Elucidation of the core betalain biosynthesis pathway in Amaranthus tricolor

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.

Integrated metabolome, full-length sequencing, and transcriptome analyses unveil the molecular mechanisms of color formation of the canary yellow and red bracts of Bougainvillea × buttiana 'Chitra'

Bougainvillea is a typical tropical flower of great ornamental value due to its colorful bracts. The molecular mechanism behind color formation is not well-understood. Therefore, this research conducted metabolome analysis, transcriptome analysis, and multi-flux full-length sequencing in two color bracts of Bougainvillea × buttiana 'Chitra' to investigate the significantly different metabolites (SDMs) and differentially expressed genes (DEGs). Overall, 261 SDMs, including 62 flavonoids and 26 alkaloids, were detected, and flavonols and betalains were significantly differentially accumulated among the two bracts. Furthermore, the complete-length transcriptome of Bougainvillea × buttiana was also developed, which contained 512 493 non-redundant isoforms. Among them, 341 210 (66.58%) displayed multiple annotations in the KOG, GO, NR, KEGG, Pfam, Swissprot, and NT databases. RNA-seq findings revealed that 3610 DEGs were identified between two bracts. Co-expression analysis demonstrated that the DEGs and SDMs involved in flavonol metabolism (such as CHS, CHI, F3H, FLS, CYP75B1, kaempferol, and quercetin) and betacyanin metabolism (DODA, betanidin, and betacyanins) were the main contributors for the canary yellow and red bract formation, respectively. Further investigation revealed that several putative transcription factors (TFs) might interact with the promoters of the genes mentioned above. The expression profiles of the putative TFs displayed that they may positively and negatively regulate the structural genes' expression profiles. The data revealed a potential regulatory network between important genes, putative TFs, and metabolites in the flavonol and betacyanin biosynthesis of Bougainvillea × buttiana 'Chitra' bracts. These findings will serve as a rich genetic resource for future studies that could create new color bracts.

Beet mosaic virus expression of a betalain transcription factor allows visual virus tracking in Beta vulgaris

In the field of plant virology, the usage of reverse genetic systems has been reported for multiple purposes. One is understanding virus-host interaction by labelling viral cDNA clones with fluorescent protein genes to allow visual virus tracking throughout a plant, albeit this visualization depends on technical devices. Here we report the first construction of an infectious cDNA full-length clone of beet mosaic virus (BtMV) that can be efficiently used for Agrobacterium-mediated leaf inoculation with high infection rate in Beta vulgaris, being indistinguishable from the natural virus isolate regarding symptom development and vector transmission. Furthermore, the BtMV clone was tagged with the genes for the monomeric red fluorescent protein or the Beta vulgaris BvMYB1 transcription factor, which activates the betalain biosynthesis pathway. The heterologous expression of BvMYB1 results in activation of betalain biosynthesis genes in planta, allowing visualization of the systemic BtMV spread with the naked eye as red pigmentation emerging throughout beet leaves. In the case of BtMV, the BvMYB1 marker system is stable over multiple mechanical host passages, allows qualitative as well as quantitative virus detection and offers an excellent opportunity to label viruses in plants of the order Caryophyllales, allowing an in-depth investigation of virus-host interactions on the whole plant level.

Effect of betanin synthesis on photosynthesis and tyrosine metabolism in transgenic carrot

BACKGROUND

Betalain is a natural pigment with important nutritional value and broad application prospects. Previously, we produced betanin biosynthesis transgenic carrots via expressing optimized genes CYP76AD1S, cDOPA5GTS and DODA1S. Betanin can accumulate throughout the whole transgenic carrots. But the effects of betanin accumulation on the metabolism of transgenic plants and whether it produces unexpected effects are still unclear.

RESULTS

The accumulation of betanin in leaves can significantly improve its antioxidant capacity and induce a decrease of chlorophyll content. Transcriptome and metabolomics analysis showed that 14.0% of genes and 33.1% of metabolites were significantly different, and metabolic pathways related to photosynthesis and tyrosine metabolism were markedly altered. Combined analysis showed that phenylpropane biosynthesis pathway significantly enriched the differentially expressed genes and significantly altered metabolites.

CONCLUSIONS

Results showed that the metabolic status was significantly altered between transgenic and non-transgenic carrots, especially the photosynthesis and tyrosine metabolism. The extra consumption of tyrosine and accumulation of betanin might be the leading causes.

