Betalain induction by l-DOPA application confers photoprotection to saline-exposed leaves of Disphyma australe

Heterologous biosynthesis of betanin triggers metabolic reprogramming in tobacco

Engineering of a specialized metabolic pathway in plants is a promising approach to produce high-value bioactive compounds to address the challenges of climate change and population growth. Understanding the interaction between the heterologous pathway and the native metabolic network of the host plant is crucial for optimizing the engineered system and maximizing the yield of the target compound. In this study, we performed transcriptomic, metabolomic and metagenomic analysis of tobacco (Nicotiana tabacum) plants engineered to produce betanin, an alkaloid pigment that is found in Caryophyllaceae plants. Our data reveals that, in a dose-dependent manor, the biosynthesis of betanin promotes carbohydrate metabolism and represses nitrogen metabolism in the leaf, but enhances nitrogen assimilation and metabolism in the root. By supplying nitrate or ammonium, the accumulation of betanin increased by 1.5-3.8-fold in leaves and roots of the transgenic plants, confirming the pivotal role of nitrogen in betanin production. In addition, the rhizosphere microbial community is reshaped to reduce denitrification and increase respiration and oxidation, assistant to suppress nitrogen loss. Our analysis not only provides a framework for evaluating the pleiotropic effects of an engineered metabolic pathway on the host plant, but also facilitates the development of novel strategies to balance the heterologous process and the native metabolic network for the high-yield and nutrient-efficient production of bioactive compounds in plants.

Melatonin application enhances salt stress-induced decreases in minerals, betalains, and phenolic acids in beet (Beta vulgaris L.) cultivars

Melatonin is a potentially active signaling molecule and plays a crucial role in regulating the growth and development of plants under stress conditions, alleviating oxidative damage, enhancing antioxidant defence mechanisms and regulating ion homeostasis. This study examined the effects of exogenous melatonin application on leaf biomass, ion concentrations, betalains, phenolic acid and endogenous melatonin contents comparing red beet (Beta vulgaris L. 'Ruby Queen' and 'Scarlet Supreme') and white beet ('Rodeo' and 'Ansa') cultivars under increasing salinity levels of 50, 150, and 250 mM NaCl. Exogenous melatonin increased salinity-induced reductions in fresh and dry weights and osmotic potential in leaves. Na+ concentrations rose significantly with increasing salinity, but cultivar-specific decreases were observed in K+ and Ca2+ concentrations. Additionally, melatonin application improved betalain, betanin and neobetanin contents induced by salt stress. Furthermore, melatonin application caused salt stress and cultivar-specific changes in phenolic acid contents e.g., ferulic acid, sinapic acid, or m-coumaric acid, in soluble free, ester- and glycoside-conjugated and cell wall-bound forms. In addition, antioxidant enzyme activities and compound contents increased significantly in the beets and were subsequently lowered in a cultivar-specific manner by salt stress + melatonin treatment. The current findings indicate that exogenous melatonin improved plant stress tolerance suppressing reactive oxygen species levels, increasing the antioxidant enzyme activities and compound contents and reducing the levels of Na+, maintaining an ionic homeostasis in the selected red and white sugar beet cultivars. It appears that melatonin application may help improve cultivar-specific salt tolerance by enhancing ion homeostasis and betalain and phenolic acid production levels in beets.

Quinoa: A Promising Crop for Resolving the Bottleneck of Cultivation in Soils Affected by Multiple Environmental Abiotic Stresses

Quinoa (Chenopodium quinoa Willd.) has gained worldwide recognition for its nutritional values, adaptability to diverse environments, and genetic diversity. This review explores the current understanding of quinoa tolerance to environmental stress, focusing on drought, salinity, heat, heavy metals, and UV-B radiation. Although drought and salinity have been extensively studied, other stress factors remain underexplored. The ever-increasing incidence of abiotic stress, exacerbated by unpredictable weather patterns and climate change, underscores the importance of understanding quinoa's responses to these challenges. Global gene banks safeguard quinoa's genetic diversity, supporting breeding efforts to develop stress-tolerant varieties. Recent advances in genomics and molecular tools offer promising opportunities to improve stress tolerance and increase the yield potential of quinoa. Transcriptomic studies have shed light on the responses of quinoa to drought and salinity, yet further studies are needed to elucidate its resilience to other abiotic stresses. Quinoa's ability to thrive on poor soils and limited water resources makes it a sustainable option for land restoration and food security enterprises. In conclusion, quinoa is a versatile and robust crop with the potential to address food security challenges under environmental constraints.

