Hulless Barley Research Articles

Mixed organic and inorganic amendments enhance soil microbial interactions and environmental stress resistance of Tibetan barley on plateau farmland

Sufficient crop yield while maintaining soil health and sustainable agricultural development is a global objective, serving a special challenge to certain climate-sensitive plateau areas. Despite conducting trails on a variety of soil amendments in plateau areas, systematic research is lacking regarding the influences of organic and inorganic amendments on soil quality, particularly soil microbiome. To our knowledge, this was the first study that compared the effects of inorganic, organic, and mixed amendments on typical plateau crop hulless barley (Hordeum vulgare L. var. Nudum, also known as “Qingke” in Chinese) over the course of tillering, jointing, and ripening. Microbial communities and their responses to amendments, soil properties and Tibetan hulless barley growth, yield were investigated. Results indicated that mixed organic and inorganic amendments promoted the abundance of rhizosphere microorganisms, enhancing the rhizosphere root-microbes interactions and resistance to pathogenic bacteria and environmental stresses. The rhizosphere abundant and significantly different genera Arthrobacter, Rhodanobacter, Sphingomona, Nocardioides and so on demonstrated their unique adaptation to the plateau environment based on the results of metagenomic binning. The abundance of 23 genes about plant growth and environmental adaptations in the mixed amendment soil were significantly higher than other treatments. Findings from this study suggest that the mixed organic/inorganic amendments can help establish a healthy microbiome and increase soil quality while achieving sufficient hulless barley yields in Tibet and presumably other similar geographic areas of high altitude.

Composition of Polysaccharides in Hull-Less Barley Sourdough Bread and Their Impact on Physical Properties of Bread.

The complex of polysaccharides of the grain transforms during processing and modifies the physical and chemical characteristics of bread. The aim of the research was to characterize the changes of glucans, mannans and fructans in hull-less barley and wholegrain wheat breads fermented with spontaneous hull-less barley sourdough, germinated hull-less barley sourdough and yeast, as well as to analyze the impact of polysaccharides on the physical parameters of bread. By using the barley sourdoughs for wholegrain wheat bread dough fermentation, the specific volume and porosity was reduced; the hardness was not significantly increased, but the content of β-glucans was doubled. Principal component analysis indicates a higher content of β-glucans and a lower content of starch, total glucans, fructans and mannans for hull-less barley breads, but wholegrain wheat breads fermented with sourdoughs have a higher amount of starch, total glucans, fructans and mannans, and a lower content of β-glucans. The composition of polysaccharides was affected by the type of flour and fermentation method used.

Inferring regulatory element landscapes and gene regulatory networks from integrated analysis in eight hulless barley varieties under abiotic stress

BackgroundThe cis-regulatory element became increasingly important for resistance breeding. There were many DNA variations identified by resequencing. To investigate the links between the DNA variations and cis-regulatory element was the fundamental work. DNA variations in cis-regulatory elements caused phenotype variations in general.ResultsWe used WGBS, ChIP-seq and RNA-seq technology to decipher the regulatory element landscape from eight hulless barley varieties under four kinds of abiotic stresses. We discovered 231,440 lowly methylated regions (LMRs) from the methylome data of eight varieties. The LMRs mainly distributed in the intergenic regions. A total of 97,909 enhancer-gene pairs were identified from the correlation analysis between methylation degree and expression level. A lot of enriched motifs were recognized from the tolerant-specific LMRs. The key transcription factors were screened out and the transcription factor regulatory network was inferred from the enhancer-gene pairs data for drought stress. The NAC transcription factor was predicted to target to TCP, bHLH, bZIP transcription factor genes. We concluded that the H3K27me3 modification regions overlapped with the LMRs more than the H3K4me3. The variation of single nucleotide polymorphism was more abundant in LMRs than the remain regions of the genome.ConclusionsEpigenetic regulation is an important mechanism for organisms to adapt to complex environments. Through the study of DNA methylation and histone modification, we found that many changes had taken place in enhancers and transcription factors in the abiotic stress of hulless barley. For example, transcription factors including NAC may play an important role. This enriched the molecular basis of highland barley stress response.

