Introduction of apple ANR genes into tobacco inhibits expression of both CHI and DFR genes in flowers, leading to loss of anthocyanin

Genome-Wide Identification and Analysis of Anthocyanidin Reductase Gene Family in Lychee (Litchi chinensis Sonn.)

Anthocyanidin reductase (ANR) is a key enzyme regulating anthocyanin synthesis and accumulation in plants. Here, lychee ANR genes were globally identified, their sequence and phylogenetic characteristics were analyzed, and their spatiotemporal expression patterns were characterized. A total of 51 ANR family members were identified in the lychee genome. The length of the encoded amino acid residues ranged from 87 aa to 289 aa, the molecular weight ranged from 9.49 KD to 32.40 KD, and the isoelectric point (pI) ranged from 4.83 to 9.33. Most of the members were acidic proteins. Most members of the LcANR family were located in the cytoplasm. The 51 LcANR family members were unevenly distributed in 11 chromosomes, and their exons and motif conserved structures were significantly different from each other. Promoters in over 90% of LcANR members contained anaerobically induced response elements, and 88% contained photoresponsive elements. Most LcANR family members had low expression in nine lychee tissues and organs (root, young leaf, bud, female flower, male flower, pericarp, pulp, seed, and calli), and some members showed tissue-specific expression patterns. The expression of one gene, LITCHI029356.m1, decreased with the increase of anthocyanin accumulation in 'Feizixiao' and 'Ziniangxi' pericarp, which was negatively correlated with pericarp coloring. The identified LcANR gene was heterologously expressed in tobacco K326, and the function of the LcANR gene was verified. This study provides a basis for the further study of LcANR function, particularly the role in lychee pericarp coloration.

Image analysis and polyphenol profiling unveil red-flesh apple phenotype complexity

BACKGROUND

The genetic basis of colour development in red-flesh apples (Malus domestica Borkh) has been widely characterised; however, current models do not explain the observed variations in red pigmentation intensity and distribution. Available methods to evaluate the red-flesh trait rely on the estimation of an average overall colour using a discrete class notation index. However, colour variations among red-flesh cultivars are continuous while development of red colour is non-homogeneous and genotype-dependent. A robust estimation of red-flesh colour intensity and distribution is essential to fully capture the diversity among genotypes and provide a basis to enable identification of loci influencing the red-flesh trait.

RESULTS

In this study, we developed a multivariable approach to evaluate the red-flesh trait in apple. This method was implemented to study the phenotypic diversity in a segregating hybrid F1 family (91 genotypes). We developed a Python pipeline based on image and colour analysis to quantitatively dissect the red-flesh pigmentation from RGB (Red Green Blue) images and compared the efficiency of RGB and CIEL*a*b* colour spaces in discriminating genotypes previously classified with a visual notation. Chemical destructive methods, including targeted-metabolite analysis using ultra-high performance liquid chromatography with ultraviolet detection (UPLC-UV), were performed to quantify major phenolic compounds in fruits' flesh, as well as pH and water contents. Multivariate analyses were performed to study covariations of biochemical factors in relation to colour expression in CIEL*a*b* colour space. Our results indicate that anthocyanin, flavonol and flavanol concentrations, as well as pH, are closely related to flesh pigmentation in apple.

CONCLUSTION

Extraction of colour descriptors combined to chemical analyses helped in discriminating genotypes in relation to their flesh colour. These results suggest that the red-flesh trait in apple is a complex trait associated with several biochemical factors.

Integration of Metabolomic and Transcriptomic Analyses Reveals the Molecular Mechanisms of Flower Color Formation in Prunus mume

Flower color is an important trait that affects the economic value of Prunus mume, a famous ornamental plant in the Rosaceae family. P. mume with purple-red flowers is uniquely charming and highly favored in landscape applications. However, little is known about its flower coloring mechanism, which stands as a critical obstacle on the path to innovative breeding for P. mume flower color. In this study, transcriptomic and targeted metabolomic analyses of purple-red P. mume and white P. mume were performed to elucidate the mechanism of flower color formation. In addition, the expression patterns of key genes were analyzed using an RT-qPCR experiment. The results showed that the differential metabolites were significantly enriched in the flavonoid synthesis pathway. A total of 14 anthocyanins emerged as the pivotal metabolites responsible for the differences in flower color between the two P. mume cultivars, comprising seven cyanidin derivatives, five pelargonium derivatives, and two paeoniflorin derivatives. Moreover, the results clarified that the metabolic pathway determining flower color in purple-red P. mume encompasses two distinct branches: cyanidin and pelargonidin, excluding the delphinidin branch. Additionally, through the integrated analysis of transcriptomic and metabolomic data, we identified 18 key genes responsible for anthocyanin regulation, thereby constructing the gene regulatory network for P. mume anthocyanin synthesis. Among them, ten genes (PmCHI, PmGT2, PmGT5, PmGST3, PmMYB17, PmMYB22, PmMYB23, PmbHLH4, PmbHLH10, and PmbHLH20) related to anthocyanin synthesis were significantly positively correlated with anthocyanin contents, indicating that they may be the key contributors to anthocyanin accumulation. Our investigation contributes a novel perspective to understanding the mechanisms responsible for flower color formation in P. mume. The findings of this study introduce novel strategies for molecular design breeding aimed at manipulating flower color in P. mume.

Integration of genome-wide association studies, metabolomics, and transcriptomics reveals phenolic acid- and flavonoid-associated genes and their regulatory elements under drought stress in rapeseed flowers

Introduction

Biochemical and metabolic processes help plants tolerate the adverse effects of drought. In plants accumulating bioactive compounds, understanding the genetic control of the biosynthesis of biochemical pathways helps the discovery of candidate gene (CG)-metabolite relationships.

Methods

The metabolic profile of flowers in 119 rapeseed (Brassica napus) accessions was assessed over two irrigation treatments, one a well-watered (WW) condition and the other a drought stress (DS) regime. We integrated information gained from 52,157 single-nucleotide polymorphism (SNP) markers, metabolites, and transcriptomes to identify linked SNPs and CGs responsible for the genetic control of flower phenolic compounds and regulatory elements.

Results

In a genome-wide association study (GWAS), of the SNPs tested, 29,310 SNPs were qualified to assess the population structure and linkage disequilibrium (LD), of which several SNPs for radical scavenging activity (RSA) and total flavanol content (TFLC) were common between the two irrigation conditions and pleiotropic SNPs were found for chlorogenic and coumaric acids content. The principal component analysis (PCA) and stepwise regression showed that chlorogenic acid and epicatechin in WW and myricetin in DS conditions were the most important components for RSA. The hierarchical cluster analysis (HCA) showed that vanillic acid, myricetin, gallic acid, and catechin were closely associated in both irrigation conditions. Analysis of GWAS showed that 60 CGs were identified, of which 18 were involved in stress-induced pathways, phenylpropanoid pathway, and flavonoid modifications. Of the CGs, PAL1, CHI, UGT89B1, FLS3, CCR1, and CYP75B137 contributed to flavonoid biosynthetic pathways. The results of RNA sequencing (RNA-seq) revealed that the transcript levels of PAL, CHI, and CYP75B137 known as early flavonoid biosynthesis-related genes and FLS3, CCR1, and UGT89B1 related to the later stages were increased during drought conditions. The transcription factors (TFs) NAC035 and ERF119 related to flavonoids and phenolic acids were upregulated under drought conditions.

Discussion

These findings expand our knowledge on the response mechanisms to DS, particularly regarding the regulation of key phenolic biosynthetic genes in rapeseed. Our data also provided specific linked SNPs for marker-assisted selection (MAS) programs and CGs as resources toward realizing metabolomics-associated breeding of rapeseed.

HaMYBA-HabHLH1 regulatory complex and HaMYBF fine-tune red flower coloration in the corolla of sunflower (Helianthus annuus L.)

Sunflowers are well-known ornamental plants, while sunflowers with red corolla are rare and the mechanisms underlying red coloration remain unclear. Here, a comprehensive analysis of metabolomics and transcriptomics on flavonoid pathway was performed to investigate the molecular mechanisms underlying the differential color formation between red sunflower Pc103 and two yellow sunflowers (Yr17 and Y35). Targeted metabolomic analysis revealed higher anthocyanin levels but lower flavonol content in Pc103 compared to the yellow cultivars. RNA-sequencing and phylogenetic analysis identified multiple genes involved in the flavonoid pathway, including series of structural genes and three MYB and bHLH genes. Specifically, HaMYBA and HabHLH1 were up-regulated in Pc103, whereas HaMYBF exhibited reduced expression. HaMYBA was found to interact with HabHLH1 in vivo and in vitro, while HaMYBF does not. Transient expression analysis further revealed that HabHLH1 and HaMYBA cooperatively regulate increased expression of dihydroflavonol 4-reductase (DFR), leading to anthocyanin accumulation. On the other hand, ectopic expression of HaMYBF independently modulates flavonol synthase (FLS) expression, but hindered anthocyanin production. Collectively, our findings suggest that the up-regulation of HaMYBA and HabHLH1, as well as the down-regulation of HaMYBF, contribute to the red coloration in Pc103. It offers a theoretical basis for improving sunflower color through genetic engineering.