Identification, expression analysis of quinoa betalain biosynthesis genes and their role in seed germination and cold stress

Betalains provide Chenopodium quinoa bright color, and the key enzyme genes for betalain biosynthesis include CYP76AD, DODA, and GTs. In this study, 59 CqCYP76AD, CqDODA and CqGTs genes in quinoa were identified and characterized by gene structural characteristics, phylogenetic relationships and gene expression patterns. The CqCYP76AD genes were divided into ɑ, β and γ types, CqDODA into ɑ and β types, and CqGTs into CqcDOPA5GT, CqB5GT and CqB6GT types according to phylogenetic relationships. The analysis of co-linearity identified eight pairs of duplicated genes which were subjected to purifying selection during evolution. CqCYP76AD and CqDODA, as well as CqcDOPA5GT and CqB5GT may have been evolutionarily linked in genetic inheritance, based on gene location and gene structure study. The tissue expression specificity of CqCYP76AD, CqDODA, and CqGTs genes in response to seed germination and cold stress was studied by RNA-Seq data. The genes CqCYP76AD, CqDODA, and CqGTs were involved in betalain biosynthesis and cold stress. CqCYP76AD, CqDODA, CqcDOPA5GT and CqB5GT gene sequences were consistent in the eight quinoa samples and showed significant variations in expression. In contrast, the inconsistency between changes in gene expression and betalain accumulation indicates that other factors may influence betalain biosynthesis in quinoa. This study offers the theoretical basis for the roles of the CqCYP76AD, CqDODA, and CqGTs genes in betalain biosynthesis and cold stress in quinoa, as well as a guide for the full utilization of betalains in quinoa plants.

Generating colorful carrot germplasm through metabolic engineering of betalains pigments

Betalains are tyrosine-derived plant pigments exclusively found in the Caryophyllales order and some higher fungi and generally classified into two groups: red-violet betacyanins and yellow-orange betaxanthins. Betalains attract great scientific and economic interest because of their relatively simple biosynthesis pathway, attractive colors and health-promoting properties. Co-expressing two core genes BvCYP76AD1 and BvDODA1 with or without a glycosyltransferase gene MjcDOPA5GT allowed the engineering of carrot (an important taproot vegetable) to produce a palette of unique colors. The highest total betalains content, 943.2 μg·g-1 DW, was obtained in carrot taproot transformed with p35S:RUBY which produces all of the necessary enzymes for betalains synthesis. Root-specific production of betalains slightly relieved tyrosine consumption revealing the possible bottleneck in betalains production. Furthermore, a unique volcano-like phenotype in carrot taproot cross-section was created by vascular cambium-specific production of betalains. The betalains-fortified carrot in this study is thus anticipated to be used as functional vegetable and colorful carrot germplasm in breeding to promote health.

Evolution and function of red pigmentation in land plants

BACKGROUND

Land plants commonly produce red pigmentation as a response to environmental stressors, both abiotic and biotic. The type of pigment produced varies among different land plant lineages. In the majority of species they are flavonoids, a large branch of the phenylpropanoid pathway. Flavonoids that can confer red colours include 3-hydroxyanthocyanins, 3-deoxyanthocyanins, sphagnorubins and auronidins, which are the predominant red pigments in flowering plants, ferns, mosses and liverworts, respectively. However, some flowering plants have lost the capacity for anthocyanin biosynthesis and produce nitrogen-containing betalain pigments instead. Some terrestrial algal species also produce red pigmentation as an abiotic stress response, and these include both carotenoid and phenolic pigments.

SCOPE

In this review, we examine: which environmental triggers induce red pigmentation in non-reproductive tissues; theories on the functions of stress-induced pigmentation; the evolution of the biosynthetic pathways; and structure-function aspects of different pigment types. We also compare data on stress-induced pigmentation in land plants with those for terrestrial algae, and discuss possible explanations for the lack of red pigmentation in the hornwort lineage of land plants.

CONCLUSIONS

The evidence suggests that pigment biosynthetic pathways have evolved numerous times in land plants to provide compounds that have red colour to screen damaging photosynthetically active radiation but that also have secondary functions that provide specific benefits to the particular land plant lineage.

