Anatomical and biochemical studies of bicolored flower development in Muscari latifolium

Effects of cell morphology, physiology, biochemistry and CHS genes on four flower colors of Impatiens uliginosa

Introduction

Flower color is one of the important ornamental traits in the plants, which plays an active role in attracting pollinators to pollinate plants and reproduce their offspring. The flower color of Impatiens uliginosa is rich, there are four main flower colors in nature: deep red, red, pink, and white. However, it remains unclear whether on four different flower colors mechanism of I. uliginosa.

Methods

We investigate colorimetric measurement, observation of epidermal cells, cellular pH determination, extraction and determination of total anthocyanins and flavonoid, semi-quantitative determination of pigment components, and gene cloning and qRT-PCR of CHS genes to study four flower colors of I. uliginosa.

Results

The L* and b* values were the highest in white flower, while the a* values were the highest in pink flower. The same shape of epidermal cells was observed in different flower colors, which was all irregular flat polygons, and there were partial lignification. Their cellular pH values were weakly acidic, while the pH values of the deep red flower was the highest and the white flower was the lowest. The highest pigment content of the four flower colors was total anthocyanin content. And malvidin-3-galactosidechloride (C23H25ClO12), cyanidin-3-O-glucoside (C21H21O11) and delphinidin (C15H11O7) were the main pigment components affecting the color of four different flower colors. The anthocyanin synthesis gene IuCHS was expressed in four flowers, and all three copies of it had the highest expression level in pink flower and the lowest expression level in white flower.

Discussion

These results revealed the influence of main internal factors on four different flower colors of I. uliginosa, and provided a basis for further understanding of the intracellular and molecular regulatory mechanisms of flower color variation, and laid a foundation for the improvement of flower color breeding of Impatiens.

Autophagic and phytochemical aspects of color changes in white petals of snapdragon flower during development and senescence

Color change in petals is a clever strategy to attract more pollinators and one of the attractive features of edible flowers for consumers. Several physiological, phytochemical, and ultrastructural factors are involved in this process. However, this phenomenon is well underexplored in white petals. In this study, we investigated the color changes of the white petals of the snapdragon (Antirrhinum majus 'Legend White') flower from different aspects during development and senescence. In the ultrastructural analysis, both epidermal and mesophyll cells were examined. During flower development, plastid transition and autophagy processes led to the fading of the green color of young petals and the reduction of starch content, chlorophyll, and carotenoids. The piecemeal chlorophagy was observed in the degradation of starch granules. Leucoplasts were converted into autophagosome-like structures and then disappeared. The presence of these structures was evidence of the transformation of the plastid to the vacuole. As the green color faded, phytochemical compounds were synthesized. With partial flower opening and progression of senescence, pH and phenolic compounds were responsible for color changes. The highest amount of phenolic compound was observed after the flower opening stages. However, Phenolic colored compounds or total anthocyanins became colorless under the influence of low pH. The decrease in starch content caused an increase in the lightness parameter, and the petal color changed to pale yellow.

Integrating Multi-Omics Analysis Reveals the Regulatory Mechanisms of White-Violet Mutant Flowers in Grape Hyacinth (Muscari latifolium)

Grape hyacinth (Muscari spp.) is a famous bulbous blue flower; however, few bicolor varieties are available in the market. Therefore, the discovery of bicolor varieties and understanding of their mechanisms are crucial to the breeding of new varieties. In this study, we report a significant bicolor mutant with white upper and violet lower portions, with both parts belonging to a single raceme. Ionomics showed that pH and metal element contents were not responsible for the bicolor formation. Targeted metabolomics illustrated that the content of the 24 color-related compounds was significantly lower in the upper part than that in the lower part. Moreover, full-length transcriptomics combined with second-generation transcriptomics revealed 12,237 differentially expressed genes in which anthocyanin synthesis gene expression of the upper part was noted to be significantly lower than that of the lower part. Transcription factor differential expression analysis was used to describe the presence of a pair of MaMYB113a/b sequences, with low levels of expression in the upper part and high expression in the lower part. Furthermore, tobacco transformation confirmed that overexpression of MaMYB113a/b can promote anthocyanin accumulation in tobacco leaves. Accordingly, the differential expression of MaMYB113a/b contributes the formation of a bicolor mutant in Muscari latifolium.

