Cytological analysis on the distribution and origin of the alien chromosome pair conferring blue aleurone color in several European common wheat (Triticum aestivum L.) strains

Cytogenetic Characterization and Molecular Marker Development for a Wheat-T. boeoticum 4Ab (4B) Disomic Substitution Line with Stripe Rust Resistance

Triticum boeoticum (2n = 2x = 14, A^bA^b) is an important relative of wheat. This species tolerates many different types of environmental stresses, including drought, salt, and pathogenic infection, and is lower in dietary fiber and higher in antioxidants, protein (15 to 18%), lipids, and trace elements than common wheat. However, the gene transfer rate from this species to common wheat is low, and few species-specific molecular markers are available. In this study, the wheat-T. boeoticum substitution line Z1889, derived from a cross between the common wheat cultivar Crocus and T. boeoticum line G52, was identified using multicolor fluorescence in situ hybridization, multicolor genomic in situ hybridization, and a 55K single-nucleotide polymorphism array. Z1889 was revealed to be a 4A^b (4B) substitution line with a high degree of resistance to stripe rust pathogen strains prevalent in China. In addition, 22 4A^b chromosome-specific molecular markers and 11 T. boeoticum genome-specific molecular markers were developed from 1,145 4A^b chromosome-specific fragments by comparing the sequences generated by specific-length amplified fragment sequencing, with an efficiency of up to 55.0%. Furthermore, the specificity of these markers was verified in four species containing the A^b genome. These markers not only can be used for the detection of the 4A^b chromosome but also provide a basis for molecular marker-assisted, selection-based breeding in wheat.

Rising Demand for Healthy Foods-Anthocyanin Biofortified Colored Wheat Is a New Research Trend

Wheat is a vital and preferred energy source in many parts of the world. Its unique processing quality helps prepare many products such as bread, biscuit, pasta, and noodles. In the world of rapid economic growth, food security, in terms of nutritional profile, began to receive more significant interest. The development of biofortified colored wheat (black, purple, and blue) adds nutritional and functional health benefits to the energy-rich wheat. Colored wheat exists in three forms, purple, blue, and black, depending upon the types and position of the anthocyanins in wheat layers, regulated by the bHLH-MYC transcription factor. Colored wheat lines with high anthocyanin, iron, and zinc contents showed antioxidant and anti-inflammatory activity and possessed desirable product-making and commercial utilization features. The anthocyanin in colored wheat also has a broad spectrum of health implications, such as protection against metabolic syndromes like obesity, diabetes, hypertension, and dyslipidemia. The idea of developing anthocyanin-biofortified wheat shapes human beings' lifestyles as it is a staple food crop in many parts of the world. This review is a compilation of the currently available information on colored wheat in the critical aspects, including biochemistry, food processing, nutrition, genetics, breeding, and its effect on human health. Market generation and consumer awareness creation are vital challenges for its exploitation as a function food on a large scale.

Anthocyanin Biosynthesis and a Regulatory Network of Different-Colored Wheat Grains Revealed by Multiomics Analysis

Colored wheat has always been a popular research area because of its high performance in the field and significant medical uses. Progress has been made mapping the genes of purple or blue grains; however, the reason why different grain colors form in wheat is not well understood. We created wheat lines with different grain colors (purple and blue) using the white grain cultivar Xiaoyan22 and located the candidate region related to the purple and blue grains in chromosome 2A, 2B, and 4D, 2A, respectively, by the bulked segregant RNA-seq. The transcriptomic and metabolomic analyses of the three grains at different developmental stages indicated that the upregulation of flavonoid 3'-hydroxylase/flavonoid 3',5'hydroxylase 2 and TaMYC1/TaMYC4 was important for the formation of purple/blue grains. The blue TaMYC4 had 16 nonsynonymous single nucleotide variants verified by Sanger sequencing and possessed a different splicing mode in the bHLH_MYC_N domain compared with the reference database. Targeted high-performance liquid chromatography-mass spectrometry/mass spectrometry analysis of anthocyanins found that the purple and blue grains contained more pelargonidin, cyanidin, and delphinidin, respectively. This study provides a comprehensive understanding of the different color formations of wheat grains and useful information about genetic improvements in wheat and other crops.