Genome-Wide Identification of WRKY Gene Family in Pitaya Reveals the Involvement of HmoWRKY42 in Betalain Biosynthesis

The WRKY gene family is a plant-specific transcription factor (TF) that regulates many physiological processes and (a) biotic stress responses. Despite this, little is known about the molecular properties and roles of WRKY TFs in pitaya betalain biosynthesis. Here we report the identification of 70 WRKY in Hylocereus undatus, their gene structure, locations on each chromosome, systematic phylogenetic analysis, conserved motif analysis, and synteny of HuWRKY genes. HmoWRKY42 is a Group IIb WRKY protein and contains a coiled-coil motif, a WRKY domain and a C₂H₂ zinc-finger motif (CX₅CX₂₃HXH). Results from yeast one-hybrid and transient dual-luciferase assays showed that HmoWRKY42 was a transcriptional repressor and could repress HmocDOPA5GT1 expression by binding to its promoter. Yeast two-hybrid assays showed that HmoWRKY42 could interact with itself to form homodimers. Knocking out the coiled-coil motif of HmoWRKY42 prevented its self-interaction and prevented it from binding to the HmocDOPA5GT1 promoter. Knocking out the WRKY domain and C₂H₂ zinc-finger motif sequence of HmoWRKY42 also prevented it from binding to the HmocDOPA5GT1 promoter. The coiled-coil motif, the WRKY domain and the C₂H₂ zinc finger motif are key motifs for the binding of HmoWRKY42 to the HmocDOPA5GT1 promoter. HmoWRKY42 is localized in the nucleus and possesses trans-activation ability responsible for pitaya betalain biosynthesis by repressing the transcription of HmocDOPA5GT1. As far as we know, no reports are available on the role of HmoWRKY42 in pitaya betalain biosynthesis. The results provide an important foundation for future analyses of the regulation and functions of the HuWRKY gene family.

Comparative transcriptomic profiling in the pulp and peel of pitaya fruit uncovers the gene networks regulating pulp color formation

Pitaya (genus Hylocereus) is a popular fruit. To develop pitaya fruit with greater marketability and high nutritional value, it is important to elucidate the roles of candidate genes and key metabolites that contribute to the coloration of the pitaya pulp and peel. By combining transcriptome and biochemical analyses, we compared and analyzed the dynamic changes in the peel and pulp of H. undatus (white pulp) and H. polyrhizus (red pulp) fruits at four key time points during ripening. Differential expression analysis and temporal analysis revealed the difference regulation in pathways of plant hormone signal transduction, phenylpropanoid biosynthesis, and betalain biosynthesis. Our results suggest that color formation of purple-red peel and pulp of pitaya is influenced by betalains. Increased tyrosine content and fluctuation in acylated betalain content may be responsible for pulp color formation, while some of the key genes in this network showed differential expression patterns during ripening between white pulp and red pulp fruits. The data and analysis results of this study provide theoretical basis for the red color formation mechanism of pitaya, which will facilitate future work to improve pitaya fruit physical appearance and marketability.

A Genome-Wide Identification Study Reveals That HmoCYP76AD1, HmoDODAα1 and HmocDOPA5GT Involved in Betalain Biosynthesis in Hylocereus

Betalains are water-soluble nitrogen-containing pigments with multiple bioactivities. Pitayas are the only at large-scale commercially grown fruit containing abundant betalains for consumers. Currently, the key genes involved in betalain biosynthesis remain to be fully elucidated. Moreover, genome-wide analyses of these genes in betalain biosynthesis are not available in betalain-producing plant species. In this study, totally 53 genes related to betalain biosynthesis were identified from the genome data of Hylocereus undatus. Four candidate genes i.e., one cytochrome P-450 R gene (HmoCYP76AD1), two L-DOPA 4,5-dioxygenase genes (HmoDODAα1 and HmoDODAα2), and one cyclo-DOPA 5-O glucosyltransferase gene (HmocDOPA5GT) were initially screened according to bioinformatics and qRT-PCR analyses. Silencing HmoCYP76AD1, HmoDODAα1, HmoDODAα2 or HmocDOPA5GT resulted in loss of red pigment. HmoDODAα1 displayed a high level of L-DOPA 4,5-dioxygenase activity to produce betalamic acid and formed yellow betaxanthin. Co-expression of HmoCYP76AD1, HmoDODAα1 and HmocDOPA5GT in Nicotiana benthamiana and yeast resulted in high abundance of betalain pigments with a red color. These results suggested that HmoCYP76AD1, HmoDODAα1, and HmocDOPA5GT play key roles in betalain biosynthesis in Hylocereus. The results of the present study provide novel genes for molecular breeding programs of pitaya.

