The developmental expression of the maize regulatory gene Hopi determines germination-dependent anthocyanin accumulation

Assessing the diversity of anthocyanin composition in various tissues of purple corn (Zea mays L.)

Anthocyanins are natural pigments used in various foods, beverages, textiles, and nutraceuticals. Anthocyanins in the grain of purple corn (Zea mays L., Poaceae) have been a focus of many studies, but not much is known about anthocyanins in other maize tissues. In this study, purple corn variety Apache Red Cob was crossed to genetic stock 320 N, which is recessive for anthocyanin 3. The result was intense anthocyanin production in portions of the plant not normally pigmented. Anthocyanin extracts from anthers, cob glumes, husks, kernels, leaf sheaths, seedlings, silks, and tassels were assessed using UHPLC. A previously undescribed pigment produced in anthers was determined by NMR to be anthocyanidin 3-6″-phenylacetylglucoside. Multivariate analysis classified maize anthocyanins into 8 major compositional profiles. Results of this study show that maize produces anthocyanins abundantly in non-grain portions of the plant and that maize anthocyanin extracts have numerous applications due to the diversity in pigment profiles and hues.

Maize Flavonoid Biosynthesis, Regulation, and Human Health Relevance: A Review

Maize is one of the most important crops for human and animal consumption and contains a chemical arsenal essential for survival: flavonoids. Moreover, flavonoids are well known for their beneficial effects on human health. In this review, we decided to organize the information about maize flavonoids into three sections. In the first section, we include updated information about the enzymatic pathway of maize flavonoids. We describe a total of twenty-one genes for the flavonoid pathway of maize. The first three genes participate in the general phenylpropanoid pathway. Four genes are common biosynthetic early genes for flavonoids, and fourteen are specific genes for the flavonoid subgroups, the anthocyanins, and flavone C-glycosides. The second section explains the tissue accumulation and regulation of flavonoids by environmental factors affecting the expression of the MYB-bHLH-WD40 (MBW) transcriptional complex. The study of transcription factors of the MBW complex is fundamental for understanding how the flavonoid profiles generate a palette of colors in the plant tissues. Finally, we also include an update of the biological activities of C3G, the major maize anthocyanin, including anticancer, antidiabetic, and antioxidant effects, among others. This review intends to disclose and integrate the existing knowledge regarding maize flavonoid pigmentation and its relevance in the human health sector.

Genome-wide characterization and expression analysis of bHLH gene family in physic nut (Jatropha curcas L.)

The basic helix loop helix (bHLH) transcription factor perform essential roles in plant development and abiotic stress. Here, a total of 122 bHLH family members were identified from the physic nut (Jatropha curcas L.) genomic database. Chromosomal localization results showed that 120 members were located on 11 chromosomes. The phylogenetic tree manifested that the JcbHLHs could be grouped into 28 subfamilies. Syntenic analysis showed that there were 10 bHLH collinear genes among the physic nut, Arabidopsis thaliana and Oryza sativa. These genes, except JcbHLH84, were highly expressed in various tissues of the physic nut, implying a key role in plant development. Gene expression profiles showed that ten genes (especially JcbHLH33, JcbHLH45 and JcbHLH55) correspond to both salinity and drought stresses; while eight genes only respond to salinity and another eight genes only respond to drought stress. Moreover, the protein interaction network revealed that the JcbHLHs are involved in growth, development and stress signal transduction pathways. These discoveries will help to excavate several key genes may involve in salt or drought stresses and seed development, elucidate the complex transcriptional regulation mechanism of JcbHLH genes and provide the theoretical basis for stress response and genetic improvement of physic nut.

A B73×Palomero Toluqueño mapping population reveals local adaptation in Mexican highland maize

Generations of farmer selection in the central Mexican highlands have produced unique maize varieties adapted to the challenges of the local environment. In addition to possessing great agronomic and cultural value, Mexican highland maize represents a good system for the study of local adaptation and acquisition of adaptive phenotypes under cultivation. In this study, we characterize a recombinant inbred line population derived from the B73 reference line and the Mexican highland maize variety Palomero Toluqueño. B73 and Palomero Toluqueño showed classic rank-changing differences in performance between lowland and highland field sites, indicative of local adaptation. Quantitative trait mapping identified genomic regions linked to effects on yield components that were conditionally expressed depending on the environment. For the principal genomic regions associated with ear weight and total kernel number, the Palomero Toluqueño allele conferred an advantage specifically in the highland site, consistent with local adaptation. We identified Palomero Toluqueño alleles associated with expression of characteristic highland traits, including reduced tassel branching, increased sheath pigmentation and the presence of sheath macrohairs. The oligogenic architecture of these three morphological traits supports their role in adaptation, suggesting they have arisen from consistent directional selection acting at distinct points across the genome. We discuss these results in the context of the origin of phenotypic novelty during selection, commenting on the role of de novo mutation and the acquisition of adaptive variation by gene flow from endemic wild relatives.

