enzymes in targeted secondary metabolite biosynthetic pathways were identified. VC1973A, a reference mungbean elite cultivar, had the highest amount of gallic acid (99.93 ± 0.13 mg/100 g DW) but showed lower contents of most metabolites than the other genotypes. Wild mungbeans contained a large amount of isoflavones compared with cultivated genotypes, especially for daidzin, genistin and glycitin. The expression of key genes involved in biosynthetic pathways had significant positive or negative correlations with the target secondary metabolite contents. The results indicate that functional substance contents are regulated at the transcriptional level, which can be applied to improve the nutritional value of mungbean sprouts in molecular breeding or genetic engineering, and wild mungbeans are a useful resource to improve the quality of mungbean sprouts.

Transcriptomic and metabolic studies on the role of inorganic and organic iodine compounds in lettuce plants

Iodine (I) is considered a beneficial element or even micronutrient for plants. The aim of this study was to determine the molecular and physiological processes of uptake, transport, and metabolism of I applied to lettuce plants. KIO3, KIO3 + salicylic acid, 5-iodosalicylic acid and 3,5-diiodosalicylic acid were applied. RNA-sequencing was executed using 18 cDNA libraries constructed separately for leaves and roots from KIO3, SA and control plants. De novo transcriptome assembly generated 1937.76 million sequence reads resulting in 27,163 transcripts with N50 of 1638 bp. 329 differentially expressed genes (DEGs) in roots were detected after application of KIO3, out of which 252 genes were up-regulated, and 77 were down-regulated. In leaves, 9 genes revealed differential expression pattern. DEGs analysis indicated its involvement in such metabolic pathways and processes as: chloride transmembrane transport, phenylpropanoid metabolism, positive regulation of defense response and leaf abscission, and also ubiquinone and other terpenoid-quinone biosynthesis, protein processing in endoplasmic reticulum, circadian rhythm including flowering induction as well as a putative PDTHA (i.e. Plant Derived Thyroid Hormone Analogs) metabolic pathway. qRT-PCR of selected genes suggested their participation in the transport and metabolism of iodine compounds, biosynthesis of primary and secondary metabolites, PDTHA pathway and flowering induction.

Genome-wide investigation of Cytochrome P450 superfamily of Aquilaria agallocha: Association with terpenoids and phenylpropanoids biosynthesis

Agarwood is a dark resinous wood, produced when Aquilaria tree responds to wounding and microbial infection resulting in the accumulation of fragrant metabolites. Sesquiterpenoids and 2-(2-phenylethyl) chromones are the major phytochemicals in agarwood and Cytochrome P450s (CYPs) are one of the important enzymes in the biosynthesis of these fragrant chemicals. Thus, understanding the repertoire of CYP superfamily in Aquilaria can not only give insights into the fundamentals of agarwood formation, but can also provide a tool for the overproduction of the aroma chemicals. Therefore, current study was designed to investigate CYPs of an agarwood producing plant, Aquilaria agallocha. We identified 136 CYP genes from A. agallocha genome (AaCYPs) and classified them into 8 clans and 38 families. The promoter regions had stress and hormone-related cis-regulatory elements which indicate their participation in the stress response. Duplication and synteny analysis revealed segmental and tandem duplicated and evolutionary related CYP members in other plants. Potential members involved in the biosynthesis of sesquiterpenoids and phenylpropanoids were identified and found to be upregulated in methyl jasmonate-induced callus and infected Aquilaria trees by real-time quantitative PCR analyses. This study highlights the possible involvement of AaCYPs in agarwood resin development and their complex regulation during stress exposure.

Yeast-based system for in vivo evaluation of alleles of the anthocyanin production pathway

Plants produce anthocyanins to incite the pollination and seed dispersion performed by pigment-attracted animals. These natural blue-to-red-coloured pigments can be used as food colourants and antioxidants. For this purpose, microbial bioproduction of anthocyanins has become of industrial interest in recent years. 20 new alleles of anthocyanin production pathway genes were extracted and characterised for protein expression level and stability using a developed single-PCR product gene-entry system for tagged protein synthesis in yeast S. cerevisiae. Enzymatic activities of these proteins in the episomally complemented in vivo systems were compared by HPLC-MS analysis. Results show that the codon optimisation of the anthocyanin pathway genes is not essential for the effective heterologous expression in yeast. Elevating the cellular abundance of CHS and F3H enzymes can increase anthocyanidin production from supplemented precursors. New alleles VmF3Hv1 and VuCHS were shown to have the best performance in the analysed system. System complementation with flavonoid 3',5'-hydroxylase substantially increases total anthocyanidin production. The described single-entry yeast episomal complementation system is a convenient and rapid tool for the complex evaluation of new alleles in vivo.

The genomic and bulked segregant analysis of Curcuma alismatifolia revealed its diverse bract pigmentation

Compared with most flowers where the showy part comprises specialized leaves (petals) directly subtending the reproductive structures, most Zingiberaceae species produce showy "flowers" through modifications of leaves (bracts) subtending the true flowers throughout an inflorescence. Curcuma alismatifolia, belonging to the Zingiberaceae family, a plant species originating from Southeast Asia, has become increasingly popular in the flower market worldwide because of its varied and esthetically pleasing bracts produced in different cultivars. Here, we present the chromosome-scale genome assembly of C. alismatifolia "Chiang Mai Pink" and explore the underlying mechanisms of bract pigmentation. Comparative genomic analysis revealed C. alismatifolia contains a residual signal of whole-genome duplication. Duplicated genes, including pigment-related genes, exhibit functional and structural differentiation resulting in diverse bract colors among C. alismatifolia cultivars. In addition, we identified the key genes that produce different colored bracts in C. alismatifolia, such as F3'5'H, DFR, ANS and several transcription factors for anthocyanin synthesis, as well as chlH and CAO in the chlorophyll synthesis pathway by conducting transcriptomic analysis, bulked segregant analysis using both DNA and RNA data, and population genomic analysis. This work provides data for understanding the mechanism of bract pigmentation and will accelerate breeding in developing novel cultivars with richly colored bracts in C. alismatifolia and related species. It is also important to understand the variation in the evolution of the Zingiberaceae family.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-022-00081-6.