Genome-Wide Transcriptomic and Proteomic Exploration of Molecular Regulations in Quinoa Responses to Ethylene and Salt Stress

Quinoa (Chenopodiumquinoa Willd.), originated from the Andean region of South America, shows more significant salt tolerance than other crops. To reveal how the plant hormone ethylene is involved in the quinoa responses to salt stress, 4-week-old quinoa seedlings of 'NL-6' treated with water, sodium chloride (NaCl), and NaCl with ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were collected and analyzed by transcriptional sequencing and tandem mass tag-based (TMT) quantitative proteomics. A total of 9672 proteins and 60,602 genes was identified. Among them, the genes encoding glutathione S-transferase (GST), peroxidase (POD), phosphate transporter (PT), glucan endonuclease (GLU), beta-galactosidase (BGAL), cellulose synthase (CES), trichome birefringence-like protein (TBL), glycine-rich cell wall structural protein (GRP), glucosyltransferase (GT), GDSL esterase/lipase (GELP), cytochrome P450 (CYP), and jasmonate-induced protein (JIP) were significantly differentially expressed. Further analysis suggested that the genes may mediate through osmotic adjustment, cell wall organization, reactive oxygen species (ROS) scavenging, and plant hormone signaling to take a part in the regulation of quinoa responses to ethylene and salt stress. Our results provide a strong foundation for exploration of the molecular mechanisms of quinoa responses to ethylene and salt stress.

Prickly Pear Betalain-Rich Extracts as New Promising Strategy for Intestinal Inflammation: Plant Complex vs. Main Isolated Bioactive Compounds

Recently, many studies have highlighted the health effects of betalains beyond their use as food dyes. The present study investigated betalain-rich extracts with different colors and their main bioactive compounds in order to provide first evidence as a new promising strategy for intestinal inflammation management. Prickly pear betalain–rich extracts, obtained by a QuEChERS method, have been characterized by LC-DAD-ESI-MS/MS analysis. The potential role of betanin, indicaxanthin, and prickly pear extracts in counteracting the antioxidant and anti-inflammatory events was evaluated by several in vitro cell-free and cell-based assays. Indicaxanthin and betanin represent the most abundant compounds (≥22.27 ± 4.50 and 1.16 ± 0.17 g/100 g dry extract, respectively). Prickly pear extracts showed the strongest antioxidant and anti-inflammatory activities with respect to the pure betalains both on in vitro cell-free and cell-based assays, demonstrating the occurrence of synergistic activity, without any cytotoxicity or alteration of the barrier systems. The release of reactive oxygen species (ROS) and key inflammatory markers (IL-6, IL-8, and NO) was strongly inhibited by both betalains and even more by prickly pear extracts, which showed a similar and sometimes better profile than the reference compounds trolox and dexamethasone in counteracting the IL-1β–induced intestinal inflammation.

A Novel WRKY Transcription Factor HmoWRKY40 Associated with Betalain Biosynthesis in Pitaya (Hylocereus monacanthus) through Regulating HmoCYP76AD1

Betalains are water-soluble nitrogen-containing pigments with multiple bioactivities. Pitaya is the only large-scale commercially grown fruit containing abundant betalains for consumers. However, the upstream regulators in betalain biosynthesis are still not clear. In this study, HmoWRKY40, a novel WRKY transcription factor, was obtained from the transcriptome data of pitaya (Hylocereus monacanthus). HmoWRKY40 is a member of the Group IIa WRKY family, containing a conserved WRKY motif, and it is located in the nucleus. The betalain contents and expression levels of HmoWRKY40 increased rapidly during the coloration of pitaya and reached their maximums on the 23rd day after artificial pollination (DAAP). Yeast one-hybrid and transient expression assays showed that HmoWRKY40 could bind and activate the promoter of HmoCYP76AD1. Silencing the HmoWRKY40 gene resulted in a significant reduction of betacyanin contents. These results indicate that HmoWRKY40 transcriptionally activates HmoCYP76AD, which is involved in the regulation of pitaya betalain biosynthesis. The results of the present study provide new regulatory networks related to betalain biosynthesis in pitaya.