New insights into the influence of NHX-type Cation/H+ antiporter on flower color in Phalaenopsis orchids

Vacuolar sodium/proton Na⁺(K⁺)/H⁺ exchanger (NHX) influence color formation because of their effects on cellular pH and Na⁺/K⁺ homeostasis. Research regarding NHXs has mainly focused on the vacuolar NHX family members. However, the NHX functions related to Phalaenopsis flower coloration remain relatively uncharacterized. In this study, we cloned and characterized PeNHX1, a vacuolar cation/H⁺ antiporter-encoding gene that is highly expressed in the Phalaenopsis equestris (orchid) flower lip. Phylogenetic and sequence analyses showed that PeNHX1 is a vacuolar NHX protein family member that is similar to other known vacuolar antiporters. The PeNHX1-GFP fusion protein was clearly localized to the vacuolar membrane in a transient transfection assay. A quantitative real-time PCR analysis revealed the increased expression of PeNHX1 in different flower developmental stages. Moreover, it was more highly expressed in the lip than in the other flower organs. On the basis of virus-induced gene silencing, we determined that decreased PeNHX1 expression significantly reduces P. equestris petal coloration. Furthermore, the overexpression of PeNHX1 in Phalaenopsis Big Chili caused the pH to increase and the petal color to change from red to blue. The results indicate that NHX1 may mediates the Na ⁺ or K⁺/H⁺ exchange, thereby regulating the vacuolar pH to promote blue coloration. This research provides a theoretical basis for the development of orchid varieties with blue flowers.

Creating a novel petal regeneration system for function identification of colour gene of grape hyacinth

BACKGROUND

Grape hyacinth (Muscari spp.) is one of the most important ornamental bulbous plants. However, its lengthy juvenile period and time-consuming transformation approaches under the available protocols impedes the functional characterisation of its genes in flower tissues. In vitro flower organogenesis has long been used to hasten the breeding cycle of plants but has not been exploited for shortening the period of gene transformation and characterisation in flowers.

RESULTS

A petal regeneration system was established for stable transformation and function identification of colour gene in grape hyacinth. By culturing on Murashige and Skoog medium (MS) with 0.45 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 8.88 μM 6-benzyladenine (6-BA), during the colour-changing period, the flower bud explants gave rise to regeneration petals in less than 3 months, instead of the 3 years required in field-grown plants. By combining this system with Agrobacterium-mediated transformation, a glucuronidase reporter gene (GUS) was delivered into grape hyacinth petals. Ultimately, 214 transgenic petals were regenerated from 24 resistant explants. PCR and GUS quantitative analyses confirmed that these putative transgenic petals have stably overexpressed GUS genes. Furthermore, an RNAi vector of the anthocyanidin 3-O-glucosyltransferase gene (MaGT) was integrated into grape hyacinth petals using the same strategy. Compared with the non-transgenic controls, reduced expression of the MaGT occurred in all transgenic petals, which caused pigmentation loss by repressing anthocyanin accumulation.

CONCLUSION

The Agrobacterium transformation method via petal organogenesis of grape hyacinth took only 3-4 months to implement, and was faster and easier to perform than other gene-overexpressing or -silencing techniques that are currently available.

