Engineering anthocyanin biosynthesis in plants

Formation of Nudicaulins In Vivo and In Vitro and the Biomimetic Synthesis and Bioactivity of O-Methylated Nudicaulin Derivatives

Nudicaulins are yellow flower pigments accounting for the color of the petals of Papaver nudicaule (Papaveraceae). These glucosidic compounds belong to the small group of indole/flavonoid hybrid alkaloids. Here we describe in vivo and in vitro experiments which substantiate the strongly pH-dependent conversion of pelargonidin glucosides to nudicaulins as the final biosynthetic step of these alkaloids. Furthermore, we report the first synthesis of nudicaulin aglycon derivatives, starting with quercetin and ending up at the biomimetic fusion of a permethylated anthocyanidin with indole. A small library of nudicaulin derivatives with differently substituted indole units was prepared, and the antimicrobial, antiproliferative and cell toxicity data of the new compounds were determined. The synthetic procedure is considered suitable for preparing nudicaulin derivatives which are structurally modified in the indole and/or the polyphenolic part of the molecule and may have optimized pharmacological activities.

Wheat TaMs1 is a glycosylphosphatidylinositol-anchored lipid transfer protein necessary for pollen development

BACKGROUND

In flowering plants, lipid biosynthesis and transport within anthers is essential for male reproductive success. TaMs1, a dominant wheat fertility gene located on chromosome 4BS, has been previously fine mapped and identified to encode a glycosylphosphatidylinositol (GPI)-anchored non-specific lipid transfer protein (nsLTP). Although this gene is critical for pollen exine development, details of its function remains poorly understood.

RESULTS

In this study, we report that TaMs1 is only expressed from the B sub-genome, with highest transcript abundance detected in anthers containing microspores undergoing pre-meiosis through to meiosis. β-glucuronidase transcriptional fusions further revealed that TaMs1 is expressed throughout all anther cell-types. TaMs1 was identified to be expressed at an earlier stage of anther development relative to genes reported to be necessary for sporopollenin precursor biosynthesis. In anthers missing a functional TaMs1 (ms1c deletion mutant), these same genes were not observed to be mis-regulated, indicating an independent function for TaMs1 in pollen development. Exogenous hormone treatments on GUS reporter lines suggest that TaMs1 expression is increased by both indole-3-acetic acid (IAA) and abscisic acid (ABA). Translational fusion constructs showed that TaMs1 is targeted to the plasma membrane.

CONCLUSIONS

In summary, TaMs1 is a wheat fertility gene, expressed early in anther development and encodes a GPI-LTP targeted to the plasma membrane. The work presented provides a new insight into the process of wheat pollen development.

A novel glycosyltransferase catalyses the transfer of glucose to glucosylated anthocyanins in purple sweet potato

Glycosylation contributes to the diversity and stability of anthocyanins in plants. The process is catalysed by various glucosyltransferases using different anthocyanidin aglycones and glycosyl donors. In this study, we found that an anthocyanidin 3-O-glucoside-2″-O-glucosyltransferase (3GGT) from purple sweet potato (Ipomoea batatas) catalyses the conversion of anthocyanidin 3-O-glucoside into anthocyanidin 3-O-sophoroside, which is functionally different from the 3GGT ortholog of Arabidopsis. Phylogenetic analysis indicated regioselectivity of 3GGT using uridine-5'-diphosphate (UDP)-xylose or UDP-glucose as the glycosyl is divergent between Convolvulaceae and Arabidopsis. Homology-based protein modeling and site-directed mutagenesis of Ib3GGT and At3GGT suggested that the Thr-138 of Ib3GGT is a key amino acid residue for UDP-glucose recognition and that it plays a major role in sugar-donor selectivity. Wild-type and ugt79b1 mutants (defective in UDP carbohydrate-dependent glycosyltransferases, UGTs) of Arabidopsis plants overexpressing Ib3GGT produced the new component cyanidin 3-O-sophoroside. Moreover, Ib3GGT expression was associated with anthocyanin accumulation in different tissues during I. batatas plant development and was regulated by the transcription factor IbMYB1. Localization assays for Ib3GGT showed that glycosyl extension occurs in the cytosol and not in the endoplasmic reticulum. This study therefore reveals the function of Ib3GGT in glycosyl extension of anthocyanins and demonstrates that Thr-138 is the key amino acid residue for UDP-glucose recognition.

Dietary phytochemicals in colorectal cancer prevention and treatment: A focus on the molecular mechanisms involved

Worldwide, colorectal cancer (CRC) remains a major cancer type and leading cause of death. Unfortunately, current medical treatments are not sufficient due to lack of effective therapy, adverse side effects, chemoresistance and disease recurrence. In recent decades, epidemiologic observations have highlighted the association between the ingestion of several phytochemical-enriched foods and nutrients and the lower risk of CRC. According to preclinical studies, dietary phytochemicals exert chemopreventive effects on CRC by regulating different markers and signaling pathways; additionally, the gut microbiota plays a role as vital effector in CRC onset and progression, therefore, any dietary alterations in it may affect CRC occurrence. A high number of studies have displayed a key role of growth factors and their signaling pathways in the pathogenesis of CRC. Indeed, the efficiency of dietary phytochemicals to modulate carcinogenic processes through the alteration of different molecular targets, such as Wnt/β-catenin, PI3K/Akt/mTOR, MAPK (p38, JNK and Erk1/2), EGFR/Kras/Braf, TGF-β/Smad2/3, STAT1-STAT3, NF-кB, Nrf2 and cyclin-CDK complexes, has been proven, whereby many of these targets also represent the backbone of modern drug discovery programs. Furthermore, epigenetic analysis showed modified or reversed aberrant epigenetic changes exerted by dietary phytochemicals that led to possible CRC prevention or treatment. Therefore, our aim is to discuss the effects of some common dietary phytochemicals that might be useful in CRC as preventive or therapeutic agents. This review will provide new guidance for research, in order to identify the most studied phytochemicals, their occurrence in foods and to evaluate the therapeutic potential of dietary phytochemicals for the prevention or treatment of CRC by targeting several genes and signaling pathways, as well as epigenetic modifications. In addition, the results obtained by recent investigations aimed at improving the production of these phytochemicals in genetically modified plants have been reported. Overall, clinical data on phytochemicals against CRC are still not sufficient and therefore the preventive impacts of dietary phytochemicals on CRC development deserve further research so as to provide additional insights for human prospective studies.

Flavonoid biosynthetic pathways in plants: Versatile targets for metabolic engineering

Plants, fungi, and microorganisms are equipped with biosynthesis machinery for producing thousands of secondary metabolites. These compounds have important functions in nature as a defence against predators or competitors as well as other ecological significances. The full utilization of these compounds for food, medicine, and other purposes requires a thorough understanding of their structures and the distinct biochemical pathways of their production in cellular systems. In this review, flavonoids as classical examples of secondary metabolites are employed to highlight recent advances in understanding how valuable compounds can be regulated at various levels. With extensive diversity in their chemistry and pharmacology, understanding the metabolic engineering of flavonoids now allows us to fine-tune the eliciting of their production, accumulation, and extraction from living systems. More specifically, recent advances in the shikimic acid and acetate biosynthetic pathways of flavonoids production from metabolic engineering point of view, from genes expression to multiple principles of regulation, are addressed. Specific examples of plants and microorganisms as the sources of flavonoids-based compounds with particular emphasis on therapeutic applications are also discussed.