Integrated analysis of the metabolome and transcriptome provides insights into anthocyanin biosynthesis of cashew apple

The cashew apple remains an underutilized agricultural product despite its abundance as a by-product of cashew nut production. Anthocyanins are water-soluble pigments responsible for red, purple, and blue hues in plant tissues and have various health-promoting properties. To investigate the anthocyanin biosynthesis in cashew apples, fruits with varying peel colors from three cultivars were subjected to integrative analyses with metabolomics and transcriptomics. Through a UPLC-ESI-MS/MS-based targeted metabolomics analysis, a total of 26 distinct anthocyanin compounds were identified in the fruits of the three cashew cultivars. Subsequent quantification revealed that Pelargonidin-3-O-galactoside, Petunidin-3-O-arabinoside, and Cyanidin-3-O-galactoside were the primary contributors responsible for the red pigmentation in cashew apple peels. Following transcriptomic analysis showed that the expression levels of anthocyanin biosynthetic genes were predominantly higher in the red cashew apples as compared to the other two cultivars. Moreover, correlation analysis revealed that eight potential transcription factors implicated in the regulation of anthocyanin biosynthesis. Among these, four transcription factors exhibited positive correlations with both anthocyanin contents and anthocyanin biosynthetic gene expression, while the remaining four transcription factors displayed negative correlations. These findings provide a comprehensive understanding of the molecular basis of anthocyanin biosynthesis in cashew apple peels.

Whole-genome resequencing and transcriptome analyses of four generation mutants to reveal spur-type and skin-color related genes in apple (Malus domestica Borkh. Cv. Red delicious)

BACKGROUND

Bud sport is a kind of somatic mutation that usually occurred in apple. 'Red Delicious' is considered to be a special plant material of bud sport, whereas the genetic basis of plant mutants is still unknown. In this study, we used whole-genome resequencing and transcriptome sequencing to identify genes related to spur-type and skin-color in the 'Red Delicious' (G0) and its four generation mutants including 'Starking Red' (G1), 'Starkrimson' (G2), 'Campbell Redchief' (G3) and 'Vallee Spur' (G4).

RESULTS

The number of single nucleotide polymorphisms (SNPs), insertions and deletions (InDels) and structural variations (SVs) were decreased in four generation mutants compared to G0, and the number of unique SNPs and InDels were over 9-fold and 4-fold higher in G1 versus (vs.) G2 and G2 vs. G3, respectively. Chromosomes 2, 5, 11 and 15 carried the most SNPs, InDels and SVs, while chromosomes 1 and 6 carried the least. Meanwhile, we identified 4,356 variation genes by whole-genome resequencing and transcriptome, and obtained 13 and 16 differentially expressed genes (DEGs) related to spur-type and skin-color by gene expression levels. Among them, DELLA and 4CL7 were the potential genes that regulate the difference of spur-type and skin-color characters, respectively.

CONCLUSIONS

Our study identified potential genes associated with spur-type and skin-color differences in 'Red Delicious' and its four generation mutants, which provides a theoretical foundation for the mechanism of the apple bud sport.

Functional identification of ANR genes in apple (Malus halliana) that reduce saline-alkali stress tolerance

As one of the major abiotic stresses restricting the development of global agriculture, saline-alkali stress causes osmotic stress, ion poisoning, ROS damage and high pH damage, which seriously restrict sustainable development of fruit industry. Therefore, it is essential to develop and cultivate saline-alkali-resistant apple rootstocks to improve the yield and quality of apples in China. Based on transcriptome data, MhANR (LOC114827797), which is significantly induced by saline-alkali stress, was cloned from Malus halliana. The physicochemical properties, evolutionary relationships and cis-acting elements were analysed. Subsequently, the tolerance of MhANR overexpression in Arabidopsis thaliana, tobacco, and apple calli to saline-alkali stress was verified through genetic transformation. Transgenic plants contained less Chl a, Chl b and proline, SOD, POD and CAT activity, and higher relative electrical conductivity (REC) compared to WT plants under saline-alkali stress. In addition, expression of saline-alkali stress-related genes in overexpressed apple calli were also lower than in WT calli, including the antioxidant genes (MhSOD and MhCAT^), the Na+ transporter genes (MhCAX5, MhCAX5, MhSOS1, MhALT1), and the H+ -ATPase genes (MhAHA2 and MhAHA8), while expression of the K+ transporter genes (MhSKOR and MhNHX4) were higher. Expression of MhANR reduced tolerance of A. thaliana, tobacco, and apple calli to saline-alkali stress by regulating osmoregulatory substances, chlorophyll content, antioxidant enzyme activity, and expression of saline-alkali stress-related genes. This research provides a theoretical basis for cultivating apple rootstocks with effective saline-alkali stress tolerance.

Identification of key genes responsible for green and white colored spathes in Anthurium andraeanum (Hort.)

Modern anthuriums, Anthurium andraeanum (Hort.) are among the most popular flowering plants and widely used for interior decoration. Their popularity is largely attributed to the exotic spathes with different colors. Previous studies have reported color development in red spathe cultivars, but limited information is available on key genes regulating white and green colored spathes. This study analyzed anthocyanin, chlorophyll, and carotenoid contents as well as transcript differences in spathes of eight cultivars that differed in spathe colors ranging from red to white and green. Results showed that increased expression of a transcription factor AaMYB2 was associated with elevated levels of anthocyanin in spathes, but decreased expression of AaMYB2 and increased expression of AaLAR (leucoanthocyanidin reductase) and AaANR (anthocyanidin reductase) were accompanied with the accumulation of colorless proanthocyanidin, thus the white spathe. As to the green colored spathe, chlorophyll content in the green spathe cultivar was substantially higher than the other cultivars. Correspondingly, transcripts of chlorophyll biosynthesis-related genes AaHemB (porphobilinogen synthase) and AaPor (protochlorophyllide oxidoreductase) were highly upregulated but almost undetectable in white and red spathes. The increased expression of AaHemB and AaPor was correlated with the expression of transcription factor AaMYB124. Subsequently, qRT-PCR analysis confirmed their expression levels in nine additional cultivars with red, white, and green spathes. A working model for the formation of white and green spathes was proposed. White colored spathes are likely due to the decreased expression of AaMYB2 which results in increased expression of AaLAR and AaANR, and the green spathes are attributed to AaMYB124 enhanced expression of AaHemB and AaPor. Further research is warranted to test this working model.

Light-Induced TaHY5-7A and TaBBX-3B Physically Interact to Promote PURPLE PERICARP-MYB 1 Expression in Purple-Grained Wheat

Purple-grained wheat (Triticum aestivum L.) is an important germplasm source in crop breeding. Anthocyanin biosynthesis in the pericarps of purple-grained wheat is largely light-dependent; however, the regulatory mechanisms underlying light-induced anthocyanin accumulation in the wheat pericarp remain unknown. Here we determined that anthocyanins rapidly accumulate in the pericarps of the purple-grained wheat cultivar Heixiaomai 76 (H76) at 16 days after pollination under light treatment. Using transcriptome sequencing, differential gene expression analysis, and phylogenetic analysis, we identified two key genes involved in light signaling in wheat: ELONGATED HYPOCOTYL 5-7A (TaHY5-7A) and B-BOX-3B (TaBBX-3B). TaHY5-7A and TaBBX-3B were highly expressed in purple-grained wheat pericarps. The heterologous expression of TaHY5-7A partially restored the phenotype of the Arabidopsis (Arabidopsis thaliana) hy5 mutant, resulting in increased anthocyanin accumulation and a shortened hypocotyl. The heterologous expression of TaBBX-3B in wild-type Arabidopsis had similar effects. TaHY5-7A and TaBBX-3B were nucleus-localized, consistent with a function in transcription regulation. However, TaHY5-7A, which lacks a transactivation domain, was not sufficient to activate the expression of PURPLE PERICARP-MYB 1 (TaPpm1), the key anthocyanin biosynthesis regulator in purple pericarps of wheat. TaHY5-7A physically interacted with TaBBX-3B in yeast two-hybrid and bimolecular fluorescence complementation assays. Additionally, TaHY5-7A, together with TaBBX-3B, greatly enhanced the promoter activity of TaPpm1 in a dual luciferase assay. Overall, our results suggest that TaHY5-7A and TaBBX-3B collaboratively activate TaPpm1 expression to promote light-induced anthocyanin biosynthesis in purple-pericarp wheat.

Ginkgo biloba GbbZIP08 transcription factor is involved in the regulation of flavonoid biosynthesis

Ginkgo biloba is the oldest relict plant on Earth and an economic plant resource derived from China. Flavonoids extracted from G. biloba are beneficial to the prevention and treatment of cardiovascular and cerebrovascular diseases. Basic leucine zipper (bZIP) transcription factors (TFs) have been recognized to play important roles in plant secondary metabolism. In this study, GbbZIP08 was isolated and characterized. It encodes a protein containing 154 amino acids, which belongs to hypocotyl 5 in group H of the bZIP family. Tobacco transient expression assay indicated that GbbZIP08 was localized in the plant nucleus. GbbZIP08 overexpression showed that the contents of total flavonoids, kaempferol, and anthocyanin in transgenic tobacco were significantly higher than those in the wild type. Transcriptome sequencing analysis revealed significant upregulation of structural genes in the flavonoid biosynthesis pathway. In addition, phytohormone signal transduction pathways, such as the abscisic acid, salicylic acid, auxin, and jasmonic acid pathways, were enriched with a large number of differentially expressed genes. TFs such as MYB, AP2, WRKY, NAC, bZIP, and bHLH, were also differentially expressed. The above results indicated that GbbZIP08 overexpression promoted flavonoid accumulation and increased the transcription levels of flavonoid-synthesis-related genes in plants.