TbMYC4A Is a Candidate Gene Controlling the Blue Aleurone Trait in a Wheat-Triticum boeoticum Substitution Line

Triticum boeoticum Boiss (A^bA^b, 2n = 2x = 14) is one of the sources of the blue grain trait controlled by blue aleurone layer 2 (Ba2). However, the underlying genes have not been cloned. In this study, a transcriptomic comparison between a blue-grained wheat-T. boeoticum substitution line and its wheat parent identified 41 unigenes related to anthocyanin biosynthesis and 29 unigenes related to transport. The bHLH transcription factor gene TbMYC4A showed a higher expression level in the blue-grained substitution line. TbMYC4A contained the three characteristic bHLH transcription factor domains (bHLH-MYC_N, HLH and ACT-like) and clustered with genes identified from other wheat lines with the blue grain trait derived from other Triticeae species. TbMYC4A overexpression confirmed that it was a functional bHLH transcription factor. The analysis of a TbMYC4A-specific marker showed that the gene was also present in T. boeoticum and T. monococcum with blue aleurone but absent in other Triticeae materials with white aleurone. These results indicate that TbMYC4A is a candidate gene of Ba2 controlling the blue aleurone trait. The isolation of TbMYC4A is helpful for further clarifying the genetic mechanism of the blue aleurone trait and is of great significance for breeding blue-grained wheat varieties.

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.

Development, identification, and characterization of blue-grained wheat-Triticum boeoticum substitution lines

Diploid wild einkorn wheat, Triticum boeoticum Boiss (A^bA^b, 2n = 2x = 14), is a wheat-related species with a blue aleurone layer. In this study, six blue-grained wheat lines were developed from F₈ progeny of crosses between common wheat and T. boeoticum. The chromosome constitutions of these lines were characterized by fluorescence in situ hybridization (FISH) using the oligonucleotide probes Oligo-pTa535-1, Oligo-pSc119.2-1, Oligo-pTa71-2, and (AAC)₇. Multicolor FISH using Oligo-pTa535-1, Oligo-pSc119.2-1, and Oligo-pTa71-2 identified all 42 common wheat chromosomes, while Oligo-pTa535-1 and (AAC)₇ discriminated the 14 chromosomes of T. boeoticum. FISH revealed that all six blue-grained lines were wheat-T. boeoticum 4A^b (4B) disomic substitution lines. The substitution lines were validated by genotyping using the wheat 55 K single nucleotide polymorphism (SNP) array containing 53,063 markers. These 4A^b (4B) substitution lines represent novel germplasm for blue-grained wheat breeding. The FISH probes and SNP markers used here can be applied in the development of blue-grained wheat-Triticum boeoticum translocation lines.

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.

Variation in genome composition of blue-aleurone wheat

Different blue-aleurone wheats display major differences in chromosome composition, ranging from disomic chromosome additions, substitutions, single chromosome arm introgressions and chromosome translocation of Thinopyrum ponticum. Anthocyanins are of great importance for human health due to their antioxidant, anti-inflammatory, anti-microbial and anti-cancerogenic potential. In common wheat (Triticum aestivum L.) their content is low. However, elite lines with blue aleurone exhibit significantly increased levels of anthocyanins. These lines carry introgressed chromatin from wild relatives of wheat such as Thinopyrum ponticum and Triticum monococcum. The aim of our study was to characterize genomic constitutions of wheat lines with blue aleurone using genomic and fluorescence in situ hybridization. We used total genomic DNA of Th. ponticum and two repetitive DNA sequences (GAA repeat and the Afa family) as probes to identify individual chromosomes. This enabled precise localization of introgressed Th. ponticum chromatin. Our results revealed large variation in chromosome constitutions of the blue-aleurone wheats. Of 26 analyzed lines, 17 carried an introgression from Th. ponticum; the remaining nine lines presumably carry T. monococcum chromatin undetectable by the methods employed. Of the Th. ponticum introgressions, six different types were present, ranging from a ditelosomic addition (cv. Blue Norco) to a disomic substitution (cv. Blue Baart), substitution of complete (homologous) chromosome arms (line UC66049) and various translocations of distal parts of a chromosome arm(s). Different types of introgressions present support a hypothesis that the introgressions activate the blue aleurone trait present, but inactivated, in common wheat germplasm.

Genetic variability in anthocyanin composition and nutritional properties of blue, purple, and red bread (Triticum aestivum L.) and durum (Triticum turgidum L. ssp. turgidum convar. durum) wheats

Renewed interest in breeding for high anthocyanins in wheat (Triticum ssp.) is due to their antioxidant potential. A collection of different pigmented wheats was used to investigate the stability of anthocyanins over three crop years. The data show higher anthocyanins in blue-aleurone bread wheat (Triticum aestivum L.), followed by purple- and red-pericarp durum wheat (Triticum turgidum L. ssp. turgidum convar. durum), using cyanidin 3-O-glucoside as standard. HPLC of the anthocyanin components shows five to eight major anthocyanins for blue wheat extracts, compared to three anthocyanins for purple and red wheats. Delphinidin 3-O-rutinoside, delphinidin 3-O-glucoside, and malvidin 3-O-glucoside are predominant in blue wheat, with cyanidin 3-O-glucoside, peonidin 3-O-galactoside, and malvidin 3-O-glucoside in purple wheat. Of the total anthocyanins, 40-70% remain to be structurally identified. The findings confirm the high heritability for anthocyanins, with small genotype × year effects, which will be useful for breeding purposes, to improve the antioxidant potential of cereal-based foods.