Comprehensive Transcriptome and Metabolic Profiling of Petal Color Development in Lycoris sprengeri

Lycoris sprengeri (L. sprengeri) is an important ornamental bulbous plant, and its numerous varieties in different color forms are widely planted. Multiple color types of petals in L. sprengeri provide us with possibilities to delineate the complicated metabolic networks underlying the biochemical traits behind color formation in this plant species, especially petal color. In this study, we sequenced and annotated a reference transcriptome of pink and white petals of L. sprengeri and analyzed the metabolic role of anthocyanin biosynthesis in regulating color pigment metabolism. Briefly, white and pink petal samples were sequenced with an Illumina platform, to obtain the reads that could be assembled into 100,778 unique sequences. Sequences expressed differentially between white vs. pink petals were further annotated with the terms of Gene Ontology (GO), Clusters of Orthologous Groups (COG), Kyoto Encyclopedia of Genes and Genomes (KEGG), and eggNOG. Gene expression analyses revealed the repression of anthocyanin and steroid biosynthesis enzymes and R2R3 MYB transcription factor (TF) genes in white petals compared to pink petals. Furthermore, the targeted metabolic profiling of anthocyanins revealed that color-related delphinidin (Del) and cyanidin (Cy) pigments are lower in white petals, which correlate well with the reduced gene expression levels of anthocyanin biosynthesis genes. Taken together, it is hypothesized that anthocyanin biosynthesis, steroid biosynthesis, and R2R3 MYB TFs may play vital regulatory roles in petal color development in L. sprengeri. This work provides a valuable genomic resource for flower breeding and metabolic engineering in horticulture and markers for studying the flower trait evolution of L. sprengeri.

Characterization of Metabolites and Transcripts Involved in Flower Pigmentation in Primula vulgaris

Primula vulgaris exhibits a wide range of flower colors and is a valuable ornamental plant. The combination of flavonols/anthocyanins and carotenoids provides various colorations ranging from yellow to violet-blue. However, the complex metabolic networks and molecular mechanisms underlying the different flower colors of P. vulgaris remain unclear. Based on comprehensive analysis of morphological anatomy, metabolites, and gene expression in different-colored flowers of P. vulgaris, the mechanisms relating color-determining compounds to gene expression profiles were revealed. In the case of P. vulgaris flower color, hirsutin, rosinin, petunidin-, and cyanidin-type anthocyanins and the copigment herbacetin contributed to the blue coloration, whereas peonidin-, cyandin-, and delphinidin-type anthocyanins showed high accumulation levels in pink flowers. The color formation of blue and pink were mainly via the regulation of F3'5'H (c53168), AOMT (c47583, c44905), and 3GT (c50034). Yellow coloration was mainly due to gossypetin and carotenoid, which were regulated by F3H (c43100), F3 1 (c53714), 3GT (c53907) as well as many carotenoid biosynthetic pathway-related genes. Co-expression network and transient expression analysis suggested a potential direct link between flavonoid and carotenoid biosynthetic pathways through MYB transcription factor regulation. This work reveals that transcription changes influence physiological characteristics, and biochemistry characteristics, and subsequently results in flower coloration in P. vulgaris.

Study of the Relationship between Leaf Color Formation and Anthocyanin Metabolism among Different Purple Pakchoi Lines

Purple pakchoi (Brassica rapa ssp. Chinensis) is particularly appreciated due to its high edible quality and ornamental value, but there are few studies on the underlying mechanisms of leaf color formation. To comprehensively assess the differences in purple formation in pakchoi, four lines of pakchoi with different purple leaves were used in this experiment to determine the pigment content and to investigate the distribution and components of anthocyanin using LCMS (Liquid Chromatography Mass Spectrometry) and leaf cross-sections. Moreover, the expression levels of anthocyanin synthesis-related genes in four lines were calculated by qRT-PCR. The results showed that three new purple lines rich in anthocyanin and of high-quality were bred, and the anthocyanin were mainly distributed in both the upper epidermis and lower epidermis of leaves. Thirteen anthocyanin components were separated and identified, all the anthocyanins were acylated and glycosylated cyanidins; the main anthocyanins in purple pakchoi were a diacylated form of cyanidin 3-trans-(feruloyl)diglucoside-5-(malonyl)glucoside. Both the ratio of non-aromatic acylated cyanidin to aromatic acylated cyanidin and the ratio of anthocyanin content to chlorophyll content were responsible for the color formation in different purple pakchoi lines. When the ratio was high, the leaf appeared reddish purple, and when the ratio was low, the leaf appeared deep purple, even blackish purple. The expression level of BrF3H was significantly correlated with the content of anthocyanin through the correlation coefficient, which was speculated to be the main anthocyanin synthesis-related gene resulting in color differences among the four purple pakchoi lines. These results will enhance our understanding for the cultivation of new purple pakchoi varieties.

