Diversification of 13S globulins, allergenic seed storage proteins, of common buckwheat

Elimination of zero-repeat subunit in allergenic seed protein 13S globulin using the novel allele GlbNB2 in common buckwheat (Fagopyrum esculentum Moench)

Common buckwheat (Fagopyrum esculentum Moench) seeds contain 13S globulin, the zero-repeat subunit of which is trypsin-resistant and allergenic. Here, its two novel alleles were analyzed for development of hypoallergenic plants. The GlbNC allele has a Miniature Inverted-repeat Transposable Element (MITE)-like insertion in the 4th exon. However, most of the insertion was spliced-out, resulting in accumulation of zero-repeat subunit in GlbNC homozygotes. Meanwhile, the GlbNB2 has a 164-bp insertion in the 3rd exon, resulting in no accumulation of zero-repeat subunit in GlbNB2 homozygotes (NB2_homo). Both the insertion sequences were predicted to form a hairpin-like structure, and that of GlbNB2 was more rigid than that of GlbNC. Trypsin digestion in NB2_homo showed that the α polypeptide of Met-rich subunit is also hard to digest, that is a next target to eliminate for hypoallergenic buckwheat development.

Insertion of ten amino acids into 13S globulin zero-repeat subunit improves trypsin digestibility in common buckwheat (Fagopyrum esculentum Moench) seeds

The 13S globulin zero-repeat subunit is resistant to trypsin and may have higher allergenicity than the 1-6 tandem repeat subunits in common buckwheat (Fagopyrum esculentum Moench). To explore alleles useful for lowering allergenicity, amplicon deep sequencing targeting the zero-repeat subunit gene was conducted in bulked genomic DNA from eight cultivars and landraces. The analysis identified a unique allele encoding a zero-repeat subunit with 10 amino acid insertion (10aa) at a position equivalent to the tandem repeat insertion. Prediction of its 3-D structure suggested that 10aa changes the β-hairpin structure in the non-10aa (native) subunit to a random coil, which is also found in 1- and 3- repeat subunits. Homozygotes of the 10aa allele were developed and showed that the 10aa subunit was more digestible than the native subunit. However, the 10aa subunit was still less digestible than the 1-6 repeat subunits, suggesting needs to explore unfunctional alleles.

Evaluation of subchronic oral dose toxicity and allergen of freeze-dried powder of Locusta migratoria (Orthoptera: Acrididae) as a novel food source

The migratory locust, Locusta migratoria (Orthoptera: Acrididae), is a well-known edible insect which may serve as new source of human food and animal feed. However, potential toxicity and food safety of L. migratoria had not been investigated extensively until now. Therefore, in this study, we aimed to investigate toxicity of freeze-dried powder of L. migratoria (fdLM) and identify allergic components in ELISA and PCR techniques. In this subchronic study, fdLM was administered once daily by oral gavage at the doses of 750, 1500, and 3000 mg/kg/day. No toxicological changes were observed in both sexes of rats for 13 weeks in accordance with the OECD guidelines and GLP conditions. In addition, fdLM did not induced increases of serum immunoglobulin E and 21 homologous proteins were not detected under our present conditions. In conclusion, the NOAEL (no-observed-adverse-effect level) was 3000 mg/kg/day and no target organ was identified in both sexes. In conclusion, we found that fdLM is safe with no adverse effects and offers the potential of its use as an edible ingredient or other biological uses.