Production of Betacyanins in Transgenic Nicotiana tabacum Increases Tolerance to Salinity

Although red betalain pigments (betacyanins) have been associated with salinity tolerance in some halophytes like Disphyma australe, efforts to determine whether they have a causal role and the underlying mechanisms have been hampered by a lack of a model system. To address this, we engineered betalain-producing Nicotiana tabacum, by the introduction of three betalain biosynthetic genes. The plants were violet-red due to the accumulation of three betacyanins: betanin, isobetanin, and betanidin. Under salt stress, betacyanic seedlings had increased survivability and leaves of mature plants had higher photochemical quantum yields of photosystem II (F _v /F _m ) and faster photosynthetic recovery after saturating light treatment. Under salt stress, compared to controls betacyanic leaf disks had no loss of carotenoids, a slower rate of chlorophyll degradation, and higher F _v /F _m values. Furthermore, simulation of betacyanin pigmentation by using a red filter cover improved F _v /F _m value of green tissue under salt stress. Our results confirm a direct causal role of betacyanins in plant salinity tolerance and indicate a key mechanism is photoprotection. A role in delaying leaf senescence was also indicated, and the enhanced antioxidant capability of the betacyanic leaves suggested a potential contribution to scavenging reactive oxygen species. The study can inform the development of novel biotechnological approaches to improving agricultural productivity in saline-affected areas.

Combined Transcriptome and Metabolome analysis of Pitaya fruit unveiled the mechanisms underlying Peel and pulp color formation

BACKGROUND

Elucidating the candidate genes and key metabolites responsible for pulp and peel coloration is essential for breeding pitaya fruit with new and improved appeal and high nutritional value. Here, we used transcriptome (RNA-Seq) and metabolome analysis (UPLC-MS/MS) to identify structural and regulatory genes and key metabolites associated with peel and pulp colors in three pitaya fruit types belonging to two different Hylocereus species.

RESULT

Our combined transcriptome and metabolome analyses suggest that the main strategy for obtaining red color is to increase tyrosine content for downstream steps in the betalain pathway. The upregulation of CYP76ADs is proposed as the color-breaking step leading to red or colorless pulp under the regulation by WRKY44 transcription factor. Supported by the differential accumulation of anthocyanin metabolites in red pulped pitaya fruit, our results showed the regulation of anthocyanin biosynthesis pathway in addition to betalain biosynthesis. However, no color-breaking step for the development of anthocyanins in red pulp was observed and no biosynthesis of anthocyanins in white pulp was found. Together, we propose that red pitaya pulp color is under the strict regulation of CYP76ADs by WRKYs and the anthocyanin coexistence with betalains is unneglectable. We ruled out the possibility of yellow peel color formation due to anthocyanins because of no differential regulation of chalcone synthase genes between yellow and green and no detection of naringenin chalcone in the metabolome. Similarly, the no differential regulation of key genes in the carotenoid pathway controlling yellow pigments proposed that the carotenoid pathway is not involved in yellow peel color formation.

CONCLUSIONS

Together, our results propose several candidate genes and metabolites controlling a single horticultural attribute i.e. color formation for further functional characterization. This study presents useful genomic resources and information for breeding pitaya fruit with commercially attractive peel and pulp colors. These findings will greatly complement the existing knowledge on the biosynthesis of natural pigments for their applications in food and health industry.

Integrated sRNAome and RNA-Seq analysis reveals miRNA effects on betalain biosynthesis in pitaya

BACKGROUND

MicroRNAs (miRNAs) and their regulatory functions in anthocyanin, carotenoid, and chlorophyll accumulation have been extensively characterized in many plant species. However, the miRNA regulatory mechanism in betalain biosynthesis remains mostly unknown.

RESULTS

In this study, 126 conserved miRNAs and 41 novel miRNAs were first isolated from Hylocereus monacanthus, among which 95 conserved miRNAs belonged to 53 miRNA families. Thirty-four candidate miRNAs related to betalain biosynthesis were differentially expressed. The expression patterns of those differential expressed miRNAs were analyzed in various pitaya tissues by RT-qPCR. A significantly negative correlation was detected between the expression levels of half those miRNAs and corresponding target genes. Target genes of miRNAs i.e. Hmo-miR157b-HmSPL6-like, Hmo-miR160a-Hpcyt P450-like3, Hmo-miR6020-HmCYP71A8-like, Hmo-novel-2-HmCYP83B1-like, Hmo-novel-15-HmTPST-like, Hmo-miR828a-HmTT2-like, Hmo-miR858-HmMYB12-like, Hmo-miR858-HmMYBC1-like and Hmo-miR858-HmMYB2-like were verified by 5'RACE and transient expression system in tobacco.