Transcriptomic analysis reveals the mechanism underlying the anthocyanin changes in Fragaria nilgerrensis Schlecht. and its interspecific hybrids

BACKGROUND

Fragaria nilgerrensis (FN) provides a rich source of genetic variations for strawberry germplasm innovation. The color of strawberry fruits is a key factor affecting consumer preferences. However, the genetic basis of the fruit color formation in F. nilgerrensis and its interspecific hybrids has rarely been researched.

RESULTS

In this study, the fruit transcriptomes and flavonoid contents of FN (white skin; control) and its interspecific hybrids BF1 and BF2 (pale red skin) were compared. A total of 31 flavonoids were identified. Notably, two pelargonidin derivatives (pelargonidin-3-O-glucoside and pelargonidin-3-O-rutinoside) were revealed as potential key pigments for the coloration of BF1 and BF2 fruits. Additionally, dihydroflavonol 4-reductase (DFR) (LOC101293459 and LOC101293749) and anthocyanidin 3-O-glucosyltransferase (BZ1) (LOC101300000), which are crucial structural genes in the anthocyanidin biosynthetic pathway, had significantly up-regulated expression levels in the two FN interspecific hybrids. Moreover, most of the genes encoding transcription factors (e.g., MYB, WRKY, TCP, bHLH, AP2, and WD40) related to anthocyanin accumulation were differentially expressed. We also identified two DFR genes (LOC101293749 and LOC101293459) that were significantly correlated with members in bHLH, MYB, WD40, AP2, and bZIP families. Two chalcone synthase (CHS) (LOC101298162 and LOC101298456) and a BZ1 gene (LOC101300000) were highly correlated with members in bHLH, WD40 and AP2 families.

CONCLUSIONS

Pelargonidin-3-O-glucoside and pelargonidin-3-O-rutinoside may be the key pigments contributing to the formation of pale red fruit skin. DFR and BZ1 structural genes and some bHLH, MYB, WD40, AP2, and bZIP TF family members enhance the accumulation of two pelargonidin derivatives. This study provides important insights into the regulation of anthocyanidin biosynthesis in FN and its interspecific hybrids. The presented data may be relevant for improving strawberry fruit coloration via genetic engineering.

Postharvest light-induced flavonoids accumulation in mango (Mangifera indica L.) peel is associated with the up-regulation of flavonoids-related and light signal pathway genes

INTRODUCTION

Flavonoids are important secondary metabolites in plants and light is a crucial environmental factor regulating flavonoids biosynthesis. However, effect of light on the different flavonoids compositions accumulation in mango and the relevant molecular mechanism still need to be clarified.

METHODS

In this study, green-mature fruits of red mango cultivar 'Zill' were subjected to postharvest light treatment, and fruit peel color, total soluble solids content, total organic acid, and firmness of flesh were measured. The flavonoids metabolites profile, and the expression of flavonoids-related genes and light signal pathway genes were also analyzed.

RESULTS

Results showed that light treatment promoted the red coloration of fruit peel and increased the total soluble solids content and firmness of flesh. The concentration of flavonols, proanthocyanidins and anthocyanins, and expression of key flavonoids biosynthetic genes including MiF3H, MiFLS, MiLAR, MiANS, MiUFGT1, and MiUFGT3 were significantly induced by light. The MYBs regulating flavonols and proanthocyanidins, i.e. MiMYB22 and MiMYB12, as well as the key light signal pathway transcription factors (TFs) MiHY5 and MiHYH, were identified in mango. The transcription of MiMYB1, MiMYB12, MiMYB22, MiHY5 and MiHYH was up-regulated by light.

DISCUSSION

Our results provide a postharvest technology to improve mango fruit appearance quality, and are helpful to reveal the molecular mechanism of light-induced flavonoids biosynthesis in mango.

High Light Intensity Triggered Abscisic Acid Biosynthesis Mediates Anthocyanin Accumulation in Young Leaves of Tea Plant (Camellia sinensis)

There is increasing interest in the production and consumption of tea (Camellia sinensis L.) processed from purple-leaved cultivar due to their high anthocyanin content and health benefits. However, how and why seasonal changes affect anthocyanin accumulation in young tea leaves still remains obscured. In this study, anthocyanin and abscisic acid (ABA) contents in young leaves of Zifuxing 1 (ZFX1), a cultivar with new shoots turning to purple in Wuyi Mountain, a key tea production region in China, were monitored over four seasons. Young leaves produced in September were highly purplish, which was accompanied with higher anthocyanin and ABA contents. Among the environmental factors, the light intensity in particular was closely correlated with anthocyanin and ABA contents. A shade experiment also indicated that anthocyanin content significantly decreased after 168 h growth under 75% shade, but ABA treatment under the shade conditions sustained anthocyanin content. To confirm the involvement of ABA in the modulation of anthocyanin accumulation, anthocyanin, carotenoids, chlorophyll, ABA, jasmonic acid (JA), and salicylic acid (SA) in the young leaves of four cultivars, including ZFX1, Zijuan (ZJ), wherein leaves are completely purple, Rougui (RG) and Fudingdabaicha (FDDB) wherein leaves are green, were analyzed, and antioxidant activities of the leaf extracts were tested. Results showed that ABA, not other tested hormones, was significantly correlated with anthocyanin accumulation in the purple-leaved cultivars. Cultivars with higher anthocyanin contents exhibited higher antioxidant activities. Subsequently, ZFX1 plants were grown under full sun and treated with ABA and fluridone (Flu), an ABA inhibitor. ABA treatment elevated anthocyanin level but decreased chlorophyll contents. The reverse was true to those treated with Flu. To pursue a better understanding of ABA involvement in anthocyanin accumulation, RNA-Seq was used to analyze transcript differences among ABA- or Flu-treated and untreated ZFX1 plants. Results indicated that the differentially expressed genes in ABA or Flu treatment were mainly ABA signal sensing and metabolism-related genes, anthocyanin accumulation-related genes, light-responsive genes, and key regulatory MYB transcription factors. Taking all the results into account, a model for anthocyanin accumulation in ZFX1 cultivar was proposed: high light intensity caused reactive oxygen stress, which triggered the biosynthesis of ABA; ABA interactions with transcription factors, such as MYB-enhanced anthocyanin biosynthesis limited chlorophyll and carotenoid accumulation; and transport of anthocyanin to vacuoles resulting in the young leaves of ZFX1 with purplish coloration. Further research is warranted to test this model.

Proanthocyanidins Delay Fruit Coloring and Softening by Repressing Related Gene Expression during Strawberry (Fragaria × ananassa Duch.) Ripening

Proanthocyanidins (PAs), also known as condensed tannins, are widespread throughout the plant kingdom, presenting diverse biological and biochemical activities. Being one of the most abundant groups of natural polyphenolic antioxidant, PAs are applied to improve plant tolerance to (a)biotic stresses and delay the senescence of fruit by scavenging the reactive oxygen species (ROS) and enhancing antioxidant responses. The effects of PAs on coloring and softening of strawberries (Fragaria × ananassa Duch.), a worldwide demanded edible fruit and typical material for studying non-climacteric fruit ripening, were firstly assessed in this work. The results showed that exogenous PAs delayed the decrease in fruit firmness and anthocyanins accumulation but improved the fruit skin brightness. Strawberries treated with PAs had similar total soluble solids, total phenolics, and total flavonoids, but lower titratable acidity content. Moreover, the contents of endogenous PAs, abscisic acid and sucrose, were somehow increased by PA treatment, while no obvious change was found in fructose and glucose content. In addition, the anthocyanin- and firmness-related genes were significantly repressed, while the PA biosynthetic gene (anthocyanin reductase, ANR) was highly up-regulated by PA treatment at the key point for fruit softening and coloring. In summary, the results presented in this study suggest that PAs slow down strawberry coloration and softening by inhibiting the expression of related genes, which could be helpful for a better understanding of the biological role of PAs and provide a new strategy to regulate strawberry ripening.

Transcriptional networks orchestrating red and pink testa color in peanut

BACKGROUND

Testa color is an important trait of peanut (Arachis hypogaea L.) which is closely related with the nutritional and commercial value. Pink and red are main color of peanut testa. However, the genetic mechanism of testa color regulation in peanut is not fully understood. To elucidate a clear picture of peanut testa regulatory model, samples of pink cultivar (Y9102), red cultivar (ZH12), and two RNA pools (bulk red and bulk pink) constructed from F₄ lines of Y9102 x ZH12 were compared through a bulk RNA-seq approach.

RESULTS

A total of 2992 differential expressed genes (DEGs) were identified among which 317 and 1334 were up-regulated and 225 and 1116 were down-regulated in the bulk red-vs-bulk pink RNA pools and Y9102-vs-ZH12, respectively. KEGG analysis indicates that these genes were divided into significantly enriched metabolic pathways including phenylpropanoid, flavonoid/anthocyanin, isoflavonoid and lignin biosynthetic pathways. Notably, the expression of the anthocyanin upstream regulatory genes PAL, CHS, and CHI was upregulated in pink and red testa peanuts, indicating that their regulation may occur before to the advent of testa pigmentation. However, the differential expression of down-stream regulatory genes including F3H, DFR, and ANS revealed that deepening of testa color not only depends on their gene expression bias, but also linked with FLS inhibition. In addition, the down-regulation of HCT, IFS, HID, 7-IOMT, and I2'H genes provided an alternative mechanism for promoting anthocyanin accumulation via perturbation of lignin and isoflavone pathways. Furthermore, the co-expression module of MYB, bHLH, and WRKY transcription factors also suggested a fascinating transcriptional activation complex, where MYB-bHLH could utilize WRKY as a co-option during the testa color regulation by augmenting anthocyanin biosynthesis in peanut.