Identification of transcription factor genes involved in anthocyanin biosynthesis in carrot (Daucus carota L.) using RNA-Seq

BACKGROUND

Anthocyanins are water-soluble colored flavonoids present in multiple organs of various plant species including flowers, fruits, leaves, stems and roots. DNA-binding R2R3-MYB transcription factors, basic helix-loop-helix (bHLH) transcription factors, and WD40 repeat proteins are known to form MYB-bHLH-WD repeat (MBW) complexes, which activates the transcription of structural genes in the anthocyanin pathway. Although black cultivars of carrots (Daucus carota L.) can accumulate large quantities of anthocyanin in their storage roots, the regulatory genes responsible for their biosynthesis are not well characterized. The current study aimed to analyze global transcription profiles based on RNA sequencing (RNA-Seq), and mine MYB, bHLH and WD40 genes that may function as positive or negative regulators in the carrot anthocyanin biosynthesis pathways.

RESULTS

RNA was isolated from differently colored calli, as well as tissue samples from taproots of various black carrot cultivars across the course of development, and gene expression levels of colored and non-colored tissue and callus samples were compared. The expression of 32 MYB, bHLH and WD40 genes were significantly correlated with anthocyanin content in black carrot taproot. Of those, 11 genes were consistently up- or downregulated in a purple color-specific manner across various calli and cultivar comparisons. The expression of 10 out of these 11 genes was validated using real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR).

CONCLUSIONS

The results of this study provide insights into regulatory genes that may be responsible for carrot anthocyanin biosynthesis, and suggest that future focus on them may help improve our overall understanding of the anthocyanin synthesis pathway.

Brassica yellows virus' movement protein upregulates anthocyanin accumulation, leading to the development of purple leaf symptoms on Arabidopsis thaliana

Poleroviruses are widely distributed and often of great economic importance because they cause a variety of symptoms, such as the rolling of young leaves, leaf color changes, and plant decline, in infected plants. However, the molecular mechanism behind these viral-induced symptoms is still unknown. Here, we verified the pathogenicity of the polerovirus Brassica yellows virus (BrYV) by transforming its full-length amplicon into Arabidopsis thaliana, which resulted in many abnormal phenotypes. To better understand the interactions between BrYV and its host, global transcriptome profiles of the transgenic plants were compared with that of non-transgenic Arabidopsis plants. An association between the BrYV- induced purple leaf symptoms and the activation of anthocyanin biosynthesis was noted. Using the transgenic approach, we found that movement protein of BrYV was responsible for the induction of these coloration symptoms. Collectively, our findings demonstrate the BrYV’ pathogenicity and show that the BrYV-induced purple leaf symptom resulted from its movement protein stimulating anthocyanin accumulation.

Protein analysis of moro blood orange pulp during storage at low temperatures

A protein analysis in the pulp of Moro blood oranges (Citrus sinensis L. Osbeck) at the onset and after 30 days of storage at either 4 or 9 °C was performed. All differential proteins belonged to different functional classes (sugar, amino acid and secondary metabolism, defense, stress response, oxidative process, transport and cellular component biogenesis), displaying a differential accumulation in those Moro oranges kept at 9 versus 4 °C, and in those stored at 4 °C versus onset. Anthocyanin biosynthesis structural proteins chalcone synthases and flavonone 3-hydroxylase and different glutathione S-transferases related with their vacuolar transport were up-accumulated in fruits kept at 9 versus 4 °C and versus the onset. Proteins related with defense and oxidative stress displayed a similar pattern, concomitant with a higher anthocyanin content, denoting a possible role of defense and other stress response pathways in anthocyanin production/accumulation.

Boolean Computation in Plants Using Post-translational Genetic Control and a Visual Output Signal

Due to autotrophic growing capacity and extremely rich secondary metabolism, plants should be preferred targets of synthetic biology. However, developments in plants usually run below those in other taxonomic groups. In this work we engineered genetic circuits capable of logic YES, OR and AND Boolean computation in plant tissues with a visual output signal. The circuits, which are deployed by means of Agrobacterium tumefaciens, perform with the conditional activity of the MYB transcription factor Rosea1 from Antirrhinum majus inducing the accumulation of anthocyanins, plant endogenous pigments that are directly visible to the naked eye or accurately quantifiable by spectrophotometric analysis. The translational fusion of Rosea1 to several viral proteins, such as potyvirus NIb or fragments thereof, rendered the transcription factor inactive. However, anthocyanin accumulation could be restored by inserting protease cleavage sites between both moieties of the fusion and by coexpressing specific proteases, such as potyvirus nuclear inclusion a protease.

Molecular Controls of Proanthocyanidin Synthesis and Structure: Prospects for Genetic Engineering in Crop Plants

Proanthocyanidins (PAs) are widespread oligomeric and polymeric flavan-3-ols with significant benefits to human and animal health. As products of the general flavonoid pathway, the biosynthesis of the flavan-3-ols is well-understood and the major enzyme-encoding genes that determine PA structure have been identified. However, the mechanism of PA polymerization remains unknown. The most important transcription factors regulating PA biosynthesis are the MYB factors, potent tools for enhancing PA biosynthesis in plants. In some species, simple overexpression of these transcription factors has led to spectacular successes in upregulating PA synthesis. However, targeted metabolic engineering of the PA structure has not yet been achieved.

Differential Accumulation of Anthocyanins in Dendrobium officinale Stems with Red and Green Peels

Dendrobium officinale stems, including red and green stems, are widely used as a dietary supplement to develop nutraceutical beverages and food products. However, there is no detailed information on pigment composition of red and green stems. Here, we investigated the content and composition of pigments in red and green stems by Ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry and assessed the differential accumulation of anthocyanins at the molecular level. The color of peels in red stems was caused by the presence of anthocyanins in epidermal cells unlike the peels of green stems. The glucoside derivatives delphinidin and cyanidin are responsible for the red color. Within the D. officinale anthocyanidin biosynthetic pathway, DoANS and DoUFGT, coding for anthocyanidin synthase and UDP-glucose flavonoid-3-O-glucosyltransferase, respectively, are critical regulatory genes related to the differential accumulation of anthocyanidin. These findings provide a more complete profile of pigments, especially anthocyanin, in D. officinale stems, and lay a foundation for producing functional foods.

Metabolic engineering of Corynebacterium glutamicum for anthocyanin production

Background

Anthocyanins such as cyanidin 3-O-glucoside (C3G) have wide applications in industry as food colorants. Their current production heavily relies on extraction from plant tissues. Development of a sustainable method to produce anthocyanins is of considerable interest for industrial use. Previously, E. coli-based microbial production of anthocyanins has been investigated extensively. However, safety concerns on E. coli call for the adoption of a safe production host. In the present study, a GRAS bacterium, Corynebacterium glutamicum, was introduced as the host strain to synthesize C3G. We adopted stepwise metabolic engineering strategies to improve the production titer of C3G.

Results

Anthocyanidin synthase (ANS) from Petunia hybrida and 3-O-glucosyltransferase (3GT) from Arabidopsis thaliana were coexpressed in C. glutamicum ATCC 13032 to drive the conversion from catechin to C3G. Optimized expression of ANS and 3GT improved the C3G titer by 1- to 15-fold. Further process optimization and improvement of UDP-glucose availability led to ~ 40 mg/L C3G production, representing a > 100-fold titer increase compared to production in the un-engineered, un-optimized starting strain.

Conclusions

For the first time, we successfully achieved the production of the specialty anthocyanin C3G from the comparatively inexpensive flavonoid precursor catechin in C. glutamicum. This study opens up more possibility of C. glutamicum as a host microbe for the biosynthesis of useful and value-added natural compounds.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0990-z) contains supplementary material, which is available to authorized users.