Metabolic and transcriptomic analysis related to flavonoid biosynthesis during the color formation of Michelia crassipes tepal

Michelia crassipes is the only plant with purple flowers amongst Michelia species, and its tepals exhibit an obvious color change from green to purple. In this study, a combination of metabolic and transcriptomic analyses was conducted at three stages of tepals in Michelia crassipes: green tepal, purple spot-containing tepal, and totally purple tepal. Several classes of flavonoid compounds were detected and cyanidin 3-rutinoside and delphinidin 3-glucoside were the major anthocyanins underlying the purple color formation, along with co-pigmentation of flavone compounds represented by luteolin derivatives and flavonol compounds represented by kaempferol and quercetin derivatives. Transcriptome analysis revealed up-regulation of genes encoding enzymes involved in the conversion of phenylpropanoid for flavonoid biosynthesis in Stage 1 vs. Stage 2, whereas up-regulation of most flavonoid biosynthesis genes was observed in Stage 1 vs. Stage 3. MYB, bHLH, and WD40 isoforms, as well as other classes of transcriptional factors, also exhibited differential expression. In addition, differentially expressed genes putatively related to the transport of flavonoids were also identified. The results of the current study provide insight into the regulatory mechanism underlying the color transition from green to purple in Michelia crassipes tepals and describe a complicated network involving PAL, transporter genes, and transcription factors, specifically responsible for the emergence of purple color in Stage 1 vs. Stage 2.

Comparative transcriptome analysis of mulberry reveals anthocyanin biosynthesis mechanisms in black (Morus atropurpurea Roxb.) and white (Morus alba L.) fruit genotypes

BACKGROUND

To gain a better understanding of anthocyanin biosynthesis in mulberry fruit, we analyzed the transcriptome of the mulberry varieties Da 10 (Morus atropurpurea Roxb., black fruit) and Baisang (Morus alba L., white fruit).

RESULTS

We found that whereas Da 10 had high levels of cyanidin 3-O-glucoside (Cy), and pelargonidin 3-O-glucoside (Pg), Baisang contained only Cy, at low levels. Based on a comparative transcriptome analysis, we annotated more than 27,085 genes (including 1735 new genes). Genes that were differentially expressed between Da 10 and Baisang were detected at three stages of fruit development: S1 [4256 genes, 10 days post-anthesis (DPA)], S2 (5612 genes, 19 DPA), and S3 (5226 genes, 28 DPA). Anthocyanin biosynthesis was found to be associated with the expression of 15 core genes and 5 transcription factors. Relative to Baisang, Da 10 showed a significant upregulation of genes involved in the early stages (production of the intermediate compounds chalcone and dihydroflavonol) and late stages (production of Cy and Pg) of anthocyanin biosynthesis. Baisang showed a significant downregulation of the genes involved in the early stages of anthocyanin biosynthesis and overexpression of flavanone 3-hydroxylase (FLS), resulting in the generation of quercetin and/or myricetin but not anthocyanins.

CONCLUSIONS

The biosynthesis of anthocyanin in mulberry fruit is initiated from the precursor, phenylalanine, and mediated by the upregulation of dihydroflavonol 4-reductase, anthocyanidin synthase, anthocyanidin 3-O-glucosyltransferase, and cyanidin-3-O-glucoside 2-O-glucuronosyltransferase, and downregulation of FLS to produce Cy and Pg.