Natural Sweeteners and Sweetness-Enhancing Compounds Identified in Citrus Using an Efficient Metabolomics-Based Screening Strategy

With the high demand for a healthy diet, it is necessary and important to explore natural sweeteners used in food that enhance palatability but minimize calories. Citrus is considered a good potential source of noncaloric sweeteners, but to date, only one sweetness modulator has been found in this most common fruit crop. Herein, an efficient strategy based on an in-house database and the untargeted and targeted metabolomics analyses was proposed to screen sweeteners or sweet-enhancing compounds from citrus. Eight sweeteners or sweetness-enhancing compounds were screened out, seven of which were newly identified from the genus Citrus. Surprisingly, we identified naturally occurring oxime V, which previously was only known as a synthetic compound. The contents of five compounds, in 11 citrus cultivars or unreleased selections across two production years, were compared. Successful identification of these natural sweeteners and sweetness-enhancing compounds in citrus fruit indicated the potential to identify the relevant biosynthetic pathways and to breed new citrus cultivars containing these compounds that provided both palatability and lower sugar consumption. This study also demonstrated that the proposed metabolomics-based screening strategy could greatly boost the identification of taste modulators with low contents in natural resources.

Flavonoid biosynthesis in four Dendrobium species based on transcriptome sequencing and metabolite analysis

BACKGROUND

Dendrobium is a genus of plants used as traditional Chinese herbal medicines, with high economic and medicinal value.

METHODS AND RESULTS

To reveal the mechanism of flavonoid biosynthesis in Dendrobium, the metabolites and transcriptomes of four Dendrobium species (D. chrysotoxum, D. nobile, D. fimbriatum, and D. denneanum) were analyzed comprehensively. Ultra-high-performance liquid chromatography-tandem mass spectrometry analysis revealed ten flavonoid compounds in Dendrobium. In total, 100,096 unigenes were obtained from the transcript database of the four Dendrobium species. Among the identified differentially expressed genes, 51 were associated with flavonoid biosynthesis, and 670 differentially expressed transcription factors were predicted, including 194 MYB, 87 bHLH, and 100 WRKY family transcription factors, respectively. Transcriptome analysis showed that the expression levels of structural genes such as chalcone synthase (CHS), cinnamate-4-hydroxylase (C4H), and flavonoid 3'-hydroxylase (F3'H) were lower in D. chrysotoxum, D. nobile, and D. fimbriatum than those in D. denneanum, which may be the main reason for the low flavonoid contents in D. chrysotoxum, D. nobile, and D. fimbriatum.

CONCLUSIONS

The expression level of structural genes corresponded to the accumulation level of flavonols in the different Dendrobium species. The results deepen the understanding of the molecular mechanism of flavonoid biosynthesis in Dendrobium and provide novel insights into the synthesis and accumulation of flavonoids in Dendrobium.

A high-quality genome assembly of Jasminum sambac provides insight into floral trait formation and Oleaceae genome evolution

As one of the most economically significant Oleaceae family members, Jasminum sambac is renowned for its distinct sweet, heady fragrance. Using Illumina reads, Nanopore long reads, and HiC-sequencing, we efficiently assembled and annotated the J. sambac genome. The high-quality genome assembly consisted of a total of 507 Mb sequence (contig N50 = 17.6 Mb) with 13 pseudomolecules. A total of 21,143 protein-coding genes and 303 Mb repeat sequences were predicted. An ancient whole-genome triplication event at the base of Oleaceae (~66 million years ago [Ma], Late Cretaceous) was identified and this may have contributed to the diversification of the Oleaceae ancestor and its divergence from the Lamiales. Stress-related (e.g., WRKY) and flowering-related (e.g., MADS-box) genes were located in the triplicated regions, suggesting that the polyploidy event might have contributed adaptive potential. Genes related to terpenoid biosynthesis, for example, FTA and TPS, were observed to be duplicated to a great extent in the J. sambac genome, perhaps explaining the strong fragrance of the flowers. Copy number changes in distinct phylogenetic clades of the MADS-box family were observed in J. sambac genome, for example, AGL6- and Mα- were lost and SOC- expanded, features that might underlie the long flowering period of J. sambac. The structural genes implicated in anthocyanin biosynthesis were depleted and this may explain the absence of vivid colours in jasmine. Collectively, assembling the J. sambac genome provides new insights into the genome evolution of the Oleaceae family and provides mechanistic insights into floral properties.

Cloning and Expression Analysis of Flavonoid 3', 5'-Hydroxylase Gene from Brunfelsia acuminata

The full-length cDNA sequence of F3′5′H gene from the Brunfelsia acuminata was obtained by RT-PCR and RACE, whose GenBank accession number is JQ678765. The sequence contains a 1521 bp open reading frame, 120 bp 5′UTR and 61 bp 3′UTR, encoding a total of 506 amino acids. The molecular mass of the predicted protein is 56.47 kDa with an estimated pI of 8.78, respectively. Sequence alignment showed that the amino acid sequence of F3′5′H was 91%, 87% and 84% with that of Petunia × hybrida, Nierembergia sp., Solanum tuberosum, respectively. Real-time quantitative PCR analysis showed that the expression of F3′5′H gene was different in petals of different days, which was the highest expression level on day 0 and significantly higher than other days. The results indicated that F3′5′H might play key role in flower color regulation and provide a theoretical reference for blue flower molecular breeding.

Overexpression of GbF3'5'H1 Provides a Potential to Improve the Content of Epicatechin and Gallocatechin

The flavonoids in Ginkgo biloba L. (ginkgo) have important medicinal uses due to their antioxidant, antitumor, and blood circulation-promoting effects. However, the genetic mechanisms underlying flavonoid biosynthesis in ginkgo remain elusive. Flavonoid 3′, 5′-hydroxylase (F3′5′H) is an important enzyme in flavonoid synthesis. We detected a novel differentially expressed GbF3′5′H1 gene homologous to the F3′5′H enzyme involved in the flavonoid synthesis pathway through transcriptome sequencing. In this study, we characterized this gene, performed an expression analysis, and heterologously overexpressed GbF3′5′H1 in Populus. Our results showed that GbF3′5′H1 is abundant in the leaf and highly expressed during April. We also found four metabolites closely related to flavonoid biosynthesis. Importantly, the contents of 4′,5-dihydroxy-7-glucosyloxyflavanone, epicatechin, and gallocatechin were significantly higher in transgenic plants than in nontransgenic plants. Our findings revealed that the GbF3′5′H1 gene functions in the biosynthesis of flavonoid-related metabolites, suggesting that GbF3′5′H1 represents a prime candidate for future studies (e.g., gene-editing) aiming to optimize ginkgo flavonoid production, especially that of flavan-3-ols.

