Anthocyanin Accumulation In Fruit Research Articles

A 224-bp Indel in the Promoter of PeMYB114 Accounts for Anthocyanin Accumulation of Skin in Passion Fruit (Passiflora spp.).

Passion fruit (Passiflora spp.) is an important fruit tree in the family Passifloraceae. The color of the fruit skin, a significant agricultural trait, is determined by the content of anthocyanin in passion fruit. However, the regulatory mechanisms behind the accumulation of anthocyanin in different passion fruit skin colors remain unclear. In the study, we identified and characterized a R2R3-MYB transcription factor, PeMYB114, which functions as a transcriptional activator in anthocyanin biosynthesis. Yeast one-hybrid system and dual-luciferase analysis showed that PeMYB114 could directly activate the expression of anthocyanin structural genes (PeCHS and PeDFR). Furthermore, a natural variation in the promoter region of PeMYB114 alters its expression. PeMYB114purple accessions with the 224-bp insertion have a higher anthocyanin level than PeMYB114yellow accessions with the 224-bp deletion. The findings enhance our understanding of anthocyanin accumulation in fruits and provide genetic resources for genome design for improving passion fruit quality.

FvWRKY50 is an important gene that regulates both vegetative growth and reproductive growth in strawberry.

The WRKY transcription factors play important roles in plant growth and resistance, but only a few members have been identified in strawberry. Here we identified a WRKY transcription factor, FvWRKY50, in diploid strawberry which played essential roles in strawberry vegetative growth, and reproductive growth. Knocking out FvWRKY50 by genome editing accelerated flowering time and leaf senescence but delayed anthocyanin accumulation in fruit. Further analysis showed that FvWRKY50 acted as a transcriptional repressor to negatively regulate the expression of flowering- and leaf senescence-related genes, including FvFT2, FvCO, FvFT3, and FvSAUR36. Notably, FvWRKY50 directly upregulated the expression of FvCHI and FvDFR by binding their promoter under normal conditions, but at low temperature FvWRKY50 was phosphorylated by FvMAPK3 and then induced protein degradation by ubiquitination, delaying anthocyanin accumulation. In addition, the homozygous mutant of FvWRKY50 was smaller while the biallelic mutant showed normal size. These new findings provide important clues for us to further reveal the regulatory mechanisms of strawberry growth and fruit ripening.

Colorful hues: insight into the mechanisms of anthocyanin pigmentation in fruit.

Anthocyanin is a vital indicator for both fruit nutritional and commercial value. Anthocyanin accumulation is a surprisingly complicated process mediated by multiple networks associated with genetic, developmental, hormonal, and environmental factors. Transcriptional regulation along with epigenetic regulation constitutes the dominant molecular framework for anthocyanin biosynthesis. Here, we focus on current knowledge on regulatory mechanisms of anthocyanin accumulation, with emphasis on the latest progress in transcriptional and epigenetic regulation and the crosstalk between various signaling pathways. We present an emerging picture of how various internal and external stimuli control anthocyanin biosynthesis. Additionally, we discuss the synergistic or antagonistic effect of developmental, hormonal and environmental cues on anthocyanin accumulation in fruit.

Tissue-specific expression of Ruby in Mexican lime (C. aurantifolia) confers anthocyanin accumulation in fruit.

Tissue specific promoters are important tools for the precise genetic engineering of crop plants. Four fruit-preferential promoters were examined for their ability to confer a novel fruit trait in transgenic Mexican lime (Citrus aurantifolia). The Ruby transcription factor activates fruit anthocyanin accumulation within Moro blood orange and has been shown to function in activating anthocyanin accumulation in heterologous plant species. Although the CitVO1, CitUNK, SlE8, and PamMybA promoters were previously shown to confer strong fruit-preferential expression in transgenic tomato, they exhibited no detectable expression in transgenic Mexican lime trees. In contrast, the CitWax promoter exhibited high fruit-preferential expression of Ruby, conferring strong anthocyanin accumulation within the fruit juice sac tissue and moderate activity in floral/reproductive tissues. In some of the transgenic trees with high levels of flower and fruit anthocyanin accumulation, juvenile leaves also exhibited purple coloration, but the color disappeared as the leaves matured. We show that the CitWax promoter enables the expression of Ruby to produce anthocyanin colored fruit desired by consumers. The production of this antioxidant metabolite increases the fruits nutritional value and may provide added health benefits.