Playing with colours: genetics and regulatory mechanisms for anthocyanin pathway in cereals

Cereals form the most important source of energy in our food. Currently, demand for coloured food grains is significantly increasing globally because of their antioxidant properties and enhanced nutritional value. Coloured grains of major and minor cereals are due to accumulation of secondary metabolites like carotenoids and flavonoids such as anthocyanin, proanthocyanin, phlobaphenes in pericarp, aleurone, lemma, testa or seed coat of grains. Differential accumulation of colour in grains is regulated by several regulatory proteins and enzymes involved in flavonoid and caroteniod biosynthesis. MYB and bHLH gene family members are the major regulators of these pathways. Genes for colour across various cereals have been extensively studied; however, only a few functional and allele-specific markers to be utilized directly in breeding programmes are reported so far. In this review, while briefly discussing the well studied and explored carotenoid pathway, we focus on a much more complex anthocyanin pathway that is found across cereals. The genes and their orthologs that are responsible for encoding key regulators of anthocyanin biosynthesis are discussed. This review also focuses on the genetic factors that influence colour change in different cereal crops, and the available/reported markers that can be used in breeding programs for utilizing this pathway for enhancing food and nutritional security.

Prospects for economical natural colorants: insights from maize

Anthocyanin pigments from maize offer a natural yet economical alternative to artificial dyes. Breeding for optimal colorant production requires understanding and integrating all facets of anthocyanin chemistry and genetics research. Replacing artificial dyes with natural colorants is becoming increasingly popular in foods and beverages. However, natural colorants are often expensive, have lower stability, and reduced variability in hue. Purple corn is rich in anthocyanins and offers a scalable and affordable alternative to synthetic dyes ranging in color from orange to reddish-purple. This diversity is attributable to differences in anthocyanin composition and concentration. Here we review the chemistry, biosynthesis, and genetics of purple corn and outline key factors associated with the feasibility of producing an economical source of natural colorants. Anthocyanin compositional modifications including acylation, methylation, and polymerization with flavan-3-ols can influence color stability and hue, yet there is more to learn regarding the genetic factors responsible for these modifications. Activators and repressors of anthocyanin biosynthesis structural genes as well as factors controlling trafficking and storage largely control anthocyanin yield. Further knowledge of these mechanisms will allow breeders to apply molecular strategies that accelerate the production of purple corn hybrids to meet growing demands for natural colorants.

Identification and Characterization of MYB-bHLH-WD40 Regulatory Complex Members Controlling Anthocyanidin Biosynthesis in Blueberry Fruits Development

Anthocyanins is the main representative of flavonoids in blueberry fruits. The anthocyanins biosynthetic pathway has been extensively studied in numerous model plants and fruit crops at biochemical, genetic, and molecular levels. However, the mechanisms by which the MYB transcription factor/basic helix-loop-helix (bHLH) domain protein/WD-repeat (MYB-bHLH-WD40) complexes regulate anthocyanin biosynthesis in blueberry is still limited. In the present study, we identified 11 MYB, 7 bHLH, and 6 WD40 genes in blueberry fruits, using amino acid sequences of homologous MYB-bHLH-WD40 complexes in Arabidopsis, apple, grape, and strawberry. To understand these mechanisms, the expression patterns of MYB-bHLH-WD40 genes were examined and validated using differentially expressed gene (DEG) analysis and quantitative real-time reverse transcription PCR (qRT-PCR), respectively. The expression patterns of MYB-bHLH-WD40 genes positively correlated with anthocyanin accumulation and color development in blueberry fruits. Consistent with the effects of other transcriptional regulators, the VcMYBL1::GFP, VcbHLH1::GFP, and VcWDL2::GFP fusion proteins were only observed in the nucleus. The protein-protein interactions (PPIs) and bimolecular fluorescence complementation (BiFC) assay suggested a possible link between VcbHLHL1 and VcMYBL1. Finally, a model was proposed and discussed for how the expression of the MYB-bHLH-WD40 complexes can promote anthocyanin biosynthesis in blueberry fruits. To our knowledge, this study was the first to evaluate MYB-bHLH-WD40 complexes in blueberry fruits, and it provides a foundation to dissect the function of the mechanism.

A high-density genetic map developed by specific-locus amplified fragment (SLAF) sequencing and identification of a locus controlling anthocyanin pigmentation in stalk of Zicaitai (Brassica rapa L. ssp. chinensis var. purpurea)

BACKGROUND

Caixin and Zicaitai (Brassica rapa) belong to Southern and Central China respectively. Zicaitai contains high amount of anthocyanin in leaf and stalk resulting to the purple color. Stalk is the major edible part and stalk color is an economically important trait for the two vegetables. The aim of this study is to construct a high density genetic map using the specific length amplified fragment sequencing (SLAF-seq) technique to explore genetic basis for anthocyanin pigmentation traits via quantitative trait loci (QTL) mapping.

