Cloning and characterization of a potato StAN11 gene involved in anthocyanin biosynthesis regulation

Prediction of cyanidin 3-rutinoside content in Michelia crassipes based on near-infrared spectroscopic techniques

Currently the determination of cyanidin 3-rutinoside content in plant petals usually requires chemical assays or high performance liquid chromatography (HPLC), which are time-consuming and laborious. In this study, we aimed to develop a low-cost, high-throughput method to predict cyanidin 3-rutinoside content, and developed a cyanidin 3-rutinoside prediction model using near-infrared (NIR) spectroscopy combined with partial least squares regression (PLSR). We collected spectral data from Michelia crassipes (Magnoliaceae) tepals and used five different preprocessing methods and four variable selection algorithms to calibrate the PLSR model to determine the best prediction model. The results showed that (1) the PLSR model built by combining the blockScale (BS) preprocessing method and the Significance multivariate correlation (sMC) algorithm performed the best; (2) The model has a reliable prediction ability, with a coefficient of determination (R2) of 0.72, a root mean square error (RMSE) of 1.04%, and a residual prediction deviation (RPD) of 2.06. The model can be effectively used to predict the cyanidin 3-rutinoside content of the perianth slices of M. crassipes, providing an efficient method for the rapid determination of cyanidin 3-rutinoside content.

Enhanced UV-B Radiation in Potato Stems and Leaves Promotes the Accumulation of Anthocyanins in Tubers

Enhanced ultraviolet-B (UV-B) radiation promotes anthocyanin biosynthesis in leaves, flowers and fruits of plants. However, the effects and underlying mechanisms of enhanced UV-B radiation on the accumulation of anthocyanins in the tubers of potatoes (Solanum tuberosum L.) remain unclear. Herein, reciprocal grafting experiments were first conducted using colored and uncolored potatoes, demonstrating that the anthocyanins in potato tubers were synthesized in situ, and not transported from the leaves to the tubers. Furthermore, the enhanced UV-B radiation (2.5 kJ·m-2·d-1) on potato stems and leaves significantly increased the contents of total anthocyanin and monomeric pelargonidin and peonidin in the red-fleshed potato '21-1' tubers, compared to the untreated control. A comparative transcriptomic analysis showed that there were 2139 differentially expressed genes (DEGs) under UV-B treatment in comparison to the control, including 1724 up-regulated and 415 down-regulated genes. The anthocyanin-related enzymatic genes in the tubers such as PAL, C4H, 4CL, CHS, CHI, F3H, F3'5'H, ANS, UFGTs, and GSTs were up-regulated under UV-B treatment, except for a down-regulated F3'H. A known anthocyanin-related transcription factor StbHLH1 also showed a significantly higher expression level under UV-B treatment. Moreover, six differentially expressed MYB transcription factors were remarkably correlated to almost all anthocyanin-related enzymatic genes. Additionally, a DEGs enrichment analysis suggested that jasmonic acid might be a potential UV-B signaling molecule involved in the UV-B-induced tuber biosynthesis of anthocyanin. These results indicated that enhanced UV-B radiation in potato stems and leaves induced anthocyanin accumulation in the tubers by regulating the enzymatic genes and transcription factors involved in anthocyanin biosynthesis. This study provides novel insights into the mechanisms of enhanced UV-B radiation that regulate the anthocyanin biosynthesis in potato tubers.

Methylation level of potato gene OMT30376 regulates tuber anthocyanin transformations

After anthocyanin synthesis, a variety of anthocyanin compounds are produced through further methylation, glycosylation, and acylation. However, the effect of the potato methylase gene on anthocyanin biosynthesis has not been reported. Red and purple mutation types appear in tubers of the potato cultivar 'Purple Viking' with chimeric skin phenotypes. In this study, transcriptome and anthocyanin metabolome analyses were performed on skin of Purple Viking tubers and associated mutants. According to the metabolome analysis, the transformation of delphinidin into malvidin-3-O-glucoside and petunidin 3-O-glucoside and that of cyanidin into rosinidin O-hexoside and peonidin-3-O-glucoside were hindered in red tubers. Expression of methyltransferase gene OMT30376 was significantly lower in red tubers than in purple ones, whereas the methylation level of OMT30376 was significantly higher in red tubers. In addition, red skin appeared in tubers from purple tuber plants treated with S-adenosylmethionine (SAM), indicating the difference between purple and red was caused by the methylation degree of the gene OMT30376. Thus, the results of the study suggest that the OMT30376 gene is involved in the transformation of anthocyanins in potato tubers. The results also provide an important reference to reveal the regulatory mechanisms of anthocyanin biosynthesis and transformation.