Transcriptome and metabolome profiling of the medicinal plant Veratrum mengtzeanum reveal key components of the alkaloid biosynthesis

Veratrum mengtzeanum is the main ingredient for Chinese folk medicine known as "Pimacao" due to its unique alkaloids. A diverse class of plant-specific metabolites having key pharmacological activities. There are limited studies on alkaloid synthesis and its metabolic pathways in plants. To elucidate the alkaloid pathway and identify novel biosynthetic enzymes and compounds in V. mengtzeanum, transcriptome and metabolome profiling has been conducted in leaves and roots. The transcriptome of V. mengtzeanum leaves and roots yielded 190,161 unigenes, of which 33,942 genes expressed differentially (DEGs) in both tissues. Three enriched regulatory pathways (isoquinoline alkaloid biosynthesis, indole alkaloid biosynthesis and tropane, piperidine and pyridine alkaloid biosynthesis) and a considerable number of genes such as AED3-like, A4U43, 21 kDa protein-like, 3-O-glycotransferase 2-like, AtDIR19, MST4, CASP-like protein 1D1 were discovered in association with the biosynthesis of alkaloids in leaves and roots. Some transcription factor families, i.e., AP2/ERF, GRAS, NAC, bHLH, MYB-related, C3H, FARI, WRKY, HB-HD-ZIP, C2H2, and bZIP were also found to have a prominent role in regulating the synthesis of alkaloids and steroidal alkaloids in the leaves and roots of V. mengtzeanum. The metabolome analysis revealed 74 significantly accumulated metabolites, with 55 differentially accumulated in leaves compared to root tissues. Out of 74 metabolites, 18 alkaloids were highly accumulated in the roots. A novel alkaloid compound viz; 3-Vanilloylygadenine was discovered in root samples. Conjoint analysis of transcriptome and metabolome studies has also highlighted potential genes involved in regulation and transport of alkaloid compounds. Here, we have presented a comprehensive metabolic and transcriptome profiling of V. mengtzeanum tissues. In earlier reports, only the roots were reported as a rich source of alkaloid biosynthesis, but the current findings revealed both leaves and roots as significant manufacturing factories for alkaloid biosynthesis.

2S albumin g13 polypeptide, less related to Fag e 2, can be eliminated in common buckwheat (Fagopyrum esculentum Moench) seeds

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2S albumin (g11, g13, g14, and g28) is an important allergen in common buckwheat.

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g13 is hydrophobic, scarce, and less related to g14 than g11/g28 is related to g14.

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g13_null allele homozygote produced no g13 protein in seeds.

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Insert-like sequence of g13_null allele resided frequently in buckwheat genome.

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g13_null homozygote lowered allergenicity in common buckwheat.

2S albumin (g11, g13, g14, and g28) is an important allergen in common buckwheat (Fagopyrum esculentum). g13 is hydrophobic, rare in seeds, and may show distinct allergenicity from the others; therefore, we tried to eliminate this protein. Phylogenetic and property distance analyses indicated g13 is less related to g14 (Fag e 2) than g11/g28 is related to g14, particularly in the second domain containing the II and III α-helices. A null allele with a 531 bp insertion in the coding region was found for g13 at an allele frequency of 2 % in natural populations of common buckwheat. The g13_null allele homozygote accumulated no g13 protein. A BLAST search for the 531 bp insertion suggested the insert-like sequence resided frequently in the buckwheat genome, including the self-incompatibility responsible gene ELF3 in Fagopyrum tataricum. The g13_null insert-like sequence could, therefore, help in producing hypoallergenic cultivars, and expand the genetic diversity of buckwheat.

Resequencing of global Tartary buckwheat accessions reveals multiple domestication events and key loci associated with agronomic traits

BACKGROUND

Tartary buckwheat (Fagopyrum tataricum) is a nutritionally balanced and flavonoid-rich crop plant that has been in cultivation for 4000 years and is now grown globally. Despite its nutraceutical and agricultural value, the characterization of its genetics and its domestication history is limited.

RESULTS

Here, we report a comprehensive database of Tartary buckwheat genomic variation based on whole-genome resequencing of 510 germplasms. Our analysis suggests that two independent domestication events occurred in southwestern and northern China, resulting in diverse characteristics of modern Tartary buckwheat varieties. Genome-wide association studies for important agricultural traits identify several candidate genes, including FtUFGT3 and FtAP2YT1 that significantly correlate with flavonoid accumulation and grain weight, respectively.