Understanding the genetic regulation of anthocyanin biosynthesis in plants - Tools for breeding purple varieties of fruits and vegetables

Anthocyanins are naturally occurring flavonoids derived from the phenylpropanoid pathway. There is increasing evidence of the preventative and protective roles of anthocyanins against a broad range of pathologies, including different cancer types and metabolic diseases. However, most of the fresh produce available to consumers typically contains only small amounts of anthocyanins, mostly limited to the epidermis of plant organs. Therefore, transgenic and non-transgenic approaches have been proposed to enhance the levels of this phytonutrient in vegetables, fruits, and cereals. Here, were review the current literature on the anthocyanin biosynthesis pathway in model and crop species, including the structural and regulatory genes involved in the differential pigmentation patterns of plant structures. Furthermore, we explore the genetic regulation of anthocyanin biosynthesis and the reasons why it is strongly repressed in specific cell types, in order to create more efficient breeding strategies to boost the biosynthesis and accumulation of anthocyanins in fresh fruits and vegetables.

Differential expression of anthocyanin structural genes and transcription factors determines coloration patterns in gerbera flowers

We investigated the expression of anthocyanin structural genes and transcription factors (TFs) associated with varying anthocyanin content during different developmental stages (S1-S4) of the gerbera cultivars 'Nathasha' and 'Rosalin'. Accumulation of anthocyanin started at S1 and reached a maximum at S3 in both cultivars. Enhancement of anthocyanin content in 'Nathasha' was associated with upregulation of ANS and MYB10, whereas in 'Rosalin', upregulation was associated with CHS1, MYB10, and MYC1. Low-temperature exposure (6 °C) enhanced anthocyanin content to a greater extent than that at 22 °C via stronger upregulation of CHS1 and MYB10 in 'Nathasha' and CHS1 in 'Rosalin', irrespective of flower developmental stage. However, differences in anthocyanin content between the two cultivars were found to be influenced by the expression levels of all structural genes and TFs, irrespective of flower developmental stage and temperature conditions. We suggest that differences in the regulation mechanisms of anthocyanin biosynthesis and coloration pattern between 'Nathasha' and 'Rosalin' are related to differences in the expression patterns of structural genes and TFs; however, further functional studies of the key genes in anthocyanin biosynthesis are needed.

The bZip transcription factor HY5 mediates CRY1a-induced anthocyanin biosynthesis in tomato

The production of anthocyanin is regulated by light and corresponding photoreceptors. In this study, we found that exposure to blue light and overexpression of CRY1a are associated with increased accumulation of anthocyanin in tomato (Solanum lycopersicum L.). These responses are the result of changes in mRNA and the protein levels of SlHY5, which is a transcription factor. In vitro and in vivo experiments using electrophoretic mobility shift assay and ChIP-qPCR assays revealed that SlHY5 could directly recognize and bind to the G-box and ACGT-containing element in the promoters of anthocyanin biosynthesis genes, such as chalcone synthase 1, chalcone synthase 2, and dihydroflavonol 4-reductase. Silencing of SlHY5 in OE-CRY1a lines decreased the accumulation of anthocyanin. The findings presented here not only deepened our understanding of how light controls anthocyanin biosynthesis and associated photoprotection in tomato leaves, but also allowed us to explore potential targets for improving pigment production.

Full-length transcriptome sequences and the identification of putative genes for flavonoid biosynthesis in safflower

Background

The flower of the safflower (Carthamus tinctorius L.) has been widely used in traditional Chinese medicine for the ability to improve cerebral blood flow. Flavonoids are the primary bioactive components in safflower, and their biosynthesis has attracted widespread interest. Previous studies mostly used second-generation sequencing platforms to survey the putative flavonoid biosynthesis genes. For a better understanding of transcription data and the putative genes involved in flavonoid biosynthesis in safflower, we carry our study.

Results

High-quality RNA was extracted from six types of safflower tissue. The RNAs of different tissues were mixed equally and used for multiple size-fractionated libraries (1–2, 2–3 and 3-6 k) library construction. Five cells were carried (2 cells for 1–2 and for 2-3 k libraries and 1 cell for 3-6 k libraries). 10.43Gb clean data and 38,302 de-redundant sequences were captured. 44 unique isoforms were annotated as encoding enzymes involved in flavonoid biosynthesis. The full length flavonoid genes were characterized and their evolutional relationship and expressional pattern were analyzed. They can be divided into eight families, with a large differences in the tissue expression. The temporal expressions under MeJA treatment were also measured, 9 genes are significantly up-regulated and 2 genes are significantly down-regulated. The genes involved in flavonoid synthesis in safflower were predicted in our study. Besides, the SSR and lncRNA are also analyzed in our study.

Conclusions

Full-length transcriptome sequences were used in our study. The genes involved in flavonoid synthesis in safflower were predicted in our study. Combined the determination of flavonoids, CtC4H2, CtCHS3, CtCHI3, CtF3H3, CtF3H1 are mainly participated in MeJA promoting the synthesis of flavonoids. Our results also provide a valuable resource for further study on safflower.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4946-9) contains supplementary material, which is available to authorized users.

The Vacuolar Transportome of Plant Specialized Metabolites

The plant vacuole is a cellular compartment that is essential to plant development and growth. Often plant vacuoles accumulate specialized metabolites, also called secondary metabolites, which constitute functionally and chemically diverse compounds that exert in planta many essential functions and improve the plant's fitness. These metabolites provide, for example, chemical defense against herbivorous and pathogens or chemical attractants (color and fragrance) to attract pollinators. The chemical composition of the vacuole is dynamic, and is altered during development and as a response to environmental changes. To some extent these alterations rely on vacuolar transporters, which import and export compounds into and out of the vacuole, respectively. During the past decade, significant progress was made in the identification and functional characterization of the transporters implicated in many aspects of plant specialized metabolism. Still, deciphering the molecular players underlying such processes remains a challenge for the future. In this review, we present a comprehensive summary of the most recent achievements in this field.

Colour bio-factories: Towards scale-up production of anthocyanins in plant cell cultures

Anthocyanins are widely distributed, glycosylated, water-soluble plant pigments, which give many fruits and flowers their red, purple or blue colouration. Their beneficial effects in a dietary context have encouraged increasing use of anthocyanins as natural colourants in the food and cosmetic industries. However, the limited availability and diversity of anthocyanins commercially have initiated searches for alternative sources of these natural colourants. In plants, high-level production of secondary metabolites, such as anthocyanins, can be achieved by engineering of regulatory genes as well as genes encoding biosynthetic enzymes. We have used tobacco lines which constitutively produce high levels of cyanidin 3-O-rutinoside, delphinidin 3-O-rutinoside or a novel anthocyanin, acylated cyanidin 3-O-(coumaroyl) rutinoside to generate cell suspension cultures. The cell lines are stable in their production rates and superior to conventional plant cell cultures. Scale-up of anthocyanin production in small scale fermenters has been demonstrated. The cell cultures have also proven to be a suitable system for production of 13C-labelled anthocyanins. Our method for anthocyanin production is transferable to other plant species, such as Arabidopsis thaliana, demonstrating the potential of this approach for making a wide range of highly-decorated anthocyanins. The tobacco cell cultures represent a customisable and sustainable alternative to conventional anthocyanin production platforms and have considerable potential for use in industrial and medical applications of anthocyanins.