Uncovering anthocyanin diversity in potato landraces (Solanum tuberosum L. Phureja) using RNA-seq

Potato (Solanum tuberosum L.) is the third largest source of antioxidants in the human diet, after maize and tomato. Potato landraces have particularly diverse contents of antioxidant compounds such as anthocyanins. We used this diversity to study the evolutionary and genetic basis of anthocyanin pigmentation. Specifically, we analyzed the transcriptomes and anthocyanin content of tubers from 37 landraces with different colorations. We conducted analyses of differential expression between potatoes with different colorations and used weighted correlation network analysis to identify genes whose expression is correlated to anthocyanin content across landraces. A very significant fraction of the genes identified in these two analyses had annotations related to the flavonoid-anthocyanin biosynthetic pathway, including 18 enzymes and 5 transcription factors. Importantly, the causal genes at the D, P and R loci governing anthocyanin accumulation in potato cultivars also showed correlations to anthocyanin production in the landraces studied here. Furthermore, we found that 60% of the genes identified in our study were located within anthocyanin QTLs. Finally, we identified new candidate enzymes and transcription factors that could have driven the diversification of anthocyanins. Our results indicate that many anthocyanins biosynthetic genes were manipulated in ancestral potato breeding and can be used in future breeding programs.

StWRKY13 promotes anthocyanin biosynthesis in potato (Solanum tuberosum) tubers

Although the role of WRKY transcription factors (TFs) in colour formation has been reported in several species, their function in potato (Solanum tuberosum L.) anthocyanin biosynthesis remains unclear. In this study, the potato WRKY gene StWRKY13 was isolated and characterised. Expression analysis revealed a significantly higher StWRKY13 expression in chromatic tubers than in yellow ones. Transient activation assays showed that StWRKY13 could enhance the role of StAN2 in promoting anthocyanin biosynthesis in tobacco (Nicotiana tabacum L.). Over-expressing the StWRKY13 gene promoted anthocyanin biosynthesis in potato tubers. Further investigations indicated that StWRKY13 could interact with the StCHS, StF3H, StDFR, and StANS gene promoters and significantly enhance their activities. Our findings showed that StWRKY13 could promote anthocyanin biosynthesis by activating StCHS, StF3H, StDFR, and StANS transcription in potato tubers, thereby supporting the theoretical basis for anthocyanins formation in coloured potato tubers.

Genetic variation and gene expression of anthocyanin synthesis and transport related enzymes in Oryza sativa against thiocyanate

Plants exposed to environmental contaminants often synthesize anthocyanins (ATHs) as an approach to safeguard themselves from adverse impact. However, the overload of ATHs in plant cells can threaten their growth and development through proteins oxidization and intercalating with DNAs inside cells. In the present study, a microcosm hydroponic experiment was conducted using rice seedlings to investigate the molecular signaling pathways involved in regulating and controlling ATHs synthesis and transport exposed to thiocyanate (SCN^-). Our results indicated that SCN^- exposure significantly (p < 0.05) increased the expression of ATHs synthesis related genes (i.e., PAL, CHS, ANS, UFGT genes) in rice tissues, altered the activities of these ATHs synthesis related enzymes, and consequently elevated the ATHs content. However, SCN^- exposure significantly decreased the expression of ATHs transport related genes (i.e., GST, ABC, MATE genes) in rice seedlings, suggesting that SCN^- exposure have restrained ATHs transport from cytosol to vacuole in cells, eventually posing a significant adverse effect on cells survival. Our findings highlight on one of the plant aspects in managing the toxicity triggered by secondary metabolites under stress conditions.

