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Background Land plants commonly produce red pigmentation as a response to environmental stressors, both abiotic and biotic. The type of pigment produced varies among different land plant lineages. In the majority of species they are flavonoids, a large branch of the phenylpropanoid pathway. Flavonoids that can confer red colours include 3-hydroxyanthocyanins, 3-deoxyanthocyanins, sphagnorubins and auronidins, which are the predominant red pigments in flowering plants, ferns, mosses and liverworts, respectively. However, some flowering plants have lost the capacity for anthocyanin biosynthesis and produce nitrogen-containing betalain pigments instead. Some terrestrial algal species also produce red pigmentation as an abiotic stress response, and these include both carotenoid and phenolic pigments. Scope In this review, we examine: which environmental triggers induce red pigmentation in non-reproductive tissues; theories on the functions of stress-induced pigmentation; the evolution of the biosynthetic pathways; and structure–function aspects of different pigment types. We also compare data on stress-induced pigmentation in land plants with those for terrestrial algae, and discuss possible explanations for the lack of red pigmentation in the hornwort lineage of land plants. Conclusions The evidence suggests that pigment biosynthetic pathways have evolved numerous times in land plants to provide compounds that have red colour to screen damaging photosynthetically active radiation but that also have secondary functions that provide specific benefits to the particular land plant lineage. [ABSTRACT FROM AUTHOR]

Paeonia delavayi is listed as an endangered species in the southwest of China. The flower colours of cultivated examples of this species are most commonly yellow and red, but a much wider range of flower colours can be found in plants growing in the natural habitat. To elucidate the basis of the colour range, pigments were extracted from flower petals of seven selected colours and profiled and quantified using High Performance Liquid Chromatography (HPLC) and Liquid Chromatography–Mass Spectrometry (LC-MS). All the petal colours were found to share the same base pigment types as the yellow flower – a composite colour based on a mix of flavonoids, carotenoids and chlorophyll. Anthocyanin profiling revealed the same anthocyanin compositions in all red coloured flowers, namely, cyanidin-3,5-diglucoside, cyanidin-3-glucoside, cyanidin-3-arabinoside, peonidin-3,5-diglucoside, peonidin-3-glucoside and peonidin 3-arabinoside. Quantitative analysis suggested the yellow colour was principally formed by the flavonoid naringenin chalcone 2'-glucoside (2',4',6',4-tetrahydroxychalcone 2'-glucoside). The various red/orange flower colours were the result of superimposing different amounts of anthocyanins onto the yellow flower background, with carotenoids and chlorophylls having only a minor contribution to the final colour. The results provide useful information for breeding programmes for ornamental varieties of P. delavayi. [ABSTRACT FROM AUTHOR]

Summary: Floral pigmentation patterning is important for pollinator attraction as well as aesthetic appeal. Patterning of anthocyanin accumulation is frequently associated with variation in activity of the Myb, bHLH and WDR transcription factor complex (MBW) that regulates anthocyanin biosynthesis.Investigation of two classic mutants in Antirrhinum majus, mutabilis and incolorata I, showed they affect a gene encoding a bHLH protein belonging to subclade bHLH‐2. The previously characterised gene, Delila, which encodes a bHLH‐1 protein, has a bicoloured mutant phenotype, with residual lobe‐specific pigmentation conferred by Incolorata I.Both Incolorata I and Delila induce expression of the anthocyanin biosynthetic gene DFR. Rosea 1 (Myb) and WDR1 proteins compete for interaction with Delila, but interact positively to promote Incolorata I activity. Delila positively regulates Incolorata I and WDR1 expression. Hierarchical regulation can explain the bicoloured patterning of delila mutants, through effects on both regulatory gene expression and the activity of promoters of biosynthetic genes like DFR that mediate MBW regulation.bHLH‐1 and bHLH‐2 proteins contribute to establishing patterns of pigment distribution in A. majus flowers in two ways: through functional redundancy in regulating anthocyanin biosynthetic gene expression, and through differences between the proteins in their ability to regulate genes encoding transcription factors. [ABSTRACT FROM AUTHOR]