A novel R2R3-MYB from grape hyacinth, MaMybA, which is different from MaAN2, confers intense and magenta anthocyanin pigmentation in tobacco

BACKGROUND

The primary pigments in flowers are anthocyanins, the biosynthesis of which is mainly regulated by R2R3-MYBs. Muscari armeniacum is an ornamental garden plant with deep cobalt blue flowers containing delphinidin-based anthocyanins. An anthocyanin-related R2R3-MYB MaAN2 has previously been identified in M. armeniacum flowers; here, we also characterized a novel R2R3-MYB MaMybA, to determine its function and highlight similarities and differences between MaMybA and MaAN2.

RESULTS

In this study, a novel anthocyanin-related R2R3-MYB gene was isolated from M. armeniacum flowers and functionally identified. A sequence alignment showed that MaMybA contained motifs typically conserved with MaAN2 and its orthologs. However, the shared identity of the entire amino acid sequence between MaMybA and MaAN2 was 43.5%. Phylogenetic analysis showed that they were both clustered into the AN2 subgroup of the R2R3-MYB family, but not in the same branch. We also identified a IIIf bHLH protein, MabHLH1, in M. armeniacum flowers. A bimolecular fluorescence complementation assay showed that MabHLH1 interacted with MaMybA or MaAN2 in vivo; a dual luciferase assay indicated that MaMybA alone or in interaction with MabHLH1 could regulate the expression of MaDFR and AtDFR, but MaAN2 required MabHLH1 to do so. When overexpressing MaMybA in Nicotiana tabacum 'NC89', the leaves, petals, anthers, and calyx of transgenic tobacco showed intense and magenta anthocyanin pigments, whereas those of OE-MaAN2 plants had lighter pigmentation. However, the ovary wall and seed skin of OE-MaMybA tobacco were barely pigmented, while those of OE-MaAN2 tobacco were reddish-purple. Moreover, overexpressing MaMybA in tobacco obviously improved anthocyanin pigmentation, compared to the OE-MaAN2 and control plants, by largely upregulating anthocyanin biosynthetic and endogenous bHLH genes. Notably, the increased transcription of NtF3'5'H in OE-MaMybA tobacco might lead to additional accumulation of delphinidin 3-rutinoside, which was barely detected in OE-MaAN2 and control plants. We concluded that the high concentration of anthocyanin and the newly produced Dp3R caused the darker color of OE-MaMybA compared to OE-MaAN2 tobacco.

CONCLUSION

The newly identified R2R3-MYB transcription factor MaMybA functions in anthocyanin biosynthesis, but has some differences from MaAN2; MaMybA could also be useful in modifying flower color in ornamental plants.

Comparative transcriptome analyses reveal genes related to pigmentation in the petals of red and white Primula vulgaris cultivars

Primula vulgaris is an important ornamental plant species with various flower color. To explore the molecular mechanism of its color formation, comparative transcriptome analyses of the petals in red and white cultivars was performed. A total of 4451 differentially expressed genes were identified and annotated into 128 metabolic pathways. Candidate genes FLS, F3'H, DFR, ANS and AOMT in the anthocyanin pathway were expressed significantly higher in the red cultivar than the white and may be responsible for the red coloration. In the red petals, a putative transcription factors bHLH (c52273.graph_c0) was up-regulated about 14-fold, while a R2R3-MYB unigene (c36140.graph_c0) was identified as a repressor involved in anthocyanin regulation and was significantly down-regulated. In addition, the anatomy analyses and pigments composition in the red and white petals were also analyzed. The papillae on the adaxial epidermis of the red petals of P. vulgaris display a triangle-shapes, in contrast with a spherical shape for the white petals. Although flavonoids were detected in both cultivars, anthocyanins could only be identified in the red cultivar. Gossypetin and peonidin/rosinin were the most abundant pigments in red petals. This study shed light on the genetic and biochemistry mechanisms underlying the flower coloration in Primula.