Removing starch granule-associated surface lipids affects structure of heat-moisture treated hull-less barley starch

The effects of starch granule-associated surface lipids removal on hull-less barley starch structure formed by heat-moisture treatment were investigated. Removing surface lipids made the peak at 2θ of 13° disappear and resulted in higher lamellar peak intensity after harsh treatment and a lower reduction in mass fractal dimension (from 2.49 to 2.43) and radius of gyration (from 24.3 to 24.0) when temperature increased from 100 to 120 °C at 20 % moisture. Treatment at 25 % moisture and 120 °C decreased relative crystallinity (from 15.73 % to 7.43 %) and Gaussian peak area (from 646.7 to 137.7) of native starch, and decreased relative crystallinity (from 14.24 % to 12.56 %) and Gaussian peak area (from 604.1 to 539.6) for starch without surface lipids. Different trends of change in lamellar thickness, linear crystallinity, peak temperatures, and enthalpy of gelatinization were observed among modified starches with increasing temperature and/or moisture content. These results demonstrate that removing surface lipids changes structure of heat-moisture treated starch.

Diet nutrient digestibility and growth performance in weaned pigs fed barley differing in fermentable starch and fibre profile

Barley grain containing both fermentable starch and fibre might be attractive as energy source in weaned pig diets because of benefits on gut health. Rapidly fermentable carbohydrates and slowly fermentable fibre may decrease diarrhoea in weaned pigs serving as prebiotics. Steam explosion processing may disrupt the fibre matrix of cereal hulls, increasing slowly fermentable fibre of barley grain. Five diets were formulated to provide 10.0 and 9.6 MJ net energy (NE)/kg, 1.32 and 1.22 g standardised ileal digestible (SID) lysine/MJ NE for phase 1 (day 0–14) and phase 2 (day 14–28), respectively. Diets contained 593–644 g cereal grain/kg: 1) low-fermentable hulled barley (LFB); 2) LFB steam-exploded (LFB-SE; 1.2 MPa, 120 s); 3) high-β-glucan (70 g/kg) hull-less barley (HFBB); 4) high amylose (168 g/kg) hull-less barley (HFAB); or 5) low-fermentable wheat (LFW). A total of 220 pigs in 11 blocks of 5 pens each were fed 1 of 5 diets starting 1-week post-weaning for 28 days. For phase 1, the coefficient of apparent total tract digestibility (CATTD) of gross energy (GE) and crude protein (CP) of diets was greatest (P < 0.05) for LFW, intermediate for HFBB, followed by LFB-SE, LFB and lowest for HFAB. The calculated NE value was greatest (P < 0.05) for LFW, intermediate for LFB-SE, and lowest for HFBB, LFB and HFAB. For phase 2, the CATTD of GE was greater (P < 0.05) for LFW and HFBB than LFB, LFB-SE and HFAB; the CATTD of CP was greatest (P < 0.05) for LFW, intermediate for HFBB, followed by LFB, HFAB, and lowest for LFB-SE; calculated NE value was greatest (P < 0.05) for HFBB and LFW, intermediate for LFB and HFAB, and lowest for LFB-SE. For the entire trial (day 0–28), average daily feed intake (ADFI) and average daily gain (ADG) of pigs did not differ among diets, but gain-to-feed (ADG/ADFI) was lowest (P < 0.05) for the LFB-SE diet. For day 21–28, pigs fed LFB-SE diet had greater (P < 0.01) ADFI than pigs fed HFAB diet, whereas pigs fed LFW, LFB and HFBB were intermediate. Faeces consistency of pigs did not differ between LFB and LFW diets, but pigs fed LFB diet had firmer (P < 0.05) faeces than pigs fed HFBB, HFAB and LFB-SE diets. To conclude, the wheat diet had greater GE and CP digestibility than barley diets. Among barley diets, the HFBB had greater GE and CP digestibility than both LFB and LFB-SE; the HFAB diet ranked lowest. However, feeding barley to replace wheat grain in nursery diets formulated to equal NE value and SID amino acid content did not affect growth performance. Finally, dietary fermentable carbohydrates in barley made faeces less firm. Steam explosion of hulled barley grain did not increase GE or CP digestibility.