RESULTS

We constructed a high generation linkage map with a mapping panel of F2 populations derived from 150 individuals of parental lines "Xianghongtai 01" and "Yinong 50D" with purple and green stalk respectively. The map was constructed containing 4253 loci, representing 10,940 single nucleotide polymorphism (SNP) markers spanning 1030.04 centiMorgans (cM) over 10 linkage groups (LGs), with an average distance between markers of 0.27 cM. Quantitative trait loci (QTL) analysis revealed that a major locus on chromosome 7 and 4 minor QTLs explaining 2.69-61.21% of phenotypic variation (PVE) were strongly responsible for variation in stalk color trait. Bioinformatics analysis of the major locus identified 62 protein-coding genes. Among the major locus, there were no biosynthetic genes related to anthocyanin. However, there were several transcription factors like helix-loop-helix (bHLH) bHLH, MYB in the locus. Seven predicted candidate genes were selected for the transcription level analysis. Only bHLH49 transcription factor, was significantly higher expressed in both stalks and young leaves of Xianghongtai01 than Yinong50D. An insertion and deletion (InDel) marker developed from deletion/insertion in the promoter region of bHLH49 showed significant correlation with the stalk color trait in the F2 population.

CONCLUSION

Using the constructed high-qualified linkage map, this study successfully identified QTLs for stalk color trait. The identified valuable markers and candidate genes for anthocyanin accumulation in stalk will provide useful information for molecular regulation of anthocyanin biosynthesis. Overall our findings will lay a foundation for functional gene cloning, marker-assisted selection (MAS) and molecular breeding of important economic traits in B. rapa.

Functional MYB transcription factor encoding gene AN2 is associated with anthocyanin biosynthesis in Lycium ruthenicum Murray

BACKGROUND

Lycium ruthenicum Murray is an important economic plant in China and contains higher levels of anthocyanins in its fruits than other Lyciums. However, the genetic mechanism of anthocyanin production in this plant is unknown.

RESULTS

Based on previous transcriptome analysis, LrAN2 and LbAN2, encoding MYB transcription factors, were isolated from L. ruthenicum and L. barbarum, respectively. Both genes contained two introns, encoded 257 amino acids with two-Aa difference, and carried the unabridged HTH-MYB, MYB-like DNA-binding, and SANT domains. In the phylogenetic trees, LrAN2 and LbAN2 were found to be closely related to NtAN2, which regulates anthocyanin biosynthesis in tobacco. Overexpression of LrAN2 and LbAN2 induced anthocyanin biosynthesis in all tissues of tobacco. The anthocyanin content in the leaves of transgenic lines with LbAN2 was lower than LrAN2. It indicated that the function of LbAN2 was weaker than LrAN2. The AN2 transcript could be detected only in the fruits of L. ruthenicum and increased during fruit development, accompanied by anthocyanin accumulation. In natural population, the alleles LrAN2 and LrAN2 were associated strictly with L. ruthenicum and L. barbarum, respectively. Moreover, an AN2 genetic diversity study suggested that Lyciums with yellow, white, purple, and jujube red fruits were derived from L. ruthenicum.

CONCLUSIONS

Two AN2 alleles, from L. ruthenicum and L. barbarum, were functional MYB transcriptor regulating anthocyanin biosynthesis. The functional diversity and high expression level of LrAN2 could be the reason for high anthocyanin content in the fruit of L. ruthenicum. Lyciums with yellow, white, purple, and jujube red fruits were derived from L. ruthenicum based on AN2 sequence diversity. The results may be advantageous in identifying new varieties and breeding new cultivars.

A genomic region harboring the Pl1 allele from the Peruvian cultivar JC072A confers purple cob on Japanese flint corn (Zea mays L.)

Purple corn is a maize variety (Zea mays L.) with high anthocyanin content. When purple corn is used as forage, its anthocyanins may mitigate oxidative stresses causing lower milk production in dairy cows. In this study, we analyzed quantitative trait loci (QTLs) for anthocyanin pigmentation of maize organs in an F₂ population derived from a cross between the Peruvian cultivar 'JC072A' (purple) and the inbred line 'Ki68' (yellowish) belonged to Japanese flint. We detected 17 significant QTLs on chromosomes 1-3, 6, and 10. Because the cob accounts for most of the fresh weight of the plant ear, we focused on a significant QTL for purple cob on chromosome 6. This QTL also conferred pigmentation of anther, spikelet, leaf sheath, culm, and bract leaf, and was confirmed by using two F₃ populations. The gene Pl1 (purple plant 1) is the most likely candidate gene in this QTL region because the amino acid sequence encoded by Pl1-JC072A is similar to that of an Andean allele, Pl-bol3, which is responsible for anthocyanin production. The markers designed for the Pl1 alleles will be useful for the breeding of F₁ lines with anthocyanin pigmentation in cobs.