CONCLUSIONS

These findings reveal candidate functional genes and potential strategies for the manipulation of anthocyanin biosynthesis to improve peanut varieties with desirable testa color.

Identification of Candidate Genes Associated with Pulp Color by Transcriptomic Analysis of 'Huaxiu' Plum (Prunus salicina Lindl.) during Fruit-Ripening

The plum (Prunus salicina Lindl.) is one of the traditional and economically important stone fruit trees in China. Anthocyanins are important pigments in plums. However, little is known about the molecular mechanisms underlying anthocyanin accumulation in plum fruits, which has hindered research on the molecular mechanism of its utilization. Our research shows that the chlorophyll content was gradually decreased and the contents of anthocyanin and flavonoid increased during the coloring process of the pulp in 'Huaxiu' plums (P. salicina). Then, the RNA-Seq technique was used to analyze the transcriptome of pulp color changes with three different stages (yellow, orange, and red) in the 'Huaxiu' plum (P. salicina). A total of 57,119 unigenes with a mean length of 953 bp were generated, and 61.6% of them were annotated to public databases. The Gene Ontology (GO) database assigned 21,438 unigenes with biological process, cellular components, and molecular function. In addition, 32,146 unigenes were clustered into 25 categories for functional classification by the COG database, and 7595 unigenes were mapped to 128 KEGG pathways by the KEGG pathway database. Of these, 1095 (YS-versus-OS), 4947 (YS-versus-RS), and 3414 (OS-versus-RS) genes were significantly expressed differentially between two coloration stages. The GO and KEGG pathway enrichment analysis revealed that 20 and 1 differentially expressed genes (DEG) are involved in flavonoid biosynthesis and anthocyanin biosynthesis, respectively. Finally, we mainly identified three structural genes as candidate genes. The transcriptome information in this study provide a basis for further studies of pulp colors in plum and contribute to our understanding of the molecular mechanisms underlying anthocyanin biosynthesis in pulp.

Antioxidant processes involving epicatechin decreased symptoms of pine wilt disease

Since the pine wood nematode (PWN, Bursaphelenchus xylophilus) invasion of Northeast China, both symptomatic and asymptomatic PWN carriers have been found. Asymptomatic PWN carriers, which are more dangerous than symptomatic carriers, constitute a source of infection in the following spring. The simultaneous presence of symptomatic and asymptomatic PWN carriers indicates that Pinus koraiensis has different tolerance levels to PWN. In this study, validity of susceptibility testing discovered differential types of P. koraiensis including Latent Reservoirs, Low Susceptibles, High Susceptibles and Bell Ringers. Among those types, the Low Susceptibles and Latent Reservoirs were asymptomatic PWN carriers, and Latent Reservoirs were the most dangerous. Transcriptome and metabolomic data showed that 5 genes (3 ans and 2 anr gene) involved in the epicatechin (EC) synthesis pathway were significantly upregulated, which increased the content of EC antioxidants in Latent Reservoirs. Hydrogen peroxide (H₂O₂) staining and content determination showed that the hypersensitive response (HR) and H₂O₂, which functions as a signaling molecule in systemic acquired resistance, decreased in Latent Reservoirs. However, low contents of EC and high contents of H₂O₂ were found in the High Susceptibles of P. koraiensis. RT-PCR results showed that the expression of ans and anr was upregulated together only in Latent Reservoirs. These results show that the susceptibility of P. koraiensis to PWN differed among different individuals, although no resistant individuals were found. Latent Reservoirs, in which more PWNs resided without visible symptoms via prolonged incubation period, inhibited the symptoms caused by H₂O₂ because of increased contents of the EC antioxidants.

Integrated transcriptome and metabolome analysis reveals the anthocyanin biosynthesis mechanisms in blueberry (Vaccinium corymbosum L.) leaves under different light qualities

INTRODUCTION

Blueberry (Vaccinium corymbosum L.) is a popular fruit with an abundance of anthocyanins in its leaves and fruits. Light is one of the pivotal environmental elements that affects plant growth and development, but the regulatory mechanism between light quality and anthocyanin formation is poorly understood.

METHODS

An integrated transcriptome and metabolome analysis was performed to investigate the effects of white (control), blue (B), red (R), and red/blue (60R/40B) light on blueberry growth and reveal the potential pathway controlling anthocyanin biosynthesis in blueberry leaves.

RESULTS

The anthocyanin content was significantly improved by the blue and red/blue light when compared with white light, whereas there was a significant reduction in the photosynthesis under the blue light, showing an inverse trend to that of anthocyanin accumulation. Transcriptomic analysis resulted in the assembly of 134,709 unigenes. Of these, 22 were differentially expressed genes (DEGs) that participate in the anthocyanin biosynthesis pathway, with the majority being significantly up-regulated under the blue light. Most of the photosynthesis-related genes that were down-regulated were expressed during anthocyanin accumulation. Targeted metabolome profiling identified 44 metabolites associated with anthocyanin biosynthesis. The contents of most of these metabolites were higher under blue light than the other light conditions, which was consistent with the transcriptome results. The integrated transcriptome and metabolome analysis suggested that, under blue light, leucoanthocyanidin dioxygenase (LDOX), O-methyltransferase (OMT), and UDP-glucose flavonoid glucosyltransferase (UFGT) were the most significantly expressed, and they promoted the synthesis of cyanidin (Cy), malvidin (Mv), and pelargonidin (Pg) anthocyanidins, respectively. The expression levels of dihydroflavonol 4-reductase (DFR) and OMT, as well as the accumulation of delphinidin (Dp), peonidin (Pn), and petunidin (Pt), were significantly increased by the red/blue light.

DISCUSSION

The blue and red/blue lights promoted anthocyanin biosynthesis via inducing the expression of key structural genes and accumulation of metabolites involved in anthocyanin synthesis pathway. Moreover, there was a possible feedback regulating correlation between anthocyanin biosynthesis and photosynthesis under different light qualities in blueberry leaves. This study would provide a theoretical basis for elucidating the underlying regulatory mechanism of anthocyanin biosynthesis of V. corymbosum.

Transcriptomic and Metabolomic Analyses Providing Insights into the Coloring Mechanism of Docynia delavayi

The metabolome and transcriptome profiles of three different variations of mature Docynia delavayi fruit were synthesized to reveal their fruit color formation mechanism. A total of 787 secondary metabolites containing 149 flavonoid metabolites, most of which were flavonoids and flavonols, were identified in the three variations using ultra performance liquid chromatography- tandem mass spectrometry (UPLC-MS/MS), and we found that the secondary metabolites cyanidin-3-O-galactoside and cyanidin-3-O-glucoside were the major coloring substances in D. delavayi. This was associated with the significant upregulation of the structural genes F3H and F3′H in the anthocyanin synthesis pathway and the control genes WRKY, MYB, bZIP, bHLH, and NAC in RP. F3′H expression may play a significant role in the selection of components for anthocyanin synthesis. Our results contribute to breeding and nutritional research in D. delavayi and provide insight into metabolite studies of the anthocyanin biosynthetic pathway.

The MdBBX22-miR858-MdMYB9/11/12 module regulates proanthocyanidin biosynthesis in apple peel

Proanthocyanidins (PAs) have antioxidant properties and are beneficial to human health. The fruit of apple (Malus × domestica Borkh.), especially the peel, is rich in various flavonoids, such as PAs, and thus is an important source of dietary antioxidants. Previous research on the regulation of PAs in apple has mainly focussed on the transcription level, whereas studies conducted at the post-transcriptional level are relatively rare. In this study, we investigated the function of mdm-miR858, a miRNA with multiple functions in plant development, in the peel of apple fruit. We showed that mdm-miR858 negatively regulated PA accumulation by targeting MdMYB9/11/12 in the peel. During fruit development, mdm-miR858 expression was negatively correlated with MdMYB9/11/12 expression and PA accumulation. A 5'-RACE experiment, GUS staining assays and transient luminescent assays indicated that mdm-miR858 cleaved and inhibited the expression of MdMYB9/11/12. Overexpression of mdm-miR858 in apple calli, tobacco and Arabidopsis reduced the accumulation of PAs induced by overexpression of MdMYB9/11/12. Furthermore, we found that MdBBX22 bound to the mdm-miR858 promoter and induced its expression. Overexpression of MdBBX22 induced the expression of mdm-miR858 to inhibit the accumulation of PAs in apple calli overexpressing MdMYB9/11/12. Under light stress, MdBBX22 induced mdm-miR858 expression to inhibit PA accumulation and thereby indirectly enhanced anthocyanin synthesis in the peel. The present results revealed that the MdBBX22-miR858-MdMYB9/11/12 module regulates PA accumulation in apple. The findings provide a reference for further studies of the regulatory mechanism of PA accumulation and the relationship between PAs and anthocyanins.

Gb_ANR-47 Enhances the Resistance of Gossypium barbadense to Fusarium oxysporum f. sp. vasinfectum (FOV) by Regulating the Content of Proanthocyanidins

Anthocyanidin reductase (ANR) is an important regulator of flavonoid metabolism, and proanthocyanidins, the secondary metabolites of flavonoids, play an important role in the response of plants to pathogenic stress. Therefore, in this study, the expression analysis of the ANR gene family of Gossypium barbadense after inoculation with Fusarium oxysporum f. sp. vasinfectum (FOV) was performed at different time points. It was found that Gb_ANR-47 showed significant differences in the disease-resistant cultivar 06-146 and the susceptible cultivar Xinhai 14, as well as in the highest root expression. It was found that the expression of Gb_ANR-47 in the resistant cultivar was significantly higher than that in the susceptible cultivar by MeJA and SA, and different amounts of methyl jasmonate (MeJA) and salicylic acid (SA) response elements were found in the promoter region of Gb_ANR-47. After silencing GbANR-47 in 06-146 material by VIGS technology, its resistance to FOV decreased significantly. The disease severity index (DSI) was significantly increased, and the anthocyanin content was significantly decreased in silenced plants, compared to controls. Our findings suggest that GbANR-47 is a positive regulator of FOV resistance in Gossypium barbadense. The research results provide an important theoretical basis for in-depth analysis of the molecular mechanism of GbANR-47 and improving the anti-FOV of Gossypium barbadense.