Transcriptomic differences between male and female Trachycarpus fortunei

Trachycarpus fortunei (Hook.) is a typical dioecious plant, which has important economic value. There is currently no sex identification method for the early stages of T. fortunei growth. The aim of this study was to obtain expression and site differences between male and female T. fortunei transcriptomes. Using the Illumina sequencing platform, the transcriptomes of T. fortunei male and female plants were sequenced. By analyzing transcriptomic differences, the chromosomal helical binding protein (CHD1), serine/threonine protein kinase (STPK), cytochrome P450 716B1, and UPF0136 were found to be specifically expressed in T. fortunei males. After single nucleotide polymorphism (SNP) detection, a total of 12 male specific sites were found and the THUMP domain protein homologs were found to be male-biased expressed. Cytokinin dehydrogenase 6 (CKX6) was upregulated in male flowers and the lower concentrations of cytokinin (CTK) may be more conducive to male flower development. During new leaf growth, flavonoid and flavonol biosynthesis were initiated. Additionally, the flavonoids, 3',5'-hydroxylase (F3'5'H), flavonoids 3'-hydroxylase, were upregulated, which may cause the pale yellow phenotype. Based on these data, it can be concluded that inter-sex differentially expressed genes (DEGs) and specific SNP loci may be associated with sex determination in T. fortunei.

Event-specific qualitative polymerase chain reaction analysis for two T-DNA copies in genetically modified orange Petunia

In 2017, various orange coloured petunia on the market turned out to be genetically modified (GM) without an official authorization for commercialization. Sequence analysis suggested these undeclared plants most probably originated from a plant transformation experiment performed in the 1980s. For a deeper understanding how GM petunia entered classical breeding programmes worldwide, and whether they originated from a single source or not, we undertook a molecular genetic characterization of the T-DNA integration sites in different GM petunia cultivars and breeding lines. By means of genome walking, we isolated different T-DNA sequences, which are located at the junctions between the T-DNA(s) and the petunia DNA. Based on the results obtained we conclude that there are at least two T-DNA copies of different lengths. This is supported by Southern blot analysis. For T-DNA1, the 3'-junction sequence was isolated, whereas the 5'-junction remained unclear. In contrast, for T-DNA2, the 5'-junction sequence was isolated, whereas the sequence isolated from the 3'-region consists only of T-DNA, but did not include the junction from the T-DNA to the petunia DNA. We developed primers for event-specific PCRs and screened a set of three orange GM petunia cultivars and 126 GM offspring from a commercial breeding program. We show that both T-DNA copies are present in all our tested GM petunia samples, which underpins the assumption of a single transgenic origin of the undeclared GM petunia. Most likely, the two T-DNAs are integrated in close proximity into the petunia genome.

Analysis of Antioxidant Activity and Flavonoids Metabolites in Peel and Flesh of Red-Fleshed Apple Varieties

In this research, we compared the phenotypical characters, total anthocyanins content, total phenols content, and antioxidant activity of red-fleshed apple cultivars ‘XJ4’, ‘QN-5’, ‘DH’ and ‘HX1’ at three fruit developmental stages. A further flavonoids metabolites study was conducted in ‘XJ4’ and ‘DH’. We found broader variation of total anthocyanins content in the peel of the four cultivars, which might result in larger differences of free radicals scavenging rate. The most significant difference in fruit phenotype, anthocyanins content, and DPPH scavenging rate was observed between ‘XJ4’ and ‘DH’ at mature stage. Therefore, the flavonoids metabolites of ‘XJ4’ and ‘DH’ at mature stage were compared to unveil the details of anthocyanins compounds. The unique compounds pelargonidin 3-O-β-d-glucoside and cyanidin-3-O-malonylhexoside were detected only in peel and flesh of ‘XJ4’ but not in ‘DH’, which might contribute to the purple peel and dark-red flesh color of ‘XJ4’. Significantly decreased upstream metabolites in the early biosynthetic genes regulated domain were found only in ‘XJ4’ peel but not in the flesh. This might explain why the anthocyanins content in ‘XJ4’ peel was decreased largely at the mature stage. Taken together, our findings will give some insight into the metabolites study in flavonoid biosynthetic pathway of red-fleshed apple.

Metabolome and Transcriptome Analysis Reveals Putative Genes Involved in Anthocyanin Accumulation and Coloration in White and Pink Tea (Camellia sinensis) Flower

A variant of tea tree (Camellia sinensis (L.)) with purple buds and leaves and pink flowers can be used as a unique ornamental plant. However, the mechanism of flower coloration remains unclear. To elucidate the molecular mechanism of coloration, as well as anthocyanin accumulation in white and pink tea flowers, metabolite profiling and transcriptome sequencing was analyzed in various tea flower developmental stages. Results of metabolomics analysis revealed that three specific anthocyanin substances could be identified, i.e., cyanidin O-syringic acid, petunidin 3-O-glucoside, and pelargonidin 3-O-β-d-glucoside, which only accumulated in pink tea flowers, and were not able to be detected in white flowers. RNA-seq and weighted gene co-expression network analysis revealed eight highly expressed structural genes involved in anthocyanin biosynthetic pathway, and particularly, different expression patterns of flavonol synthase and dihydroflavonol-4-reductase genes were observed. We deduced that the disequilibrium of expression levels in flavonol synthases and dihydroflavonol-4-reductases resulted in different levels of anthocyanin accumulation and coloration in white and pink tea flowers. Results of qRT-PCR performed for 9 key genes suggested that the expression profiles of differentially expressed genes were generally consistent with the results of high-throughput sequencing. These findings provide insight into anthocyanin accumulation and coloration mechanisms during tea flower development, which will contribute to the breeding of pink-flowered and anthocyanin-rich tea cultivars.

Molecular Characterization and Event-Specific Real-Time PCR Detection of Two Dissimilar Groups of Genetically Modified Petunia (Petunia x hybrida) Sold on the Market

Petunia plants with unusual orange flowers were noticed on the European market and confirmed to be genetically modified (GM) by the Finnish authorities in spring 2017. Later in 2017, inspections and controls performed by several official laboratories of national competent authorities in the European Union detected several GM petunia varieties with orange flowers, but also another group of unusually colored flowers. In the latter group, a so far undetected gene coding for a flavonoid 3'5' hydroxylase (F3'5'H) responsible for the purple color was identified by German and Dutch authorities, suggesting that the petunias found on the markets contain different genetic constructs. Here, a strategy is described for the identification of GM petunia varieties. It is based on an initial GMO screening for known elements using (real-time) PCR and subsequent identification of the insertion sites by a gene walking-like approach called ALF (amplification of linearly-enriched fragments) in combination with Sanger and MinION sequencing. The results indicate that the positively identified GM petunias can be traced back to two dissimilar GM events used for breeding of the different varieties. The test results also confirm that the transgenic petunia event RL01-17 used in the first German field trial in 1991 is not the origin of the GM petunias sold on the market. On basis of the obtained sequence data, event-specific real-time PCR confirmatory methods were developed and validated. These methods are applicable for the rapid detection and identification of GM petunias in routine analysis. In addition, a decision support system was developed for revealing the most likely origin of the GM petunia.

