O. Y. Shoeva

The Regulation of Anthocyanin Synthesis in the Wheat Pericarp

Bread wheat producing grain in which the pericarp is purple is considered to be a useful source of dietary anthocyanins. The trait is under the control of the Pp-1 homoealleles (mapping to each of the group 7 chromosomes) and Pp3 (on chromosome 2A). Here, TaMyc1 was identified as a likely candidate for Pp3. The gene encodes a MYC-like transcription factor. In genotypes carrying the dominant Pp3 allele, TaMyc1 was strongly transcribed in the pericarp and, although at a lower level, also in the coleoptile, culm and leaf. The gene was located to chromosome 2A. Three further copies were identified, one mapping to the same chromosome arm as TaMyc1 and the other two mapping to the two other group 2 chromosomes; however none of these extra copies were transcribed in the pericarp. Analysis of the effect of the presence of combinations of Pp3 and Pp-1 genotype on the transcription behavior of TaMyc1 showed that the dominant allele Pp-D1 suppressed the transcription of TaMyc1.

The homoeologous genes encoding chalcone–flavanone isomerase in Triticum aestivum L.: Structural characterization and expression in different parts of wheat plant

Chalcone-flavanone isomerase (CHI; EC 5.5.1.6.) participates in the early step of flavonoid biosynthesis, related to plant adaptive and protective responses to environmental stress. The bread wheat genomic sequences encoding CHI were isolated, sequenced and mapped to the terminal segment of the long arms of chromosomes 5A, 5B and 5D. The loss of the final Chi intron and junction of the two last exons was found in the wheat A, B and D genomes compared to the Chi sequences of most other plant species. Each of the three diploid genomes of hexaploid wheat encodes functional CHI; however, transcription of the three homoeologous genes is not always co-regulated. In particular, the three genes demonstrated different response to salinity in roots: Chi-D1 was up-regulated, Chi-A1 responds medially, whereas Chi-B1 was not activated at all. The observed variation in transcriptional activity between the Chi homoeologs is in a good agreement with structural diversification of their promoter sequences. In addition, the correlation between Chi transcription and anthocyanin pigmentation in different parts of wheat plant has been studied. The regulatory genes controlling anthocyanin pigmentation of culm and pericarp modulated transcription of the Chi genes. However, in other organs, there was no strong relation between tissue pigmentation and the transcription of the Chi genes, suggesting complex regulation of the Chi expression in most parts of wheat plant.

Marker-assisted development of bread wheat near-isogenic lines carrying various combinations of purple pericarp (Pp) alleles

The commercial interest in pigmented wheat grain flows from an understanding that they are nutritionally superior to white kernels. The pigment of purple coloured bread and durum wheat grains results from the accumulation of anthocyanins in the pericarp; its genetic basis is the action of Pp-1 and Pp3 genes. Here, the development of a set of bread wheat near isogenic lines (NILs) carrying various combinations of Pp alleles is described, along with a demonstration of their utility for the genetic dissection of the purple pericarp trait. A marker-assisted backcrossing strategy was based on the use of microsatellite markers linked to Pp3 (chromosome 2A), Pp-A1 (7A) and Pp-D1 (7D). Pp-A1 is a newly uncovered gene of weak effect. A qRT-PCR-based analysis of the anthocyanin synthesis structural genes [Chi (chalcone-flavanone isomerase) and F3h (flavanone 3-hydroxylase)] transcript abundance in the pericarp of the NILs suggested that the Pp genes up-regulate their transcription in contrasting ways. These NILs represent a resource for studying the effect of grain pigmentation on other wheat traits and end products.