Combined bulked segregant sequencing and traditional linkage analysis for identification of candidate gene for purple leaf sheath in maize

Anthocyanin accumulation in various maize tissues plays important roles in plant growth and development. In addition, some color-related traits can be used as morphological markers in conventional maize breeding processes and purity identification of hybrid seeds. Here, we noticed that the leaf sheath color was controlled by a dominant gene, because purple (PSH) and green leaf sheaths (GSH) were separated at a ratio of 3:1 in an F2 population. To map the gene, an F2 and a recombinant inbred line (RIL) population were derived from a cross between inbred line T877 (PSH) and DH1M (GSH). The PSH locus was mapped to the genomic region within 128.8 to 138.4 Mb using a bulked segregant sequencing approach. This position was further validated by linkage mapping using 190 F2 plants with GSH. Subsequently, the PSH locus was fine-mapped into an interval of 304.2 kb. A maize gene, GRMZM5G822829, was identified in this region, encoding a bHLH transcription factor. The expression level of this gene in T877 was found to be 9-fold higher than that of DH1M. In conclusion, our results suggest that GRMZM5G822829 is the putative candidate gene conferring leaf sheath color in maize.

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.

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.

Effects of different depth of grain colour on antioxidant capacity during water imbibition in wheat (Triticum aestivum L.)

BACKGROUND

The importance of the effect of phytochemical accumulation in wheat grain on grain physiology has been recognised. In this study, we tracked phytochemical concentration in the seed coat of purple wheat during the water-imbibition phase and also hypothesised that the speed of germination was only relevant to its initial phytochemical concentration.

RESULTS

The results indicate that the speed of germination was significantly reduced in the darker grain groups within the purple wheat. Total phenol content was slightly increased in all groups compared to their initial state, but the levels of other phytochemicals varied among groups. It is revealed that anthocyanin was significantly degraded during the water imbibition stage. Also, the activities of peroxidase, ascorbate peroxidase, catalase, glutathione S-transferase, glutathione reductase, and glutathione peroxidase in each grain colour group did not correlated with germination speed. Overall antioxidant activity was reduced as imbibition progressed in each group. Generally, darker grain groups showed higher total antioxidant activities than did lighter grain groups.

CONCLUSION

These findings suggested that the reduced activity of reactive oxygen species, as controlled by internal antioxidant enzymes and phytochemicals, related with germination speed during the water imbibition stage in grains with greater depth of purple colouring. © 2016 Society of Chemical Industry.

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.

Identification of differentially expressed genes implicated in peel color (red and green) of Dimocarpus confinis

Nowadays, there are few reports about regulatory genes implicated in peel color of longan. The basic genetic research of longan has been in stagnation for a long time as a lack of transcriptomic and genetic information. To predict candidate genes associated with peel color, Gene Functional Annotation and Coding Sequence prediction were used to perform functional annotation for our assembled unigenes and investigate differentially expressed genes (DEGs) of fruitlet peels from Longli (Dimocarpus confinis). Finally, a total of 24,044 (44.19 %) unigenes were annotated at least in one database after BLAST search to NCBI non-redundant protein sequence, NCBI non-redundant nucleotide sequences, Kyoto Encyclopedia of Genes and Genomes (KEGG) Ortholog, manually annotated and reviewed protein sequence database (Swiss-Prot), Protein family, Gene Ontology, euKaryotic Ortholog Groups databases. After searching against the KEGG-GENE protein database, a result of 6228 (11.45 %) unigenes were assigned to 245 KEGG pathways. Via comparing the distributions of expression value of all corresponding unigenes from red peel and green peel fruit, it could be intuitively concluded that high similarity was existed in the two distributions; however, on the whole, between two distributions of log RPKM expression value, some differences indicated that expression level in green-peel fruit group is slightly higher than values in red-peel fruit group. Finally, a total of 1349 unigenes were identified as DEGs after blasting the DEGs to public sequence databases, and 32 peel-color-related genes were identified in longan. Our results suggest that a number of unigenes involved in longan metabolic process, including anthocyanin biosynthesis. In addition, DRF, F3H, ANS, CYP75A1 and C1 may be the key ones. The study on key genes related to peel color will be contributed to revealing the molecular mechanisms of regulating peel color in woody plants.

Dietary anthocyanins and health: data from FLORA and ATHENA EU projects

Adherence to a 'Mediterranean diet' has been shown to be beneficial to human health. Fruit and vegetables represent some of the main components of the Mediterranean diet and their role has been increasingly considered in the process of preventing or reducing the risk of chronic degenerative diseases, such as cerebrovascular or coronary heart disorders, cancer and neurodegenerative diseases. To investigate the beneficial effect of these dietary compounds, two EU-funded projects were conducted during the last 10 years. Their results from experimental models suggest that dietary anthocyanin enrichment is beneficial against a number of ischemic and degenerative conditions. On the other hand, human studies demonstrated that anthocyanin supplementation can counteract the inflammatory response to stress conditions, such as a fatty meal. Moreover, an intervention trial in patients with breast cancer undergoing radiotherapy is presently testing the possible beneficial effect of the administration of a product enriched in anthocyanins on the inflammatory response to radiation and on its consequent skin toxicity, as well as on systemic low-grade inflammation reaction.