CONCLUSIONS

Hmo-miR157b, Hmo-miR160a, Hmo-miR6020 Hmo-novel-2, Hmo-novel-15, Hmo-miR828a and Hmo-miR858 play important roles in pitaya fruit coloration and betalain accumulation. Our findings provide new insights into the roles of miRNAs and their target genes of regulatory functions involved in betalain biosynthesis of pitaya.

New insights into red plant pigments: more than just natural colorants

Pigments make nature both colorful and attractive. Humans have always incorporated the natural pigments of fruits, vegetables and spices into their dietary requirements. Naturally occurring red pigments in plants are carotenoids, anthocyanins and betacyanins. Natural pigments, apart from colour, provide added properties and are therefore considered to be bioactive constituents. Red natural colorants are one of the most widely used in the food industry. The interest in these pigments lies in the enhancement of the healthy effects of the diet. In this context, attention is given to carotenoids, anthocyanins and betacyanins, with emphasis on the basic chemical and biochemical attributes and wide-ranging health-promoting benefits of these pigments. Thus, in this review, we systematically present the advantages and limitations of these natural pigments as food colorants in relation to their physico-chemical properties, reactivity and bioactivity.

Isolation of amaranthin synthetase from Chenopodium quinoa and construction of an amaranthin production system using suspension-cultured tobacco BY-2 cells

Betalains are plant pigments primarily produced by plants of the order Caryophyllales. Because betalain possesses anti-inflammatory and anticancer activities, it may be useful as a pharmaceutical agent and dietary supplement. Recent studies have identified the genes involved in the betalain biosynthesis of betanin. Amaranthin and celosianin II are abundant in the quinoa (Chenopodium quinoa Willd.) hypocotyl, and amaranthin comprises glucuronic acid bound to betanin; therefore, this suggests the existence of a glucuronyltransferase involved in the synthesis of amaranthin in the quinoa hypocotyl. To identify the gene involved in amaranthin biosynthesis, we performed a BLAST analysis and phylogenetic tree analysis based on sequences homologous to flavonoid glycosyltransferase, followed by expression analysis on the quinoa hypocotyl to obtain three candidate proteins. Production of amaranthin in a transient Nicotiana benthamiana expression system was evaluated for these candidates and one was identified as having the ability to produce amaranthin. The gene encoding this protein was quinoa amaranthin synthetase 1 (CqAmaSy1). We also created a transgenic tobacco bright yellow-2 (BY-2) cell line wherein four betalain biosynthesis genes were introduced to facilitate amaranthin production. This transgenic cell line produced 13.67 ± 4.13 μm (mean ± SEM) amaranthin and 26.60 ± 1.53 μm betanin, whereas the production of isoamaranthin and isobetanin could not be detected. Tests confirmed the ability of amaranthin and betanin to slightly suppress cancer cell viability. Furthermore, amaranthin was shown to significantly inhibit HIV-1 protease activity, whereas betanin did not.

A virus-induced gene-silencing system for functional genetics in a betalainic species, Amaranthus tricolor (Amaranthaceae)

PREMISE OF THE STUDY

Research in Amaranthaceae could be accelerated by developing methods for targeted gene silencing. Most amaranths, including Amaranthus tricolor, produce betalains. However, the physiological and ecological roles of these pigments are uncertain. We sought to establish a virus-induced gene-silencing (VIGS) method for amaranths, using silencing of betalain pigments as a proof-of-principle.

METHODS

We targeted AtriCYP76AD1, a putative cytochrome P450 component of the betalain biosynthetic pathway, using VIGS, and compared two different methods of introducing the VIGS construct into plants. We measured transcript abundance and concentrations of betalains and their l-DOPA precursor in VIGS-treated plants, and compared these to controls.

RESULTS

We observed that when AtriCYP76AD1 was targeted by VIGS in normally red plants, AtriCYP76AD1 and the related genes AtriCYP76AD6 and AtriCYP76AD5 had diminished transcript abundance. Furthermore, newly emergent petioles and leaves of VIGS-treated plants appeared green, betacyanin accumulation was strongly reduced, and l-DOPA accumulation was increased. No betaxanthin could be detected in this variety of A. tricolor, either before or after VIGS treatment.