Comparative Transcriptome Analysis and Expression of Genes Reveal the Biosynthesis and Accumulation Patterns of Key Flavonoids in Different Varieties of Zanthoxylum bungeanum Leaves

Zanthoxylum bungeanum (Rutaceae), a popular food flavoring and traditional Chinese medicine ingredient, is an important cash crop. Its leaves are rich in flavonoids with multiple bioactivities. However, the transcriptional sequencing has not been investigated, and the molecular basis for the flavonoid biosynthesis remains unclear in this plant. This paper, the key flavonoids (epicatechin, rutin, hyperoside, trifolin, quercitrin, and afzelin) contents were determined in the leaves of 10 Z. bungeanum varieties from a common garden. Results show the leaves of Z. bungeanum mainly contained hyperoside (11.410-21.721 mg/g) and quercitrin (9.401-18.016 mg/g). The total content of these key components was the highest in Fengxian Dahongpao (66.012 mg/g) and the lowest in Fugu (32.223 mg/g). Three varieties (Hancheng stingless, Fugu, and Fengxian Dahongpao) with significant differences in the total content of key flavonoids were selected for transcriptome analysis to obtain flavonoid biosynthesis-related genes. In total, 83 522 unigenes were obtained, 40 668 (48.69%) unigenes were annotated, and 6656 differentially expressed genes (DEGs) were identified. Comparison of the other two varieties, Fugu had many differentially expressed genes indicating the particularity of its variety. Flavonoid-related DEGs of 22 structural genes, including three PALs, one CYP73A, three 4CLs, six CHSs, one CHI, one F3H, one DFR, two ANSs, one ANR, one FLS, and two CYP75B1s, as well as nine MYBs were obtained. These structural genes had different expression patterns in different Z. bungeanum varieties. It is worth noting that the genes expressing the flavonoid 3'5' hydroxylase are absent in Z. bungeanum. Furthermore, quantitative real-time PCR experiment showed consistent results in transcriptome analysis. The RNA-Seq data set of this study sheds lights on the molecular mechanism of flavonoid biosynthesis in Z. bungeanum, provides valuable information for the metabolic regulation of flavonoids, and may serve as a guide for future breeding programs.

A bHLH transcription factor TsMYC2 is associated with the blue grain character in triticale (Triticum × Secale)

RNA-Seq was employed to compare the transcriptome differences between the triticale lines and to identify the key gene responsible for the blue aleurone trait. The accumulation of anthocyanins in the aleurone of triticale results in the formation of the blue-grained trait, but the identity of the genes associated with anthocyanin biosynthesis in the aleurone has not yet been reported. In this manuscript, RNA-Seq was employed to compare the transcriptome differences between the triticale lines HM13 (blue aleurone) and HM5 (white aleurone), and to identify the key genes responsible for the blue aleurone trait. There were 32,406 differentially expressed genes between HM13 and HM5. Seventy-three unigenes were homologous to the structural genes related to anthocyanin biosynthesis, and the average transcript level of the structural genes was higher in HM13 than in HM5, so that quantitative differences between the two lines in transcription rates could be the cause of the blue aleurone. The MYB and bHLH transcription factors had two homologous unigenes, but contained only one differentially expressed unigene each. The relative transcript level of bHLH Unigene5672_All (TsMYC2) in HM13 was 42.71 times that in HM5, while the relative transcript level of the MYB transcription factor Unigene12228_All in HM13 was 2.20 times that in HM5. qPCR experiments determined the relative transcript level of TsMYC2 in developing grain, with the expression of TsMYC2 in grain being the highest compared with that in root, stem or leaf tissue. TsMYC2 was homologous to the bHLH transcription factor regulating anthocyanin biosynthesis and contained three entire functional domains: bHLH-MYC_N, HLH and ACT-like, which were important for exercising regulation of anthocyanin biosynthesis as a bHLH transcription factor. Transient expression of ZmC1 and TsMYC2 could induce anthocyanin biosynthesis in white wheat coleoptile cells, demonstrating that TsMYC2 was a functional bHLH transcription factor. These results indicated that TsMYC2 was associated with the blue aleurone trait and could prove to be a valuable gene with which to breed new triticale cultivars with the blue aleurone trait.

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

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

MinION sequencing technology to characterize unauthorized GM petunia plants circulating on the European Union market

In order to characterize unauthorized genetically modified petunia, an integrated strategy has been applied here on several suspected petunia samples from the European market. More precisely, DNA fragments of interest were produced by DNA walking anchored on key targets, earlier detected by real-time PCR screening analysis, to be subsequently sequenced using the MinION platform from Oxford Nanopore Technologies. This way, the presence of genetically modified petunia was demonstrated via the characterization of their transgene flanking regions as well as unnatural associations of elements from their transgenic cassette.

Functional MYB transcription factor encoding gene AN2 is associated with anthocyanin biosynthesis in Lycium ruthenicum Murray

BACKGROUND

Lycium ruthenicum Murray is an important economic plant in China and contains higher levels of anthocyanins in its fruits than other Lyciums. However, the genetic mechanism of anthocyanin production in this plant is unknown.

RESULTS

Based on previous transcriptome analysis, LrAN2 and LbAN2, encoding MYB transcription factors, were isolated from L. ruthenicum and L. barbarum, respectively. Both genes contained two introns, encoded 257 amino acids with two-Aa difference, and carried the unabridged HTH-MYB, MYB-like DNA-binding, and SANT domains. In the phylogenetic trees, LrAN2 and LbAN2 were found to be closely related to NtAN2, which regulates anthocyanin biosynthesis in tobacco. Overexpression of LrAN2 and LbAN2 induced anthocyanin biosynthesis in all tissues of tobacco. The anthocyanin content in the leaves of transgenic lines with LbAN2 was lower than LrAN2. It indicated that the function of LbAN2 was weaker than LrAN2. The AN2 transcript could be detected only in the fruits of L. ruthenicum and increased during fruit development, accompanied by anthocyanin accumulation. In natural population, the alleles LrAN2 and LrAN2 were associated strictly with L. ruthenicum and L. barbarum, respectively. Moreover, an AN2 genetic diversity study suggested that Lyciums with yellow, white, purple, and jujube red fruits were derived from L. ruthenicum.