Metabolome and transcriptome profiling reveal regulatory network and mechanism of flavonoid biosynthesis during color formation of Dioscorea cirrhosa L

Dioscorea cirrhosa is a plant that is used as a dye as well as in medicine. Many metabolites with pharmacological activity exist in the tubers of D. cirrhosa. However, little is known about the mechanism regulating biosynthesis in these metabolites. In this study, transcriptome and metabolome profiling were performed in four color tubers. A total of 531 metabolites, including 62 flavonoids, were identified. Epicatechin and proanthocyanin B2 were the key metabolites that exhibited high content levels in the four tubers. These metabolites were divided into nine classes with distinct change patterns. A total of 22,865 differentially expressed genes (DEGs) were identified by transcriptome analysis. Among these DEGs, we identified 67 candidate genes related to the flavonoid biosynthesis pathway and three genes that played pivotal roles in proanthocyanin (PA) synthesis. A weighted gene co-expression network analysis (WGCNA) revealed that the two modules, "MEblue" and "MEblack," were two key gene sets strongly associated with phenylpropanoid and flavonoid biosynthesis. We also found that the plant hormone signal transduction biological process exhibited activity in the late stage of tuber color formation. Additionally, we identified 37 hub transcript factors related to flavonoid biosynthesis, of which 24 were found to be highly associated with flavonoid pathway genes. In addition to the MYB-bHLH-WD40 (MBW) genes, we found that the plant hormone gene families exhibited high expression levels. This study provides a reference for understanding the synthesis of D. cirrhosa tuber metabolites at the molecular level and provides a foundation for the further development of D. cirrhosa related plant pigments as well as its further use in the pharmaceutical industry.

Metabolomic and Transcriptomic Profiling Uncover the Underlying Mechanism of Color Differentiation in Scutellaria baicalensis Georgi. Flowers

Scutellaria baicalensis Georgi. (Chinese skullcap or Huang-qin) is an extremely crucial medicinal plant in the Labiate family, and the color of its flowers naturally appears purple. However, during the long-term cultivation of S. baicalensis, very few plants of S. baicalensis also present white and purple-red flower colors under the same ecological conditions. However, the complex metabolic and transcriptional networks underlying color formation in white, purple-red, and purple flowers of S. baicalensis remain largely unclarified. To gain an insight into this issue, we conducted transcriptome and metabolomic profiling to elucidate the anthocyanin synthesis metabolic pathway in the flowers of S. baicalensis, and to identify the differentially expressed candidate genes potentially involved in the biosynthesis of anthocyanins. The results showed that 15 anthocyanins were identified, among which cyanidin 3-rutinoside and delphin chloride were the primary anthocyanins, and accumulation was significantly related to the flower color changes of S. baicalensis. Furthermore, the down-regulation of SbDFR (Sb02g31040) reduced the anthocyanin levels in the flowers of S. baicalensis. The differential expression of the Sb3GT (Sb07g04780 and Sb01g72290) gene in purple and purple-red flowers affected anthocyanin accumulation, suggesting that anthocyanin levels were closely associated with the expression of SbDFR and Sb3GT, which play important roles in regulating the anthocyanin biosynthesis process of S. baicalensis flowers. Transcriptomic analysis revealed that transcription factors WRKY, bHLH, and NAC were also highly correlated with anthocyanin accumulation, especially for NAC35, which positively regulated SbDFR (Sb02g31040) gene expression and modulated anthocyanin biosynthesis in flower color variation of S. baicalensis. Overall, this study presents the first experimental evidence for the metabolomic and transcriptomic profiles of S. baicalensis in response to flower coloration, which provides a foundation for dynamic metabolic engineering and plant breeding, and to understand floral evolution in S. baicalensis plants.

A single-base insertion in BoDFR1 results in loss of anthocyanins in green-leaved ornamental kale

A CRISPR/Cas9-based knockout assay verified that BoDFR1 drives anthocyanin accumulation in ornamental kale and that BoDFR2, an ortholog of BoDFR1, is redundant. Anthocyanins are widely distributed in nature and give plants their brilliant colors. Leaf color is an important trait for ornamental kale. In this study, we measured anthocyanin contents and performed transcriptome deep sequencing (RNA-seq) of leaves from pink and green ornamental kale. We observed substantial differences in the expression levels of the two DIHYDROFLAVONOL 4-REDUCTASE-encoding genes BoDFR1 (Bo9g058630) and its ortholog BoDFR2 (Bo2g116380) between green-leaved and pink-leaved kale by RNA-seq and RT-qPCR. We cloned and sequenced BoDFR1 and BoDFR2 from both types of kale. We identified a 1-bp insertion in BoDFR1 and a 2-bp insertion in BoDFR2 in green-leaved kale compared to the sequences obtained from pink-leaved kale, both mapping to the second exon of their corresponding gene and leading to premature termination of translation. To confirm the genetic basis of the absence of anthocyanins in green kale, we used CRISPR/Cas9 genome editing to separately knock out BoDFR1 or BoDFR2 in the pink-leaved ornamental kale inbred line P23. We detected very low accumulation of anthocyanins in the resulting mutants Bodfr1-1 and Bodfr1-2, while Bodfr2-1 and Bodfr2-2 had anthocyanin levels comparable to those of the wild-type. We conclude that the insertion in BoDFR1, rather than that in BoDFR2, underlies the lack of anthocyanins in green-leaved ornamental kale. This work provides insight into the function of DFR and will contribute to germplasm improvement of ornamental plants.

Regulation mechanisms of flavonoids biosynthesis of Hancheng Dahongpao peels (Zanthoxylum bungeanum Maxim) at different development stages by integrated metabolomics and transcriptomics analysis

BACKGROUND

Flavonoids have strong free radical scavenging and antioxidant capacity. The high abundance of flavonoids in Chinese prickly ash peels have many benefits to human health. In this study, 'Hancheng Dahongpao', a main cultivar, was taken as materials to investigate the flavonoids biosynthesis mechanism of Zanthoxylum bungeanum Maxim at three key development stages by integration of metabolomics and transcriptomics analysis.

RESULTS

A total of 19 differentially accumulated metabolites were identified, the key flavonoids compounds were kaempferol, quercetin and their glycoside derivatives, and two major anthocyanins (peonidin O-hexoside and peonidin 3-O-glucoside). 5 gene networks/modules including 15 important candidate genes were identified, which was highly correlated with flavonoids. Among these genes, ZM-163828 and ZM-184209 were strongly correlated with kaempferol and quercetin, and ZM-125833 and ZM-97481 were controlled the anthocyanins biosynthesis. Moreover, it was shown that MYB-ZM1, MYB-ZM3, MYB-ZM5, MYB-ZM6 and MYB-ZM7 coordinately controlled flavonoids accumulation through regulating the structural genes.

CONCLUSIONS

Generally, this study systematically revealed the flavonoids metabolic pathways and candidate genes involved in flavonoids biosynthesis and laid a foundation for the potential targets for the breeding of new valuable Chinese prickly ash cultivars.

Metabolomic and transcriptomic analyses reveal the effects of self- and hetero-grafting on anthocyanin biosynthesis in grapevine

Grafting, which joins a scion from a cultivar with the stem of a rootstock from a grapevine wild relative, is commonly used in viticulture. Grafting has crucial effects on various phenotypes of the cultivar, including its phenology, biotic and abiotic resistance, berry metabolome, and coloration, but the underlying genetics and regulatory mechanisms are largely unexplored. In this study, we investigated the phenotypic, metabolomic, and transcriptomic profiles at three developmental stages (45, 75, and 105 days after flowering) of the Crimson Seedless cultivar (Vitis vinifera) grafted onto four rootstocks (three heterografts, CS/101-14, CS/SO4, and CS/110R and one self-graft, CS/CS) with own-rooted graft-free Crimson Seedless (CS) as the control. All the heterografts had a significant effect on berry reddening as early as ~45 days after flowering. The grafting of rootstocks promoted anthocyanin biosynthesis and accumulation in grape berries. The metabolomic features showed that cyanidin 3-O-glucoside, delphinidin 3-O-glucoside, malvidin 3-O-glucoside, peonidin 3-O-glucoside, and petunidin 3-O-glucoside were the pigments responsible for the purplish-red peel color. Transcriptomic analyses revealed that anthocyanin biosynthesis-related genes, from upstream (phenylalanine ammonia-lyase) to downstream (anthocyanidin 3-O-glucosyltransferase and anthocyanidin synthase), were upregulated with the accumulation of anthocyanins in the heterografted plants. At the same time, all these genes were also highly expressed and more anthocyanin was accumulated in self-grafted CS/CS samples compared with own-rooted graft-free CS samples, suggesting that self-grafting may also have promoted berry reddening in grapevine. Our results reveal global transcriptomic and metabolomic features in berry color regulation under different grafting conditions that may be useful for improving berry quality in viticulture.