BpCYP76AD15 is involved in betaxanthin biosynthesis in bougainvillea callus

MAIN CONCLUSION

BpCYP76AD15 is involved in betaxanthin biosynthesis in callus, but not in bracts, in bougainvillea. Bougainvillea (Bougainvillea peruviana) is a climbing tropical ornamental tree belonging to Nyctaginaceae. Pigments that are conferring colorful bracts in bougainvillea are betalains, and that conferring yellow color are betaxanthins. In general, for red-to-purple betacyanin biosynthesis, α clade CYP76AD that has tyrosine hydroxylase and DOPA oxygenase activity is required, while for betaxanthin biosynthesis, β clade CYP76AD that has only tyrosine hydroxylase is required. To date, betaxanthin biosynthesis pathway genes have not been identified yet in bougainvillea. Since bougainvillea is phylogenetically close to four-O-clock (Mirabilis jalapa), and it was reported that β clade CYP76AD, MjCYP76AD15, is involved in floral betaxanthin biosynthesis in four-O-clock. Thus, we hypothesized that orthologous gene of MjCYP76AD15 in bougainvillea might be involved in bract betaxanthin biosynthesis. To test the hypothesis, we attempted to identify β clade CYP76AD gene from yellow bracts by RNA-seq; however, we could not. Instead, we found that callus accumulated betaxanthin and that β clade CYP76AD gene, BpCYP76AD15, were expressed in callus. We validated BpCYP76AD15 function by transgenic approach (agro-infiltration and over-expression in transgenic tobacco), and it was suggested that BpCYP76AD15 is involved in betaxanthin biosynthesis in callus, but not in bracts in bougainvillea. Interestingly, our data also indicate the existence of two pathways for betaxanthin biosynthesis (β clade CYP76AD-dependent and -independent), and the latter pathway is important for betaxanthin biosynthesis in bougainvillea bracts.

Betalain biosynthesis in red pulp pitaya is regulated via HuMYB132: a R-R type MYB transcription factor

BACKGROUND

Multiple MYB transcription factors (TFs) are involved in the regulation of plant coloring. Betalain is a kind of natural plant pigment and its biosynthesis is regulated by a number of enzymes. Despite this, little is known about the molecular properties and roles of MYB TFs in pitaya betalain biosynthesis.

RESULTS

In the present study, we identified a 1R-MYB gene, HuMYB132, which is preferentially expressed in red-pulp pitaya at the mature stage. It was clustered with Arabidopsis R-R-type genes and had two DNA-binding domains and a histidine-rich region. The expression assays in N. benthamiana and yeast indicated that HuMYB132 is a nucleus-localized protein with transcriptional activation activity. Dual luciferase reporter assay and electrophoretic mobility shift assays (EMSA) demonstrated that HuMYB132 could promote the transcriptional activities of HuADH1, HuCYP76AD1-1, and HuDODA1 by binding to their promoters. Silencing HuMYB132 reduced betalain accumulation and the expression levels of betalain biosynthetic genes in pitaya pulps.

CONCLUSIONS

According to our findings, HuMYB132, a R-R type member of 1R-MYB TF subfamily, positively regulates pitaya betalain biosynthesis by regulating the expression of HuADH1, HuCYP76AD1-1, and HuDODA1. The present study provides a new theoretical reference for the management of pitaya betalain biosynthesis and also provides an essential basis for future regulation of betalain biosynthesis in Hylocereus.

Chromosome-scale Amaranthus tricolor genome provides insights into the evolution of the genus Amaranthus and the mechanism of betalain biosynthesis

Amaranthus tricolor is a vegetable and ornamental amaranth, with high lysine, dietary fibre and squalene content. The red cultivar of A. tricolor possesses a high concentration of betalains, which has been used as natural food colorants. Here, we constructed the genome of A. tricolor, the first reference genome for the subgenus Albersia, combining PacBio HiFi, Nanopore ultra-long and Hi-C data. The contig N50 size was 906 kb, and 99.58% of contig sequence was anchored to the 17 chromosomes, totalling 520 Mb. We annotated 27,813 protein-coding genes with an average 1.3 kb coding sequence and 5.3 exons. We inferred that A. tricolor underwent a whole-genome duplication (WGD) and that the WGD shared by amaranths occurred in the last common ancestor of subfamily Amaranthoideae. Moreover, we comprehensively identified candidate genes in betalain biosynthesis pathway. Among them, DODAα1 and CYP76ADα1, located in one topologically associated domain (TAD) of an active (A) compartment on chromosome 16, were more highly expressed in red leaves than in green leaves, and DODAα1 might be the rate-limiting enzyme gene in betalains biosynthesis. This study presents new genome resources and enriches our understanding of amaranth evolution, betalains production, facilitating molecular breeding improvements and the understanding of C4 plants evolution.