The Tomato Hoffman's Anthocyaninless Gene Encodes a bHLH Transcription Factor Involved in Anthocyanin Biosynthesis That Is Developmentally Regulated and Induced by Low Temperatures

Anthocyanin pigments play many roles in plants, including providing protection against biotic and abiotic stresses. Many of the genes that mediate anthocyanin accumulation have been identified through studies of flowers and fruits; however, the mechanisms of genes involved in anthocyanin regulation in seedlings under low-temperature stimulus are less well understood. Genetic characterization of a tomato inbred line, FMTT271, which showed no anthocyanin pigmentation, revealed a mutation in a bHLH transcription factor (TF) gene, which corresponds to the ah (Hoffman's anthocyaninless) locus, and so the gene in FMTT271 at that locus was named ah. Overexpression of the wild type allele of AH in FMTT271 resulted in greater anthocyanin accumulation and increased expression of several genes in the anthocyanin biosynthetic pathway. The expression of AH and anthocyanin accumulation in seedlings was shown to be developmentally regulated and induced by low-temperature stress. Additionally, transcriptome analyses of hypocotyls and leaves from the near-isogenic lines seedlings revealed that AH not only influences the expression of anthocyanin biosynthetic genes, but also genes associated with responses to abiotic stress. Furthermore, the ah mutation was shown to cause accumulation of reactive oxidative species and the constitutive activation of defense responses under cold conditions. These results suggest that AH regulates anthocyanin biosynthesis, thereby playing a protective role, and that this function is particularly important in young seedlings that are particularly vulnerable to abiotic stresses.

Anthocyanins in corn: a wealth of genes for human health

Different epidemiological and preclinical studies have demonstrated that regular consumption of anthocyanin-rich foods is associated to a reduced risk of chronic diseases, such as cardiovascular diseases, cancer and obesity. However, assigning a health property to anthocyanins or other classes of flavonoids may be limited by the influence of other metabolites of plant-based food consumed in the diet, acting as possible confounding factors. The development of model foods essentially isogenic and nutritionally identical except that in the type and quantity of plant bioactives to be studied represents an important tool in nutritional studies. The extensive knowledge of the regulation of flavonoid pathway in maize can be exploited to obtain 'near-isogenic' model foods, which differ only in the content of specific classes of flavonoids. Being obtainable by breeding strategies, maize model foods can provide functional foods that can be used for both animal feeding studies and human intervention trials for assessing the role of flavonoids or other bioactives in preventing chronic diseases. This review will be focused on recent advances regarding the anthocyanin biosynthesis in maize, the role of anthocyanins from corn in preventing chronic diseases and finally on the breeding activities to produce maize functional foods with increased anthocyanin content.

Anthocyanins in corn: a wealth of genes for human health

Different epidemiological and preclinical studies have demonstrated that regular consumption of anthocyanin-rich foods is associated to a reduced risk of chronic diseases, such as cardiovascular diseases, cancer and obesity. However, assigning a health property to anthocyanins or other classes of flavonoids may be limited by the influence of other metabolites of plant-based food consumed in the diet, acting as possible confounding factors. The development of model foods essentially isogenic and nutritionally identical except that in the type and quantity of plant bioactives to be studied represents an important tool in nutritional studies. The extensive knowledge of the regulation of flavonoid pathway in maize can be exploited to obtain 'near-isogenic' model foods, which differ only in the content of specific classes of flavonoids. Being obtainable by breeding strategies, maize model foods can provide functional foods that can be used for both animal feeding studies and human intervention trials for assessing the role of flavonoids or other bioactives in preventing chronic diseases. This review will be focused on recent advances regarding the anthocyanin biosynthesis in maize, the role of anthocyanins from corn in preventing chronic diseases and finally on the breeding activities to produce maize functional foods with increased anthocyanin content.

Regulation of anthocyanin biosynthesis in peach fruits

MYB10.1 and MYB10.3, with bHLH3, are the likely regulators of anthocyanin biosynthesis in peach fruit. MYB10.1/2/3 forms a cluster on the same genomic fragment where the Anther color ( Ag ) trait is located. Anthocyanins are bioactive compounds responsible for the pigmentation of many plant parts such as leaves, flowers, fruits and roots, and have potential benefits to human health. In peach [Prunus persica (L.) Batsch], peel color is a key determinant for fruit quality and is regulated by flavonoids including anthocyanins. The R2R3 MYB transcription factors (TFs) control the expression of anthocyanin biosynthetic genes with the help of co-activators belonging to the basic-helix-loop-helix (bHLH) and WD40 repeat families. In the peach genome six MYB10-like and three bHLH-like TFs were identified as candidates to be the regulators of the anthocyanin accumulation, which, in yellow flesh fruits, is highest in the peel, abundant in the part of the mesocarp surrounding the stone and lowest in the mesocarp. The expression of MYB10.1 and MYB10.3 correlates with anthocyanin levels of different peach parts. They also have positive correlation with the expression of key structural genes of the anthocyanin pathway, such as CHS, F3H, and UFGT. Functions of peach MYB10s were tested in tobacco and shown to activate key genes in the anthocyanin pathway when bHLHs were co-expressed as partners. Overexpression of MYB10.1/bHLH3 and MYB10.3/bHLH3 activated anthocyanin production by up-regulating NtCHS, NtDFR and NtUFGT while other combinations were not, or much less, effective. As three MYB10 genes are localized in a genomic region where the Ag trait, responsible for anther pigmentation, is localized, it is proposed they are key determinant to introduce new peach cultivars with higher antioxidant level and pigmented fruit.