Discovery of a DFR gene that controls anthocyanin accumulation in the spiny Solanum group: roles of a natural promoter variant and alternative splicing.

Anthocyanins are important pigments that impart color in plants. In Solanum, different species display various fruit or flower colors due to varying degrees of anthocyanin accumulation. Here we identified two anthocyanin-free mutants from an ethylmethane sulfonate-induced mutant library and naturally occurring mutants in Solanum melongena, with mutations in the 5' splicing site of the second intron of dihydroflavonol-4-reductase (DFR) - leading to altered splicing. Further study revealed that alternative splicing of the second intron was closely related to anthocyanin accumulation in 17 accessions from three cultivated species: S. melongena, Solanum macrocarpon and Solanum aethiopicum, and their wild related species. Analysis of natural variations of DFR, using an expanded population including 282 accessions belonging to the spiny Solanum group, identified a single-nucleotide polymorphism in the MYB recognition site in the promoter region, which causes differential expression of DFR and affects anthocyanin accumulation in fruits of the detected accessions. Our study suggests that, owing to years of domestication, the natural variation in the DFR promoter region and the alternative splicing of the DFR gene account for altered anthocyanin accumulation during spiny Solanum domestication.

An Anthocyanin-Related Glutathione S-Transferase, MrGST1, Plays an Essential Role in Fruit Coloration in Chinese Bayberry (Morella rubra).

Chinese bayberry (Morella rubra) is a fruit tree economically important in China and accumulates abundant amounts of anthocyanins in fruit as it ripens. Owing to the fact that all anthocyanin containing fruit tissues in Chinese bayberry are edible and anthocyanins can provide various health benefits in human body, the mechanisms underpinning anthocyanin accumulation in this fruit are worthy of investigation. It has been known that in plants anthocyanins are synthesized in the cytoplasmic surface of the endoplasmic reticulum and subsequently transported into the vacuole for storage, and glutathione S-transferases (GSTs) have been verified to be involved in this process. But the characterization and functionalization of the GST counterpart in Chinese bayberry is not available. The GST anthocyanin transporter MrGST1 was discovered to be related with anthocyanin accumulation in fruit from distinct developmental stages of “Biqi,” a staple cultivar that accumulates over 1 mg/g anthocyanins in ripe fruit. The expression of MrGST1 was well associated with anthocyanin accumulation either in fruit collected at six developmental stages or in ripe fruit from 12 cultivars. MrGST1 was found to be responsible for the transport of anthocyanins but not proanthocyanidins when the Arabidopsis tt19 mutant was functionally complemented. Transient ectopic expression of MrGST1 in combination with MrMYB1.1 and MrbHLH1 dramatically boosted pigmentation in Nicotiana tabacum leaves in contrast to MrMYB1.1 and MrbHLH1. The promoter of MrGST1 comprised eight MYB binding sites (MBSs) according to cis-element analysis. Data from yeast one-hybrid assay and dual-luciferase tests demonstrated that MrMYB1.1 exerted considerable transactivation effect on the MrGST1 promoter by recognizing the MBS4, the fourth MBS from the ATG start site. Our results together provided molecular evidence for the contribution of MrGST1 in regulating anthocyanin accumulation in Chinese bayberry fruit.

PpHYH is responsible for light-induced anthocyanin accumulation in fruit peel of Prunus persica.

Peach Prunus persica is an economically important fruit tree crop worldwide. Although the external color of fruit is an important aspect of fruit quality, the mechanisms underlying its formation remain elusive in peach. Here, we report an elongated hypocotyl 5-homolog gene PpHYH involved in the regulation of anthocyanin pigmentation in peach fruit peel. Anthocyanin accumulation in fruit peel is light-dependent in peach. PpHYH had no auto-activation activity and its transcription was induced by sunlight. PpHYH activated transcription of a cluster of three PpMYB10 genes in the present of a cofactor PpBBX4 encoding a B-BOX protein, leading to anthocyanin accumulation in the sun-exposed peel. However, the PpHYH activity was repressed by a negative regulator of PpCOP1 encoding constitutive photomorphogenesis protein 1 which accumulated in the nucleus under dark condition, resulting in failure of anthocyanin accumulation in the shaded peel. PpCOP1 was re-localized into the cytosol under light condition, in accordance with fruit peel pigmentation. Additionally, transport of anthocyanins from the cytoplasm to the vacuole was a rate-limiting step for anthocyanin accumulation in peach fruit peel. Our results reveal for the first time the HYH gene involved in the regulation of anthocyanin accumulation in fruits, and provide target genes for genetic manipulation of fruit coloration.