The Vaccinium genus in the family Ericaceae comprises many species, including the fruit-bearing blueberry, bilberry, cranberry, huckleberry, and lingonberry. Commercially, the most important are the blueberries (Vaccinium section Cyanococcus), such as Vaccinium corymbosum (northern highbush blueberry), Vaccinium virgatum (rabbiteye blueberry), and Vaccinium angustifolium (lowbush blueberry). The rising popularity of blueberries can partly be attributed to their “superfood” status, with an increasing body of evidence around human health benefits resulting from the fruit metabolites, particularly products of the phenylpropanoid pathway such as anthocyanins. Activation of anthocyanin production by R2R3-MYB transcription factors (TFs) has been characterized in many species, but despite recent studies on blueberry, cranberry, and bilberry, no MYB anthocyanin regulators have been reported for Vaccinium. Indeed, there has been conjecture that at least in bilberry, MYB TFs divergent to the usual type are involved. We report identification of MYBA from blueberry, and show through sequence analysis and functional studies that it is homologous to known anthocyanin-promoting R2R3-MYBs of subgroup 6 of the MYB superfamily. In transient assays, MYBA complemented an anthocyanin MYB mutant of Antirrhinum majus and, together with a heterologous bHLH anthocyanin regulator, activated anthocyanin production in Nicotiana benthamiana. Furthermore anthocyanin accumulation and anthocyanin structural gene expression (assayed by qPCR and RNA-seq analyses) correlated with MYBA expression, and MYBA was able to transactivate the DFR promoter from blueberry and other species. The RNA-seq data also revealed a range of other candidate genes involved in the regulation of anthocyanin production in blueberry fruit. The identification of MYBA will help to resolve the regulatory mechanism for anthocyanin pigmentation in the Vaccinium genus. The sequence information should also prove useful in developing tools for the accelerated breeding of new Vaccinium cultivars. [ABSTRACT FROM AUTHOR]

Flower color polymorphisms are widely used as model traits from genetics to ecology, yet determining the biochemical and molecular basis can be challenging. Anthocyanin-based flower color variations can be caused by at least 12 structural and three regulatory genes in the anthocyanin biosynthetic pathway (ABP). We use mRNA-Seq to simultaneously sequence and estimate expression of these candidate genes in nine samples of Silene littorea representing three color morphs (dark pink, light pink and white) across three developmental stages in hopes of identifying the cause of flower color variation. We identified 29 putative paralogs for the 15 candidate genes in the ABP. We assembled complete coding sequences for 16 structural loci and nine of ten regulatory loci. Among these 29 putative paralogs, we identified 622 SNPs, yet only nine synonymous SNPs in Ans had allele frequencies that differentiated pigmented petals (dark pink and light pink) from white petals. These Ans allele frequency differences were further investigated with an expanded sequencing survey of 38 individuals, yet no SNPs consistently differentiated the color morphs. We also found one locus, F3h1, with strong differential expression between pigmented and white samples (>42x). This may be caused by decreased expression of Myb1a in white petal buds. Myb1a in S. littorea is a regulatory locus closely related to Subgroup 7 Mybs known to regulate F3h and other loci in the first half of the ABP in model species. We then compare the mRNA-Seq results with petal biochemistry which revealed cyanidin as the primary anthocyanin and five flavonoid intermediates. Concentrations of three of the flavonoid intermediates were significantly lower in white petals than in pigmented petals (rutin, quercetin and isovitexin). The biochemistry results for rutin, quercetin, luteolin and apigenin are consistent with the transcriptome results suggesting a blockage at F3h, possibly caused by downregulation of Myb1a. [ABSTRACT FROM AUTHOR]