DISCUSSION

These results help to establish the genetic basis of betalain synthesis in amaranths. Furthermore, this is the first report of VIGS in amaranths and demonstrates the potential of this technique for basic and applied research in these species.

Transcriptome Analysis Clarified Genes Involved in Betalain Biosynthesis in the Fruit of Red Pitayas (Hylocereus costaricensis)

The red flesh trait gives red pitayas more healthful components and a higher price, while the genetic mechanism behind this trait is unknown. In this manuscript, transcriptome analysis was employed to discover the genetic differences between white and red flesh in pitayas. A total of 27.99 Gb clean data were obtained for four samples. Unigenes, 79,049 in number, were generated with an average length of 1333 bp, and 52,618 Unigenes were annotated. Compared with white flesh, the expression of 10,215 Unigenes was up-regulated, and 4853 Unigenes were down-regulated in red flesh. The metabolic pathways accounted for 64.6% of all differentially expressed Unigenes in KEGG pathways. The group with high betalain content in red flesh and all structural genes, related to betalain biosynthesis, had a higher expression in red flesh than white flesh. The expression of the key gene, tyrosine hydroxylase CYP76AD1, was up-regulated 245.08 times, while 4,5-DOPA dioxygenase DODA was up-regulated 6.46 times. Moreover, the special isomers CYP76AD1α and DODAα were only expressed in red flesh. The competitive anthocyanin biosynthesis pathway had a lower expression in red flesh. Two MYB transcription factors were of the same branch as BvMYB1, regulating betalain biosynthesis in beet, and those transcription factors had expression differences in two kinds of pitayas, which indicated that they should be candidate genes controlling betalain accumulation in red pitayas. This research would benefit from identifying the major gene controlling red flesh trait and breed new cultivars with the red flesh trait. Future research should aim to prove the role of each candidate gene in betalain biosynthesis in red pitayas.

Quinoa Abiotic Stress Responses: A Review

Quinoa (Chenopodium quinoa Willd.) is a genetically diverse Andean crop that has earned special attention worldwide due to its nutritional and health benefits and its ability to adapt to contrasting environments, including nutrient-poor and saline soils and drought stressed marginal agroecosystems. Drought and salinity are the abiotic stresses most studied in quinoa; however, studies of other important stress factors, such as heat, cold, heavy metals, and UV-B light irradiance, are severely limited. In the last few decades, the incidence of abiotic stress has been accentuated by the increase in unpredictable weather patterns. Furthermore, stresses habitually occur as combinations of two or more. The goals of this review are to: (1) provide an in-depth description of the existing knowledge of quinoa's tolerance to different abiotic stressors; (2) summarize quinoa's physiological responses to these stressors; and (3) describe novel advances in molecular tools that can aid our understanding of the mechanisms underlying quinoa's abiotic stress tolerance.

Redirecting Primary Metabolism to Boost Production of Tyrosine-Derived Specialised Metabolites in Planta

L-Tyrosine-derived specialized metabolites perform many important functions in plants, and have valuable applications in human health and nutrition. A necessary step in the overproduction of specialised tyrosine-derived metabolites in planta is the manipulation of primary metabolism to enhance the availability of tyrosine. Here, we utilise a naturally occurring de-regulated isoform of the key enzyme, arogenate dehydrogenase, to re-engineer the interface of primary and specialised metabolism, to boost the production of tyrosine-derived pigments in a heterologous plant host. Through manipulation of tyrosine availability, we report a 7-fold increase in the production of tyrosine-derived betalain pigments, with an upper range of 855 mg·kg-1·FW, which compare favourably to many in vitro and commercial sources of betalain pigments. Since the most common plant pathway for tyrosine synthesis occurs via arogenate, the de-regulated arogenate dehydrogenase isoform is a promising route for enhanced production of tyrosine-derived pharmaceuticals in diverse plant hosts.