Regulation of the Flavonoid Biosynthesis Pathway Genes in Purple and Black Grains of Hordeum vulgare

Barley grain at maturity can have yellow, purple, blue, and black pigmentations which are suggested to play a protective role under stress conditions. The first three types of the colors are caused by phenolic compounds flavonoids; the last one is caused by phytomelanins, oxidized and polymerized phenolic compounds. Although the genetic basis of the flavonoid biosynthesis pathway in barley has been thoroughly studied, there is no data yet on its regulation in purple and black barley grains. In the current study, genetic model of Hordeum vulgare ‘Bowman’ near-isogenic lines (NILs) was used to investigate the regulation of the flavonoid biosynthesis in white, purple, and black barley grains. Microsatellite genotyping revealed donor segments in the purple- and black-grained lines on chromosomes 2H (in region of the Ant2 gene determining purple color of grains) and 1H (in region of the Blp gene determining black lemma and pericarp), respectively. The isolated dominant Ant2 allele of the purple-grained line has high level of sequence similarity with the recessive Bowman’s ant2 in coding region, whereas an insertion of 179 bp was detected in promoter region of ant2. This structural divergence between Ant2 and ant2 alleles may underlie their different expression in grain pericarp: Bowman’s Ant2 is not transcribed, whereas it was up-regulated in the purple-grained line with coordinately co-expressed flavonoid biosynthesis structural genes (Chs, Chi, F3h, F3’h, Dfr, Ans). This led to total anthocyain content increase in purple-grained line identified by ultra-performance liquid chromatography (HPLC). Collectively, these results proved the regulatory function of the Ant2 gene in anthocyanin biosynthesis in barley grain pericarp. In the black-grained line, the specific transcriptional regulation of the flavonoid biosynthesis pathway genes was not detected, suggesting that flavonoid pigments are not involved in development of black lemma and pericarp trait.

Flavonoid Biosynthesis Genes in Wheat

Biosynthesis of flavonoid compounds is one of the most studied plant metabolic pathways. Researchers’ attention to the biochemical, physiological and genetic aspects of the flavonoid biosynthesis is associated primarily with a wide range of their biological properties. In addition, a genetic system for the flavonoid biosynthesis is an excellent genetic model. The recent development of molecular and genomics methods has led to considerable progress in understanding the molecular-genetic basis of the flavonoid biosynthesis in bread wheat (Triticum aestivum L.). This article provides a brief review of the structural and functional organization of genes involved in the flavonoid biosynthesis in wheat and its relatives.

Cold Stress Response of Wheat Genotypes Having Different Rc Alleles

Nine wheat genotypes differing by Rc (red coleoptile) alleles were investigated for the dynamics of seedling growth and relative anthocyanin content in the coleoptiles in response to cold. The stressed genotypes showed either reduced, similar or increased anthocyanin content compared to unstressed plants. This difference can be partially explained by the allelic state of the Rc genes. In ‘Saratovskaya 29’ weak Rc allele causes low anthocyanin content under optimal growth conditions. Upon cold treatment the level of anthocyanins decreased, whereas it increased in two near isogenic lines (NILs) with strong Rc alleles developed on ‘Saratovskaya 29’, and in some other genotypes having high anthocyanin content under optimal growth conditions. The changes in anthocyanin content correlated negatively with the changes of growth parameters in response to cold stress, suggesting the presence of some stress-dependent regulation of anthocyanin biosynthesis in wheat coleoptiles.

Molecular genetic mechanisms of the development of fruit and seed coloration in plants

The diverse coloration of plant fruits and seeds is determined by the presence of two important types of pigments, carotenoids (red, orange, yellow) and anthocyanins (purple, blue, red). They belong to two groups of secondary metabolites (isoprenoids and flavonoids). Recently, increased interest in the study of genetic mechanisms controlling coloration traits in plants is observed due to the antioxidant and antimicrobial properties of certain pigments and their colorless precursors consumed with plant food. The genes encoding enzymes required for successive transformations of the initial organic molecules in the final pigment compounds are referred to as the group of structural genes. The factors activating the expression of the structural genes and controlling the synthesis of certain pigments at a particular time in certain part of the plant are referred to as regulatory biosynthesis genes. The data accumulated in the field of plant genetics indicate that the interspecific and intraspecific diversity by the coloration traits (observed at the phenotypical level) is associated with regulatory genes. The creation of rich collections and accurate genetic models by the coloration traits in dicotyledonous and monocotyledonous plants in previous years, as well as the development of molecular genetic methods of plant research, allowed to study in detail the mechanisms of the genetic regulation of the synthesis of pigment compounds at the molecular level. In this article, the peculiarities of regulating carotenoid biosynthesis are illustrated on the example of their production in fruits of the Solanaceae family. Genetic regulation of the synthesis of different flavonoid pigments is demonstrated on the example of the study of the seed coloration in the Poaceae family plants. The prospects of the practical use of regulatory genes controlling the fruit and seed coloration are discussed in the final part of the work; specific examples of their use in breeding of vegetable and cereal crops are given.