Chalcone Synthase-Encoding AeCHS is Involved in Normal Petal Coloration in Actinidia eriantha

Studies on anthocyanin biosynthesis have been mainly concentrated on the fruit, whereas few have focused the mechanism of flower coloration in kiwifruit. Here, we report that the structural gene, AeCHS, is involved in anthocyanin accumulation and indispensable for normal petal coloration in Actinidia eriantha. Petals from three different species including Actinidia eriantha (red petals), Actinidia hemsleyana (light pink petals) and Actinidia arguta (white petals) were selected for anthocyanin determination and gene expression analysis. The anthocyanin components in A. eriantha were significantly higher than in A. hemsleyana or A. arguta. Consistently, gene expression profiles suggested that AeCHS expression in A. eriantha was higher than in A. hemsleyana or A. arguta. Cluster analysis showed that AeCHS was clustered into a single group and distinctly separated from other genes, indicating the expression pattern of AeCHS gene was different from any other. Additionally, correlation analysis revealed AeCHS expression significantly correlated with anthocyanin content. The complete coding sequence of AeCHS was cloned from petals of A. eriantha 'Zaoxu', showing the length of AeCHS was 1170 bp encoding a protein of 389 amino acids. AeCHS was located in the cytoplasm, indicating it is indeed a structural gene involved in anthocyanin biosynthesis. AeCHS silencing performed by infiltration grafting-mediated virus-induced gene silencing (VIGS) reduced petal anthocyanin content and bleached red petals in A. eriantha. Our results confirm a crucial role of AeCHS in anthocyanin biosynthesis and accumulation in A. eriantha petals; furthermore, they offer important basic information and constitute a reference point for further research.

MicroRNA858-mediated regulation of anthocyanin biosynthesis in kiwifruit (Actinidia arguta) based on small RNA sequencing

As important regulators, miRNAs could play pivotal roles in regulation of fruit coloring. Actinidia arguta is a newly emerged fruit tree with extensively application prospects. However, miRNAs involved in A. arguta fruit coloring are unknown. In this study, A. arguta fruit were investigated at three developmental stages by small RNAs high-throughput sequencing. A total of 482 conserved miRNAs corresponding to 526 pre-miRNAs and 581 novel miRNAs corresponding to 619 pre-miRNAs were grouped into 46 miRNA families. Target gene prediction and analysis revealed that miR858, a strongly candidate miRNA, was involved in anthocyanin biosynthesis in which contributes to fruit coloring. The anthocyanin level was determined in three A. arguta cultivars by UPLC-MS/MS (ultra-performance liquid chromatography coupled with tandem mass spectrometry). In addition, qPCR (quantitative real-time PCR), cluster analysis were conducted as well as correlation analysis. All results were combined to propose a model in which describes an association of miRNA and anthocyanin biosynthesis in A. arguta. The data presented herein is the first report on miRNA profile analysis in A. arguta, which can provide valuable information for further research into the regulation of the miRNAs in anthocyanin biosynthesis and fruit coloring.

Looking at Flavonoid Biodiversity in Horticultural Crops: A Colored Mine with Nutritional Benefits

Flavonoids represent a wide group of plant secondary metabolites implicated in many physiological roles, from the attraction of pollinators to the protection against biotic or abiotic stresses. Flavonoids are synthetized in a number of horticultural crops that are important components of our daily diet. In the last decades, the consumption of vegetables rich in antioxidants has been strongly promoted from the perspective of prevention/protection against chronic diseases. Therefore, due to their nutritional importance, several attempts have been made to enhance flavonoid levels in species of agronomic interest. In this review, we focus on the flavonoid biodiversity among the major horticultural species, which is responsible of differences among closely related species and influences the qualitative/quantitative composition. We also review the role of flavonoids in the nutritional quality of plant products, contributing to their organoleptic and nutritional properties, and the main strategies of biofortification to increase their content.

Subfunctionalization of duplicate MYB genes in Solanum commersonii generated the cold-induced ScAN2 and the anthocyanin regulator ScAN1

Wild potato species are useful sources of allelic diversity and loci lacking in the cultivated potato. In these species, the presence of anthocyanins in leaves has been associated with a greater tolerance to cold stress. However, the molecular mechanisms that allow potatoes to withstand cold exposure remain unclear. Here, we show that the expression of AN2, a MYB transcription factor, is induced by low temperatures in wild, cold-tolerant Solanum commersonii, and not in susceptible Solanum tuberosum varieties. We found that AN2 is a paralog of the potato anthocyanin regulator AN1, showing similar interaction ability with basic helix-loop-helix (bHLH) co-partners. Their sequence diversity resulted in a different capacity to promote accumulation of phenolics when tested in tobacco. Indeed, functional studies demonstrated that AN2 is less able to induce anthocyanins than AN1, but nevertheless it has a strong ability to induce accumulation of hydroxycinnamic acid derivatives. We propose that the duplication of R2R3 MYB genes resulted in subsequent subfunctionalization, where AN1 specialized in anthocyanin production and AN2 conserved the ability to respond to cold stress, inducing mainly the synthesis of hydroxycinnamic acid derivatives. These results contribute to understanding the evolutionary significance of gene duplication on phenolic compound regulation.