Genome-wide identification and comparative analysis of GST gene family in apple (Malus domestica) and their expressions under ALA treatment.

Anthocyanins, a subclass of flavonoids, are synthesized at the cytoplasmic surface of the endoplasmic reticulum (ER), which then accumulate in vacuoles. Plant glutathione S-transferase (GST) genes are involved in anthocyanin transportation. Here, a total of 52, 42, 50, and 29 GST genes were identified from apple, pear, peach, and strawberry, respectively, through a comprehensive genome-wide survey. Based on phylogenetic analyses, the GST proteins of the four crops could be divided into the classes Phi, Tau, DHAR, TCHQD, and Lambda. The structure and chromosomal distribution of apple GST genes were further analyzed. The GST gene family expansion in apple likely occurred through tandem duplications, and purifying selection played a pivotal role in the evolution of GST genes. Synteny analysis showed strong microsynteny between apple and Arabidopsis/strawberry, but no microsynteny was detected between apple/strawberry/Arabidopsis and rice. Aminolevulinic acid (ALA), a key precursor of tetrapyrrole compounds, can significantly improve anthocyanin accumulation in fruits, Using RNA-seq and qRT-PCR analysis, we found that ALA treatment led to the differential expression of GST genes in apples. MdGSTF12 was strongly induced by ALA, suggesting that MdGSTF12 may play a role in ALA-induced anthocyanin accumulation. These results provide a detailed overview of GST genes in four Rosaceae species and indicate that GSTs are involved in ALA-induced anthocyanin accumulation.

Study of the Myb-factor polymorphism based on comparative genomics of vegetable Solanaceae crops (tomato, pepper, eggplant) to search for DNA markers that differentiate samples by the anthocyans accumulation

Anthocyanins are high-value plant antioxidants; they also determine biotic and abiotic stress resistance. The aim of our research was to study the allelic polymorphism of Antocyanin 1 orthologs in the vegetable Solanaceae crops of C. annuum and S. melongena. The search revealed the following closest genes in C. annuum: Myb113-like1 TF and Myb113like2 transcription factors and Myb1 in S. melongena. Exon amplicons of those genes were obtained and then sequenced in the pepper and eggplant samples with contrasting anthocyanin fruit coloration. Primers to the identified polymorphisms were developed and their correlation with the anthocyanin accumulation in fruits was studied. A close correlation was found between a minimum accumulation or the complete absence of anthocyanin synthesis in fruits with a single nucleotide deletion (Myb113-like1), and in the pepper samples, 2 SNP (Myb113-like2) was detected using the CAPS marker Myb 113-AccI. In the eggplant samples, the deletions of 6 and 26 bp were detected using the SCAR marker MybMel and the CAPS marker MybmelPst1. The disturbance of anthocyanin synthesis in pepper forms with 1Indel in Myb113-like1 TF was determined by a shift in the reading frame and SNPs in Myb113-like2 TF lead to amino acid substitutions: Lys → Arg and Thr → Lys. In the eggplant, a deletion of 6 bp leads to the loss of ala and arg in the protein; a deletion of 26 bp causes disorder during the mRNA maturation. The developed markers allow identifying the Myb-like TF alleles under study, resulting in anthocyanin synthesis disturbance in fruits. C. annuum and S. melongena samples with different alleles were selected for a further study and new varieties in agriculture.

Identification of DNA Markers of Anthocyanin Biosynthesis Disorders Based on the Polymorphism of Anthocyanin 1 Tomato Ortholog Genes in Pepper and Eggplant