Evaluation of Natural Pigments Production in Response to Various Stress Signals in Cell Lines of Stenocereus queretaroensis

Stenocereus queretaroensis (F.A.C. Weber ex Mathes.) Buxb is a cactus that has long been used as a source food in central and northern México. Its fruits, commonly called pitayas, biosynthesize high amounts of betalains. These molecules are water-soluble nitrogenous compounds; that compared to other pigments, such as anthocyanins or carotenoids, stand out for their physicochemical stability in industrial processes. Due to genetic and environmental factors involved in the biosynthesis and accumulation of secondary metabolites in plants, we tested different stress-inducing agents (elicitor, osmotic, salt, and temperature) to induce betalains accumulation in cell culture from fruits of Stenocereus queretaroensis. This work aimed to understand stress conditions that induce the metabolic pathways required for the accumulation of betalains. The results show how betacyanin concentration increases under high sugar conditions, thus affecting the expression of L-DOPA 4, 5 dioxygenase resulting in a strong dark red coloration. This suggests this enzyme is part of a rate-limiting step in betalain production. In addition, we found that betalains accumulation occurs under particular stress conditions. Cells that have a high level of betacyanins show better resistance to stress in the cell culture, as well as an overall different behavior including cell aggregation and alterations in nuclear size. Together the results shown here may provide new strategies to manipulate and mass produce the pigments from Stenocereus queretaroensis in cell culture.

Prospects and potentials of underutilized leafy Amaranths as vegetable use for health-promotion

Climate change causes environmental variation worldwide, which is one of the most serious threats to global food security. In addition, more than 2 billion people in the world are reported to suffer from serious malnutrition, referred to as 'hidden hunger.' Dependence on only a few crops could lead to the loss of genetic diversity and high fragility of crop breeding in systems adapting to global scale climate change. The exploitation of underutilized species and genetic resources, referred to as orphan crops, could be a useful approach for resolving the issue of adaptability to environmental alteration, biodiversity preservation, and improvement of nutrient quality and quantity to ensure food security. Moreover, the use of these alternative crops will help to increase the human health benefits and the income of farmers in developing countries. In this review, we highlight the potential of orphan crops, especially amaranths, for use as vegetables and health-promoting nutritional components. This review highlights promising diversified sources of amaranth germplasms, their tolerance to abiotic stresses, and their nutritional, phytochemical, and antioxidant values for vegetable purposes. Betalains (betacyanins and betaxanthins), unique antioxidant components in amaranth vegetables, are also highlighted regarding their chemodiversity across amaranth germplasms and their stability and degradation. In addition, we discuss the physiological functions, antioxidant, antilipidemic, anticancer, and antimicrobial activities, as well as the biosynthesis pathway, molecular, biochemical, genetics, and genomic mechanisms of betalains in detail.

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.

Natural or light-induced pigment accumulation in grain amaranths coincides with enhanced resistance against insect herbivory

MAIN CONCLUSION

Increased resistance to insect herbivory in grain amaranth plants is associated with increased betalain pigmentation, either naturally acquired or accumulated in response to blue-red light irradiation. Betalains are water-soluble pigments characteristic of plants of the Caryophyllales order. Their abiotic stress-induced accumulation is believed to protect against oxidative damage, while their defensive function against biotic aggressors is scarce. A previous observation of induced betalain-biosynthetic gene expression in stressed grain amaranth plants led to the proposal that these pigments play a defensive role against insect herbivory. This study provided further support for this premise. First, a comparison of "green" and "red" Amaranthus cruentus phenotypes showed that the latter suffered less insect herbivory damage. Coincidentally, growth and vitality of Manduca sexta larvae were more severely affected when fed on red-leafed A. cruentus plants or on an artificial diet supplemented with red-leaf pigment extracts. Second, the exposure of A. cruentus and A. caudatus plants, having contrasting pigmentation phenotypes, to light enriched in the blue and red wavelength spectra led to pigment accumulation throughout the plant and to increased resistance to insect herbivory. These events were accompanied by the induced expression of known betalain-biosynthetic genes, including uncharacterized DODA genes believed to participate in this biosynthetic pathway in a still undefined way. Finally, transient co-expression of different combinations of betalain-biosynthetic genes in Nicotiana benthamiana led to detectable accumulation of betalamic acid and betanidin. This outcome supported the participation of certain AhDODA and other genes in the grain amaranth betalain-biosynthetic pathway.