Genetic architecture of inducible and constitutive metabolic profile related to drought resistance in qingke (Tibetan hulless barley).

Qingke (Tibetan hulless barley, Hordeum vulgare L. var. nudum) is the primary food crop on the Tibet Plateau, the long-term drought and other harsh environments makes qingke an important resource for the study of abiotic resistance. Here, we evaluated the drought sensitivity of 246 qingke varieties. Genome-wide association studies (GWAS) found that root-specific expressed gene CYP84 may be involved in the regulation of drought resistance. Based on widely targeted metabolic profiling, we identified 2,769 metabolites in qingke leaves, of which 302 were significantly changed in response to drought stress, including 4-aminobutyric acid (GABA), proline, sucrose and raffinose. Unexpectedly, these drought-induced metabolites changed more violently in drought-sensitive qingkes, while the constitutive metabolites that had little response to drought stress, such as C-glycosylflavonoids and some amino acids, accumulated excessively in drought-resistant qingkes. Combined with metabolite-based genome-wide association study (mGWAS), a total of 1,006 metabolites under optimal condition and 1,031 metabolites under mild drought stress had significant associated loci. As a marker metabolite induced by drought stress, raffinose was significantly associated with two conservatively adjacent α-galactosidase genes, qRT-PCR suggests that these two genes may jointly regulate the raffinose content in qingke. Besides, as constituent metabolites with stable differences between drought-sensitive and drought-resistant qingkes, a class of C-glycosylflavonoids are simultaneously regulated by a UDP-glucosyltransferase gene. Overall, we performed GWAS for sensitivity and widely targeted metabolites during drought stress in qingke for the first time, which provides new insights into the response mechanism of plant drought stress and drought resistance breeding.

Effects of urea addition on anaerobic digestion characteristics of hulless barley straw pretreated with KOH

Effects of urea addition on anaerobic digestion characteristics of hulless barley straw pretreated with KOH

Determination of Grain Yield and Nutrition Traits in Hull-less Barley Genotypes

Determination of Grain Yield and Nutrition Traits in Hull-less Barley Genotypes

Effect of acid hydrolysis on the structural and antioxidant characteristics of β-glucan extracted from Qingke (Tibetan hulless barley).

In this study, we explored the effect of acid hydrolysis on the molecular, structural, rheological, thermal, and antioxidant characteristics of Qingke β-glucan. The acid hydrolysis reduced the molecular weights of β-glucans from 510 to 155 KDa. The results of the structural analysis by nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction, and fourier transforms infrared (FTIR) spectroscopy indicated that acid hydrolysis did not change the primary functional groups of β-glucans. The rheological behavior of β-glucan without and with acid hydrolysis can be described as pseudoplastic and Newtonian, respectively. The DSC curves of the β-glucans with high molecular weights showed the highest transition temperature. The 2, 2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging activity and the reducing power of soluble β-glucans in Qingke showed a dose-dependent pattern. Meanwhile, the antioxidant activities of Qingke β-glucan of different molecular weights were similar. This study demostrated that the acid hydrolysis almost have no effect on antioxidant activity of Qingke β-glucans.

Integrative metabolomic and transcriptomic analyses reveal the mechanisms of Tibetan hulless barley grain coloration.