Higher anthocyanin accumulation associated with higher transcription levels of anthocyanin biosynthesis genes in spinach

Spinach (Spinacia oleracea L.) is widely cultivated as an economically important green leafy vegetable crop for fresh and processing consumption. The red-purple spinach shows abundant anthocyanin accumulation in the leaf and leaf petiole. However, the molecular mechanisms of anthocyanin synthesis in this species are still undetermined. In the present study, we investigated pigment formation and identified anthocyanin biosynthetic genes in spinach. We also analyzed the expression of these genes in purple and green cultivars by quantitative PCR. The accumulation of anthocyanin showed that it was the dominant pigment resulting in the red coloration in spinach. In total, 22 biosynthesis genes and 25 regulatory genes were identified in spinach, based on the spinach genomic and transcriptomic database. Furthermore, the expression patterns of genes encoding enzymes indicated that SoPAL, SoUFGT3, and SoUFGT4 were possible candidate genes for anthocyanin biosynthesis in red-purple spinach. The expression patterns of transcription factors indicated that two SoMYB genes, three SobHLH genes, and one SoWD40 gene were drastically up-regulated and co-expression in red-purple spinach, suggesting an essential role of regulatory genes in the anthocyanin biosynthesis of spinach. These results will enhance our understanding of the molecular mechanisms of anthocyanin biosynthesis in purple spinach.

Molecular Cloning and Functional Characterization of a Dihydroflavonol 4-Reductase from Vitis bellula

Vitis bellula is a new grape crop in southern China. Berries of this species are rich in antioxidative anthocyanins and proanthocyanidins. This study reports cloning and functional characterization of a cDNA encoding a V. bellula dihydroflavonol reductase (VbDFR) involved in the biosynthesis of anthocyanins and proanthocyanidins. A cDNA including 1014 bp was cloned from young leaves and its open reading frame (ORF) was deduced encoding 337 amino acids, highly similar to V. vinifera DFR (VvDFR). Green florescence protein fusion and confocal microscopy analysis determined the cytosolic localization of VbDFR in plant cells. A soluble recombinant VbDFR was induced and purified from E. coli for enzyme assay. In the presence of NADPH, the recombinant enzyme catalyzed dihydrokaempferol (DHK) and dihydroquercetin (DHQ) to their corresponding leucoanthocyanidins. The VbDFR cDNA was introduced into tobacco plants via Agrobacterium-mediated transformation. The overexpression of VbDFR increased anthocyanin production in flowers. Anthocyanin hydrolysis and chromatographic analysis revealed that transgenic flowers produced pelargonidin and delphinidin, which were not detected in control flowers. These data demonstrated that the overexpression of VbDFR produced new tobacco anthocyanidins. In summary, all data demonstrate that VbDFR is a useful gene to provide three types of substrates for metabolic engineering of anthocyanins and proanthocyanidins in grape crops and other crops.

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.

Anthocyanin Biosynthesis and Degradation Mechanisms in Solanaceous Vegetables: A Review

Anthocyanins are a group of polyphenolic pigments that are ubiquitously found in the plant kingdom. In plants, anthocyanins play a role not only in reproduction, by attracting pollinators and seed dispersers, but also in protection against various abiotic and biotic stresses. There is accumulating evidence that anthocyanins have health-promoting properties, which makes anthocyanin metabolism an interesting target for breeders and researchers. In this review, the state of the art knowledge concerning anthocyanins in the Solanaceous vegetables, i.e., pepper, tomato, eggplant, and potato, is discussed, including biochemistry and biological function of anthocyanins, as well as their genetic and environmental regulation. Anthocyanin accumulation is determined by the balance between biosynthesis and degradation. Although the anthocyanin biosynthetic pathway has been well-studied in Solanaceous vegetables, more research is needed on the inhibition of biosynthesis and, in particular, the anthocyanin degradation mechanisms if we want to control anthocyanin content of Solanaceous vegetables. In addition, anthocyanin metabolism is distinctly affected by environmental conditions, but the molecular regulation of these effects is poorly understood. Existing knowledge is summarized and current gaps in our understanding are highlighted and discussed, to create opportunities for the development of anthocyanin-rich crops through breeding and environmental management.

ROS-Induced anthocyanin production provides feedback protection by scavenging ROS and maintaining photosynthetic capacity in Arabidopsis

Anthocyanins are water-soluble pigments with antioxidant activities. In plants, multiple factors can trigger the accumulation of anthocyanins, including chemicals and environmental factors. Reactive oxygen species (ROS) are common by-products produced under different biotic and abiotic conditions and cause oxidative stress when accumulated at a high level in plant cells. This in turn leads to the production of anthocyanins. However, the mechanisms of ROS-induced anthocyanin accumulation and the role of anthocyanins in the response of plants to different stresses are largely unknown. We have recently reported the cross-regulation between ROS and anthocyanin production through analyzing ten Arabidopsis mutants covering the main anthocyanin regulatory and biosynthetic genes grown under different ROS-generating stresses. Here, we describe the general phenotypic response of anthocyanin mutants under normal and ROS-generating stress conditions, showing the changing levels of anthocyanin accumulation and their sensitivity to stresses. In addition, we propose a model that describes a particular gene interaction that highlights how the cross-regulation mechanisms between ROS and anthocyanin production are essential for plant resistance to various stresses through removing excessive ROS and maintaining photosynthetic capacity.

Production of red-flowered oilseed rape via the ectopic expression of Orychophragmus violaceus OvPAP2

Oilseed rape (Brassica napus L.), which has yellow flowers, is both an important oil crop and a traditional tourism resource in China, whereas the Orychophragmus violaceus, which has purple flowers, likely possesses a candidate gene or genes to alter the flower colour of oilseed rape. A previously established B. napus line has a particular pair of O. violaceus chromosomes (M4) and exhibits slightly red petals. In this study, the transcriptomic analysis of M4, B. napus (H3), and O. violaceus with purple petals (OvP) and with white petals (OvW) revealed that most anthocyanin biosynthesis genes were up-regulated in both M4 and OvP. Read assembly and sequence alignment identified a homolog of AtPAP2 in M4, which produced the O. violaceus transcript (OvPAP2). The overexpression of OvPAP2 via the CaMV35S promoter in Arabidopsis thaliana led to different levels of anthocyanin accumulation in most organs, including the petals. However, the B. napus overexpression plants showed anthocyanin accumulation primarily in the anthers, but not the petals. However, when OvPAP2 was driven by the petal-specific promoter XY355, the transgenic B. napus plants produced red anthers and red petals. The results of metabolomic experiments showed that specific anthocyanins accumulated to high levels in the red petals. This study illustrates the feasibility of producing red-flowered oilseed rape, thereby enhancing its ornamental value, via the ectopic expression of the OvPAP2 gene. Moreover, the practical application of this study for insect pest management in the crop is discussed.

Next-Generation Plant Metabolic Engineering, Inspired by an Ancient Chinese Irrigation System

Specialized secondary metabolites serve not only to protect plants against abiotic and biotic challenges, but have also been used extensively by humans to combat diseases. Due to the great importance of medicinal plants for health, we need to find new and sustainable ways to improve the production of the specialized metabolites. In addition to direct extraction, recent progress in metabolic engineering of plants offers an alternative supply option. We argue that metabolic engineering for producing the secondary metabolites in plants may have distinct advantages over microbial production platforms, and thus propose new approaches of plant metabolic engineering, which are inspired by an ancient Chinese irrigation system. Metabolic engineering strategies work at three levels: introducing biosynthetic genes, using transcription factors, and improving metabolic flux including increasing the supply of precursors, energy, and reducing power. In addition, recent progress in biotechnology contributes markedly to better engineering, such as the use of specific promoters and the deletion of competing branch pathways. We propose that next-generation plant metabolic engineering will improve current engineering strategies, for the purpose of producing valuable metabolites in plants on industrial scales.