An Efficient Agrobacterium-Mediated Genetic Transformation System for Persimmon (Diospyros kaki Thunb.)

Persimmon (Diospyros kaki Thunb.) is an important fruit crop in East Asia and has great commercial potential due to the high demand for fresh edible fruits or processed dried persimmon, as well as its being a source of raw materials for the chemical industry. Genetic engineering has shown great potential in persimmon fruit improvement and compensated for the limitations of conventional breeding. In this study, we developed an efficient transformation system and in vivo regeneration protocol by using the leaf disc culture of ‘Gongcheng Shuishi’ persimmon through the optimization of different basic media and hormone combinations. Based on the secondary induction system on 1/2DKW (DKW medium) + ZT (2.0 mg/L) + TDZ (0.5 mg/L) and MS (1/2 N) + ZT (2.0 mg/L) + IAA (0.1 mg/L), the callus induction rate and adventitious bud induction rate were 96.0% and 94.0%, respectively, and RNA interference of DkANR (ANR, anthocyanidin reductase) was achieved after transformation, thus resulting in a reduction in proanthocyanidin accumulation. The GFP (green fluorescent protein) fluorescence signal was visualized in the transgenic seedlings with GFP gene cotransformation. A total of 17.9% of the positive regenerated transgenic seedlings with empty vector were confirmed by both hyg gene and 35S promoter PCR analysis. Southern blotting assays showed that 20 positive transgenic persimmon seedlings were obtained from 135 regenerated transformants derived from DkANRi. Altogether, a reliable and highly efficient transformation system was achieved in persimmon, which may contribute to gene function identification and genetic improvement in the future.

Combined transcriptome and metabolome integrated analysis of Acer mandshuricum to reveal candidate genes involved in anthocyanin accumulation

The red color formation of Acer mandshuricum leaves is caused by the accumulation of anthocyanins primarily, but the molecular mechanism researches which underlie anthocyanin biosynthesis in A. mandshuricum were still lacking. Therefore, we combined the transcriptome and metabolome and analyzed the regulatory mechanism and accumulation pattern of anthocyanins in three different leaf color states. In our results, 26 anthocyanins were identified. Notably, the metabolite cyanidin 3-O-glucoside was found that significantly correlated with the color formation, was the predominant metabolite in anthocyanin biosynthesis of A. mandshuricum. By the way, two key structural genes ANS (Cluster-20561.86285) and BZ1 (Cluster-20561.99238) in anthocyanidin biosynthesis pathway were significantly up-regulated in RL, suggesting that they might enhance accumulation of cyanidin 3-O-glucoside which is their downstream metabolite, and contributed the red formation of A. mandshuricum leaves. Additionally, most TFs (e.g., MYBs, bZIPs and bHLHs) were detected differentially expressed in three leaf color stages that could participate in anthocyanin accumulation. This study sheds light on the anthocyanin molecular regulation of anthocyanidin biosynthesis and accumulation underlying the different leaf color change periods in A. mandshuricum, and it could provide basic theory and new insight for the leaf color related genetic improvement of A. mandshuricum.

Analysis of Light-Independent Anthocyanin Accumulation in Mango (Mangifera indica L.)

Light dependent anthocyanin accumulation contributes to the red pigmentation of the fruit skin of mango (Mangifera indica L.). Light-independent pigmentation has also been reported, but remains poorly characterized. In this study, the pigmentation patterns in the skin of two red mango cultivars, ‘Ruby’ and ‘Sensation’, were evaluated. Metabolomic profiling revealed that quercetin-3-O-glucoside, cyanidin-3-O-galactoside, procyanidin B1, and procyanidin B3 are the predominant flavonoid compounds in the skin of ‘Ruby’ and ‘Sensation’ fruit. Young fruit skin mainly accumulates flavonol and proanthocyanidin, while anthocyanin is mainly accumulated in the skin of mature fruit. Bagging treatment inhibited the biosynthesis of flovonol and anthocyanin, but promoted the accumulation of proanthocyanidin. Compared with ‘Sensation’, matured ‘Ruby’ fruit skin showed light red pigmentation at 120 days after full bloom (DAFB), showing a light-independent anthocyanin accumulation pattern. However, the increase of anthocyanin concentration, and the expression of key anthocyanin structural and regulatory genes MiUFGT1, MiUFGT3, and MiMYB1 in the skin of bagged ‘Ruby’ fruit versus ‘Sensation’ at 120 DAFB was very limited. There was no mutation in the crucial elements of MiMYB1 promoter between ‘Ruby’ and ‘Sensation’. We hypothesize that the light-independent anthocyanin accumulation in the skin of mature ‘Ruby’ fruit is regulated by plant hormones, and that ‘Ruby’ can be used for breeding of new more easily pigmented red mango cultivars.

Transcriptomics Integrated With Widely Targeted Metabolomics Reveals the Mechanism Underlying Grain Color Formation in Wheat at the Grain-Filling Stage

Colored wheat grains have a unique nutritional value. To elucidate the color formation mechanism in wheat seeds, comprehensive metabolomic and transcriptomic analyses were conducted on purple (Dianmai 20-1), blue (Dianmai 20-8), and white (Dianmai 16) wheat at the grain-filling stage. The results showed that the flavonoid biosynthesis pathway was closely related to grain color formation. Among the 603 metabolites identified in all varieties, there were 98 flavonoids. Forty-six flavonoids were detected in purple and blue wheat, and there were fewer flavonoids in white wheat than in colored wheat. Integrated transcriptomic and metabolomic analyses showed that gene expression modulated the flavonoid composition and content, resulting in different metabolite levels of pelargonidin, cyanidin, and delphinidin, thus affecting the color formation of wheat grains. The present study clarifies the mechanism by which pigmentation develops in wheat grains and provides an empirical reference for colored wheat breeding.

Integrated mRNA and small RNA sequencing reveals a regulatory network associated with flower color in oriental hybrid lily

Anthocyanins are one of the main components of pigments, that are responsible for a wide range of colors in plants. To clarify the regulatory mechanism of anthocyanin biosynthesis in oriental hybrid lily, UPLC/MS analysis was performed to identify the pigments in two cultivars (white and pink). Four major anthocyanins were identified in pink cultivar, and no anthocyanins were detected in white cultivar. Transcriptome and small RNA sequencing (sRNAseq) analyses were performed using tepal tissues at two floral developmental stages from the two cultivars. In total, 55,698 transcripts were assembled, among which 233 were annotated as putative anthocyanin-related transcripts. Differential expression analysis and qRT-PCR results confirmed that most of the anthocyanin-related structural genes had higher expression levels in pink cultivar than in white cultivar. Conversely, LhANR showed a significantly high expression level in white cultivar. Annotated transcription factors (TFs), including MYB activators, MYB repressors and bHLHs, that putatively inhibit or enhance the expression of anthocyanin-related genes were identified. LhMYBA1, an anthocyanin activator, was isolated, and its heterologous expression resulted in a remarkably high level of anthocyanin accumulation. Additionally, 73 differentially expressed microRNAs (miRNAs), including 23 known miRNAs, were detected through sRNAseq. The miRNA target prediction showed that several anthocyanin-related genes might be targeted by miRNAs. Expression profile analysis revealed that these miRNAs showed higher expression levels at later floral developmental stages in white cultivar than in pink cultivar. The results indicated that anthocyanin deficiency in white cultivar might be influenced by multiple levels of suppressive mechanisms, including mRNAs and sRNAs.

Comparative Metabolite and Gene Expression Analyses in Combination With Gene Characterization Revealed the Patterns of Flavonoid Accumulation During Cistus creticus subsp. creticus Fruit Development

Cistus creticus L. subsp. creticus (rockrose) is a shrub widespread in Greece and the Mediterranean basin and has been used in traditional medicine as herb tea for colds, for healing and digestive hitches, for the treatment of maladies, as perfumes, and for other purposes. Compounds from its flavonoid fraction have recently drawn attention due to antiviral action against influenza virus and HIV. Although several bioactive metabolites belonging to this group have been chemically characterized in the leaves, the genes involved in their biosynthesis in Cistus remain largely unknown. Flavonoid metabolism during C. creticus fruit development was studied by adopting comparative metabolomic and transcriptomic approaches. The present study highlights the fruit of C. creticus subsp. creticus as a rich source of flavonols, flavan-3-ols, and proanthocyanidins, all of which displayed a decreasing trend during fruit development. The majority of proanthocyanidins recorded in Cistus fruit are B-type procyanidins and prodelphinidins, while gallocatechin and catechin are the dominant flavan-3-ols. The expression patterns of biosynthetic genes and transcription factors were analyzed in flowers and throughout three fruit development stages. Flavonoid biosynthetic genes were developmentally regulated, showing a decrease in transcript levels during fruit maturation. A high degree of positive correlations between the content of targeted metabolites and the expression of biosynthetic genes indicated the transcriptional regulation of flavonoid biosynthesis during C. creticus fruit development. This is further supported by the high degree of significant positive correlations between the expression of biosynthetic genes and transcription factors. The results suggest that leucoanthocyanidin reductase predominates the biosynthetic pathway in the control of flavan-3-ol formation, which results in catechin and gallocatechin as two of the major building blocks for Cistus proanthocyanidins. Additionally, there is a decline in ethylene production rates during non-climacteric Cistus fruit maturation, which coincides with the downregulation of the majority of flavonoid- and ethylene-related biosynthetic genes and corresponding transcription factors as well as with the decline in flavonoid content. Finally, functional characterization of a Cistus flavonoid hydroxylase (F3'5'H) was performed for the first time.