The evolution of phenylpropanoid metabolism in the green lineage

Phenolic secondary metabolites are only produced by plants wherein they play important roles in both biotic and abiotic defense in seed plants as well as being potentially important bioactive compounds with both nutritional and medicinal benefits reported for animals and humans as a consequence of their potent antioxidant activity. During the long evolutionary period in which plants have adapted to the environmental niches in which they exist (and especially during the evolution of land plants from their aquatic algal ancestors), several strategies such as gene duplication and convergent evolution have contributed to the evolution of this pathway. In this respect, diversity and redundancy of several key genes of phenolic secondary metabolism such as polyketide synthases, cytochrome P450s, Fe(2+)/2-oxoglutarate-dependent dioxygenases and UDP-glycosyltransferases have played an essential role. Recent technical developments allowing affordable whole genome sequencing as well as a better inventory of species-by-species chemical diversity have resulted in a dramatic increase in the number of tools we have to assess how these pathways evolved. In parallel, reverse genetics combined with detailed molecular phenotyping is 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. In this review, phenolic metabolite-related gene sequences (for a total of 65 gene families including shikimate biosynthetic genes) are compared across 23 independent species, and the phenolic metabolic complement of various plant species are compared with one another, in attempt to better understand the evolution of diversity in this crucial pathway.

Recent advances on the regulation of anthocyanin synthesis in reproductive organs

Anthocyanins represent the major red, purple, violet and blue pigments in many flowers and fruits. They attract pollinators and seed dispersers and defend plants against abiotic and biotic stresses. Anthocyanins are produced by a specific branch of the flavonoid pathway, which is differently regulated in monocot and dicot species. In the monocot maize, the anthocyanin biosynthesis genes are activated as a single unit by a ternary complex of MYB-bHLH-WD40 transcription factors (MBW complex). In the dicot Arabidopsis, anthocyanin biosynthesis genes can be divided in two subgroups: early biosynthesis genes (EBGs) are activated by co-activator independent R2R3-MYB transcription factors, whereas late biosynthesis genes (LBGs) require an MBW complex. In addition to this, a complex regulatory network of positive and negative feedback mechanisms controlling anthocyanin synthesis in Arabidopsis has been described. Recent studies have broadened our understanding of the regulation of anthocyanin synthesis in flowers and fruits, indicating that a regulatory system based on the cooperation of MYB, bHLH and WD40 proteins that control floral and fruit pigmentation is common to many dicot species.

Recent advances in the transcriptional regulation of the flavonoid biosynthetic pathway

Flavonoids are secondary metabolites involved in several aspects of plant development and defence. They colour fruits and flowers, favouring seed and pollen dispersal, and contribute to plant adaptation to environmental conditions such as cold or UV stresses, and pathogen attacks. Because they affect the quality of flowers (for horticulture), fruits and vegetables, and their derivatives (colour, aroma, stringency, etc.), flavonoids have a high economic value. Furthermore, these compounds possess pharmaceutical properties extremely attractive for human health. Thanks to easily detectable mutant phenotypes, such as modification of petal pigmentation and seeds exhibiting transparent testa, the enzymes involved in the flavonoid biosynthetic pathway have been characterized in several plant species. Conserved features as well as specific differences have been described. Regulation of structural gene expression appears tightly organized in a spatial and temporal way during plant development, and is orchestrated by a ternary complex involving transcription factors from the R2R3-MYB, basic helix-loop-helix (bHLH), and WD40 classes. This MYB-bHLH-WD40 (MBW) complex regulates the genes that encode enzymes specifically involved in the late steps of the pathway leading to the biosynthesis of anthocyanins and condensed tannins. Although several genes encoding transcription factors from these three families have been identified, many gaps remain in our understanding of the regulation of this biosynthetic pathway, especially about the respective roles of bHLH and WD40 proteins. A better knowledge of the regulatory mechanisms of the flavonoid pathway is likely to favour the development of new biotechnological tools for the generation of value-added plants with optimized flavonoid content.

How can research on plants contribute to promoting human health?

One of the most pressing challenges for the next 50 years is to reduce the impact of chronic disease. Unhealthy eating is an increasing problem and underlies much of the increase in mortality from chronic diseases that is occurring worldwide. Diets rich in plant-based foods are strongly associated with reduced risks of major chronic diseases, but the constituents in plants that promote health have proved difficult to identify with certainty. This, in turn, has confounded the precision of dietary recommendations. Plant biochemistry can make significant contributions to human health through the identification and measurement of the many metabolites in plant-based foods, particularly those known to promote health (phytonutrients). Plant genetics and metabolic engineering can be used to make foods that differ only in their content of specific phytonutrients. Such foods offer research tools that can provide significant insight into which metabolites promote health and how they work. Plant science can reduce some of the complexity of the diet-health relationship, and through building multidisciplinary interactions with researchers in nutrition and the pathology of chronic diseases, plant scientists can contribute novel insight into which foods reduce the risk of chronic disease and how these foods work to impact human health.