On the natural diversity of phenylacylated-flavonoid and their in planta function under conditions of stress

Plants contain light signaling systems and undergo metabolic perturbation and reprogramming under light stress in order to adapt to environmental changes. Flavonoids are one of the largest classes of natural phytochemical compounds having several biological functions conferring stress defense to plants and health benefits in animal diets. A recent study of phenylacylated-flavonoids (also called hydroxycinnamoylated-flavonoids) of natural accessions of Arabidopsis suggested that phenylacylation of flavonoids relates to selection under different natural light conditions. Phenylacylated-flavonoids which are decorated with hydroxycinnamoyl units, namely cinnamoyl, 4-coumaroyl, caffeoyl, feruloyl and sinapoyl moieties, are widely distributed in the plant kingdom. Currently, more than 400 phenylacylated flavonoids have been reported. Phenylacylation renders enhanced phytochemical functions such as ultraviolet-absorbance and antioxidant activity, although, the physiological role of phenylacylation of flavonoids in plants is largely unknown. In this review, we provide an overview of the occurrence and natural diversity of phenylacylated-flavonoids as well as postulating their biological functions both in planta and with respect to biological activity following their consumption.

AetMYC1, the Candidate Gene Controlling the Red Coleoptile Trait in Aegilops tauschii Coss. Accession As77

The red coleoptile trait can help monocotyledonous plants withstand stresses, and key genes responsible for the trait have been isolated from Triticum aestivum, Triticum urartu, and Triticum monococcum, but no corresponding research has been reported for Aegilops tauschii. In this research, transcriptome analysis was performed to isolate the candidate gene controlling the white coleoptile trait in Ae. tauschii. There were 5348 upregulated, differentially-expressed genes (DEGs) and 4761 downregulated DEGs in red coleoptile vs. white coleoptile plants. Among these DEGs, 12 structural genes and two transcription factors involved in anthocyanin biosynthesis were identified. The majority of structural genes showed lower transcript abundance in the white coleoptile of accession ‘As77’ than in the red coleoptile of accession ‘As60’, which implied that transcription factors related to anthocyanin biosynthesis could be the candidate genes. The MYB and MYC transcription factors AetMYB7D and AetMYC1 were both isolated from Ae. tauschii accessions ‘As60’ and ‘As77’, and their transcript levels analyzed. The coding sequence and transcript level of AetMYB7D showed no difference between ‘As60’ and ‘As77’. AetMYC1p encoded a 567-amino acid polypeptide in ‘As60’ containing the entire characteristic domains, bHLH-MYC_N, HLH, and ACT-like, belonging to the gene family involved in regulating anthocyanin biosynthesis. AetMYC1w encoded a 436-amino acid polypeptide in ‘As77’ without the ACT-like domain because a single nucleotide mutation at 1310 bp caused premature termination. Transient expression of AetMYC1p induced anthocyanin biosynthesis in ‘As77’ with the co-expression of AetMYB7D, while AetMYC1w could not cause induced anthocyanin biosynthesis under the same circumstances. Moreover, the transcript abundance of AetMYC1w was lower than that of AetMYC1p. AetMYC1 appears to be the candidate gene controlling the white coleoptile trait in Ae. tauschii, which can be used for potential biotech applications, such as producing new synthetic hexaploid wheat lines with different coleoptile colors.

Production of anthocyanins in metabolically engineered microorganisms: Current status and perspectives

Microbial production of plant-derived natural products by engineered microorganisms has achieved great success thanks to large extend to metabolic engineering and synthetic biology. Anthocyanins, the water-soluble colored pigments found in terrestrial plants that are responsible for the red, blue and purple coloration of many flowers and fruits, are extensively used in food and cosmetics industry; however, their current supply heavily relies on complex extraction from plant-based materials. A promising alternative is their sustainable production in metabolically engineered microbes. Here, we review the recent progress on anthocyanin biosynthesis in engineered bacteria, with a special focus on the systematic engineering modifications such as selection and engineering of biosynthetic enzymes, engineering of transportation, regulation of UDP-glucose supply, as well as process optimization. These promising engineering strategies will facilitate successful microbial production of anthocyanins in industry in the near future.

ROS Induces Anthocyanin Production Via Late Biosynthetic Genes and Anthocyanin Deficiency Confers the Hypersensitivity to ROS-Generating Stresses in Arabidopsis

Anthocyanins are known to have antioxidant activities. Their accumulation can be triggered by many chemical and environmental factors, including reactive oxygen species (ROS). However, the mechanism of ROS-induced anthocyanin accumulation and the role of anthocyanins in the response of Arabidopsis (Arabidopsis thaliana) to different stresses are largely unknown. Here, we study the cross-regulation between ROS and anthocyanin production. Ten Arabidopsis mutants covering the main anthocyanin regulatory and biosynthetic genes are systematically analyzed under ROS-generating stresses. We find that ROS triggers anthocyanin accumulation by up-regulating the anthocyanin late biosynthetic and the corresponding regulatory genes. The anthocyanin-deficient mutants have more endogenous ROS and are more sensitive to ROS-generating stresses while having decreased antioxidant capacity. Supplementation with cyanidin makes them less susceptible to ROS, with increased anthocyanin and reduced ROS accumulation. In contrast, pap1-D, which overaccumulates anthocyanins, shows the opposite responses. Gene expression analysis reveals that photosynthetic capacity is more impaired in anthocyanin-deficient mutants under high-light stress. Expression levels of ROS-scavenging enzyme genes are not correlated with the radical-scavenging activity in different mutants. We conclude that ROS are an important source signal to induce anthocyanin accumulation by up-regulating late biosynthetic and the corresponding regulatory genes and, as a feed-back regulation, anthocyanins modulate the ROS level and the sensitivity to ROS-generating stresses in maintaining photosynthetic capacity.

ThMYC4E, candidate Blue aleurone 1 gene controlling the associated trait in Triticum aestivum

Blue aleurone is a useful and interesting trait in common wheat that was derived from related species. Here, transcriptomes of blue and white aleurone were compared for isolating Blue aleurone 1 (Ba1) transferred from Thinopyrum ponticum. In the genes involved in anthocyanin biosynthesis, only a basic helix-loop-helix (bHLH) transcription factor, ThMYC4E, had a higher transcript level in blue aleurone phenotype, and was homologous to the genes on chromosome 4 of Triticum aestivum. ThMYC4E carried the characteristic domains (bHLH-MYC_N, HLH and ACT-like) of a bHLH transcription factor, and clustered with genes regulating anthocyanin biosynthesis upon phylogenetic analysis. The over-expression of ThMYC4E regulated anthocyanin biosynthesis with the coexpression of the MYB transcription factor ZmC1 from maize. ThMYC4E existed in the genomes of the addition, substitution and near isogenic lines with the blue aleurone trait derived from Th. ponticum, and could not be detected in any germplasm of T. urartu, T. monococcum, T. turgidum, Aegilops tauschii or T. aestivum, with white aleurone. These results suggested that ThMYC4E was candidate Ba1 gene controlling the blue aleurone trait in T. aestivum genotypes carrying Th. ponticum introgression. The ThMYC4E isolation aids in better understanding the genetic mechanisms of the blue aleurone trait and in its more effective use during wheat breeding.

Current understanding of the pathways of flavonoid biosynthesis in model and crop plants

Flavonoids are a signature class of secondary metabolites formed from a relatively simple collection of scaffolds. They are extensively decorated by chemical reactions including glycosylation, methylation, and acylation. They are present in a wide variety of fruits and vegetables and as such in Western populations it is estimated that 20-50 mg of flavonoids are consumed daily per person. In planta they have demonstrated to contribute to both flower color and UV protection. Their consumption has been suggested to presenta wide range of health benefits. Recent technical advances allowing affordable whole genome sequencing, as well as a better inventory of species-by-species chemical diversity, have greatly advanced our understanding as to how flavonoid biosynthesis pathways vary across species. In parallel, reverse genetics combined with detailed molecular phenotyping is currently allowing us to elucidate the functional importance of individual genes and metabolites and by this means to provide further mechanistic insight into their biological roles. Here we provide an inventory of current knowledge of pathways of flavonoid biosynthesis in both the model plant Arabidopsis thaliana and a range of crop species, including tomato, maize, rice, and bean.