The aim of this research was the identification of DNA markers to Antocyanin 1 (Ant1) tomato orthologs in 30 Capsicum annuum, 30 Solanum melongena and 1 Solanum aethiopicum accessions with different anthocyanin accumulation. A search for orthologs to the Ant1 allele in the GenBank database revealed the following closest nucleotide sequences of Myb113-like TF: in C. annuum, mRNA XM_016689227, mRNA NM_001324618; in S. melongena, mRNA KT259043. In Capsicum spp. samples, 4 SNP and a single base deletion in exon 3 of the Myb113-like 1 allele and 2 SNP in exon 4 of the Myb113-like2 allele were detected in forms with the impaired anthocyanin synthesis, based on their phenotype. In S. melongena samples, a 6 bp deletion at the end of exon 1 of the Myb-1 gene was detected in accessions with a green fruit coloration. A 26 bp deletion between intron 1 and exon 2, 11 SNP in exon regions and a 52 bp insertion at the beginning of intron 2 were detected in forms with a white fruit coloration. A 9-nucleotide insertion and 11 SNP in exon 3 of the Myb-1 gene were detected in the S. aethiopicum accession with no anthocyanin accumulation in fruits. Optimal SCAR and CAPS markers were developed to identify a number of genetic polymorphisms of Myb-like TF genes that might cause the impaired anthocyanin synthesis in pepper and eggplant. CAPS Myb 113-AccI and dCAPS Myb 113-AciI markers allow to identify C.annuum accessions without an anthocyanin coloration of fruits. SCAR MybMel and CAPS Mybmel-PstI markers allow to identify S. melongena accessions with white and green fruit colorations. Samples with different allelic polymorphism combinations were selected as models for the further study of the genetic regulation of anthocyanin accumulation in various parts of plants and for improved plant breeding.

PacCOP1 negatively regulates anthocyanin biosynthesis in sweet cherry (Prunus avium L.)

Light is a key environmental factors affecting anthocyanin accumulation in plants. Ubiquitin E3 ligase COP1 has been proved to be a negative regulator involved in light-regulated plant development process, whereas the function and expression specificity of COP1 in anthocyanin biosynthesis in sweet cherry remains unclear. In the present study, we identified a COP1 in sweet cherry, named PacCOP1, it exhibited apparent different expression patterns in red-colored ‘Hongdeng’ and bi-colored ‘Satonishiki’, with increasing trend largely in ‘Satonishiki’, but decreasing trend in ‘Hongdeng’ after veraison, which was contrary to their variation tendency of anthocyanin content. While the expression abundance of anthocyanin biosynthesis related genes were largely increased after veraison, in accordance with anthocyanin content. Correlation analysis proved that the expression of PacCOP1 was negative correlated with the major genes on anthocyanin accumulation in ‘Hongdeng’ and ‘Satonishiki’ fruit, in especial PacDFR, PacANS, PacMYBA and PacbHLH33. Furthermore, over-expression of PacCOP1 in Arabidopsis displayed increased COP1 transcript level with negligible pigmentation and corresponding lower expression level of AtPAP1, AtDFR, AtLDOX, and AtUFGT. These results revealed the negative regular role of PacCOP1 in anthocyanin biosynthesis by repressing the PacMYBA transcription level, followed by down-regulating the structural genes expression abundance, eventually leading to attenuated anthocyanin accumulation in fruits.

Genetic variations underlying anthocyanin accumulation in tomato fruits

Fruits of cultivated tomato (Solanum lycopersicum) generally do not present significant amounts of anthocyanins. However, the Aft and atv loci present in some wild tomato wild relatives are responsible for the presence of anthocyanins in these wild species. Suggested candidate genes for Aft and atv are SlANT1 and SlMYBATV, respectively. Herein, we reported variations in SlANT1 and SlMYBATV in two partially purple and three fully purple tomatoes, and the genetic requirements of both variations to induce full anthocyanin pigmentation. Twelve SNPs at SlANT1 leading to eight missense mutations and a 4-bp insertion at SlMYBATV leading to a premature termination codon were found in the purple tomatoes. Anthocyanin levels were 2–7 folds higher in fully purple tomato fruits than in partially purple tomato fruits and anthocyanin levels in the stems and leaves did not significantly differ between the two types. DNA markers of SlANT1 and SlMYBATV were developed and used for the genetic assessment of purple tomatoes. In two different F2 populations, segregating partial and full pigmentation, SlANT1 co-segregated with the presence of anthocyanin accumulation in fruits and the combination of SlANT1 and slmybatv was necessary for full purple pigmentation. These results will be useful for marker-assisted selection of anthocyanin-rich fruits in tomato.

Abscisic Acid Regulates Anthocyanin Biosynthesis and Gene Expression Associated With Cell Wall Modification in Ripening Bilberry (Vaccinium myrtillus L.) Fruits.