Cereal grains accumulate anthocyanin during developmental process. The anthocyanin content increases at grain filling stages to develop grain coloration in cereals. However, anthocyanin biosynthesis responsible for grain coloring and its regulatory mechanisms controlled by structural and functional genes remain unclear. Therefore, this study aimed to explore the global map of metabolic changes linked to grain coloration of Tibetan hulless barley (qingke) using an integrative metabolome and transcriptome approach. Grains from three colored qingke cultivars at different developmental stages were considered for molecular and metabolic investigations. A total of 120 differentially accumulated metabolites (DAMs) and 8,327 differentially expressed genes (DEGs) were filtered. DEGs were mainly enriched in the phenylpropanoid and flavonoid pathways. The transcript levels of anthocyanin biosynthesis genes (PAL, C4H, 4CL, CHS, FLS, F3H, F3'H, DFR, ANS, GT, OMT, and MAT) significantly upregulate in colored qingke compared to the non-colored variety. During grain development and maturation, the strong correlation of HvMYC2 expression with anthocyanin contents and anthocyanin biosynthesis genes suggested it as a critical gene in anthocyanin accumulation. Further results confirmed that HvMYC2 could be activated by HvMYB and be a positive regulator of UV-B and cold tolerance in qingke. In addition, verification based on enzymatic assays indicated that six key modifier enzymes could catalyze glycosylation, malonylation, and methylation of anthocyanins, thereby dissecting the major anthocyanin modification pathway in colored qingke. Overall, our study provides global insight into anthocyanin accumulation and the mechanism underlying grain coloration in qingke.

Study on the microbial inactivation of whole hulless barley flour using a continuous instant pressure drop sterilizer

AbstractThis work evaluated the microbial reduction and quality change of the whole hulless barley flour (WHBF) treated by a continuous instant pressure drop (CIPD) sterilizer. The microbial reduction of WHBF was proportional to steam‐material ratio under the conditions of 165°C, 0.2 MPa steam, and 0.2 MPa Laval nozzle, and the microbial reduction was 3.87 ± 0.09 log cfu/g with the steam‐material ratio of 3.0:1. The work was followed‐up with the quality testing of CIPD, UV‐C, hot air, and ozone treated WHBF. The microbial reduction of hot air, UV‐C, and ozone treated WHBF was 3.98 ± 0.09, 3.33 ± 0.04, and 3.68 ± 0.12 log cfu/g, respectively, while the CIPD treatment achieved similar bactericidal effect at a unit treatment time of 22 s. Moreover, there is no measurable quality degradation in CIPD treated WHBF compared with the untreated WHBF. These results showed CIPD sterilizer had a great potential for microbial inactivation of powdery foods industry.

Optimum seeding rates for hulless barley production in eastern Canada

Hulless barley is a relatively new crop in eastern Canada. Best cultural practices must be developed for hulless barley to achieve its maximum yield potential. A study was carried out to identify the optimum seeding rates for hulless barley in eastern Canada. Six barley lines consisting of two-row and six-row covered and hulless varieties (AAC Azimuth, AAC Starbuck, CDC Ascent, AAC Bloomfield, AAC Ling, and CH2720-1) were seeded in six different seeding rates (250, 350, 450, 550, 650, and 750 seeds m−2) in a factorial experiment with four replications at seven sites across eastern Canada. The results showed that the optimum seeding rate for covered barley was 250–350 seeds m−2, but those for hulless barley higher yield potentials were achieved at seeding rate from 450 to 550 seeds m−2. Two-row varieties were higher yielding and had higher protein concentration than six-row varieties. The results of this study show that there is potential for further development of high-yielding two-row cultivars for eastern Canada.

Distribution of free and bound phenolic compounds, β-glucan, and araboxylan in fractions of milled hulless barley