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

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

Biochemical and Comparative Transcriptomic Analyses Identify Candidate Genes Related to Variegation Formation in Paeonia rockii

Paeonia rockii is a wild tree peony species with large and dark purple variegations at the base of its petals. It is the genetic resource for various variegation patterns in tree peony cultivars, which is in contrast to the pure white petals of Paeonia ostii. However, the molecular mechanism underlying the formation of variegation in this plant is still unknown. Here, we conducted Illumina transcriptome sequencing for P. rockii, P. ostii (with pure white petals) and their F1 individuals (with purple-red variegation). A total of 181,866 unigenes were generated, including a variety of unigenes involved in anthocyanin biosynthesis and sequestration and the regulation of anthocyanin biosynthesis. The dark purple or purple-red variegation patterns mainly occurred due to the proportions of cyanidin (Cy)- and peonidin (Pn)-based anthocyanins. The variegations of P. rockii exhibited a “Cy > Pn” phenotype, whereas the F1 progeny showed a “Pn > Cy” phenotype. The CHS, DFR, ANS, and GST genes might play key roles in variegation pigmentation in P. rockii according to gene expression and interaction network analysis. Two R2R3-MYB transcription factors (c131300.graph_c0 and c133735.graph_c0) regulated variegation formation by controlling CHS, ANS and GST genes. Our results indicated that the various variegation patterns were caused by transcriptional regulation of anthocyanin biosynthesis genes, and the transcription profiles of the R2R3-MYBs provided clues to elucidate the mechanisms underlying this trait. The petal transcriptome data produced in this study will provide a valuable resource for future association investigations of the genetic regulation of various variegation patterns in tree peonies.

Anthocyanin Profiles in Flowers of Grape Hyacinth

Grape hyacinth (Muscari spp.) is a popular ornamental bulbous perennial famous for its blue flowers. To understand the chemical basis of the rich blue colors in this plant, anthocyanin profiles of six blue flowering grape hyacinths as well as one pink and one white cultivar were determined using high-performance liquid chromatography and mass spectrometry. Along with two known compounds, eight putative anthocyanins were identified in the tepals of grape hyacinth for the first time. The accumulation and distribution of anthocyanins in the plant showed significant cultivar and flower development specificity. Violet-blue flowers mainly contained simple delphinidin-type anthocyanins bearing one or two methyl-groups but no acyl groups, whereas white and pink flowers synthesised more complex pelargonidin/cyanidin-derivatives with acyl-moieties but no methyl-groups. The results partially reveal why solid blue, orange or red flowers are rare in this plant in nature. In addition, pelargonidin-type anthocyanins were found for the first time in the genus, bringing more opportunities in terms of breeding of flower color in grape hyacinth.

Identification and comparative profiling of miRNAs in herbaceous peony (Paeonia lactiflora Pall.) with red/yellow bicoloured flowers

Herbaceous peony (Paeonia lactiflora Pall.) is popular worldwide because of its gorgeous flower colour, and the yellow flower is the rarest. However, its mechanism of yellow formation is still unexplored from the post-translational level. In this study, the anatomy of the petal, cell sap pH and metal elements were investigated in bicoloured flower cultivar 'Jinhui' with red outer-petal and yellow inner-petal, and the yellow formation was influenced by the anatomy of petal, while not by the cell sap pH and metal elements. Subsequently, microRNAs sequencing (miRNA-seq) was used to identify small RNAs (sRNAs). A total of 4,172,810 and 3,565,152 specific unique sRNAs were obtained, 207 and 204 conserved miRNAs and 38 and 42 novel miRNAs were identified from red outer-petal and yellow inner-petal, respectively, which were confirmed by subcloning. Among these miRNAs, 163 conserved and 28 novel miRNAs were differentially expressed in two wheel of petals. And 5 differentially expressed miRNAs and their corresponding target genes related to yellow formation were screened, and their dynamic expression patterns confirmed that the yellow formation might be under the regulation of miR156e-3p-targeted squamosa promoter binding protein-like gene (SPL1). These results improve the understanding of miRNA regulation of the yellow formation in P. lactiflora.