Ripening of non-climacteric bilberry (Vaccinium myrtillus L.) fruit is characterized by a high accumulation of health-beneficial anthocyanins. Plant hormone abscisic acid (ABA) and sucrose have been shown to be among the central signaling molecules coordinating non-climacteric fruit ripening and anthocyanin accumulation in some fruits such as strawberry. Our earlier studies have demonstrated an elevation in endogenous ABA level in bilberry fruit at the onset of ripening indicating a role for ABA in the regulation of bilberry fruit ripening. In the present study, we show that the treatment of unripe green bilberry fruits with exogenous ABA significantly promotes anthocyanin biosynthesis and accumulation both in fruits attached and detached to the plant. In addition, ABA biosynthesis inhibitor, fluridone, delayed anthocyanin accumulation in bilberries. Exogenous ABA also induced the expression of several genes involved in cell wall modification in ripening bilberry fruits. Furthermore, silencing of VmNCED1, the key gene in ABA biosynthesis, was accompanied by the down-regulation in the expression of key anthocyanin biosynthetic genes. In contrast, the treatment of unripe green bilberry fruits with exogenous sucrose or glucose did not lead to an enhancement in the anthocyanin accumulation neither in fruits attached to plant nor in post-harvest fruits. Moreover, sugars failed to induce the expression of genes associated in anthocyanin biosynthesis or ABA biosynthesis while could elevate expression of some genes associated with cell wall modification in post-harvest bilberry fruits. Our results demonstrate that ABA plays a major role in the regulation of ripening-related processes such as anthocyanin biosynthesis and cell wall modification in bilberry fruit, whereas sugars seem to have minor regulatory roles in the processes. The results indicate that the regulation of bilberry fruit ripening differs from strawberry that is currently considered as a model of non-climacteric fruit ripening. In this study, we also identified transcription factors, which expression was enhanced by ABA, as potential regulators of ABA-mediated bilberry fruit ripening processes.

Effect of Red and Blue Light on Anthocyanin Accumulation and Differential Gene Expression in Strawberry (Fragaria × ananassa).

Light conditions can cause quantitative and qualitative changes in anthocyanin. However, little is known about the underlying mechanism of light quality-regulated anthocyanin accumulation in fruits. In this study, light-emitting diodes (LEDs) were applied to explore the effect of red and blue light on strawberry coloration. The results showed contents of total anthocyanins (TA), pelargonidin 3-glucoside (Pg3G) and pelargonidin 3-malonylglucoside (Pg3MG) significantly increased after blue and red light treatment. Pg3G was the major anthocyanin component in strawberry fruits, accounting for more than 80% of TA, whereas Pg3MG accounted for a smaller proportion. Comparative transcriptome analysis was conducted using libraries from the treated strawberries. A total of 1402, 5034, and 3764 differentially-expressed genes (DEGs) were identified in three pairwise comparisons (red light versus white light, RL-VS-WL; blue light versus white light, BL-VS-WL; blue light versus red light, BL-VS-RL), respectively. Photoreceptors and light transduction components remained dynamic to up-regulate the expression of regulatory factors and structural genes related to anthocyanin biosynthesis under red and white light, whereas most genes had low expression levels that were not consistent with the highest total anthocyanin content under blue light. Therefore, the results indicated that light was an essential environmental factor for anthocyanin biosynthesis before the anthocyanin concentration reached saturation in strawberry fruits, and blue light could quickly stimulate the accumulation of anthocyanin in the fruit. In addition, red light might contribute to the synthesis of proanthocyanidins by inducing LAR and ANR.

Genome-wide survey and analysis of the TIFY gene family and its potential role in anthocyanin synthesis in Chinese sand pear (Pyrus pyrifolia)

The TIFY family is an important gene family which can be found only in plant and involved in different biologic processes. Jasmonic acid (JA) promotes anthocyanin accumulation in fruit. To explore the role of PpTIFY genes in anthocyanin biosynthesis of Chinese sand pear (Pyrus pyrifolia Nakai), we first cloned 21 PpTIFY genes from the pear genome and further identified 11 PpJAZ genes. The sequence similarity among the PpTIFY genes was relatively low, which indicated that PpTIFY genes in higher plants differentiated early during land plant evolution and have experienced considerable mutation. Transcripts of PpTIFY genes were detected in all organs and tissues of pear analyzed. The spatial and temporal expression patterns indicated that PpTIFY genes were associated with anthocyanin accumulation and JA signaling. The expression levels of PpTIFY genes were highest in leaves, whereas during fruit maturation, the expression level dramatically decreased. Furthermore, PpTIFY was induced after JA and light treatment in conjunction with anthocyanin accumulation in the peel of red fruit of Chinese sand pear. Genome-wide identification and characterization of pear PpTIFY genes will be helpful for further functional analysis of this gene family and cultivar improvement in pears.