Key message: The Md - MYB10 gene from apple is capable of self-regulating in heterologous host species and enhancing anthocyanin pigmentation, but the activity of MYB10 is dependent on endogenous protein partners. Abstract: Coloured foliage due to anthocyanin pigments (bronze/red/black) is an attractive trait that is often lacking in many bedding, ornamental and horticultural plants. Apples ( Malus × domestica) containing an allelic variant of the anthocyanin regulator, Md- MYB10, are highly pigmented throughout the plant, due to autoregulation by MYB10 upon its own promoter. We investigated whether Md- MYB10 from apple is capable of functioning within the heterologous host Petunia hybrida to generate plants with novel pigmentation patterns. The Md- MYB10 transgene ( MYB10- R6 :MYB10:MYB10) activated anthocyanin synthesis when transiently expressed in Antirrhinum rosea petals and petunia leaf discs. Stable transgenic petunias containing Md- MYB10 lacked foliar pigmentation but had coloured flowers, complementing the an2 phenotype of 'Mitchell' petunia. The absence of foliar pigmentation was due to the failure of the Md- MYB10 gene to self-activate in vegetative tissues, suggesting that additional protein partners are required for Md-MYB10 to activate target genes in this heterologous system. In petunia flowers, where endogenous components including MYB-bHLH-WDR (MBW) proteins were present, expression of the Md- MYB10 promoter was initiated, allowing auto-regulation to occur and activating anthocyanin production. Md-MYB10 is capable of operating within the petunia MBW gene regulation network that controls the expression of the anthocyanin biosynthesis genes, AN1 (bHLH) and MYBx (R3-MYB repressor) in petals. [ABSTRACT FROM AUTHOR]

Plant betalain pigments are intriguing because they are restricted to the Caryophyllales and are mutually exclusive with the more common anthocyanins. However, betalain biosynthesis is poorly understood compared to that of anthocyanins. In this study, betalain production and betalain-related genes were characterized in Parakeelya mirabilis (Montiaceae). RT-PCR and transcriptomics identified three sequences related to the key biosynthetic enzyme Dopa 4,5-dioxgenase (DOD). In addition to a LigB gene similar to that of non-Caryophyllales species (Class I genes), two other P. mirabilis LigB genes were found (DOD and DOD-like, termed Class II). PmDOD and PmDOD-like had 70% amino acid identity. Only PmDOD was implicated in betalain synthesis based on transient assays of enzyme activity and correlation of transcript abundance to spatio-temporal betalain accumulation. The role of PmDOD-like remains unknown. The striking pigment patterning of the flowers was due to distinct zones of red betacyanin and yellow betaxanthin production. The major betacyanin was the unglycosylated betanidin rather than the commonly found glycosides, an occurrence for which there are a few previous reports. The white petal zones lacked pigment but had DOD activity suggesting alternate regulation of the pathway in this tissue. DOD and DOD-like sequences were also identified in other betalain-producing species but not in examples of anthocyanin-producing Caryophyllales or non-Caryophyllales species. A Class I LigB sequence from the anthocyanin-producing Caryophyllaceae species Dianthus superbus and two DOD-like sequences from the Amaranthaceae species Beta vulgaris and Ptilotus spp. did not show DOD activity in the transient assay. The additional sequences suggests that DOD is part of a larger LigB gene family in betalain-producing Caryophyllales taxa, and the tandem genomic arrangement of two of the three B. vulgaris LigB genes suggests the involvement of duplication in the gene family evolution. [ABSTRACT FROM AUTHOR]