A comparative transcriptome analysis of a wild purple potato and its red mutant provides insight into the mechanism of anthocyanin transformation

In this study, a red mutant was obtained through in vitro regeneration of a wild purple potato. High-performance liquid chromatography and Mass spectrometry analysis revealed that pelargonidin-3-O-glucoside and petunidin-3-O-glucoside were main anthocyanins in the mutant and wild type tubers, respectively. In order to thoroughly understand the mechanism of anthocyanin transformation in two materials, a comparative transcriptome analysis of the mutant and wild type was carried out through high-throughput RNA sequencing, and 295 differentially expressed genes (DEGs) were obtained. Real-time qRT-PCR validation of DEGs was consistent with the transcriptome date. The DEGs mainly influenced biological and metabolic pathways, including phenylpropanoid biosynthesis and translation, and biosynthesis of flavone and flavonol. In anthocyanin biosynthetic pathway, the analysis of structural genes expressions showed that three genes, one encoding phenylalanine ammonia-lyase, one encoding 4-coumarate-CoA ligase and one encoding flavonoid 3′,5′-hydroxylasem were significantly down-regulated in the mutant; one gene encoding phenylalanine ammonia-lyase was significantly up-regulated. Moreover, the transcription factors, such as bZIP family, MYB family, LOB family, MADS family, zf-HD family and C2H2 family, were significantly regulated in anthocyanin transformation. Response proteins of hormone, such as gibberellin, abscisic acid and brassinosteroid, were also significantly regulated in anthocyanin transformation. The information contributes to discovering the candidate genes in anthocyanin transformation, which can serve as a comprehensive resource for molecular mechanism research of anthocyanin transformation in potatoes.

The factors affecting the evolution of the anthocyanin biosynthesis pathway genes in monocot and dicot plant species

BACKGROUND

The available data demonstrate that even in universal metabolic pathways, some species-specific regulatory features of structural genes are present. For instance, in the anthocyanin biosynthesis pathway (ABP), genes may be regulated by ABP-specific regulatory factors, and their expression levels may be strongly associated with anthocyanin pigmentation, or they may be expressed independently of pigmentation. A dataset of orthologous ABP genes (Chs, Chi, F3h, F3'h, Dfr, Ans) from monocot and dicot plant species that have distinct gene regulation patterns and different types of pollination was constructed to test whether these factors affect the evolution of the genes.

RESULTS

Using a maximum likelihood approach, we demonstrated that although the whole set of the ABP genes is under purifying selection, with greater selection acting on the upstream genes than on the downstream genes, genes from distinct groups of plant species experienced different strengths of selective pressure. The selective pressure on the genes was higher in dicots than in monocots (F3h and further downstream genes) and in pollinator-dependent plants than in pollinator-independent species (Chi and further downstream genes), suggesting an important role of pollination type in the evolution of the anthocyanin biosynthesis gene network. Contrasting effects of the regulation patterns on evolution were detected for the F3h and Dfr genes, with greater selective pressure on the F3h gene in plant species where the gene expression was not strongly associated with pigmentation and greater selective pressure on Dfr in plant species where the gene expression was associated with pigmentation.

CONCLUSIONS

We demonstrated the effects of pollination type and patterns of regulation on the evolution of the ABP genes, but the evolution of some of the genes could not be explained in the framework of these factors, such as the weaker selective pressure acting on Chs in species that attract pollinators or the stronger selective pressure on F3h in plant species where the gene expression was not associated with pigmentation. The observations suggest that additional factors could affect the evolution of these genes. One such factor could be an effect of gene duplication with further division of functions among gene copies and relaxed selective pressure acting on them. Additional tests with an appropriate dataset combining data on duplicated gene sequences and their functions in the flavonoid biosynthesis pathway are required to test this hypothesis.

