Background and Aims Vitamin E (tocochromanol) is a lipid-soluble antioxidant and an essential nutrient for human health. Among cereal crops, barley (Hordeum vulgare L.) contains a high level of vitamin E, which includes both tocopherols and tocotrienols. Although the vitamin E biosynthetic pathway has been characterized in dicots, such as Arabidopsis, which only accumulate tocopherols, knowledge regarding vitamin E biosynthesis in monocots is limited because of the lack of functional mutants. This study aimed to obtain gene knockout mutants to elucidate the genetic control of vitamin E composition in barley. Methods Targeted knockout mutations of HvHPT and HvHGGT in barley were created with CRISPR/Cas9-enabled genome editing. High-performance liquid chromatography (HPLC) was performed to analyse the content of tocochromanol isomers in transgene-free homozygous Hvhpt and Hvhggt mutants. Key Results Mutagenesis efficiency among T0 regenerated plantlets was 50–65 % as a result of two simultaneously expressed gRNAs targeting each gene; most of the mutations were stably inherited by the next generation. The transgene-free homozygous mutants of Hvhpt and Hvhggt exhibited decreased grain size and weight, and the HvHGGT mutation led to a shrunken phenotype and significantly lower total starch content in grains. HPLC analysis revealed that targeted mutation of HvHPT significantly reduced the content of both tocopherols and tocotrienols, whereas mutations in HvHGGT completely blocked tocotrienol biosynthesis in barley grains. Transient overexpression of an HvHPT homologue in tobacco leaves significantly increased the production of γ- and δ-tocopherols, which may partly explain why targeted mutation of HvHPT in barley grains did not eliminate tocopherol production. Conclusions Our results functionally validated that HvHGGT is the only committed gene for the production of tocotrienols, whereas HvHPT is partly responsible for tocopherol biosynthesis in barley..

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Barley has abundant anthocyanin-rich accessions, which renders it an ideal model to investigate the regulatory mechanism of anthocyanin biosynthesis. This study functionally characterized two transcription factors: Ant1 and Ant2. Sequence alignment showed that the coding sequences of Ant1 and Ant2 are conserved among 11 colored hulless barley and noncolored barley varieties. The expression profiles of Ant1 and Ant2 were divergent between species, and significantly higher expression was found in two colored Qingke accessions. The co-expression of Ant1 and Ant2 resulted in purple pigmentation in transient transformation systems via the promotion of the transcription of four structural genes. Ant1 interacted with Ant2, and overexpression of Ant1 activated the transcription of Ant2. Moreover, overexpression of Ant1 led to anthocyanin accumulation in the pericarp and aleurone layer of transgenic barley grains. Overall, our results suggest that anthocyanin-enriched barley grains can be produced by manipulating Ant1 expression.

Background Barley is known to be recalcitrant to tissue culture, which hinders genetic transformation and its biotechnological application. To date, the ideal explant for transformation remains limited to immature embryos; the mechanism underlying embryonic callus formation is elusive. Results This study aimed to uncover the different transcription regulation pathways between calli formed from immature (IME) and mature (ME) embryos through transcriptome sequencing. We showed that incubation of embryos in an auxin-rich medium caused dramatic changes in gene expression profiles within 48 h. Overall, 9330 and 11,318 differentially expressed genes (DEGs) were found in the IME and ME systems, respectively. 3880 DEGs were found to be specific to IME_0h/IME_48h, and protein phosphorylation, regulation of transcription, and oxidative-reduction processes were the most common gene ontology categories of this group. Twenty-three IAA, fourteen ARF, eight SAUR, three YUC, and four PIN genes were found to be differentially expressed during callus formation. The effect of callus-inducing medium (CIM) on IAA genes was broader in the IME system than in the ME system, indicating that auxin response participates in regulating cell reprogramming during callus formation. BBM, LEC1, and PLT2 exhibited a significant increase in expression levels in the IME system but were not activated in the ME system. WUS showed a more substantial growth trend in the IME system than in the ME system, suggesting that these embryonic, shoot, and root meristem genes play crucial roles in determining the acquisition of competency. Moreover, epigenetic regulators, including SUVH3A, SUVH2A, and HDA19B/703, exhibited differential expression patterns between the two induction systems, indicating that epigenetic reprogramming might contribute to gene expression activation/suppression in this process. Furthermore, we examined the effect of ectopic expression of HvBBM and HvWUS on Agrobacterium-mediated barley transformation. The transformation efficiency in the group expressing the PLTPpro:HvBBM + Axig1pro:HvWUS construct was increased by three times that in the control (empty vector) because of enhanced plant regeneration capacity. Conclusions We identified some regulatory factors that might contribute to the differential responses of the two explants to callus induction and provide a promising strategy to improve transformation efficiency in barley.

Background: Barley is known to be recalcitrant to tissue culture, which hinders genetic transformation and its biotechnological application. To date, the ideal explant for transformation is still limited to immature embryos; however, the mechanism underlying embryonic callus formation remains elusive.Results: The aim of this study was to uncover the differential transcription regulation pathways between immature embryo (IME)- and mature embryo (ME)-derived callus formation through transcriptome sequencing. We showed that incubation of embryos on auxin-rich medium caused dramatic changes in gene expression profiles within 48 h. A total of 9330 and 11318 differentially expressed genes (DEGs) were found in the IME and ME systems, respectively. Protein phosphorylation, regulation of transcription, and oxidative-reduction process were the most common gene ontology categories of DEGs specific to the IME system. Twenty-three IAA, 14 ARF, 8 SAUR, 3 YUC, and 4 PIN genes were found to be differentially expressed during callus formation. The effect of callus-inducing medium (CIM) on IAA genes was broader in the IME system than in the IM system, indicating that auxin response and transport cooperate in regulating cell reprogramming during callus formation. BBM, LEC1 and PLT2 exhibited a significant increase in expression level during IME system but were not activated in the ME system, WUS showed a more substantial growth trend in the IME system than in the ME system, suggesting that these embryonic, shoot, and root meristems genes play crucial roles in determining the acquisition of competency. In addition, epigenetic regulators—including SUVH3A, SUVH2A, HDA19B/703—exhibited differential expression patterns between the two induction systems, indicating that epigenetic reprogramming might contribute to gene expression activation/suppression in this process. Furthermore, we examined the effect of ectopic expression of HvBBM and HvWUS on Agrobacterium-mediated barley transformation. The transformation efficiency was increased by three times in the group expressing the PLTPpro:HvBBM +Axig1pro:HvWUS construct, compared to that in the control (empty vector), which was due to an enhancement of plant regeneration capacity. Conclusions: We identified some regulatory factors that might contribute to the differential responses of the two explants to callus induction and provide a promising strategy to improve transformation efficiency in barley.