Cyanidin 3-O-galactoside: A Natural Compound with Multiple Health Benefits

Cyanidin 3-O-galactoside (Cy3Gal) is one of the most widespread anthocyanins that positively impacts the health of animals and humans. Since it is available from a wide range of natural sources, such as fruits (apples and berries in particular), substantial studies were performed to investigate its biosynthesis, chemical stability, natural occurrences and content, extraction methods, physiological functions, as well as potential applications. In this review, we focus on presenting the previous studies on the abovementioned aspects of Cy3Gal. As a conclusion, Cy3Gal shares a common biosynthesis pathway and analogous stability with other anthocyanins. Galactosyltransferase utilizing uridine diphosphate galactose (UDP-galactose) and cyanidin as substrates is unique for Cy3Gal biosynthesis. Extraction employing different methods reveals chokeberry as the most practical natural source for mass-production of this compound. The antioxidant properties and other health effects, including anti-inflammatory, anticancer, antidiabetic, anti-toxicity, cardiovascular, and nervous protective capacities, are highlighted in purified Cy3Gal and in its combination with other polyphenols. These unique properties of Cy3Gal are discussed and compared with other anthocyanins with related structure for an in-depth evaluation of its potential value as food additives or health supplement. Emphasis is laid on the description of its physiological functions confirmed via various approaches.

Transcriptomic and chemical analyses to identify candidate genes involved in color variation of sainfoin flowers

BACKGROUND

Sainfoin (Onobrychis viciifolia Scop) is not only a high-quality legume forage, but also a nectar-producing plant. Therefore, the flower color of sainfoin is an important agronomic trait, but the factors affecting its flower phenotype are still unclear. To gain insights into the regulatory networks associated with metabolic pathways of coloration compounds (flavonoids or anthocyanins) and identify the key genes, we conducted a comprehensive analysis of the phenotype, metabolome and transcriptome of WF and AF of sainfoin.

RESULTS

Delphinidin, petunidin and malvidin derivatives were the main anthocyanin compounds in the AF of sainfoin. These substances were not detected in the WF of sainfoin. The transcriptomes of WF and AF in sainfoin at the S1 and S3 stages were obtained using the Illumina HiSeq4000 platform. Overall, 10,166 (4273 upregulated and 5893 downregulated) and 15,334 (8174 upregulated and 7160 downregulated) DEGs were identified in flowers at S1 and S3 stages, respectively (WF-VS-AF). KEGG pathway annotations showed that 6396 unigenes were annotated to 120 pathways and contained 866 DEGs at S1 stages, and 6396 unigenes were annotated to 131 pathways and included 1546 DEGs at the S3 stage. Nine DEGs belonging to the "flavonoid biosynthesis"and "phenylpropanoid biosynthesis" pathways involved in flower color formation were identified and verified by RT-qPCR analyses. Among these DEGs, 4CL3, FLS, ANS, CHS, DFR and CHI2 exhibited downregulated expression, and F3H exhibited upregulated expression in the WF compared to the AF, resulting in a decrease in anthocyanin synthesis and the formation of WF in sainfoin.

CONCLUSIONS

This study is the first to use transcriptome technology to study the mechanism of white flower formation in sainfoin. Our transcriptome data will be a great enrichment of the genetic information for sainfoin. In addition, the data presented herein will provide valuable molecular information for genetic breeding and provide insight into the future study of flower color polymorphisms in sainfoin.

Contribution of phenylpropanoid metabolism to plant development and plant-environment interactions

Phenylpropanoid metabolism is one of the most important metabolisms in plants, yielding more than 8,000 metabolites contributing to plant development and plant-environment interplay. Phenylpropanoid metabolism materialized during the evolution of early freshwater algae that were initiating terrestrialization and land plants have evolved multiple branches of this pathway, which give rise to metabolites including lignin, flavonoids, lignans, phenylpropanoid esters, hydroxycinnamic acid amides, and sporopollenin. Recent studies have revealed that many factors participate in the regulation of phenylpropanoid metabolism, and modulate phenylpropanoid homeostasis when plants undergo successive developmental processes and are subjected to stressful environments. In this review, we summarize recent progress on elucidating the contribution of phenylpropanoid metabolism to the coordination of plant development and plant-environment interaction, and metabolic flux redirection among diverse metabolic routes. In addition, our review focuses on the regulation of phenylpropanoid metabolism at the transcriptional, post-transcriptional, post-translational, and epigenetic levels, and in response to phytohormones and biotic and abiotic stresses.

Transcriptome profiling provides insights into the fruit color development of wild Lycium ruthenicum Murr. from Qinghai-Tibet Plateau

Lycium ruthenicum Murr. is an important ecological and economic species in the Qaidam Basin of Qinghai-Tibet Plateau. Its black fruits (BF) are rich in anthocyanins, which have health-promoting properties for humans and thus provide nutritional benefits for this plant. Although the fruit quality of natural white fruit (WF) is affected by the disappearance of pigmentation in phenotypes, this phenomenon provides an opportunity to unravel the complex color metabolic networks. In this study, anthocyanin profiling confirmed that WF was formed due to anthocyanin loss. Transcriptome analysis of BF and WF revealed 101,466 unigenes, 261 of which were identified as the putative homologs of color-related genes in other species. Genes encoding the enzymes involved in flavonoid biosynthesis were also identified systematically. The structural gene expression levels of chalcone synthase (CHS), chalcone isomerase (CHI), flavonoid 3'5'-hydroxylase (F3'5'H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and anthocyanidin 3-O-glucosyltransferase (UFGT) were highly similar and significantly positively correlated with anthocyanin accumulation rate in BF. In particular, F3'5'H, UFGT, ANS, and DFR expression levels in BF were 2391, 119, 96, and 85 times higher than those in WF at S3 (35 days after anthesis), respectively. This result strongly suggests that the low expression of these genes in WF is responsible for the anthocyanin loss. Meanwhile, the expression patterns of the anthocyanin regulatory genes were also investigated by qRT-PCR. Mass sequencing data were obtained and annotated by deep sequencing and provided a platform for future function and molecular biological research on L. ruthenicum Murr.

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

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

Integrated metabolomic and transcriptomic analysis of the anthocyanin regulatory networks in Salvia miltiorrhiza Bge. flowers

BACKGROUND

The objectives of this study were to reveal the anthocyanin biosynthesis metabolic pathway in white and purple flowers of Salvia miltiorrhiza using metabolomics and transcriptomics, to identify different anthocyanin metabolites, and to analyze the differentially expressed genes involved in anthocyanin biosynthesis.

RESULTS

We analyzed the metabolomics and transcriptomics data of S. miltiorrhiza flowers. A total of 1994 differentially expressed genes and 84 flavonoid metabolites were identified between the white and purple flowers of S. miltiorrhiza. Integrated analysis of transcriptomics and metabolomics showed that cyanidin 3,5-O-diglucoside, malvidin 3,5-diglucoside, and cyanidin 3-O-galactoside were mainly responsible for the purple flower color of S. miltiorrhiza. A total of 100 unigenes encoding 10 enzymes were identified as candidate genes involved in anthocyanin biosynthesis in S. miltiorrhiza flowers. Low expression of the ANS gene decreased the anthocyanin content but enhanced the accumulation of flavonoids in S. miltiorrhiza flowers.

CONCLUSIONS

Our results provide valuable information on the anthocyanin metabolites and the candidate genes involved in the anthocyanin biosynthesis pathways in S. miltiorrhiza.

Changes in the Proanthocyanidin Composition and Related Gene Expression in Bilberry (Vaccinium myrtillus L.) Tissues

Berries of genus Vaccinium are rich in flavonoids and proanthocyanidins (PAs). We studied the PA composition and biosynthesis in bilberry (Vaccinium myrtillus L.) tissues and during fruit development. Soluble PAs, analyzed by UHPLC-MS/MS, were most abundant in stem and rhizome with the mean PA polymerization level varying between 4 and 6 in all tissues. Both A- and B-type PAs were present in all tissues. Procyanidin subunits were more common than prodelphinidin subunits in PAs. During fruit ripening, the amount of procyanidin subunits decreased while prodelphinidin subunits and F3'5'H expression increased, indicating a shift in biosynthesis toward the delphinidin branch of the flavonoid pathway. Epicatechin was the most abundant flavan-3-ol in all tissues. Expression of ANR and three isolated LAR genes, analyzed by qRT-PCR, showed connection to accumulation of PAs and flavan-3-ols biosynthesized from different flavonoid branches. Insoluble PAs accumulated during berry development, suggesting that PAs are not recycled after biosynthesis.

Mulberry genes MnANR and MnLAR confer transgenic plants with resistance to Botrytis cinerea

Proanthocyanidins (PAs) are major defense-related phenolics in mulberry, but the mechanism underlying their biosynthesis remains uncharacterized. In this study, the relationship between the expression of genes encoding anthocyanidin reductase (ANR) or leucoanthocyanidin reductase (LAR) and PA biosynthesis was investigated in white and red mulberry fruits. In ripening fruits, the MnANR and MnLAR transcription levels tended to decrease, whereas the catechin and epicatechin contents initially increased and then decreased. In contrast, the PA content exhibited a clearly different trend. The ectopic expression of MnANR and MnLAR in tobacco increased the resistance to Botrytis cinerea, as evidenced by the less extensive disease symptoms of the transgenic plants compared with the wild-type plants. In vitro experiments revealed that the transgenic tobacco crude leaf extract had an obvious inhibitory effect on B. cinerea. Moreover, the ectopic expression of MnANR and MnLAR in tobacco inhibited the expression of anthocyanin biosynthesis genes, resulting in decreased anthocyanin contents in flowers. The results of this study may be useful for elucidating the mechanism underlying PA biosynthesis. Furthermore, ANR and LAR represent potential targets for improving the resistance of mulberry and related plant species to B. cinerea.