Anthocyanin biosynthesis is regulated by a transcription factor complex. Here, it is determined that the potential bHLH partners in this complex function in a hierarchy to control each other and the anthocyanin biosynthesis pathway.The anthocyanin biosynthetic pathway is regulated by a transcription factor complex consisting of an R2R3 MYB, a bHLH, and a WD40. Although R2R3 MYBs belonging to the anthocyanin-activating class have been identified in many plants, and their role well elucidated, the subgroups of bHLH implicated in anthocyanin regulation seem to be more complex. It is not clear whether these potential bHLH partners are biologically interchangeable with redundant functions, or even if heterodimers are involved. In this study, AcMYB110, an R2R3 MYB isolated from kiwifruit (Actinidia sp.) showing a strong activation of the anthocyanin pathway in tobacco (Nicotiana tabacum) was used to examine the function of interacting endogenous bHLH partners. Constitutive expression of AcMYB110 in tobacco leaves revealed different roles for two bHLHs, NtAN1 and NtJAF13. A hierarchical mechanism is shown to control the regulation of transcription factors and consequently of the anthocyanin biosynthetic pathway. Here, a model is proposed for the regulation of the anthocyanin pathway in Solanaceous plants in which AN1 is directly involved in the activation of the biosynthetic genes, whereas JAF13 is involved in the regulation of AN1 transcription. [ABSTRACT FROM PUBLISHER]

Main conclusion: This study confirmed pigment profiles in different colour groups, isolated key anthocyanin biosynthetic genes and established a basis to examine the regulation of colour patterning in flowers of Cymbidium orchid. Cymbidium orchid ( Cymbidium hybrida) has a range of flower colours, often classified into four colour groups; pink, white, yellow and green. In this study, the biochemical and molecular basis for the different colour types was investigated, and genes involved in flavonoid/anthocyanin synthesis were identified and characterised. Pigment analysis across selected cultivars confirmed cyanidin 3- O-rutinoside and peonidin 3- O-rutinoside as the major anthocyanins detected; the flavonols quercetin and kaempferol rutinoside and robinoside were also present in petal tissue. β-carotene was the major carotenoid in the yellow cultivars, whilst pheophytins were the major chlorophyll pigments in the green cultivars. Anthocyanin pigments were important across all eight cultivars because anthocyanin accumulated in the flower labellum, even if not in the other petals/sepals. Genes encoding the flavonoid biosynthetic pathway enzymes chalcone synthase, flavonol synthase, flavonoid 3′ hydroxylase (F3′H), dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS) were isolated from petal tissue of a Cymbidium cultivar. Expression of these flavonoid genes was monitored across flower bud development in each cultivar, confirming that DFR and ANS were only expressed in tissues where anthocyanin accumulated. Phylogenetic analysis suggested a cytochrome P450 sequence as that of the Cymbidium F3′H, consistent with the accumulation of di-hydroxylated anthocyanins and flavonols in flower tissue. A separate polyketide synthase, identified as a bibenzyl synthase, was isolated from petal tissue but was not associated with pigment accumulation. Our analyses show the diversity in flower colour of Cymbidium orchid derives not from different individual pigments but from subtle variations in concentration and pattern of pigment accumulation. [ABSTRACT FROM AUTHOR]

Plants require sophisticated regulatory mechanisms to ensure the degree of anthocyanin pigmentation is appropriate to myriad developmental and environmental signals. Central to this process are the activity of MYB-bHLH-WD repeat (MBW) complexes that regulate the transcription of anthocyanin genes. In this study, the gene regulatory network that regulates anthocyanin synthesis in petunia (Petunia hybrida) has been characterized. Genetic and molecular evidence show that the R2R3-MYB, MYB27, is an anthocyanin repressor that functions as part of the MBW complex and represses transcription through its C-terminal EAR motif. MYB27 targets both the anthocyanin pathway genes and basic-helix-loop-helix (bHLH) ANTHOCYANIN1 (AN1), itself an essential component of the MBW activation complex for pigmentation. Other features of the regulatory network identified include inhibition of AN1 activity by the competitive R3-MYB repressor MYBx and the activation of AN1 , MYB27 , and MYBx by the MBW activation complex, providing for both reinforcement and feedback regulation. We also demonstrate the intercellular movement of the WDR protein (AN11) and R3-repressor (MYBx), which may facilitate anthocyanin pigment pattern formation. The fundamental features of this regulatory network in the Asterid model of petunia are similar to those in the Rosid model of Arabidopsis thaliana and are thus likely to be widespread in the Eudicots. [ABSTRACT FROM AUTHOR]