To study the effect of milling process on active compounds in hulless barley, the β-glucan, araboxylan, the free and bound forms of phenolic compounds and antioxidant activities were evaluated. The results showed that total araboxylan content (9.64 g/100 g → 2.35 g/100 g) decreased significantly (P < 0.05) from the outer to the inner layer, while the β-glucan content first increased significantly going towards the inner layers and showed a gradual decrease moving toward the endosperm. Total free and bound forms of total phenolics and total flavonoids decreased by 91% and 95% with the increase of the degree of milling and anthocyanins mostly existed in the outer layers. The total DPPH (2,2-Diphenyl-1-picrylhydrazyl) and ABTS (2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonate)) antioxidant activities decreased by 90% and 97% from the outer to the inner layers. Both free and bound forms of 21 phenolic compounds decreased significantly (P < 0.05) with increased milling and were mostly in the outermost layer. Moreover, eight diferulic acids were reported for the first time in hulless barley, and ferulic acid was the most abundant monomeric phenolic acid, with 8-O-4′ diferulic acid being the most abundant diferulic acid and chrysoeriol-7-O-glucouronide being the dominant flavonoid. Therefore, a lower degree milling is recommended for the higher retainment of bioactive compounds during daily processing.

Mechanism of Early Flowering in a Landrace Naked Barley eam8.l Mutant

The EARLY MATURITY 8 (EAM8) gene of barley is homologous to the EARLY FLOWERING 3 (ELF3) gene in Arabidopsis, as loss-of-function mutations in this circadian clock gene promote rapid flowering. A previous study demonstrated that the early flowering phenotype of a hulless barley, Lalu, was due to allele eam8.l carrying an alternative splicing mutation in intron 3 that led to intron retention. In the present study, we verified that eam8.l encoded a truncated protein. Although EAM8 was expressed at a higher level in Lalu than in other barley lines with a longer growth period, it did not negatively regulate flowering time. This result further proved that the eam8.l protein was nonfunctional in regulating flowering in barley. The early flowering phenotype of Lalu plants was strongly dependent on the biosynthesis of gibberellin (GA). The eam8.l mutation stopped the suppression of GA biosynthesis, and Lalu accumulated excessive GA, especially in leaves. This was achieved through the upregulated expression of genes in the GA pathway, including GA20ox2, LFY1, SOC1, PAP2, and FPF3. The mutation of the EAM8 gene also abolished the inhibition of FLOWERING LOCUS T-like (FT1) gene expression at night. During the night, expression levels of the FT1 gene were higher than those during the day in Lalu. However, the GA-dependent pathway and FT1 gene mechanism are two independent pathways that promote flowering in Lalu. Alleles of EAM8, therefore, demonstrated an important breeding value in barley, which is probably effective in many other day-length-sensitive crop plants as well; thus, they could be used to tune adaptation in different geographic regions and climatic conditions, a critical issue in times of global warming.

Is Tritordeum (×Tritordeum martinii A. Pujadas, nothosp. nov.) grain a potentially useful source of essential minerals in the human diet?

Tritordeum grain is known for its high content of protein, carotenoids and polyphenols, but its mineral composition has not been analyzed to date. The experimental material comprised 11 breeding lines of Tritordeum, two reference cultivars of durum wheat, and one hulless barley cultivar. The thousand kernel weight (TKW) of the studied Tritordeum lines was 23% lower than in durum wheat and more than 18% lower than in barley. Tritordeum grain contained around 24% more ash than durum wheat. During the entire two-year study, the concentrations of the 31 analyzed elements were similar to those reported in various small grain cereals in the literature. Tritordeum grain was characterized by a very high content of potassium and magnesium which was more than 16% and 6% higher, respectively, than in durum wheat, and 27% and 17% higher, respectively, than in hulless barley. In comparison with the reference durum wheat and barley cultivars, Tritordeum was also more abundant in copper (by 24% and 62%, respectively), zinc (by 11% and 17%, respectively) and cobalt (by 24% and more than 314%, respectively. The limits for the lead and cadmium content of grain were not exceeded.

Distribution of Core Root Microbiota of Tibetan Hulless Barley along an Altitudinal and Geographical Gradient in the Tibetan Plateau.