CONCLUSIONS

Two AN2 alleles, from L. ruthenicum and L. barbarum, were functional MYB transcriptor regulating anthocyanin biosynthesis. The functional diversity and high expression level of LrAN2 could be the reason for high anthocyanin content in the fruit of L. ruthenicum. Lyciums with yellow, white, purple, and jujube red fruits were derived from L. ruthenicum based on AN2 sequence diversity. The results may be advantageous in identifying new varieties and breeding new cultivars.

Metabolome and Transcriptome Sequencing Analysis Reveals Anthocyanin Metabolism in Pink Flowers of Anthocyanin-Rich Tea (Camellia sinensis)

Almost all flowers of the tea plant (Camellia sinensis) are white, which has caused few researchers to pay attention to anthocyanin accumulation and color changing in tea flowers. A new purple-leaf cultivar, Baitang purple tea (BTP) was discovered in the Baitang Mountains of Guangdong, whose flowers are naturally pink, and can provide an opportunity to understand anthocyanin metabolic networks and flower color development in tea flowers. In the present study, twelve anthocyanin components were identified in the pink tea flowers, namely cyanidin O-syringic acid, petunidin 3-O-glucoside, pelargonidin 3-O-beta-d-glucoside, which marks the first time these compounds have been found in the tea flowers. The presence of these anthocyanins seem most likely to be the reason for the pink coloration of the flowers. Twenty-one differentially expressed genes (DEGs) involved in anthocyanin pathway were identified using KEGG pathway functional enrichment, and ten of these DEG’s screened using venn and KEGG functional enrichment analysis during five subsequent stages of flower development. By comparing DEGs and their expression levels across multiple flower development stages, we found that anthocyanin biosynthesis and accumulation in BTP flowers mainly occurred between the third and fourth stages (BTP3 to BTP4). Particularly, during the period of peak anthocyanin synthesis 17 structural genes were upregulated, and four structural genes were downregulated only. Ultimately, eight critical genes were identified using weighted gene co-expression network analysis (WGCNA), which were found to have direct impact on biosynthesis and accumulation of three flavonoid compounds, namely cyanidin 3-O-glucoside, petunidin 3-O-glucoside and epicatechin gallate. These results provide useful information about the molecular mechanisms of coloration in rare pink tea flower of anthocyanin-rich tea, enriching the gene resource and guiding further research on anthocyanin accumulation in purple tea.

Gene co-expression network analysis reveals coordinated regulation of three characteristic secondary biosynthetic pathways in tea plant (Camellia sinensis)

BACKGROUND

The leaves of tea plants (Camellia sinensis) are used to produce tea, which is one of the most popular beverages consumed worldwide. The nutritional value and health benefits of tea are mainly related to three abundant characteristic metabolites; catechins, theanine and caffeine. Weighted gene co-expression network analysis (WGCNA) is a powerful system for investigating correlations between genes, identifying modules among highly correlated genes, and relating modules to phenotypic traits based on gene expression profiling. Currently, relatively little is known about the regulatory mechanisms and correlations between these three secondary metabolic pathways at the omics level in tea.

RESULTS

In this study, levels of the three secondary metabolites in ten different tissues of tea plants were determined, 87,319 high-quality unigenes were assembled, and 55,607 differentially expressed genes (DEGs) were identified by pairwise comparison. The resultant co-expression network included 35 co-expression modules, of which 20 modules were significantly associated with the biosynthesis of catechins, theanine and caffeine. Furthermore, we identified several hub genes related to these three metabolic pathways, and analysed their regulatory relationships using RNA-Seq data. The results showed that these hub genes are regulated by genes involved in all three metabolic pathways, and they regulate the biosynthesis of all three metabolites. It is notable that light was identified as an important regulator for the biosynthesis of catechins.

CONCLUSION

Our integrated omics-level WGCNA analysis provides novel insights into the potential regulatory mechanisms of catechins, theanine and caffeine metabolism, and the identified hub genes provide an important reference for further research on the molecular biology of tea plants.

Metabolic and molecular analyses of white mutant Vaccinium berries show down-regulation of MYBPA1-type R2R3 MYB regulatory factor

MYBPA1-type R2R3 MYB transcription factor shows down-regulation in white mutant berries of Vaccinium uliginosum deficient in anthocyanins but not proanthocyanidins suggesting a role in the regulation of anthocyanin biosynthesis. Berries of the genus Vaccinium are among the best natural sources of flavonoids. In this study, the expression of structural and regulatory flavonoid biosynthetic genes and the accumulation of flavonoids in white mutant and blue-colored wild-type bog bilberry (V. uliginosum) fruits were measured at different stages of berry development. In contrast to high contents of anthocyanins in ripe blue-colored berries, only traces were detected by HPLC-ESI-MS in ripe white mutant berries. However, similar profile and high levels of flavonol glycosides and proanthocyanidins were quantified in both ripe white and ripe wild-type berries. Analysis with qRT-PCR showed strong down-regulation of structural genes chalcone synthase (VuCHS), dihydroflavonol 4-reductase (VuDFR) and anthocyanidin synthase (VuANS) as well as MYBPA1-type transcription factor VuMYBPA1 in white berries during ripening compared to wild-type berries. The profiles of transcript accumulation of chalcone isomerase (VuCHI), anthocyanidin reductase (VuANR), leucoanthocyanidin reductase (VuLAR) and flavonoid 3'5' hydroxylase (VuF3'5'H) were more similar between the white and the wild-type berries during fruit development, while expression of UDP-glucose: flavonoid 3-O-glucosyltransferase (VuUFGT) showed similar trend but fourfold lower level in white mutant. VuMYBPA1, the R2R3 MYB family member, is a homologue of VmMYB2 of V. myrtillus and VcMYBPA1 of V. corymbosum and belongs to MYBPA1-type MYB family which members are shown in some species to be related with proanthocyanidin biosynthesis in fruits. Our results combined with earlier data of the role of VmMYB2 in white mutant berries of V. myrtillus suggest that the regulation of anthocyanin biosynthesis in Vaccinium species could differ from other species studied.