Development of "Purple Endosperm Rice" by Engineering Anthocyanin Biosynthesis in the Endosperm with a High-Efficiency Transgene Stacking System

Anthocyanins have high antioxidant activities, and engineering of anthocyanin biosynthesis in staple crops, such as rice (Oryza sativa L.), could provide health-promoting foods for improving human health. However, engineering metabolic pathways for biofortification remains difficult, and previous attempts to engineer anthocyanin production in rice endosperm failed because of the sophisticated genetic regulatory network of its biosynthetic pathway. In this study, we developed a high-efficiency vector system for transgene stacking and used it to engineer anthocyanin biosynthesis in rice endosperm. We made a construct containing eight anthocyanin-related genes (two regulatory genes from maize and six structural genes from Coleus) driven by the endosperm-specific promoters,plus a selectable marker and a gene for marker excision. Transformation of rice with this construct generated a novel biofortified germplasm "Purple Endosperm Rice" (called "Zijingmi" in Chinese), which has high anthocyanin contents and antioxidant activity in the endosperm. This anthocyanin production results from expression of the transgenes and the resulting activation (or enhancement) of expression of 13 endogenous anthocyanin biosynthesis genes that are silenced or expressed at low levels in wild-type rice endosperm. This study provides an efficient, versatile toolkit for transgene stacking and demonstrates its use for successful engineering of a sophisticated biological pathway, suggesting the potential utility of this toolkit for synthetic biology and improvement of agronomic traits in plants.

Ectopic Expression of the Grape Hyacinth (Muscari armeniacum) R2R3-MYB Transcription Factor Gene, MaAN2, Induces Anthocyanin Accumulation in Tobacco

Anthocyanins are responsible for the different colors of ornamental plants. Grape hyacinth (Muscari armeniacum), a monocot plant with bulbous flowers, is popular for its fascinating blue color. In the present study, we functionally characterized an R2R3-MYB transcription factor gene MaAN2 from M. armeniacum. Our results indicated that MaAN2 participates in controlling anthocyanin biosynthesis. Sequence alignment and phylogenetic analysis suggested that MaAN2 belonged to the R2R3-MYB family AN2 subgroup. The anthocyanin accumulation of grape hyacinth flowers was positively correlated with the expression of MaAN2. And the transcriptional expression of MaAN2 was also consistent with that of M. armeniacum dihydroflavonol 4-reductase (MaDFR) and M. armeniacum anthocyanidin synthase (MaANS) in flowers. A dual luciferase transient expression assay indicated that when MaAN2 was co-inflitrated with Arabidopsis thaliana TRANSPARENT TESTA8 (AtTT8), it strongly activated the promoters of MaDFR and MaANS, but not the promoters of M. armeniacum chalcone synthase (MaCHS), M. armeniacum chalcone isomerase (MaCHI), and M. armeniacum flavanone 3-hydroxylase (MaF3H). Bimolecular fluorescence complementation assay confirmed that MaAN2 interacted with AtTT8 in vivo. The ectopic expression of MaAN2 in Nicotiana tabacum resulted in obvious red coloration of the leaves and much redder flowers. Almost all anthocyanin biosynthetic genes were remarkably upregulated in the leaves and flowers of the transgenic tobacco, and NtAn1a and NtAn1b (two basic helix-loop-helix anthocyanin regulatory genes) were highly expressed in the transformed leaves, compared to the empty vector transformants. Collectively, our results suggest that MaAN2 plays a role in anthocyanin biosynthesis.

Meta-Analyses of QTLs Associated with Protein and Oil Contents and Compositions in Soybean [Glycine max (L.) Merr.] Seed

Soybean [Glycine max (L.) Merr.] is a valuable and nutritious crop in part due to the high protein meal and vegetable oil produced from its seed. Soybean producers desire cultivars with both elevated seed protein and oil concentrations as well as specific amino acid and fatty acid profiles. Numerous studies have identified quantitative trait loci (QTLs) associated with seed composition traits, but validation of these QTLs has rarely been carried out. In this study, we have collected information, including genetic location and additive effects, on each QTL for seed contents of protein and oil, as well as amino acid and fatty acid compositions from over 80 studies. Using BioMercator V. 4.2, a meta-QTL analysis was performed with genetic information comprised of 175 QTLs for protein, 205 QTLs for oil, 156 QTLs for amino acids, and 113 QTLs for fatty acids. A total of 55 meta-QTL for seed composition were detected on 6 out of 20 chromosomes. Meta-QTL possessed narrower confidence intervals than the original QTL and candidate genes were identified within each meta-QTL. These candidate genes elucidate potential natural genetic variation in genes contributing to protein and oil biosynthesis and accumulation, providing meaningful information to further soybean breeding programs.

Anthocyanin biosynthesis and accumulation in blood oranges during postharvest storage at different low temperatures

Blood oranges require low temperature for anthocyanin production. We have investigated the activation of anthocyanin biosynthesis and accumulation in the pulp of Moro blood and Pera blond oranges (Citrus sinensis L. Osbeck) stored at either 4 or 9°C after harvesting. Both temperatures stimulated anthocyanin accumulation in blood but not in blond oranges. Nonetheless, blood orange fruits stored at 9°C reached a darker purple coloration, higher anthocyanin contents and enhanced upregulation of genes from the flavonoid pathway in the pulp and juice than those kept at 4°C. Our results indicated that dihydroflavonol channeling toward anthocyanin production was boosted during the storage at 9°C compared to 4°C, providing more leucoanthocyanidins to enzymes downstream in the pathway. Finally, despite both low temperatures stimulated the expression of key transcription factors likely regulating the pathway, their expression profiles could not explain the differences observed at 9 and 4°C.

A Recombinant Potato virus Y Infectious Clone Tagged with the Rosea1 Visual Marker (PVY-Ros1) Facilitates the Analysis of Viral Infectivity and Allows the Production of Large Amounts of Anthocyanins in Plants

Potato virus Y (PVY) is a major threat to the cultivation of potato and other solanaceous plants. By inserting a cDNA coding for the Antirrhinum majus Rosea1 transcription factor into a PVY infectious clone, we created a biotechnological tool (PVY-Ros1) that allows infection by this relevant plant virus to be tracked by the naked eye with no need for complex instrumentation. Rosea1 is an MYB-type transcription factor whose expression activates the biosynthesis of anthocyanin pigments in a dose-specific and cell-autonomous manner. Our experiments showed that the mechanical inoculation of solanaceous plants with PVY-Ros1 induced the formation of red infection foci in inoculated tissue and solid dark red pigmentation in systemically infected tissue, which allows disease progression to be easily monitored. By using silver nanoparticles, a nanomaterial with exciting antimicrobial properties, we proved the benefits of PVY-Ros1 to analyze novel antiviral treatments in plants. PVY-Ros1 was also helpful for visually monitoring the virus transmission process by an aphid vector. Most importantly, the anthocyanin analysis of infected tobacco tissues demonstrated that PVY-Ros1 is an excellent biotechnological tool for molecular farming because it induces the accumulation of larger amounts of anthocyanins, antioxidant compounds of nutritional, pharmaceutical and industrial interest, than those that naturally accumulate in some fruits and vegetables well known for their high anthocyanin content. Hence these results support the notion that the virus-mediated expression of regulatory factors and enzymes in plants facilitates easy quick plant metabolism engineering.