The heterologous expression of Arabidopsis PAP2 induces anthocyanin accumulation and inhibits plant growth in tomato.

Anthocyanins are naturally occurring secondary metabolites, responsible for the color of many plants. The Arabidopsis thaliana MYB90/PAP2 (production of anthocyanin pigment 2) was introduced into tomato to study its effect on anthocyanin accumulation. The transgenic tomato displayed much greater anthocyanin accumulation than wild type in all plant organs, but the organs were not fully purple in color except for the stamen. The expression of anthocyanin biosynthetic genes and an anthocyanin-related basic helix-loop-helix (bHLH) gene SlAN1 was significantly increased in the transgenic line, suggesting that ectopic expression of AtPAP2 increases the expression of anthocyanin-related structural and regulatory genes to enhance anthocyanin content. Yeast two-hybrid assays revealed that the endogenous MYB protein SlAN2 interacted with two putative bHLH partners, SlAN1 and SlJAF13, while AtPAP2 only interacted with SlJAF13, which may be why AtPAP2 transgenic plants showed limited anthocyanin accumulation in fruits. In addition to anthocyanin accumulation, the transgenic tomato plants were significantly smaller in size, and the length of primary roots and number of lateral roots were obviously decreased. The expression of lignin biosynthetic genes was downregulated in transgenic tomato plants, which may be the reason for the inhibited growth. The lateral organ boundaries-domain (LBD) genes, which regulate lateral root organogenesis in the auxin signaling pathway, were downregulated in transgenic tomato roots, which may partly account for the disturbed lateral root formation in the transformants. Taken together, the results demonstrate that heterologous expression of transcription factor AtPAP2 not only resulted in anthocyanin accumulation but also inhibited plant growth in tomato.

Response of miR156-SPL Module during the Red Peel Coloration of Bagging-Treated Chinese Sand Pear (Pyrus pyrifolia Nakai).

MicroRNA156 is an evolutionarily highly conserved plant micro-RNA (miRNA) that controls an age-dependent flowering pathway. miR156 and its target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes regulate anthocyanin accumulation in plants, but it is unknown whether this process is affected by light. Red Chinese sand pear (Pyrus pyrifolia) fruits exhibit a unique coloration pattern in response to bagging treatments, which makes them appropriate for studying the molecular mechanism underlying light-induced anthocyanin accumulation in fruit. Based on high-throughput miRNA and degradome sequencing data, we determined that miR156 was expressed in pear fruit peels, and targeted four SPL genes. Light-responsive elements were detected in the promoter regions of the miR156a and miR156ba precursors. We identified 19 SPL genes using the “Suli” pear (Pyrus pyrifolia Chinese White Pear Group) genome database, of which seven members were putative miR156 targets. The upregulated expression of anthocyanin biosynthetic and regulatory genes and downregulated expression of PpSPL2, PpSPL5, PpSPL7, PpSPL9, PpSPL10, PpSPL13, PpSPL16, PpSPL17, and PpSPL18 were observed in pear fruits after bags were removed from plants during the anthocyanin accumulation period. Additionally, miR156a/ba/g/s/sa abundance increased after bags were removed. Yeast two-hybrid results suggested that PpMYB10, PpbHLH, and PpWD40 could form a protein complex, probably involved in anthocyanin biosynthesis. Additionally, PpSPL10 and PpSPL13 interacted with PpMYB10. The results obtained in this study are helpful in understanding the possible role of miR156 and its target PpSPL genes in regulating light-induced red peel coloration and anthocyanin accumulation in pear.

Transcriptome analysis and transient transformation suggest an ancient duplicated MYB transcription factor as a candidate gene for leaf red coloration in peach.