Functional analysis of flavonoid 3',5'-hydroxylase from tea plant (Camellia sinensis): critical role in the accumulation of catechins

BACKGROUND

Flavonoid 3',5'-hydroxylase (F3'5'H), an important branch point enzyme in tea plant flavan-3-ol synthesis, belongs to the CYP75A subfamily and catalyzes the conversion of flavones, flavanones, dihydroflavonols and flavonols into 3',4',5'-hydroxylated derivatives. However, whether B-ring hydroxylation occurs at the level of flavanones and/or dihydroflavonols, in vivo remains unknown.

RESULTS

The Camellia sinensis F3'5'H (CsF3'5'H) gene was isolated from tea cDNA library. Expression pattern analysis revealed that CsF3'5'H expression was tissue specific, very high in the buds and extremely low in the roots. CsF3'5'H expression was enhanced by light and sucrose. Over-expression of CsF3'5'H produced new-delphinidin derivatives, and increased the cyanidin derivative content of corollas of transgenic tobacco plants, resulting in the deeper transgenic plant flower color. Heterologous expressions of CsF3'5'H in yeast were carried out to demonstrate the function of CsF3'5'H enzyme in vitro. Heterologous expression of the modified CsF3'5'H (CsF3'5'H gene fused with Vitis vinifera signal peptide, FSI) revealed that 4'-hydroxylated flavanone (naringenin, N) is the optimum substrate for CsF3'5'H, and was efficiently converted into both 3'4'- and 3'4'5'-forms. The ratio of 3'4'5'- to 3'4'-hydroxylated products in FSI transgenic cells was significantly higher than VvF3'5'H cells.

CONCLUSIONS

CsF3'5'H is a key controller of tri-hydroxyl flavan-3-ol synthesis in tea plants, which can effectively convert 4'-hydroxylated flavanone into 3'4'5'- and/or 3'4'-hydroxylated products. These findings provide animportant basis for further studies of flavonoid biosynthesis in tea plants. Such studies would help accelerate flavonoid metabolic engineering in order to increase B-ring tri-hydroxyl product yields.

De novo transcriptome characterization of Lilium 'Sorbonne' and key enzymes related to the flavonoid biosynthesis

Lily is an important cut-flower and bulb crop in the commercial market. Here, transcriptome profiling of Lilium 'Sorbonne' was conducted through de novo sequencing based on Illumina platform. This research aims at revealing basic information and data that can be used for applied purposes especially the molecular regulatory information on flower color formation in lily. In total, 36,920,680 short reads which corresponded to 3.32 GB of total nucleotides, were produced through transcriptome sequencing. These reads were assembled into 39,636 Unigenes, of which 30,986 were annotated in Nr, Nt, Swiss-Prot, KEGG, COG, GO databases. Based on the three public protein databases, a total of 32,601 coding sequences were obtained. Meanwhile, 19,242 Unigenes were assigned to 128 KEGG pathways. Those with the greatest representation by unique sequences were for ''metabolic pathways'' (5,406 counts, 28.09 %). Our transcriptome revealed 156 Unigenes that encode key enzymes in the flavonoid biosynthesis pathway including CHS, CHI, F3H, FLS, DFR, etc. MISA software identified 2,762 simple sequence repeats, from which 1,975 primers pairs were designed. Over 2,762 motifs were identified, of which the most frequent was AG/CT (659, 23.86 %), followed by A/T (615, 22.27 %) and CCG/CGG (416, 15.06 %). Based on the results, we believe that the color formation of the Lilium 'Sorbonne' flower was mainly controlled by the flavonoid biosynthesis pathway. Additionally, this research provides initial genetic resources that will be valuable to the lily community for other molecular biology research, and the SSRs will facilitate marker-assisted selection in lily breeding.

Research progress relating to the role of cytochrome P450 in the biosynthesis of terpenoids in medicinal plants

Terpenoids are an extensive and diverse group of plant secondary metabolites. To date, they have been applied in many fields including industry, medicine and health. The wide variety of terpenoid compounds cannot arise solely from simple cyclisations of a precursor molecule or from a single-step reaction; their structural diversity depends on the modification of many specific chemical groups, rearrangements of their skeletal structures and on the post-modification reactions. Most of the post-modification enzymes that catalyse these reactions are cytochrome P450 monooxygenases. Therefore, the discovery and identification of plant P450 genes plays a vital role in the exploration of terpenoid biosynthesis pathways. This review summarises recent research progress relating to the function of plant cytochrome P450 enzymes, describes P450 genes that have been cloned from full-length cDNA and identifies the function of P450 enzymes in the terpenoid biosynthesis pathways of several medicinal plants.

Isolation and functional analysis of a homolog of flavonoid 3',5'-hydroxylase gene from Pericallis × hybrida

As the key enzyme in the biosynthesis of blue flower color pigments, flavonoid 3',5'-hydroxylase (F3'5'H) can catalyze the conversion of its major substrates, 2-S naringenin and dihydrokaempferol, into 3',4',5'-hydroxylated pentahydroxyflavanone and dihydromyricetin, respectively. Unlike other F3'5'Hs belonging to the CYP75A subfamily, Asteraceae-specific F3'5'Hs belong to the CYP75B subfamily. Furthermore, cineraria F3'5'H expressed in yeast exhibited not only F3'H (flavonoid 3'-hydroxylase) activity but also F3'5'H activity in vitro. In this study, Southern blotting showed that there was only one copy of a homolog of the F3'5'H gene PCFH in the Pericallis × hybrida genome. This gene could be detected by Northern blot in the primary developmental stages of ligulate florets of the purple- and blue-flowered cultivars, and its transcripts also accumulated in the leaves. Heterologous expression of PCFH could produce new delphinidin derivatives in the corollas of transgenic tobacco plants, increased the content of cyanidin derivatives and lead to the blue- and red-shifting of flower color in T₀ generation plants. These results indicate that cineraria F3'5'H exhibited both F3'5'H- and F3'H-activity in vivo. The types and contents of anthocyanins and flower color phenotypes of the T₁ generation were similar to those of T₀ generation plants. PCFH exhibited stable inheritance and normal functions between generations. This study supplies new evidence to understand Asteraceae-specific F3'5'Hs and provides important references for the further study of molecular breeding of blue-flowered chrysanthemums using the PCFH gene.