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.

Integrated Metabolome and Transcriptome Analysis Uncovers the Role of Anthocyanin Metabolism in Michelia maudiae

Michelia maudiae Dunn is one of the important ornamental plants in the Magnoliaceae family, and the color of its flowers usually appears naturally pure white. The discovery of a rubellis flower named M. maudiae Dunn var. rubicunda provides an opportunity to reveal the metabolism of the flavonoids and anthocyanins of this “early angiosperm” plant. Combined metabolome and transcriptome analyses were applied using white and rubellis mutant tepals. Seven stages have been divided for flower development, and forty-eight differentially altered metabolites were identified between white and rubellis tepals at a later stage. The major anthocyanins including peonidin O-hexoside, cyanidin O-syringic acid, cyanidin 3,5-O-diglucoside, cyanidin 3-O-glucoside, and pelargonidin 3-O-glucoside were upregulated over 157-fold in the mutant. Conversely, the highly significant accumulation of the colorless procyanidin or the slightly yellow epicatechin and catechin was found in white flowers. Putative homologues of color-related genes involved in the phenylpropanoid and flavonoid biosynthesis pathway were identified in the transcriptome. The increasing expression of dihydroflavonol 4-reductase (DFR) might play an important role in the occurrence of rubellis pigments, while the overexpression of anthocyanidin reductase (ANR) in white flowers may promote the biosynthesis of proanthocyanidins. Additionally, several coloration-related repressor R2R3-MYB transcription factors showed different expression levels in the tepals of the rubellis mutant. This study provides a comprehensive analysis relating color compounds to gene expression profiles of the Magnoliids plant M. maudiae. The newly generated information will provide a profound effect on horticultural applications of Magnoliaceae.

Amplification of miniature inverted-repeat transposable elements and the associated impact on gene regulation and alternative splicing in mulberry (Morus notabilis)

Background

Miniature inverted-repeat transposable elements (MITEs) are common in eukaryotic genomes, and are important for genomic evolution.

Results

In the present study, the identification of MITEs in the mulberry genome revealed 286,122 MITE-related sequences, including 90,789 full-length elements. The amplification of mulberry MITEs and the influence of MITEs on the evolution of the mulberry genome were analyzed. The timing of MITE amplifications varied considerably among the various MITE families. Fifty-one MITE families have undergone a single round of amplification, while the other families developed from multiple amplifications. Most mulberry MITEs were inserted near genes and some could regulate gene expression through small RNAs. An analysis of transgenic plants indicated that MITE insertions can upregulate the expression of a target gene. Moreover, MITEs are frequently associated with alternative splicing events (exonizations).

Conclusion

The data presented herein provide insights into the generation of MITEs as well as their impact on gene regulation and evolution in mulberry.

Electronic supplementary material

The online version of this article (10.1186/s13100-019-0169-0) contains supplementary material, which is available to authorized users.

Identification of leucoanthocyanidin reductase and anthocyanidin reductase genes involved in proanthocyanidin biosynthesis in Malus crabapple plants

Proanthocyanidins (PAs) from plants are a nutritionally valuable component of the human diet and play important roles in defense against pests and diseases. PAs are products of the flavonoid pathway, which also leads to the production of anthocyanins and flavonols. The enzymes leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) are involved in PA biosynthesis. The PA biosynthetic pathway has been characterized in several plant species, but the relationship between its expression and PA accumulation in Malus crabapple remains unclear. Here, we cloned the LAR genes MrLAR1, 2, and the ANR genes MrANR1, 2, from the red leaved Malus crabapple cultivar 'Royalty'. The contents of PAs and the expression levels of the LAR and ANR genes were investigated in different organs of the two crabapple cultivars. The transcript levels of two LAR genes and two ANR genes correlated with the contents of the catechin and epicatechin, which are proanthocyanidin precursors. Over-expression of the MrLAR1, 2 and MrANR1, 2 in tobacco (Nicotiana tabacum) promoted the accumulation of PAs, while transient silencing of their expression in crabapple resulted in reduced PA levels. In addition, a negative correlation between quercetin, anthocyanin, and PA biosynthesis was also found during crabapple leaf and fruit peel development. We also found that MrLAR1 and 2 may contribute to epicatechin biosynthesis. In summary, the LAR and ANR genes are critical factors in PA biosynthesis, and there is competition between the quercetin, anthocyanin, and PA biosynthetic pathways during leaf and fruit peel development in Malus crabapple.

Transcriptome Analysis Reveals the Accumulation Mechanism of Anthocyanins in Buckwheat (Fagopyrum esculentum Moench) Cotyledons and Flowers

Buckwheat (Fagopyrum esculentum) is a valuable crop which can produce multiple human beneficial secondary metabolites, for example, the anthocyanins in sprouts and flowers. However, as the predominant group of visible polyphenols in pigmentation, little is known about the molecular mechanisms underlying the anthocyanin biosynthesis within buckwheat. In this study, a comparative transcriptome analysis of green and red common buckwheat cultivars was carried out through RNA sequencing. Overall, 3727 and 5323 differently expressed genes (DEGs) were identified in flowers and cotyledons, respectively. Through GO and KEGG analysis, we revealed that DEGs in flowers and cotyledons are predominately involved in biosynthesis of anthocyanin. A total of 42 unigenes encoding 11 structural enzymes of the anthocyanin biosynthesis were identified as DEGs. We also identified some transcription factor families involved in the regulation of anthocyanin biosynthesis. Real-time qPCR validation of candidate genes was performed in flowers and cotyledons, and the results suggested that the high expression level of structural genes involved in anthocyanin biosynthetic pathway promotes anthocyanin accumulation. Our results provide the insight understanding for coloration of red common buckwheat.

PpMYB15 and PpMYBF1 Transcription Factors Are Involved in Regulating Flavonol Biosynthesis in Peach Fruit

Flavonoids are major polyphenol compounds in plants and contribute substantially to the health-promoting benefits of fruit and vegetables. Peach is rich in polyphenols with flavonols as the main flavonoids. To investigate the regulation of flavonol biosynthesis in peach fruit, two R2R3-MYB transcription factor (TF) genes, PpMYB15 and PpMYBF1, were isolated and characterized. Sequence analysis revealed that the PpMYB15 and PpMYBF1 proteins are members of the flavonol clade of the R2R3-MYB family. Real-time quantitative PCR analysis showed that PpMYB15 and PpMYBF1 transcript levels correlated well with the flavonol content and the expression of flavonol synthase ( PpFLS1) in different fruit samples. Dual-luciferase assays indicated that both PpMYB15 and PpMYBF1 could trans-activate promoters of flavonoid biosynthesis genes, including chalcone synthase ( PpCHS1), chalcone isomerase ( PpCHI1), flavanone 3-hydroxylase ( PpF3H), and PpFLS1. Transient overexpression of 35S::PpMYB15 or 35S::PpMYBF1 both triggered flavonol biosynthesis but not anthocyanin and proanthocyanidin biosynthesis in tobacco leaves. In transgenic tobacco flowers, overexpression of 35S::PpMYB15 or 35S::PpMYBF1 caused a significant increase in flavonol levels and significantly reduced anthocyanin accumulation, resulting in pale-pink or pure white flowers. These results suggest that PpMYB15 and PpMYBF1 are functional flavonol-specific positive regulators in peach fruit and are important candidates for biotechnological engineering flavonol biosynthesis in plants.

AaMYB3 interacts with AabHLH1 to regulate proanthocyanidin accumulation in Anthurium andraeanum (Hort.)-another strategy to modulate pigmentation

Proanthocyanidins (PAs), also known as "condensed tannins", are colorless metabolites produced through the flavonoid pathway that are involved in stress resistance in plants. Because PAs are involved in the anthocyanin biosynthetic pathway, they play a role in the modification of pigmentation conferred by anthocyanins in ornamental organs. In this study, we isolated the gene and functionally characterized an R2R3-MYB transcription factor (TF), AaMYB3, and a basic helix-loop-helix TF, AabHLH1, from Anthurium andraeanum (Hort.), a typical tropical flower. AaMYB3 is primarily expressed in the spathe and negatively correlates with anthocyanin accumulation. A complementation test in an Arabidopsis tt8 mutant showed that AabHLH1 successfully restores the PA-deficient seed coat phenotype. The ectopic overexpression of AaMYB3 alone or its coexpression with AabHLH1 in transgenic tobacco resulted in light pink or even pale-pink corolla limbs by reducing their anthocyanin levels and greatly enhancing their accumulation of PAs. This overexpression of the anthurium TF genes upregulated the late anthocyanin enzyme-encoding genes (NtDFR and NtANS) and the key PA genes (NtLAR and NtANR) in transgenic tobacco. The interaction between AaMYB3 and the AabHLH1 protein was confirmed using yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. In the developing red spathes of the cultivars "Vitara" and "Tropical", the expression of AaMYB3 was closely linked to PA accumulation, and AaMYB3 was coexpressed with AaCHS, AaF3H, AaDFR, AaANS, AaLAR, and AaANR. The expression pattern of AabHLH1 was similar to that of AaF3'H. Our results suggest that AaMYB3 and AabHLH1 are involved in the regulation of PA biosynthesis in anthurium and could potentially be used to metabolically engineer PA biosynthesis in plants.