Anatomical and biochemical analysis reveal the role of anthocyanins in flower coloration of herbaceous peony

Herbaceous peony (Paeonia lactiflora Pall.) is particularly appreciated because of its elegant and gorgeous flower color, but little is known about the underlying mechanisms of flower coloration. In this study, three P. lactiflora cultivars 'Xuefeng', 'Fenyulou' and 'Dahonglou' with white, pink and red flower were selected as the materials. Their anatomical structures, cell sap pH and metal elements were investigated, and the colored pigment mainly distributed in palisade mesophyll was only found in 'Fenyulou' and 'Dahonglou', and their shape of epidermal cells, cell sap pH and metal elements were not the key factors deciding phenotype color. Moreover, the qualitative and quantitative analysis of flavonoids were performed, their total anthocyanin, anthoxanthin and flavonoid contents were decreased during flower development, and only anthocyanin content in 'Dahonglou' was always higher than that in 'Xuefeng' and 'Fenyulou'. Subsequently, three anthocyanin compositions were found, and peonidin 3,5-di-O-glucoside (Pn3G5G) was identified as the main anthocyanin composition. In addition, the full-length of flavonol synthase gene (FLS) was isolated with the GenBank accession number KM259902, and the expression patterns of eight flavonoid biosynthetic genes showed that only PlDFR and PlANS basically had the highest levels in 'Dahonglou' and the lowest levels in 'Xuefeng', and they basically displayed a descended trend during flower development especially PlDFR, suggesting that these two genes might play a key role in the anthocyanin biosynthesis which resulted in the shift from white to pink and red in flowers. These results would contribute to understand the underlying molecular mechanisms of flower coloration in P. lactiflora.

Recent advances on the development and regulation of flower color in ornamental plants

Flower color is one of the most important features of ornamental plants. Its development and regulation are influenced by many internal and external factors. Therefore, understanding the mechanism of color development and its regulation provides an important theoretical basis and premise for the cultivation and improvement of new color varieties of ornamental plants. This paper outlines the functions of petal tissue structure, as well as the distribution and type of pigments, especially anthocyanins, in color development. The progress of research on flower color regulation with a focus on physical factors, chemical factors, and genetic engineering is introduced. The shortcomings of flower color research and the potential directions for future development are explored to provide a broad background for flower color improvements in ornamental plants.

Transcriptome sequencing and metabolite analysis reveals the role of delphinidin metabolism in flower colour in grape hyacinth

Grape hyacinth (Muscari) is an important ornamental bulbous plant with an extraordinary blue colour. Muscari armeniacum, whose flowers can be naturally white, provides an opportunity to unravel the complex metabolic networks underlying certain biochemical traits, especially colour. A blue flower cDNA library of M. armeniacum and a white flower library of M. armeniacum f. album were used for transcriptome sequencing. A total of 89 926 uni-transcripts were isolated, 143 of which could be identified as putative homologues of colour-related genes in other species. Based on a comprehensive analysis relating colour compounds to gene expression profiles, the mechanism of colour biosynthesis was studied in M. armeniacum. Furthermore, a new hypothesis explaining the lack of colour phenotype of the grape hyacinth flower is proposed. Alteration of the substrate competition between flavonol synthase (FLS) and dihydroflavonol 4-reductase (DFR) may lead to elimination of blue pigmentation while the multishunt from the limited flux in the cyanidin (Cy) synthesis pathway seems to be the most likely reason for the colour change in the white flowers of M. armeniacum. Moreover, mass sequence data obtained by the deep sequencing of M. armeniacum and its white variant provided a platform for future function and molecular biological research on M. armeniacum.