Flower colour and cytochromes P450

Cytochromes P450 play important roles in biosynthesis of flavonoids and their coloured class of compounds, anthocyanins, both of which are major floral pigments. The number of hydroxyl groups on the B-ring of anthocyanidins (the chromophores and precursors of anthocyanins) impact the anthocyanin colour, the more the bluer. The hydroxylation pattern is determined by two cytochromes P450, flavonoid 3'-hydroxylase (F3'H) and flavonoid 3',5'-hydroxylase (F3'5'H) and thus they play a crucial role in the determination of flower colour. F3'H and F3'5'H mostly belong to CYP75B and CYP75A, respectively, except for the F3'5'Hs in Compositae that were derived from gene duplication of CYP75B and neofunctionalization. Roses and carnations lack blue/violet flower colours owing to the deficiency of F3'5'H and therefore lack the B-ring-trihydroxylated anthocyanins based upon delphinidin. Successful redirection of the anthocyanin biosynthesis pathway to delphinidin was achieved by expressing F3'5'H coding regions resulting in carnations and roses with novel blue hues that have been commercialized. Suppression of F3'5'H and F3'H in delphinidin-producing plants reduced the number of hydroxyl groups on the anthocyanidin B-ring resulting in the production of monohydroxylated anthocyanins based on pelargonidin with a shift in flower colour to orange/red. Pelargonidin biosynthesis is enhanced by additional expression of a dihydroflavonol 4-reductase that can use the monohydroxylated dihydrokaempferol (the pelargonidin precursor). Flavone synthase II (FNSII)-catalysing flavone biosynthesis from flavanones is also a P450 (CYP93B) and contributes to flower colour, because flavones act as co-pigments to anthocyanins and can cause blueing and darkening of colour. However, transgenic plants expression of a FNSII gene yielded paler flowers owing to a reduction of anthocyanins because flavanones are precursors of anthocyanins and flavones.

Ectopic expression of apple F3'H genes contributes to anthocyanin accumulation in the Arabidopsis tt7 mutant grown under nitrogen stress

Three genes encoding flavonoid 3'-hydroxylase (F3'H) in apple (Malus x domestica), designated MdF3'HI, MdF3'HIIa, and MdF3'HIIb, have been identified. MdF3'HIIa and MdF3'HIIb are almost identical in amino acid sequences, and they are allelic, whereas MdF3'HI has 91% nucleotide sequence identity in the coding region to both MdF3'HIIa and MdF3'HIIb. MdF3'HI and MdF3'HII genes are mapped onto linkage groups 14 and 6, respectively, of the apple genome. Throughout the development of apple fruit, transcriptional levels of MdF3'H genes along with other anthocyanin biosynthesis genes are higher in the red-skinned cv Red Delicious than that in the yellow-skinned cv Golden Delicious. Moreover, patterns of MdF3'H gene expression correspond to accumulation patterns of flavonoids in apple fruit. These findings suggest that MdF3'H genes are coordinately expressed with other genes in the anthocyanin biosynthetic pathway in apple. The functionality of these apple F3'H genes has been demonstrated via their ectopic expression in both the Arabidopsis (Arabidopsis thaliana) transparent testa7-1 (tt7) mutant and tobacco (Nicotiana tabacum). When grown under nitrogen-deficient conditions, transgenic Arabidopsis tt7 seedlings expressing apple F3'H regained red color pigmentation and significantly accumulated both 4'-hydrylated pelargonidin and 3',4'-hydrylated cyanidin. When compared with wild-type plants, flowers of transgenic tobacco lines overexpressing apple F3'H genes exhibited enhanced red color pigmentation. This suggests that the F3'H enzyme may coordinately interact with other flavonoid enzymes in the anthocyanin biosynthesis pathway.

Genetic engineering of novel flower colors in floricultural plants: recent advances via transgenic approaches

Since the first successful genetic engineering of flower color in petunia, several new techniques have been developed and applied to modify flower color not only in model plants but also in floricultural plants. A typical example is the commercial violet-flowered carnation "Moondust series" developed by Suntry Ltd. and Florigene Ltd. More recently, blue-flowered roses have been successfully produced and are expected to be commercially available in the near future. In recent years, successful modification of flower color by sophisticated regulation of flower-pigment metabolic pathways has become possible. In this chapter, we review recent advances in flower color modification by genetic engineering, especially focusing on the methodology. We have included our own recent results on successful production of flower-color-modified transgenic plants in a model plant, tobacco and an ornamental plant, gentian. Based on these results, genetic engineering of flower color for improvement of floricultural plants is discussed.

Blue flower color development by anthocyanins: from chemical structure to cell physiology

Blue flower colors are primarily due to anthocyanin, a flavonoid pigment. Anthocyanin itself is purple in neutral aqueous solutions, ans its color is very unstable and quickly fades. Therefore, the mechanism of blue color development in living flower petals is one of the most intriguing problems in natural product chemistry. Much progress has been made in understanding blue flower coloration since the comprehensive review by Goto and Kondo in 1991. This review focuses on the advances in the last 15 years, and cites 149 references.

Simultaneous separation by reversed-phase high-performance liquid chromatography and mass spectral identification of anthocyanins and flavonols in Shiraz grape skin

A limitation of large-scale viticultural trials is the time and cost of comprehensive compositional analysis of the fruit by high-performance liquid chromatography (HPLC). In addition, separate methods have generally been required to identify and quantify different classes of metabolites. To address these shortcomings a reversed-phase HPLC method was developed to simultaneously separate the anthocyanins and flavonols present in grape skins. The method employs a methanol and water gradient acidified with 10% formic acid with a run-time of 48 min including re-equilibration. Identity of anthocyanins and flavonols in Shiraz (Vitis vinifera L.) skin was confirmed by mass spectral analysis.