Background: With the explosive numbers of sequences generated by next generation sequencing, the demand for high throughput screening to understand gene function has grown. Plant viral vectors have been widely used as tools in down-regulating plant gene expression. However, plant viral vectors can also express proteins in a very efficient manner and, therefore, can also serve as a valuable tool for characterizing proteins and their functions in metabolic pathways in planta. Results: In this study, we have developed a Gateway®-based high throughput viral vector cloning system from Narcissus Mosaic Virus (NMV). Using the reporter genes of GFP and GUS, and the plant genes PAP1 (an R2R3 MYB which activates the anthocyanin pathway) and selenium-binding protein 1 (SeBP), we show that NMV vectors and the model plant Nicotiana benthamiana can be used for efficient protein expression, protein subcellular localization and secondary metabolite production. Conclusions: Our results suggest that not only can the plant viral vector system be employed for protein work but also can potentially be amenable to producing valuable secondary metabolites on a large scale, as the system does not require plant regeneration from seed or calli, which are stages where certain secondary metabolites can interfere with development. [ABSTRACT FROM AUTHOR]

Background: Red colour in kiwifruit results from the presence of anthocyanin pigments. Their expression, however, is complex, and varies among genotypes, species, tissues and environments. An understanding of the biosynthesis, physiology and genetics of the anthocyanins involved, and the control of their expression in different tissues, is required. A complex, the MBW complex, consisting of R2R3-MYB and bHLH transcription factors together with a WD-repeat protein, activates anthocyanin 3-O-galactosyltransferase (F3GT1) to produce anthocyanins. We examined the expression and genetic control of anthocyanins in flowers of Actinidia hybrid families segregating for red and white petal colour. Results: Four inter-related backcross families between Actinidia chinensis Planch. var. chinensis and Actinidia eriantha Benth. were identified that segregated 1:1 for red or white petal colour. Flower pigments consisted of five known anthocyanins (two delphinidin-based and three cyanidin-based) and three unknowns. Intensity and hue differed in red petals from pale pink to deep magenta, and while intensity of colour increased with total concentration of anthocyanin, no association was found between any particular anthocyanin data and hue. Real time qPCR demonstrated that an R2R3 MYB, MYB110a, was expressed at significant levels in red-petalled progeny, but not in individuals with white petals. A microsatellite marker was developed that identified alleles that segregated with red petal colour, but not with ovary, stamen filament, or fruit flesh colour in these families. The marker mapped to chromosome 10 in Actinidia. The white petal phenotype was complemented by syringing Agrobacterium tumefaciens carrying Actinidia 35S:: MYB110a into the petal tissue. Red pigments developed in white petals both with, and without, co-transformation with Actinidia bHLH partners. MYB110a was shown to directly activate Actinidia F3GT1 in transient assays. Conclusions: The transcription factor, MYB110a, regulates anthocyanin production in petals in this hybrid population, but not in other flower tissues or mature fruit. The identification of delphinidin-based anthocyanins in these flowers provides candidates for colour enhancement in novel fruits. [ABSTRACT FROM AUTHOR]

We present an investigation of anthocyanin regulation over the entire petunia plant, determining the mechanisms governing complex floral pigmentation patterning and environmentally induced vegetative anthocyanin synthesis. DEEP PURPLE ( DPL) and PURPLE HAZE ( PHZ) encode members of the R2R3-MYB transcription factor family that regulate anthocyanin synthesis in petunia, and control anthocyanin production in vegetative tissues and contribute to floral pigmentation. In addition to these two MYB factors, the basic helix-loop-helix (bHLH) factor ANTHOCYANIN1 (AN1) and WD-repeat protein AN11, are also essential for vegetative pigmentation. The induction of anthocyanins in vegetative tissues by high light was tightly correlated to the induction of transcripts for PHZ and AN1. Interestingly, transcripts for PhMYB27, a putative R2R3-MYB active repressor, were highly expressed during non-inductive shade conditions and repressed during high light. The competitive inhibitor PhMYBx (R3-MYB) was expressed under high light, which may provide feedback repression. In floral tissues DPL regulates vein-associated anthocyanin pigmentation in the flower tube, while PHZ determines light-induced anthocyanin accumulation on exposed petal surfaces (bud-blush). A model is presented suggesting how complex floral and vegetative pigmentation patterns are derived in petunia in terms of MYB, bHLH and WDR co-regulators. [ABSTRACT FROM AUTHOR]