Expression analysis of anthocyanin regulatory genes in response to different light qualities in Arabidopsis thaliana

In this work we analysed, at the transcript level, the response of Arabidopsis anthocyanin regulatory genes of the MYB (PAP1 and PAP2), bHLH (TT8, EGL3 and GL3) and WD40 (TTG1) families to white light in seedlings and to different light qualities in rosette leaves. Our experiments showed strong light induction of the MYB genes PAP1 and PAP2. In particular, the kinetics of PAP1 expression preceded those of PAP2 and all of the structural genes (CHS, DFR, F3H, LDOX), consistent with the hypothesis that it has a key role in light induction of anthocyanin biosynthesis. All bHLH genes analysed showed light induction, and in seedlings their expression preceded that of the late structural genes, suggesting their possible role in light regulation of these structural genes. TTG1 expression is essentially constitutive in both systems. Experiments with transgenic lines over-expressing the MYB factors show that PAP1, but not PAP2, strongly stimulates expression of the anthocyanin structural gene encoding dihydroflavonol reductase, but neither factor affected expression of the early flavonoid biosynthesis gene encoding chalcone synthase. Consistent with these findings, PAP1, but not PAP2, stimulated light induction of anthocyanin biosynthesis in seedlings. We conclude that specific members of the MYB and bHLH families play important roles in regulating anthocyanin biosynthesis in response to different light qualities in Arabidopsis.

Chronic dietary intake of plant-derived anthocyanins protects the rat heart against ischemia-reperfusion injury

Consumption of flavonoid-rich foods and beverages is thought to reduce the risk of cardiovascular diseases. Whereas the biological activities of flavonoids have been characterized in vitro, there are no clear experimental data demonstrating that chronic dietary intake and intestinal absorption of flavonoids actually protects the heart against ischemia-reperfusion injury. We tested whether long-term consumption of specific flavonoids (anthocyanins) included in normal food could render the heart of rats more resistant to myocardial infarction. Maize kernels that differed specifically in their accumulation of anthocyanins were used to prepare rodent food in which anthocyanins were either present or absent. Male Wistar rats were fed the anthocyanin-rich (ACN-rich) or the anthocyanin-free (ACN-free) diet for a period of 8 wk. Anthocyanins were significantly absorbed and detected in the blood and urine of only rats fed the ACN-rich diet. In Langendorff preparations, the hearts of rats fed the ACN-rich diet were more resistant to regional ischemia and reperfusion insult. Moreover, on an in vivo model of coronary occlusion and reperfusion, infarct size was reduced in rats that ate the ACN-rich diet than in those that consumed the ACN-free diet (P < 0.01). Cardioprotection was associated with increased myocardial glutathione levels, suggesting that dietary anthocyanins might modulate cardiac antioxidant defenses. Our findings suggest important potential health benefits of foods rich in anthocyanins and emphasize the need to develop anthocyanin-rich functional foods with protective activities for promoting human health.

Light-induced morphological alteration in anthocyanin-accumulating vacuoles of maize cells

BACKGROUND

Plant pigmentation is affected by a variety of factors. Light, an important plant developmental signal, influences the accumulation of anthocyanins primarily through the activation of the transcription factors that regulate the flavonoid biosynthetic pathway. In this study, we utilized maize Black Mexican Sweet (BMS) cells expressing the R and C1 regulators of anthocyanin biosynthesis from a light-insensitive promoter as a means to investigate the existence of additional levels of control of pigmentation by light.

RESULTS

BMS cells expressing the R and C1 regulators from the CaMV 35S constitutive promoter accumulate anthocyanins when grown in complete darkness, suggesting that the transcription factors R and C1 are sufficient for the transcription of the genes corresponding to the structural enzymes of the pathway, with no requirement for additional light-induced regulators. Interestingly, light induces a "darkening" in the color of the purple anthocyanin pigmentation of transgenic BMS cells expressing R and C1. This change in the pigment hue is not associated with a variation in the levels or types of anthocyanins present, or with an alteration of the transcript levels of several flavonoid biosynthetic genes. However, cytological observations show that light drives unexpected changes in the morphology and distribution of the anthocyanins-containing vacuolar compartments.

CONCLUSION

By uncoupling the effect of light on anthocyanin accumulation, we have found light to induce the fusion of anthocyanin-containing vacuoles, the coalescence of anthocyanic vacuolar inclusion (AVI)-like structures contained, and the spread of anthocyanins from the inclusions into the vacuolar sap. Similar light-induced alterations in vacuolar morphology are also evident in the epidermal cells of maize floral whorls accumulating anthocyanins. Our findings suggest a novel mechanism for the action of light on the vacuolar storage of anthocyanin.