Aromatic Decoration Determines the Formation of Anthocyanic Vacuolar Inclusions

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

Allelic Variation and Transcriptional Isoforms of Wheat TaMYC1 Gene Regulating Anthocyanin Synthesis in Pericarp

Recently the TaMYC1 gene encoding bHLH transcription factor has been isolated from the bread wheat (Triticum aestivum L.) genome and shown to co-locate with the Pp3 gene conferring purple pericarp color. As a functional evidence of TaMYC1 and Pp3 being the same, higher transcriptional activity of the TaMYC1 gene in colored pericarp compared to uncolored one has been demonstrated. In the current study, we present additional strong evidences of TaMYC1 to be a synonym of Pp3. Furthermore, we have found differences between dominant and recessive Pp3(TaMyc1) alleles. Light enhancement of TaMYC1 transcription was paralleled with increased AP accumulation only in purple-grain wheat. Coexpression of TaMYC1 and the maize MYB TF gene ZmC1 induced AP accumulation in the coleoptile of white-grain wheat. Suppression of TaMYC1 significantly reduced AP content in purple grains. Two distinct TaMYC1 alleles (TaMYC1p and TaMYC1w) were isolated from purple- and white-grained wheat, respectively. A unique, compound cis-acting regulatory element had six copies in the promoter of TaMYC1p, but was present only once in TaMYC1w. Analysis of recombinant inbred lines showed that TaMYC1p was necessary but not sufficient for AP accumulation in the pericarp tissues. Examination of larger sets of germplasm lines indicated that the evolution of purple pericarp in tetraploid wheat was accompanied by the presence of TaMYC1p. Our findings may promote more systematic basic and applied studies of anthocyanins in common wheat and related Triticeae crops.

Dicer-Like 4 Is Involved in Restricting the Systemic Movement of Zucchini yellow mosaic virus in Nicotiana benthamiana

Zucchini yellow mosaic virus (ZYMV) induces serious diseases in cucurbits. To create a tool to screen for resistance genes, we cloned a wild ZYMV isolate and inserted the visual marker Rosea1 to obtain recombinant clone ZYMV-Ros1. While in some plant-virus combinations Rosea1 induces accumulation of anthocyanins in infected tissues, ZYMV-Ros1 infection of cucurbits did not lead to detectable anthocyanin accumulation. However, the recombinant virus did induce dark red pigmentation in infected tissues of the model plant Nicotiana benthamiana. In this species, ZYMV-Ros1 multiplied efficiently in local inoculated tissue but only a few progeny particles established infection foci in upper leaves. We used this system to analyze the roles of Dicer-like (DCL) genes, core components of plant antiviral RNA silencing pathways, in ZYMV infection. ZYMV-Ros1 local replication was not significantly affected in single DCL knockdown lines nor in double DCL2/4 and triple DCL2/3/4 knockdown lines. ZYMV-Ros1 systemic accumulation was not affected in knockdown lines DCL1, DCL2, and DCL3. However in DCL4 and also in DCL2/4 and DCL2/3/4 knockdown lines, ZYMV-Ros1 systemic accumulation dramatically increased, which highlights the key role of DCL4 in restricting virus systemic movement. The effect of DCL4 on ZYMV systemic movement was confirmed with a wild-type version of the virus.

Infiltration-RNAseq: transcriptome profiling of Agrobacterium-mediated infiltration of transcription factors to discover gene function and expression networks in plants

BACKGROUND

Transcription factors (TFs) coordinate precise gene expression patterns that give rise to distinct phenotypic outputs. The identification of genes and transcriptional networks regulated by a TF often requires stable transformation and expression changes in plant cells. However, the production of stable transformants can be slow and laborious with no guarantee of success. Furthermore, transgenic plants overexpressing a TF of interest can present pleiotropic phenotypes and/or result in a high number of indirect gene expression changes. Therefore, fast, efficient, high-throughput methods for assaying TF function are needed.

RESULTS

Agroinfiltration is a simple plant biology method that allows transient gene expression. It is a rapid and powerful tool for the functional characterisation of TF genes in planta. High throughput RNA sequencing is now a widely used method for analysing gene expression profiles (transcriptomes). By coupling TF agroinfiltration with RNA sequencing (named here as Infiltration-RNAseq), gene expression networks and gene function can be identified within a few weeks rather than many months. As a proof of concept, we agroinfiltrated Medicago truncatula leaves with M. truncatula LEGUME ANTHOCYANIN PRODUCITION 1 (MtLAP1), a MYB transcription factor involved in the regulation of the anthocyanin pathway, and assessed the resulting transcriptome. Leaves infiltrated with MtLAP1 turned red indicating the production of anthocyanin pigment. Consistent with this, genes encoding enzymes in the anthocyanin biosynthetic pathway, and known transcriptional activators and repressors of the anthocyanin biosynthetic pathway, were upregulated. A novel observation was the induction of a R3-MYB transcriptional repressor that likely provides transcriptional feedback inhibition to prevent the deleterious effects of excess anthocyanins on photosynthesis.

CONCLUSIONS

Infiltration-RNAseq is a fast and convenient method for profiling TF-mediated gene expression changes. We utilised this method to identify TF-mediated transcriptional changes and TF target genes in M. truncatula and Nicotiana benthamiana. This included the identification of target genes of a TF not normally expressed in leaves, and targets of TFs from other plant species. Infiltration-RNAseq can be easily adapted to other plant species where agroinfiltration protocols have been optimised. The ability to identify downstream genes, including positive and negative transcriptional regulators, will result in a greater understanding of TF function.

Transcriptomics and Metabolite Analysis Reveals the Molecular Mechanism of Anthocyanin Biosynthesis Branch Pathway in Different Senecio cruentus Cultivars

The cyanidin (Cy), pelargonidin (Pg), and delphinidin (Dp) pathways are the three major branching anthocyanin biosynthesis pathways that regulate flavonoid metabolic flux and are responsible for red, orange, and blue flower colors, respectively. Different species have evolved to develop multiple regulation mechanisms that form the branched pathways. In the current study, five Senecio cruentus cultivars with different colors were investigated. We found that the white and yellow cultivars do not accumulate anthocyanin and that the blue, pink, and carmine cultivars mainly accumulate Dp, Pg, and Cy in differing densities. Subsequent transcriptome analysis determined that there were 43 unigenes encoding anthocyanin biosynthesis genes in the blue cultivar. We also combined chemical and transcriptomic analyses to investigate the major metabolic pathways that are related to the observed differences in flower pigmentation in the series of S. cruentus. The results showed that mutations of the ScbHLH17 and ScCHI1/2 coding regions abolish anthocyanin formation in the white and the yellow cultivars; the competition of the ScF3'H1, ScF3'5'H, and ScDFR1/2 genes for naringenin determines the differences in branching metabolic flux of the Cy, Dp, and Pg pathways. Our findings provide new insights into the regulation of anthocyanin branching and also supplement gene resources (including ScF3'5 'H, ScF3'H, and ScDFRs) for flower color modification of ornamentals.

Identification of a R2R3-MYB gene regulating anthocyanin biosynthesis and relationships between its variation and flower color difference in lotus (Nelumbo Adans.)