MdHB1 down-regulation activates anthocyanin biosynthesis in the white-fleshed apple cultivar 'Granny Smith'

Coloration in apple (Malus×domestica) flesh is mainly caused by the accumulation of anthocyanin. Anthocyanin is biosynthesized through the flavonoid pathway and regulated by MYB, bHLH, and WD40 transcription factors (TFs). Here, we report that the HD-Zip I TF MdHB1 was also involved in the regulation of anthocyanin accumulation. MdHB1 silencing caused the accumulation of anthocyanin in 'Granny Smith' flesh, whereas its overexpression reduced the flesh content of anthocyanin in 'Ballerina' (red-fleshed apple). Moreover, flowers of transgenic tobacco (Nicotiana tabacum 'NC89') overexpressing MdHB1 showed a remarkable reduction in pigmentation. Transient promoter activation assays and yeast one-hybrid results indicated that MdHB1 indirectly inhibited expression of the anthocyanin biosynthetic genes encoding dihydroflavonol-4-reductase (DFR) and UDP-glucose:flavonoid 3-O-glycosyltransferase (UFGT). Yeast two-hybrid and bimolecular fluorescence complementation determined that MdHB1 acted as a homodimer and could interact with MYB, bHLH, and WD40 in the cytoplasm, consistent with its cytoplasmic localization by green fluorescent protein fluorescence observations. Together, these results suggest that MdHB1 constrains MdMYB10, MdbHLH3, and MdTTG1 to the cytoplasm, and then represses the transcription of MdDFR and MdUFGT indirectly. When MdHB1 is silenced, these TFs are released to activate the expression of MdDFR and MdUFGT and also anthocyanin biosynthesis, resulting in red flesh in 'Granny Smith'.

Comparative Transcriptome Analysis of White and Purple Potato to Identify Genes Involved in Anthocyanin Biosynthesis

INTRODUCTION

The potato (Solanum tuberosum) cultivar 'Xin Daping' is tetraploid with white skin and white flesh, while the cultivar 'Hei Meiren' is also tetraploid with purple skin and purple flesh. Comparative transcriptome analysis of white and purple cultivars was carried out using high-throughput RNA sequencing in order to further understand the mechanism of anthocyanin biosynthesis in potato.

METHODS AND RESULTS

By aligning transcript reads to the recently published diploid potato genome and de novo assembly, 209 million paired-end Illumina RNA-seq reads from these tetraploid cultivars were assembled on to 60,930 transcripts, of which 27,754 (45.55%) are novel transcripts and 9393 alternative transcripts. Using a comparison of the RNA-sequence datasets, multiple versions of the genes encoding anthocyanin biosynthetic steps and regulatory transcription factors were identified. Other novel genes potentially involved in anthocyanin biosynthesis in potato tubers were also discovered. Real-time qPCR validation of candidate genes revealed good correlation with the transcriptome data. SNPs (Single Nucleotide Polymorphism) and indels were predicted and validated for the transcription factors MYB AN1 and bHLH1 and the biosynthetic gene anthocyanidin 3-O-glucosyltransferase (UFGT).

CONCLUSIONS

These results contribute to our understanding of the molecular mechanism of white and purple potato development, by identifying differential responses of biosynthetic gene family members together with the variation in structural genes and transcription factors in this highly heterozygous crop. This provides an excellent platform and resource for future genetic and functional genomic research.

Changing trends in biotechnology of secondary metabolism in medicinal and aromatic plants

Medicinal and aromatic plants are known to produce secondary metabolites that find uses as flavoring agents, fragrances, insecticides, dyes and drugs. Biotechnology offers several choices through which secondary metabolism in medicinal plants can be altered in innovative ways, to overproduce phytochemicals of interest, to reduce the content of toxic compounds or even to produce novel chemicals. Detailed investigation of chromatin organization and microRNAs affecting biosynthesis of secondary metabolites as well as exploring cryptic biosynthetic clusters and synthetic biology options, may provide additional ways to harness this resource. Plant secondary metabolites are a fascinating class of phytochemicals exhibiting immense chemical diversity. Considerable enigma regarding their natural biological functions and the vast array of pharmacological activities, amongst other uses, make secondary metabolites interesting and important candidates for research. Here, we present an update on changing trends in the biotechnological approaches that are used to understand and exploit the secondary metabolism in medicinal and aromatic plants. Bioprocessing in the form of suspension culture, organ culture or transformed hairy roots has been successful in scaling up secondary metabolite production in many cases. Pathway elucidation and metabolic engineering have been useful to get enhanced yield of the metabolite of interest; or, for producing novel metabolites. Heterologous expression of putative plant secondary metabolite biosynthesis genes in a microbe is useful to validate their functions, and in some cases, also, to produce plant metabolites in microbes. Endophytes, the microbes that normally colonize plant tissues, may also produce the phytochemicals produced by the host plant. The review also provides perspectives on future research in the field.