The Tibetan Plateau is regarded as the third pole of the earth and is one of the least explored places on the planet. Tibetan hull-less barley (Hordeum vulgare L. var. nudum) is the only cereal crop grown widely in the Tibetan Plateau as a staple food. Extensive and long-term cropping of barley may influence the soil’s chemical and biological properties, including microbial communities. However, microbiota associated with hull-less barley is largely unexplored. This study aimed to reveal the composition and diversity of bacterial and fungal communities associated with the hull-less barley at different elevations in the Tibetan Plateau. The core bacterial and fungal taxa of Tibetan hull-less barley were identified, with Bacillaceae, Blastocatellaceae, Comamonadaceae, Gemmatimonadaceae, Planococcaceae, Pyrinomonadaceae, Sphingomonadaceae, and Nitrospiraceae being the most abundant bacterial taxa and Ceratobasidiaceae, Chaetomiaceae, Cladosporiaceae, Didymellaceae, Entolomataceae, Microascaceae, Mortierellaceae, and Nectriaceae being the most abundant fungal taxa (relative abundance > 1%). Both bacterial and fungal diversities of hull-less barley were affected by altitude and soil properties such as total carbon, total nitrogen, and available phosphorus and potassium. Both bacterial and fungal diversities showed a significant negative correlation with altitude, indicating that the lower elevations provide a conducive environment for the survival and maintenance of hull-less barley-associated microbiota. Our results also suggest that the high altitude-specific microbial taxa may play an important role in the adaptation of the hull-less barley to the earth’s third pole.

Effect of the Addition of Hulless Barley Flour on the Quality of Short-Dough Cookies.

Short-dough cookies are one of the most popular cereal-based products in the world, but usually they are considered as foods with a low nutritional value. Therefore, the aim of this study was to investigate the possibility of replacing part of the wheat flour (WF) with hulless barley flour (HLBF), in order to improve the functional properties and nutritional value of the cookies. Cookies were prepared from composite flours in the ratios HLBF:WF 0:100, 25:75, 50:50, 75:25, and 100:0. The results show that as the HLBF content in the composite flour increases, the viscosity of the corresponding HLBF:WF slurries also increases, due to the high dietary fiber content (especially the high β-glucan content), which is significantly higher when HLBF is included in the formulation. The addition of HLBF decreases the spread factor of the cookies, and increases their softness compared to the control cookies (100% WF), but these changes are not statistically significant up to 50% HLBF addition. The color of the HLBF:WF cookies is not significantly affected. A significant increase in total phenolic content (TPC) and increased antioxidant capacity (AOC) are observed in the HLBF:WF cookies. In addition, sensory evaluation confirms that WF can be replaced by up to 50% with HLBF without significant deterioration of the organoleptic properties of the cookies. It can be concluded that hulless barley serves as a promising raw material if the nutritional and functional properties of cereal-based products are to be improved.

Effects of different thermal processing methods on bioactive components, phenolic compounds, and antioxidant activities of Qingke (highland hull-less barley)

Qingke (highland hull-less barley) is a grain replete with substantial nutrients and bioactive ingredients. In this study, we evaluated the effects of boiling (BO), steaming (ST), microwave baking (MB), far-infrared baking (FB), steam explosion (SE), and deep frying (DF) on bioactive components, phenolic compounds, and antioxidant activities of Qingke compared with the effects of traditional roast (TR). Results showed that the soluble dietary fiber, beta-glucan and water-extractable pentosans of Qingke in dry heat processes of TR, SE, MB and FB had a higher content compared with other thermal methods and had a better antioxidant activity of hydroxyl radical scavenging and a better reduction capacity, while those in wet heat processes of BO and ST had a better antioxidant activity of ABTS radical scavenging and a better Fe2+ chelating ability. DF- and SE-Qingke had a higher content of tocopherol, phenolic, and flavonoid. Overall, 6 free phenolic compounds and 12 bound phenolic compounds of Qingke were identified, and free phenolic compounds suffered more damage during thermal processing. Principal component analysis showed that SE had more advantages in retaining and improving the main biological active ingredients of Qingke, and it may be the best method for treating Qingke.

Hulless barley polyphenol extract inhibits adipogenesis in 3T3-L1 cells and obesity related-enzymes.