The lotus (Nelumbonaceae: Nelumbo Adans.) is a highly desired ornamental plant, comprising only two extant species, the sacred lotus (N. nucifera Gaerten.) with red flowers and the American lotus (N. lutea Willd.) with yellow flowers. Flower color is the most obvious difference of two species. To better understand the mechanism of flower color differentiation, the content of anthocyanins and the expression levels of four key structural genes (e.g., DFR, ANS, UFGT and GST) were analyzed in two species. Our results revealed that anthocyanins were detected in red flowers, not yellow flowers. Expression analysis showed that no transcripts of GST gene and low expression level of three UFGT genes were detected in yellow flowers. In addition, three regulatory genes (NnMYB5, NnbHLH1 and NnTTG1) were isolated from red flowers and showed a high similarity to corresponding regulatory genes of other species. Sequence analysis of MYB5, bHLH1 and TTG1 in two species revealed striking differences in coding region and promoter region of MYB5 gene. Population analysis identified three MYB5 variants in Nelumbo: a functional allele existed in red flowers and two inactive forms existed in yellow flowers. This result revealed that there was an association between allelic variation in MYB5 gene and flower color difference. Yeast two-hybrid experiments showed that NnMYB5 interacts with NnbHLH1, NlbHLH1 and NnTTG1, and NnTTG1 also interacts with NnbHLH1 and NlbHLH1. The over-expression of NnMYB5 led to anthocyanin accumulation in immature seeds and flower stalks and up-regulation of expression of TT19 in Arabidopsis. Therefore, NnMYB5 is a transcription activator of anthocyanin synthesis. This study helps to elucidate the function of NnMYB5 and will contribute to clarify the mechanism of flower coloration and genetic engineering of flower color in lotus.

The characteristics and functions of a miniature inverted-repeat transposable element TaMITE81 in the 5' UTR of TaCHS7BL from Triticum aestivum

Miniature inverted-repeat transposable elements (MITEs) are truncated derivatives of autonomous DNA transposons, and are dispersed abundantly in eukaryotic and prokaryotic genomes. In this article, a MITE, TaMITE81, was isolated from the 5' untranslated region (UTR) of TaCHS7BL, chalcone synthase (CHS) catalyzing the first committed step of anthocyanin biosynthesis, in the wheat cultivar 'Opata' with white grain. TaMITE81 was only 81 nucleotides, including a terminal inverted repeat with 39 nucleotides and was flanked by two nucleotides, "TA", target site duplications that were typical features of stowaway-like MITEs. Compared with the wheat cultivar 'Gy115' with purple grain, which is without the insertion, the expression of TaCHS7BL was lower in several organs of 'Opata'. The insertion of TaMITE81 into the 5' UTR of the GUS gene also reduced the transient expression of GUS on the coleoptiles of 'Opata', which means the insertion of TaMITE81 was the reason for the low expression of TaCHS7BL in 'Opata'. But the genotype of TaCHS7BL was not linked to phenotype of grain color in the RILs derived from a cross 'Gy115' and 'Opata'. The TaMITE81 density of the hexaploid variety of T. aestivum was more than 10 times that of diploid relatives, which implies that polyploidization caused the amplification of TaMITE81 homologous sequences. Further research should be conducted on decoding the relationship between TaCHS7BL and other traits relative to anthocyanin biosynthesis in wheat, and discovering the mechanism of TaMITE81 transposon action.

Novel insight into the mechanism underlying light-controlled anthocyanin accumulation in eggplant (Solanum melongena L.)

Eggplant is rich in anthocyanins, which are the major secondary metabolites and beneficial to human health. We discovered that the anthocyanin biosynthesis of eggplant cultivar 'Lanshan Hexian' was regulated by light. In this study, we isolated two blue light receptor genes, SmCRY1 and SmCRY2, and negative/positive anthocyanin regulatory factors SmCOP1 and SmHY5 from eggplant. In terms of transcript levels, SmCRY1, SmCRY2 and SmHY5 were up-regulated by light, while SmCOP1 was down-regulated. Subsequently, the four genes were functionally complemented in phenotype of corresponding mutants, indicating that they act as counterparts of Arabidopsis genes. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that SmCRY1 and SmCRY2 interact with SmCOP1 in a blue-light-dependent manner. It also obtained the result that SmCOP1 interacts with SmHY5 and SmMYB1. Furthermore, using yeast one-hybrid assay, we found that SmHY5 and SmMYB1 both bind the promoters of anthocyanin biosynthesis structural genes (SmCHS and SmDFR). Taken together, blue-light-triggered CRY1/CRY2-COP1 interaction creates the condition that HY5 and MYB1 combine with the downstream anthocyanin synthesis genes (CHS and DFR) in eggplant. Our finding provides a new working model by which light controls anthocyanin accumulation in eggplant.

iTRAQ-Based Quantitative Proteomics Analysis of Black Rice Grain Development Reveals Metabolic Pathways Associated with Anthocyanin Biosynthesis

BACKGROUND

Black rice (Oryza sativa L.), whose pericarp is rich in anthocyanins (ACNs), is considered as a healthier alternative to white rice. Molecular species of ACNs in black rice have been well documented in previous studies; however, information about the metabolic mechanisms underlying ACN biosynthesis during black rice grain development is unclear.

RESULTS

The aim of the present study was to determine changes in the metabolic pathways that are involved in the dynamic grain proteome during the development of black rice indica cultivar, (Oryza sativa L. indica var. SSP). Isobaric tags for relative and absolute quantification (iTRAQ) MS/MS were employed to identify statistically significant alterations in the grain proteome. Approximately 928 proteins were detected, of which 230 were differentially expressed throughout 5 successive developmental stages, starting from 3 to 20 days after flowering (DAF). The greatest number of differentially expressed proteins was observed on 7 and 10 DAF, including 76 proteins that were upregulated and 39 that were downregulated. The biological process analysis of gene ontology revealed that the 230 differentially expressed proteins could be sorted into 14 functional groups. Proteins in the largest group were related to metabolic process, which could be integrated into multiple biochemical pathways. Specifically, proteins with a role in ACN biosynthesis, sugar synthesis, and the regulation of gene expression were upregulated, particularly from the onset of black rice grain development and during development. In contrast, the expression of proteins related to signal transduction, redox homeostasis, photosynthesis and N-metabolism decreased during grain maturation. Finally, 8 representative genes encoding different metabolic proteins were verified via quantitative real-time polymerase chain reaction (qRT-PCR) analysis, these genes had differed in transcriptional and translational expression during grain development.

CONCLUSIONS

Expression analyses of metabolism-related protein groups belonging to different functional categories and subcategories indicated that significantly upregulated proteins were related to flavonoid and starch synthesis. On the other hand, the downregulated proteins were determined to be related to nitrogen metabolism, as well as other functional categories and subcategories, including photosynthesis, redox homeostasis, tocopherol biosynthetic, and signal transduction. The results provide valuable new insights into the characterization and understanding of ACN pigment production in black rice.

Scutellaria baicalensis, the golden herb from the garden of Chinese medicinal plants

Scutellaria baicalensis Georgi, or Chinese skullcap, has been widely used as a medicinal plant in China for thousands of years, where the preparation from its roots is called Huang-Qin. It has been applied in the treatment of diarrhea, dysentery, hypertension, hemorrhaging, insomnia, inflammation and respiratory infections. Flavones such as baicalin, wogonoside and their aglycones baicalein wogonin are the major bioactive compounds extracted from the root of S. baicalensis. These flavones have been reported to have various pharmacological functions, including anti-cancer, hepatoprotection, antibacterial and antiviral, antioxidant, anticonvulsant and neuroprotective effects. In this review, we focus on clinical applications and the pharmacological properties of the medicinal plant and the flavones extracted from it. We also describe biotechnological and metabolic methods that have been used to elucidate the biosynthetic pathways of the bioactive compounds in Scutellaria.

Current status and biotechnological advances in genetic engineering of ornamental plants

Cut flower markets are developing in many countries as the international demand for cut flowers is rapidly growing. Developing new varieties with modified characteristics is an important aim in floriculture. Production of transgenic ornamental plants can shorten the time required in the conventional breeding of a cultivar. Biotechnology tools in combination with conventional breeding methods have been used by cut flower breeders to change flower color, plant architecture, post-harvest traits, and disease resistance. In this review, we describe advances in genetic engineering that have led to the development of new cut flower varieties.