Cloning and characterization of the UDP-glucose:anthocyanin 5-O-glucosyltransferase gene from blue-flowered gentian

Blue-flowered gentian (Gentiana triflora) is known to accumulate gentiodelphin, a unique polyacylated delphinidin-type anthocyanin, in the petals. Almost all of the structural genes involved in gentiodelphin biosynthesis have been isolated, but an important gene encoding UDP-glucose:anthocyanin 5-O-glucosyltransferase (5GT) remained to be identified. In this study, an attempt was made to isolate and characterize gentian 5GT, which is responsible for glucosylation of anthocyanidin 3-glucoside. A PCR-based cloning strategy identified seven 5GT candidates from gentian flowers. Among them, the deduced amino acid sequence of the 5GT gene from gentian petal cDNA, designated Gt5GT7, exhibited 36.0-41.7% identities with those of 5GTs from other plant species, and phylogenic analysis also suggested that Gt5GT7 belongs to the 5GT subfamily. The expression analysis showed that Gt5GT7 transcripts were detected predominantly in petals and weakly in filaments but not in leaves, stems, and other floral organs. In addition, increased levels of Gt5GT7 transcripts in petals coincided with flower development, a pattern identical to that of 5GT enzymatic activity as determined by in vitro assay using petal crude proteins. The substrate specificity of Gt5GT7 was analysed in vitro using the recombinant enzyme produced by Escherichia coli. Gt5GT7 could transfer a glucosyl moiety to anthocyanidin 3-glycosides but not to other flavonoid compounds. Delphinidin 3-glucoside, the precursor of gentiodelphin, was the best substrate among several anthocyanidin 3-glycosides tested. Heterologous expression of Gt5GT7 in tobacco plants led to additional accumulation of cyanidin 3-rutinoside-5-glucoside, confirming that Gt5GT7 has a valid enzymatic activity in planta.

Cloning, functional identification and sequence analysis of flavonoid 3'-hydroxylase and flavonoid 3',5'-hydroxylase cDNAs reveals independent evolution of flavonoid 3',5'-hydroxylase in the Asteraceae family

Flavonoids are ubiquitous secondary plant metabolites which function as protectants against UV light and pathogens and are involved in the attraction of pollinators as well as seed and fruit dispersers. The hydroxylation pattern of the B-ring of flavonoids is determined by the activity of two members of the vast and versatile cytochrome P450 protein (P450) family, the flavonoid 3'-hydroxylase (F3'H) and flavonoid 3',5'-hydroxylase (F3'5'H). Phylogenetic analysis of known sequences of F3'H and F3'5'H indicated that F3'5'H was recruited from F3'H before the divergence of angiosperms and gymnosperms. Seven cDNAs were isolated from species of the Asteraceae family, all of which were predicted to code for F3'Hs based on their sequences. The recombinant proteins of four of the heterologously in yeast expressed cDNAs exhibited the expected F3'H activity but surprisingly, three recombinant proteins showed F3'5'H activity. Phylogenetic analyses indicated the independent evolution of an Asteraceae-specific F3'5'H. Furthermore, sequence analysis of these unusual F3'5'H cDNAs revealed an elevated rate of nonsynonymous substitutions as typically found for duplicated genes acquiring new functions. Since F3'5'H is necessary for the synthesis of 3',4',5'-hydroxylated delphinidin-derivatives, which normally provide the basis for purple to blue flower colours, the evolution of an Asteraceae-specific F3'5'H probably reflects the adaptive value of efficient attraction of insect pollinators.

Identification of the flavonoid hydroxylases from grapevine and their regulation during fruit development

Flavonoids are important secondary metabolites in many fruits, and their hydroxylation pattern determines their color, stability, and antioxidant capacity. Hydroxylation of the B-ring of flavonoids is catalyzed by flavonoid 3'-hydroxylase (F3'H) and flavonoid 3',5'-hydroxylase (F3'5'H), and may also require cytochrome b5. We report the identification of genes encoding F3'H, F3'5'H, and a putative cytochrome b5 from grapevine (Vitis vinifera L. cv Shiraz) and their transcriptional regulation in fruit. Functionality of the genes VvF3'H and VvF3'5'H1 was demonstrated by ectopic expression in petunia (Petunia hybrida), which altered flower color and flavonoid composition as expected. VvF3'H was expressed in grapes before flowering, when 3'-hydroxylated flavonols are made, and all three genes were expressed after flowering, when proanthocyanidins (PAs) are synthesized. In berry skin, expression of all three genes was low at the onset of ripening (véraison) but increased after véraison concomitant with the accumulation of 3'- and 3',5'-hydroxylated anthocyanins. VvF3'H and VvCytoB5 were expressed in seeds but not VvF3'5'H1, consistent with the accumulation of 3'-hydroxylated PAs in this tissue. VvCytoB5 expression was correlated with expression of both VvF3'H and VvF3'5'H1 in the different grape tissues. In contrast to red grapes, where VvF3'H, VvF3'5'H1, and VvCytoB5 were highly expressed during ripening, the expression of VvF3'5'H1 and VvCytoB5 in white grapes during ripening was extremely low, suggesting a difference in transcriptional regulation. Our results show that temporal and tissue-specific expression of VvF3'H, VvF3'5'H1, and VvCytoB5 in grapes is coordinated with the accumulation of the respective hydroxylated flavonols and PAs, as well as anthocyanins. Understanding the regulation of flavonoid hydroxylases could be used to modify flavonoid composition of fruits.

Functional genomics of P450s

Plant systems utilize a diverse array of cytochrome P450 monooxygenases (P450s) in their biosynthetic and detoxicative pathways. Those P450s in biosynthetic pathways play critical roles in the synthesis of lignins, UV protectants, pigments, defense compounds, fatty acids, hormones, and signaling molecules. Those in catabolic pathways participate in the breakdown of endogenous compounds and toxic compounds encountered in the environment. Because of their roles in this wide diversity of metabolic processes, plant P450 proteins and transcripts can serve as downstream reporters for many different biochemical pathways responding to chemical, developmental, and environmental cues. This review focuses initially on defining P450 biochemistries, nomenclature systems, and the relationships between genes in the extended P450 superfamily that exists in all plant species. Subsequently, it focuses on outlining the many approaches being used to assign function to individual P450 proteins and gene loci. The examples of assigned P450 activities that are spread throughout this review highlight the importance of understanding and utilizing P450 sequences as markers for linking biochemical pathway responses to physiological processes.

Metabolic engineering and applications of flavonoids

During the past decade, the increasing knowledge of flavonoid biosynthesis and the important function of flavonoid compounds in plants and in human and animal nutrition have made the biosynthetic pathways to flavonoids and isoflavonoids excellent targets for metabolic engineering. Recent strategies have included introducing novel structural or regulatory genes, and the antisense or sense suppression of genes in these pathways.

Cytochrome P450s as genes for crop improvement

In the past year, several cytochrome P450 genes have been identified that will be important for generating crop protectants and natural medicinal products. Among these are the 2-hydroxyisoflavone synthase (CYP93C) and the indole-3-acetaldoxime N-hydroxylase (CYP83B1) genes, which catalyze the formation of isoflavones and glucosinolates, respectively.