Isolation and characterization of the betalain biosynthesis gene involved in hypocotyl pigmentation of the allotetraploid Chenopodium quinoa

In quinoa seedlings, the pigment betalain accumulates in the hypocotyl. To isolate the genes involved in betalain biosynthesis in the hypocotyl, we performed ethyl methanesulfonate (EMS) mutagenesis on the CQ127 variety of quinoa seedlings. While putative amaranthin and celosianin II primarily accumulate in the hypocotyls, this process produced a green hypocotyl mutant (ghy). This MutMap+ method using the quinoa draft genome revealed that the causative gene of the mutant is CqCYP76AD1-1. Our results indicated that the expression of CqCYP76AD1-1 was light-dependent. In addition, the transient expression of CqCYP76AD1-1 in Nicotiana benthamiana leaves resulted in the accumulation of betanin but not isobetanin, and the presence of a polymorphism in CqCYP76A1-2 in the CQ127 variety was shown to have resulted in its loss of function. These findings suggested that CqCYP76AD1-1 is involved in betalain biosynthesis during the hypocotyl pigmentation process in quinoa. To our knowledge, CqCYP76AD1-1 is the first quinoa gene identified by EMS mutagenesis using a draft gene sequence.

"La Vie en Rose": Biosynthesis, Sources, and Applications of Betalain Pigments

Betalains are tyrosine-derived red-violet and yellow pigments found exclusively in plants of the Caryophyllales order, which have drawn both scientific and economic interest. Nevertheless, research into betalain chemistry, biochemistry, and function has been limited as comparison with other major classes of plant pigments such as anthocyanins and carotenoids. The core biosynthetic pathway of this pigment class has only been fully elucidated in the past few years, opening up the possibility for betalain pigment engineering in plants and microbes. In this review, we discuss betalain metabolism in light of recent advances in the field, with a current survey of characterized genes and enzymes that take part in betalain biosynthesis, catabolism, and transcriptional regulation, and an outlook of what is yet to be discovered. A broad view of currently used and potential new sources for betalains, including utilization of natural sources or metabolic engineering, is provided together with a summary of potential applications of betalains in research and commercial use.

Proteomic Analysis of Hylocereus polyrhizus Reveals Metabolic Pathway Changes

Red dragon fruit or red pitaya (Hylocereus polyrhizus) is the only edible fruit that contains betalains. The color of betalains ranges from red and violet to yellow in plants. Betalains may also serve as an important component of health-promoting and disease-preventing functional food. Currently, the biosynthetic and regulatory pathways for betalain production remain to be fully deciphered. In this study, isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analyses were used to reveal the molecular mechanism of betalain biosynthesis in H. polyrhizus fruits at white and red pulp stages, respectively. A total of 1946 proteins were identified as the differentially expressed between the two samples, and 936 of them were significantly highly expressed at the red pulp stage of H. polyrhizus. RNA-seq and iTRAQ analyses showed that some transcripts and proteins were positively correlated; they belonged to “phenylpropanoid biosynthesis”, “tyrosine metabolism”, “flavonoid biosynthesis”, “ascorbate and aldarate metabolism”, “betalains biosynthesis” and “anthocyanin biosynthesis”. In betalains biosynthesis pathway, several proteins/enzymes such as polyphenol oxidase, CYP76AD3 and 4,5-dihydroxy-phenylalanine (DOPA) dioxygenase extradiol-like protein were identified. The present study provides a new insight into the molecular mechanism of the betalain biosynthesis at the posttranscriptional level.

Identification and developmental expression profiling of putative alkaloid biosynthetic genes in Corydalis yanhusuo bulbs

Alkaloids in bulbs of Corydalis (C.) yanhusuo are the major pharmacologically active compounds in treatment of blood vessel diseases, tumors and various pains. However, due to the absence of gene sequences in C. yanhusuo, the genes involved in alkaloid biosynthesis and their expression during bulb development remain unknown. We therefore established the first transcriptome database of C. yanhusuo via Illumina mRNA-Sequencing of a RNA composite sample collected at Bulb initiation (Day 0), early enlargement (Day 10) and maturation (Day 30). 25,013,630 clean 90 bp paired-end reads were de novo assembled into 47,081 unigenes with an average length of 489 bp, among which 30,868 unigenes (65.56%) were annotated in four protein databases. Of 526 putative unigenes involved in biosynthesis o f various alkaloids, 187 were identified as the candidate genes involved in the biosynthesis of benzylisoquinoline alkaloids (BIAs), the only alkaloid type reported in C. yanhusuo untill now. BIAs biosynthetic genes were highly upregulated in the overall pathway during bulb development. Identification of alkaloid biosynthetic genes in C. yanhusuo provide insights on pathways and molecular regulation of alkaloid biosynthesis, to initiate metabolic engineering in order to improve the yield of interesting alkaloids and to identify potentially new alkaloids predicted from the transcriptomic information.