BackgroundLeaf red coloration is an important characteristic in many plant species, including cultivars of ornamental peach (Prunus persica). Peach leaf color is controlled by a single Gr gene on linkage group 6, with a red allele dominant over the green allele. Here, we report the identification of a candidate gene of Gr in peach.ResultsThe red coloration of peach leaves is due to accumulation of anthocyanin pigments, which is regulated at the transcriptional level. Based on transcriptome comparison between red- and green-colored leaves, an MYB transcription regulator PpMYB10.4 in the Gr interval was identified to regulate anthocyanin pigmentation in peach leaf. Transient expression of PpMYB10.4 in tobacco and peach leaves can induce anthocyain accumulation. Moreover, a functional MYB gene PpMYB10.2 on linkage group 3, which is homologous to PpMYB10.4, is also expressed in both red- and green-colored leaves, but plays no role in leaf red coloration. This suggests a complex mechanism underlying anthocyanin accumulation in peach leaf. In addition, PpMYB10.4 and other anthocyanin-activating MYB genes in Rosaceae responsible for anthocyanin accumulation in fruit are dated to a common ancestor about 70 million years ago (MYA). However, PpMYB10.4 has diverged from these anthocyanin-activating MYBs to generate a new gene family, which regulates anthocyanin accumulation in vegetative organs such as leaves.ConclusionsActivation of an ancient duplicated MYB gene PpMYB10.4 in the Gr interval on LG 6, which represents a novel branch of anthocyanin-activating MYB genes in Rosaceae, is able to activate leaf red coloration in peach.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0388-y) contains supplementary material, which is available to authorized users.

Isolation of anthocyanin biosynthetic genes in red Chinese sand pear (Pyrus pyrifolia Nakai) and their expression as affected by organ/tissue, cultivar, bagging and fruit side

Recently, red Chinese sand pears (Pyrus pyrifolia Nakai) have become widely cultivated throughout China. To clarify the molecular mechanism underlying anthocyanin accumulation in red Chinese sand pears, genes encoding the anthocyanin biosynthesis enzymes including phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS) and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) were isolated from the mature fruit of ‘Meirensu’ pears and were designated as PpPAL, PpCHI, PpCHS, PpDFR, PpF3H, PpANS and PpUFGT, respectively. The expression of PyMYB10 and all seven anthocyanin biosynthetic genes were detected in two red pear cultivars under fruit bagging treatments during fruit maturation. The transcription level of all these genes was markedly up-regulated in two cultivars and peaked at 1 DABR (days after the bag removal) followed by a decline. All seven anthocyanin biosynthetic genes were differentially expressed among various organs or tissues, and none was fruit specific. Higher mRNA abundance of all seven anthocyanin biosynthetic genes and PyMYB10 was detected in the skin of sun-side ‘Yunhongli No. 1’ than in ‘Meirensu’ in all surveys, and in the skin of sunlit side of ‘Meirensu’ (M) than in the skin of the shaded side of ‘Meirensu’ which positively correlated with anthocyanin accumulation. Our results suggest that (1) anthocyanin accumulation in fruit of red Chinese sand pears was closely related to the coordinated expression of PyMYB10 and multiple biosynthetic genes and the level was modified by the genetic background of cultivars, and (2) light exposure after bag removal enhanced anthocyanin accumulation by inducing the expression of PyMYB10 and the anthocyanin biosynthetic genes. The results obtained in this study will be helpful in understanding the molecular mechanism of anthocyanin accumulation in red Chinese sand pears and can serve as the basis for the development of marker-assisted selection or for anthocyanin metabolic engineering of pears.

Expression of Anthocyanin Biosynthetic Genes during Fruit Development in ‘Fengxiang’ Strawberry

Anthocyanins are the main pigments in flowers and fruits. In most cases, anthocyanin accumulation in fruit is highly controlled by the developmental level. In this study, the cDNA fragments of three genes, chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS), which are involved in the flavonoid pathway, were isolated from total RNA of strawberry ripe fruit by using polymerase chain reaction technique and labeled as probes to determine the expression of anthocyanin biosynthetic genes. Northern analysis showed that a correlation between anthocyanin accumulation and expression of the flavonoid pathway genes during the ripening of strawberry fruits. At the early stages of fruit development, the mRNA levels encoding CHS, DFR, ANS were high probably responsible for the accumulation of condensed tannins, but the levels decreased dramatically when fruits turned white from green. During the stage of pigment accumulation, their mRNA levels increased strongly to be involved anthocyanin biosynthesis. Difference of CHS in mRNA abundance was correlated with differential accumulation of anthocyanins throughout the process of fruit development. Therefore, CHS could be a key structure gene involved in anthocyanin synthesis. Furthermore, the co-ordination of expression of anthocyanin biosynthetic genes implied a common regulatory mechanism controlling the expression of structural genes in the flavonoid pathway.