Obesity is characterized by excessive lipid accumulation, hypertrophy, and hyperplasia of adipose cells. Hulless barley (Hordeum vulgare L. var. nudum Hook. f.) is the principal crop grown in the Qinghai-Tibet plateau. Polyphenols, the major bioactive compound in hulless barley, possess antioxidant, anti-inflammatory, and antibacterial properties. However, the anti-obesity effect of hulless barley polyphenol (HBP) extract has not been explored. Therefore, the current study assessed the impact of HBP extract on preventing obesity. For this purpose, we evaluated the inhibitory effect of HBP extract against obesity-related enzymes. Moreover, we investigated the effect of HBP extract on adipocyte differentiation and adipogenesis through 3T3-L1 adipocytes. Our results demonstrated that HBP extract could inhibit α-amylase, α-glucosidase (α-GLU), and lipase in a dose-dependent manner. In addition, HBP extract inhibited the differentiation of 3T3-L1 preadipocytes by arresting the cell cycle at the G0/G1 phase. Furthermore, the extract suppressed the expression of adipogenic transcription factors such as peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), regulating fatty acid synthase (FAS), fatty acid-binding protein 4 (FABP4), and adipose triglyceride lipase (ATGL). It was also observed that HBP extract alleviated intracellular lipid accumulation by attenuating oxidative stress. These findings specify that HBP extract could inhibit obesity-related enzymes, adipocyte differentiation, and adipogenesis. Therefore, it is potentially beneficial in preventing obesity.

Accumulation and regulation of anthocyanins in white and purple Tibetan Hulless Barley (Hordeum vulgare L. var. nudum Hook. f.) revealed by combined de novo transcriptomics and metabolomics

BackgroundColored barley, which may have associated human health benefits, is more desirable than the standard white variety, but the metabolites and molecular mechanisms underlying seedcoat coloration remain unclear.ResultsHere, the development of Tibetan hulless barley was monitored, and 18 biological samples at 3 seedcoat color developmental stages were analyzed by transcriptomic and metabolic assays in Nierumuzha (purple) and Kunlun10 (white). A total of 41 anthocyanin compounds and 4186 DEGs were identified. Then we constructed the proanthocyanin-anthocyanin biosynthesis pathway of Tibetan hulless barley, including 19 genes encoding structural enzymes in 12 classes (PAL, C4H, 4CL, CHS, CHI, F3H, F3’H, DFR, ANS, ANR, GT, and ACT). 11 DEGs other than ANR were significantly upregulated in Nierumuzha as compared to Kunlun10, leading to high levels of 15 anthocyanin compounds in this variety (more than 25 times greater than the contents in Kunlun10). ANR was significantly upregulated in Kunlun10 as compared to Nierumuzha, resulting in higher contents of three anthocyanins compounds (more than 5 times greater than the contents in Nierumuzha). In addition, 22 TFs, including MYBs, bHLHs, NACs, bZips, and WD40s, were significantly positively or negatively correlated with the expression patterns of the structural genes. Moreover, comparisons of homologous gene sequences between the two varieties identified 61 putative SNPs in 13 of 19 structural genes. A nonsense mutation was identified in the coding sequence of the ANS gene in Kunlun10. This mutation might encode a nonfunctional protein, further reducing anthocyanin accumulation in Kunlun10. Then we identified 3 modules were highly specific to the Nierumuzha (purple) using WGCNA. Moreover, 12 DEGs appeared both in the putative proanthocyanin-anthocyanin biosynthesis pathway and the protein co-expression network were obtained and verified.ConclusionOur study constructed the proanthocyanin-anthocyanin biosynthesis pathway of Tibetan hulless barley. A series of compounds, structural genes and TFs responsible for the differences between purple and white hulless barley were obtained in this pathway. Our study improves the understanding of the molecular mechanisms of anthocyanin accumulation and biosynthesis in barley seeds. It provides new targets for the genetic improvement of anthocyanin content and a framework for improving the nutritional quality of barley.