CONCLUSIONS

We describe the domestication history of Tartary buckwheat and provide a detailed resource of genomic variation to allow for genomic-assisted breeding in the improvement of elite cultivars.

Structure and diversity of 13S globulin zero-repeat subunit, the trypsin-resistant storage protein of common buckwheat (Fagopyrum esculentum M.) seeds

The zero-repeat subunit of 13S globulin, which lacks tandem repeat inserts, is trypsin-resistant and suggested to show higher allergenicity than the other subunits in common buckwheat (Fagopyrum esculentum Moench). To evaluate allelic variations and find novel alleles, the diversity of the zero-repeat genes was examined for two Japanese elite cultivars and 15 Pakistani landraces. The results demonstrated that two new alleles GlbNA1 and GlbNC1, plus three additional new alleles GlbNA2, GlbNA3, and GlbND, were identified besides the already-known GlbNA, GlbNB, and GlbNC alleles. In the Pakistani landraces, GlbNA was the most dominant allele (0.60-0.88 of allele frequency) in all except one landrace, where GlbNB was the most dominant allele (0.50 of allele frequency). Similar to GlbNC, the alleles GlbNA2 and GlbNA3 had extra ~200 bp MITE-like sequences around the stop codon. Secondary structure predictions of a sense strand demonstrated that the extra ~200 bp sequences of GlbNC, GlbNA2, and GlbNA3 can form rigid hairpin structures with free energies of -78.95, -67.06, and -29.90 kcal/mol, respectively. These structures may affect proper transcription and/or translation. In the GlbNC homozygous line, no transcript of a zero-repeat gene was detected, suggesting the material would be useful for developing hypoallergenic buckwheat.

Efficient transient gene expression system using buckwheat hypocotyl protoplasts for large-scale experiments

Buckwheat (Fagopyrum esculentum) is cultivated worldwide and its flour is used in a variety of food products. Although functional analyses of genes in buckwheat are highly desired, reliable methods to do it have yet to be developed. In this study we established a simple and efficient transient gene expression system using buckwheat protoplasts isolated from young hypocotyls using 96-well plates as a high-throughput platform. The transformation efficiency was comparable with that of similar systems, such as Arabidopsis mesophyll protoplasts. Stable results were obtained in a typical example of the experiment to examine transcription factor activity. This system shows potential for the large-scale analysis of gene function using protoplast isolated from fewer and younger plants than the conventional system and may provide novel information for efficient buckwheat breeding.

Global transcriptome analysis and identification of genes involved in nutrients accumulation during seed development of rice tartary buckwheat (Fagopyrum Tararicum)

Tartary buckwheat seeds are rich in various nutrients, such as storage proteins, starch, and flavonoids. To get a good knowledge of the transcriptome dynamics and gene regulatory mechanism during the process of seed development and nutrients accumulation, we performed a comprehensive global transcriptome analysis using rice tartary buckwheat seeds at different development stages, namely pre-filling stage, filling stage, and mature stage. 24 819 expressed genes, including 108 specifically expressed genes, and 11 676 differentially expressed genes (DEGs) were identified. qRT-PCR analysis was performed on 34 DEGs to validate the transcriptome data, and a good consistence was obtained. Based on their expression patterns, the identified DEGs were classified to eight clusters, and the enriched GO items in each cluster were analyzed. In addition, 633 DEGs related to plant hormones were identified. Furthermore, genes in the biosynthesis pathway of nutrients accumulation were analyzed, including 10, 20, and 23 DEGs corresponding to the biosynthesis of seed storage proteins, flavonoids, and starch, respectively. This is the first transcriptome analysis during seed development of tartary buckwheat. It would provide us a comprehensive understanding of the complex transcriptome dynamics during seed development and gene regulatory mechanism of nutrients accumulation.