Background: The genetic regulation of flower color has been widely studied, notably as a character used by Mendel and his predecessors in the study of inheritance in pea. Methodology/Principal Findings: We used the genome sequence of model legumes, together with their known synteny to the pea genome to identify candidate genes for the A and A2 loci in pea. We then used a combination of genetic mapping, fast neutron mutant analysis, allelic diversity, transcript quantification and transient expression complementation studies to confirm the identity of the candidates. Conclusions/Significance: We have identified the pea genes A and A2. A is the factor determining anthocyanin pigmentation in pea that was used by Gregor Mendel 150 years ago in his study of inheritance. The A gene encodes a bHLH transcription factor. The white flowered mutant allele most likely used by Mendel is a simple G to A transition in a splice donor site that leads to a mis-spliced mRNA with a premature stop codon, and we have identified a second rare mutant allele. The A2 gene encodes a WD40 protein that is part of an evolutionarily conserved regulatory complex. [ABSTRACT FROM AUTHOR]

Background: Cyclamen is a popular and economically significant pot plant crop in several countries. Molecular breeding technologies provide opportunities to metabolically engineer the well-characterized flavonoid biosynthetic pathway for altered anthocyanin profile and hence the colour of the flower. Previously we reported on a genetic transformation system for cyclamen. Our aim in this study was to change pigment profiles and flower colours in cyclamen through the suppression of flavonoid 3', 5'-hydroxylase, an enzyme in the flavonoid pathway that plays a determining role in the colour of anthocyanin pigments. Results: A full-length cDNA putatively identified as a F3'5'H (CpF3'5'H) was isolated from cyclamen flower tissue. Amino acid and phylogeny analyses indicated the CpF3'5'H encodes a F3'5'H enzyme. Two cultivars of minicyclamen were transformed via Agrobacterium tumefaciens with an antisense CpF3'5'H construct. Flowers of the transgenic lines showed modified colour and this correlated positively with the loss of endogenous F3'5'H transcript. Changes in observed colour were confirmed by colorimeter measurements, with an overall loss in intensity of colour (C) in the transgenic lines and a shift in hue from purple to red/pink in one cultivar. HPLC analysis showed that delphinidinderived pigment levels were reduced in transgenic lines relative to control lines while the percentage of cyanidinderived pigments increased. Total anthocyanin concentration was reduced up to 80% in some transgenic lines and a smaller increase in flavonol concentration was recorded. Differences were also seen in the ratio of flavonol types that accumulated. Conclusion: To our knowledge this is the first report of genetic modification of the anthocyanin pathway in the commercially important species cyclamen. The effects of suppressing a key enzyme, F3'5'H, were wide ranging, extending from anthocyanins to other branches of the flavonoid pathway. The results illustrate the complexity involved in modifying a biosynthetic pathway with multiple branch points to different end products and provides important information for future flower colour modification experiments in cyclamen. [ABSTRACT FROM AUTHOR]