The B-, G- and S-genomic Chi genes in family Triticeae

As result of a close evolutionary relationship between Triticeae B, G, and S genomes, the exchange of genetic material between them is possible and may be beneficial for broadening the genetic diversity of cultivated bread wheat. However, the extent to which regulatory networks are conserved remains poorly researched. Here, the structural organization and transcriptional activity of the B, S, and G genome copies of a gene encoding flavonoid biosynthesis enzyme chalcone-flavanone isomerase (CHI) were explored using introgression lines which differ from the wild type by carrying a non-bread wheat Chi-1 gene. Chi-S1, Chi-G1, and Chi-B1 all mapped to a comparable region of chromosomes 5S, 5G, and 5B, respectively. Nucleotide sequences of Aegilops speltoides Chi-S1 and Triticum timopheevii Chi-G1 were determined and compared with T. aestivum Chi-B1 sequences. The enzymes encoded by these three genes shared the same predicted tertiary structure and active sites. However, the replacement of Chi-B1 by Chi-S1 or Chi-G1 in a wheat background resulted in a significant decrease in the global amount of the Chi-1 transcript present in the seedling shoot indicating divergence in regulation of expression of the orthologous Chi-1 genes among Triticeae ssp.

The Specific Features of Anthocyanin Biosynthesis Regulation in Wheat

Anthocyanins are flavonoid pigments important for plant adaptation under biotic and abiotic stress conditions. In bread wheat (Triticum aestivum L.), purple pigmentation caused by anthocyanins can be present on leaves, culm, auricles, glumes, grains, coleoptile, and anthers. Since the first mentions on expression of purple color traits in wheat, the studies into inheritance of these characters have made big steps toward revealing molecular-genetic mechanisms of anthocyanin pigment biosynthesis and its regulation in wheat. Most of the structural genes, encoding enzymes of the biosynthesis, have been cloned and localized in wheat genome. The genetic mapping data suggest that different pigmentation patterns in wheat are determined by genetic loci, distinct from the enzyme encoding loci. The data on functional role of the genes underpinning phenotypic variation together with results of inter-genera comparative mapping suggest these genes to encode transcriptional activators of the anthocyanin biosynthesis structural genes. Here, a brief review is provided of recent findings in the genetic regulation of anthocyanin biosynthesis in wheat.

Differently expressed ‘Early’ flavonoid synthesis genes in wheat seedlings become to be co-regulated under salinity stress

Synthesis of flavonoid compounds in plants is associated with their response to environmental stress; however, the way in which the transcription of the relevant structural genes is regulated in stressed plants is still obscure. Transcription of the ‘early’ flavonoid synthesis genes Chi-1 and F3h-1 in the wheat coleoptile was investigated by quantitative real-time PCR in seedlings exposed to 100 mM or 200 mM NaCl. Under mild stress, transcript abundance of both Chi-1 and F3h-1 was increased significantly after six days of exposure. Under severe stress, the level of transcription was the same or even lower than that seen in nonstressed seedlings. In non-stressed conditions, the transcription patterns of Chi-1 and F3h-1 were quite distinct from one another, whereas under stress they became similar. An observed alteration in structural genes regulation mode under stress conditions may optimize flavonoid biosynthesis pathway to produce protective compounds with maximum efficiency.