Structure and evolution of the r/b chromosomal regions in rice, maize and sorghum

The r1 and b1 genes of maize, each derived from the chromosomes of two progenitors that hybridized >4.8 million years ago (MYA), have been a rich source for studying transposition, recombination, genomic imprinting, and paramutation. To provide a phylogenetic context to the genetic studies, we sequenced orthologous regions from maize and sorghum (>600 kb) surrounding these genes and compared them with the rice genome. This comparison showed that the homologous regions underwent complete or partial gene deletions, selective retention of orthologous genes, and insertion of nonorthologous genes. Phylogenetic analyses of the r/b genes revealed that the ancestral gene was amplified independently in different grass lineages, that rice experienced an intragenomic gene movement and parallel duplication, that the maize r1 and b1 genes are descendants of two divergent progenitors, and that the two paralogous r genes of sorghum are almost as old as the sorghum lineage. Such sequence mobility also extends to linked genes. The cisZOG genes are characterized by gene amplification in an ancestral grass, parallel duplications and deletions in different grass lineages, and movement to a nonorthologous position in maize. In addition to gene mobility, both maize and rice regions experienced recent transposition (<3 MYA).

pl-bol3, a complex allele of the anthocyanin regulatory pl1 locus that arose in a naturally occurring maize population

The pl1 gene encodes a MYB-related transcriptional activator committed to the regulation of anthocyanin biosynthesis in maize. Here, we report the genetic and molecular characterisation of pl-bol3, an Andean allele displaying features that make it different from all the known pl1 alleles. pl-bol3 has partial, light-independent expression, and it is active mainly in the juvenile phase of growth. It has a complex molecular structure, containing multiple pl1 gene copies, thus being the first complex locus discovered in the c1/pl1 family. Although the composite genes of the complex locus encode proteins identical to other functional PL1 proteins, the putative promoters of the pl-bol3 gene are different from the promoters of Pl-Rhoades (Pl-Rh) and pl1 sun-red alleles. The intensity and the tissue specificity of anthocyanin production directed by pl-bol3 differ significantly from that of Pl-Rh and the original pl-W22, and are specified by the interaction of pl-bol3 with the different r1/b1 gene family members and the competence of pl-bol3 to different pigment tissues. This allele represents a natural example of gene duplication and diversification of expression, giving rise to a significant change in phenotype and, in this way, is analogous to the complex r1 locus in maize. Analysis of the pl-bol3 allele contributes to understanding the generation of diversity associated with multiple-copy genes and the molecular basis of allele-specific gene expression.

A maize r1 gene is regulated post-transcriptionally by differential splicing of its leader

Anthocyanin biosynthesis in Zea mays is controlled by regulatory genes of the r1/b1 family that encode bHLH transcription factors. Analysis of the 381 nucleotide leader sequence of a member of this family, Sn, discloses the presence of five ATG triplets upstream of the coding region and three upstream open reading frames (uORFs) of 38, 15 and 13 amino acids respectively. RT-PCR studies revealed that a splicing event occurs in the leader region in the different tissues tested. Splicing deletes 146 nucleotides which include uORF2 and uORF3. By trans-activation experiments in maize protoplasts we find that the spliced leader, compared to the non-spliced one, reduces the number of pigmented protoplasts by four-fold. We suggest a multilevel regulation of the Sn transcription factor acting not only at the transcriptional but also at the post-transcriptional level.

Members of the c1/pl1 regulatory gene family mediate the response of maize aleurone and mesocotyl to different light qualities and cytokinins

We investigated the role of transcription factors (R, SN, C1, and PL) in the regulation of anthocyanin biosynthesis by different light qualities (white, red, blue, and ultraviolet) and by cytokinin in maize (Zea mays). We analyzed anthocyanin accumulation, structural gene expression, and regulatory gene expression in the seed aleurone and the seedling mesocotyl. In the mesocotyl, white, blue, and ultraviolet-B light strongly induced anthocyanin accumulation and expression of two key structural genes. In contrast, red light had little effect. Cytokinin enhanced the response to light but was not sufficient to induce anthocyanin accumulation in darkness. Plants with the pl-bol3 allele showed high levels of anthocyanin accumulation in response to light, whereas those with the pl-W22 allele did not, demonstrating the importance of pl1 in the light response. The expression of the pl-bol3 gene, encoding an MYB-related transcription factor, was induced by light and enhanced by cytokinin in a very similar manner to the structural genes and anthocyanin accumulation. Expression of the bHLH (basic helix-loop-helix) Sn1-bol3 gene was stimulated by several light qualities, but not enhanced by cytokinin, and was less well correlated with the induction of anthocyanin biosynthesis. In the aleurone, white, red, and blue light were effective in stimulating anthocyanin accumulation and expression of the MYB-related gene C1. The bHLH R gene was constitutively expressed. We conclude that specific members of the MYB-related c1/pl1 gene family play important roles in the regulation of anthocyanin synthesis in maize in response to different light qualities and cytokinin.