The Lc petunia system, which displays enhanced, light-induced vegetative pigmentation, was used to investigate how high light affects anthocyanin biosynthesis, and to assess the effects of anthocyanin pigmentation upon photosynthesis. Lc petunia plants displayed intense purple anthocyanin pigmentation throughout the leaves and stems when grown under high-light conditions, yet remain acyanic when grown under shade conditions. The coloured phenotypes matched with an accumulation of anthocyanins and flavonols, as well as the activation of the early and late flavonoid biosynthetic genes required for flavonol and anthocyanin production. Pigmentation in Lc petunia only occurred under conditions which normally induce a modest amount of anthocyanin to accumulate in wild-type Mitchell petunia [Petunia axillaris×(Petunia axillaris×Petunia hybrida cv. ‘Rose of Heaven’)]. Anthocyanin pigmentation in Lc petunia leaves appears to screen underlying photosynthetic tissues, increasing light saturation and light compensation points, without reducing the maximal photosynthetic assimilation rate (Amax). In the Lc petunia system, where the bHLH factor Leaf colour is constitutively expressed, expression of the bHLH (Lc) and WD40 (An11) components of the anthocyanin regulatory system were not limited, suggesting that the high-light-induced anthocyanin pigmentation is regulated by endogenous MYB transcription factors. [ABSTRACT FROM PUBLISHER]

The Rosea1, Rosea2, and Venosa genes encode MYB-related transcription factors active in the flowers of Antirrhinum majus. Analysis of mutant phenotypes shows that these genes control the intensity and pattern of magenta anthocyanin pigmentation in flowers. Despite the structural similarity of these regulatory proteins, they influence the expression of target genes encoding the enzymes of anthocyanin biosynthesis with different specificities. Consequently, they are not equivalent biochemically in their activities. Different species of the genus Antirrhinum, native to Spain and Portugal, show striking differences in their patterns and intensities of floral pigmentation. Differences in anthocyanin pigmentation between at least six species are attributable to variations in the activity of the Rosea and Venosa loci. Set in the context of our understanding of the regulation of anthocyanin production in other genera, the activity of MYB-related genes is probably a primary cause of natural variation in anthocyanin pigmentation in plants. [ABSTRACT FROM AUTHOR]

The expression of anthocyanin biosynthesis genes during flower colour development inAnthurium andraeanum(anthurium) was studied. A cDNA library was constructed from mRNA from the anthurium spathe, and full-length cDNA clones identified for the flavonoid biosynthetic enzymes chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS). These were used to measure transcript levels in the spathe during flower development, in cultivars with different flower colours, over the diurnal cycle, and in the spadix.CHS,F3HandANSwere expressed at all stages of spathe and spadix development. However,DFRtranscript levels varied significantly between stages, and DFR may represent a key point of regulation. A diurnal rhythm ofDFRtranscript abundance in the spathe was also observed, with transcript levels high at dawn and dusk and low at noon. Control of anthocyanin biosynthesis in anthurium spathe differs from that described for flowers of other species, withDFRa key regulatory point and a complex mix of developmental and environmental control signals. [ABSTRACT FROM AUTHOR]

Flavonoids, in particular the anthocyanins, are responsible for flower colour in many species. The dihydroflavonols represent a branch point in flavonoid biosynthesis, being the intermediates for production of both the coloured anthocyanins, through the action of the enzyme dihydroflavonol 4-reductase (DFR), and the colourless flavonols, produced by flavonol synthase (FLS). In this study the white-flowered, flavonol accumulating Mitchell line of petunia was used as a model to examine the interaction between DFR and FLS enzyme activities and possibilities for redirecting flavonoid biosynthesis away from production of flavonols and towards anthocyanins. Introduction of a 35S CaMV-DFR sense transgene construct caused the production of anthocyanins, resulting in a pink-flowered phenotype. Furthermore, inhibition of FLS production through introduction of an FLS antisense RNA construct also led to anthocyanin production and a pink-flowered phenotype. A combination of both transgenes gave the highest level of anthocyanin formation. Anthocyanins were produced in the DFR-sense and FLS-antisense transgenic lines in spite of the greatly reduced levels of gene expression in the Mitchell line for three enzymes late in anthocyanin biosynthesis, anthocyanindin synthase, UDP-glucose: flavonoid 3-O-glucosyltransferase and UDP-rhamnose: anthocyanidin-3-glucoside rhamnosyltransferase. Thus, the level of gene activity required for visible anthocyanin formation is much lower than the high levels normally induced during petal development. Altering the balance between the DFR and FLS enzyme activities, using genetic modification, may be a useful strategy for introducing or increasing anthocyanin production in target ornamental species. [ABSTRACT FROM AUTHOR]

Betalains are bright red and yellow pigments, which are produced in only one order of plants, the Caryophyllales, and replace the more familiar anthocyanin pigments. The evolutionary origin of betalain production is a mystery, but a new study has identified the first regulator of betalain production and discovered a previously unknown link between the two pigment pathways. [ABSTRACT FROM AUTHOR]

Summary Anthocyanins are some of the most widely occurring secondary metabolites in plants, responsible for the orange, red, purple, and blue colors of flowers and fruits and red colors of autumn leaves. These pigments accumulate in vacuoles, and their color is influenced by chemical decorations, vacuolar pH, the presence of copigments, and metal ions. Anthocyanins are usually soluble in the vacuole, but in some plants, they accumulate as discrete sub-vacuolar structures. Studies have distinguished intensely colored intra-vacuolar bodies observed in the cells of highly colored tissues, termed anthocyanic vacuolar inclusions (AVIs), from more globular, membrane-bound anthocyanoplasts. We describe a system in tobacco that adds additional decorations to the basic anthocyanin, cyanidin 3- O -rutinoside, normally formed by this species. Using this system, we have been able to establish which decorations underpin the formation of AVIs, the conditions promoting AVI formation, and, consequently, the mechanism by which they form. [ABSTRACT FROM AUTHOR]

Vegetative shoots of a naturalized population of purple-leaved plectranthus ( Plectranthus ciliatus , Lamiaceae) were found to contain four main anthocyanins: peonidin 3-(6″-caffeoyl-β-glucopyranoside)-5-β-glucopyranoside, peonidin 3-(6″-caffeoyl-β-glucopyranoside)-5-(6‴-malonyl-β-glucopyranoside), peonidin 3-(6″- E - p -coumaroyl-β-glucopyranoside)-5-(6‴-malonyl-β-glucopyranoside), and peonidin 3-(6″- E - p -coumaroyl-β-glucopyranoside)-5-β-glucopyranoside. The first three of these pigments have not been reported previously from any plant. They all follow the typical anthocyanin pattern of Lamiaceae, with universal occurrence of anthocyanidin 3,5-diglucosides and aromatic acylation with p -coumaric and sometimes caffeic acids; however, they differ by being based on peonidin. The four anthocyanins were present in the leaves (22.2 mg g −1 DW), and in the xylem and interfascicular parenchyma of the stem. They were exceptionally abundant, among the highest reported for any plant organ, in epidermal hairs on some of the stem internodes (101 mg g −1 DW). Anthocyanin content in these hairs increased more than three-fold from the youngest to the fourth-youngest internodes. In situ absorbances (λ max ≈ 545 nm) were bathochromic in comparison to absorbances of the isolated anthocyanins in their flavylium form in acidified aqueous solutions (λ max = 525 nm), suggesting that the anthocyanins occur both in quinoidal and flavylium forms in constant proportions in the anthocyanic hair cells. The most distinctive observation with respect to relative proportions of individual anthocyanins was found in de-haired internodes, for which anthocyanin caffeoyl-derivatives decreased, and anthocyanin coumaroyl-derivatives increased, from the youngest to the fourth-youngest internode. [ABSTRACT FROM AUTHOR]

Highlights: [•] New identifications of anthocyanins in the reproductive and vegetative organs of Rhabdothamnus solandri. [•] The differential accumulation of pelargonidin-based and cyanidin-based anthocyanins underlies the colour patterns observed in the bird-pollinated Gesneriaceae species. [•] Anthocyanin patterning in R. solandri is likely regulated through the differential activity of the flavonoid-3′-hydroxylase. [•] Anthocyanic vacuolar inclusions (AVIs) in the flowers suggest that basic anthocyanin structures without aromatic acylation can also form AVIs. [•] A valuable system for studying regulatory mechanisms of anthocyanins, providing new insights into ornamental breeding. [Copyright &y& Elsevier]