Proteomics characterization nitrogen fertilizer promotes the starch synthesis and metabolism and amino acid biosynthesis in common buckwheat.

Nitrogen (N) affects common buckwheat quality by affecting starch and amino acids (AAs) content, but its molecular mechanism is still unclear. We selected two common buckwheat varieties with high and low starch content, and designed two treatments with 180 and 0 kg N/ha. Application of high-N led to significant increases in starch, amylose and amylopectin content. Of 1337 differentially expressed proteins (DEPs) induced by high-N conditions. 472DEPs were significantly upregulated and 176DEPs downregulated for Xinong9976. 239DEPs were significantly upregulated and 126DEPs downregulated for Beizaosheng. The six alpha-glucan phosphorylases, three alpha-amylases, one granule-bound starch synthase 1 and one sucrose synthase exhibited higher expression at the 180 kg N/ha than at the 0 kg N/ha. In addition, high-N application promoted arginine, leucine, isoleucine and valine biosynthesis. This study revealed the effect of N on the starch and AA content of common buckwheat and its mechanism. The crucial proteins identified may develop the quality of common buckwheat.

Comparative cellular, physiological and transcriptome analyses reveal the potential easy dehulling mechanism of rice-tartary buckwheat (Fagopyrum Tararicum).

BACKGROUND: Tartary buckwheat has gained popularity in the food marketplace due to its abundant nutrients and high bioactive flavonoid content. However, its difficult dehulling process has severely restricted its food processing industry development. Rice-tartary buckwheat, a rare local variety, is very easily dehulled, but the cellular, physiological and molecular mechanisms responsible for this easy dehulling remains largely unclear. RESULTS: In this study, we integrated analyses of the comparative cellular, physiological, transcriptome, and gene coexpression network to insight into the reason that rice-tartary buckwheat is easy to dehull. Compared to normal tartary buckwheat, rice-tartary buckwheat has significantly brittler and thinner hull, and thinner cell wall in hull sclerenchyma cells. Furthermore, the cellulose, hemicellulose, and lignin contents of rice-tartary buckwheat hull were significantly lower than those in all or part of the tested normal tartary buckwheat cultivars, respectively, and the significant difference in cellulose and hemicellulose contents between rice-tartary buckwheat and normal tartary buckwheat began at 10 days after pollination (DAP). Comparative transcriptome analysis identified a total of 9250 differentially expressed genes (DEGs) between the rice- and normal-tartary buckwheat hulls at four different development stages. Weighted gene coexpression network analysis (WGCNA) of all DEGs identified a key module associated with the formation of the hull difference between rice- and normal-tartary buckwheat. In this specific module, many secondary cell wall (SCW) biosynthesis regulatory and structural genes, which involved in cellulose and hemicellulose biosynthesis, were identified as hub genes and displayed coexpression. These identified hub genes of SCW biosynthesis were significantly lower expression in rice-tartary buckwheat hull than in normal tartary buckwheat at the early hull development stages. Among them, the expression of 17 SCW biosynthesis relative-hub genes were further verified by quantitative real-time polymerase chain reaction (qRT-PCR). CONCLUSIONS: Our results showed that the lower expression of SCW biosynthesis regulatory and structural genes in rice-tartary buckwheat hull in the early development stages contributes to its easy dehulling by reducing the content of cell wall chemical components, which further effects the cell wall thickness of hull sclerenchyma cells, and hull thickness and mechanical strength.

Comparison of high temperature resistance in two buckwheat species Fagopyrum esculentum and Fagopyrum tataricum.

In the context of ongoing climate change, expected temperature rise may significantly limit plant growth and productivity of crop species. In this study, we investigated the effects of a sub-optimal temperature on buckwheat, a pseudocereal known for its nutraceutical advantages. Two buckwheat species differing by their reproduction method, namely Fagopyrum esculentum and Fagopyrum tataricum were grown at 21 °C and 27 °C in growth chambers. High temperature increased leaf production mainly in F. tataricum but decreased leaf area in both species. Water and photosynthesis-related parameters were affected by high temperature but our results suggested that although transpiration rate was increased, adaptive mechanisms were developed to limit the negative impact on photosynthesis. High temperature mainly affected the reproductive stage. It delayed flowering time but boosted inflorescence and flower production. Nevertheless, flower and seed abortions were observed in both species at 27 °C. Regarding flower fertility, heat affected more the female stage than the male stage and reduced the stigma receptivity. Pollen production increased with temperature in F. esculentum while it decreased in F. tataricum. Such discrepancy could be related to the self-incompatibility of F. esculentum. Both species increased their antioxidant production under high temperature to limit oxidative stress and antioxidant capacity was higher in the inflorescences than in the leaves. Total flavonoid content was particularly increased in the leaves of F. esculentum and in the inflorescences of F. tataricum. Altogether, our results showed that even if high temperature may negatively affect reproduction in buckwheat, it improves its antioxidant content.

Nutraceutical crop buckwheat: a concealed wealth in the lap of Himalayas.

Buckwheat is a crop that has gained considerable interest worldwide due to its nutritional, economical, and pharmaceutical values. To ensure food and nutritional security in a scenario of global climate change, this pseudocereal is a competent alternative to staple crops. With rising knowledge regarding the nutraceutical potential, the popularity of this species is expected to increase further in coming years. The main bioactive component of this species is rutin that has been proven to have a wide range of health-promoting benefits. Due to breeding constraints, asynchronous maturity, seed shattering, and restricted distribution, this species holds the status of an underutilized or neglected crop in many parts of the world. In the North-western Himalayan zone, it is an integral part of local dietary intake and is grown as a second crop after harvesting barley and peas. Fagopyrum esculentum and F. tataricum are the species of buckwheat cultivated in the North-western Himalayas. However, more studies in the direction of conservation, utilization, and genetic amelioration of plant genetic resources are needed to sustain food security in Southeast Asia. The present review paper accentuates the multicore potential of buckwheat besides highlighting the commercial and pharmaceutical perspective. This article also focuses on the conservation and sustainable utilization of Himalayan gene pools, desirable agronomic traits, and genetic diversity besides focusing on the biochemical and molecular response of Fagopyrum to biotic and abiotic stress including modulation of the rutin content. The role of biotechnological interventions and future prospects are also summarized.

The Effect of Tartary Buckwheat Flavonoids in Inhibiting the Proliferation of MGC80-3 Cells during Seed Germination.

Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn) is rich in functional compounds such as rutin, quercetin, d-chiro-inositol, dietary fiber, and essential amino acids. Electric field (EF) treatment before sprout germination results in physiological and chemical changes, and some alterations might lead to positive applications in plant seeds. MTT assay showed that the effect of total flavonoids on human gastric cancer cell line MGC80-3 was significantly changed after EF treatment for different germination days (3-7 days). Among them, the total flavonoids of tartary buckwheat (BWTF) on the third day had the most obvious inhibitory effect on MGC80-3 (p < 0.01). In addition, flow cytometry evidenced that different ratios of quercetin and rutin had effects on the proliferation of MGC80-3. The same content of quercetin and rutin had the best effect, reaching 6.18 ± 0.82%. The anti-cancer mechanism was mainly promoted by promoting the expression of apoptotic proteins. The expression of Bax/Bcl-2 and caspase-8 in MGC80-3 cells was mediated by BWTFs. This study has good research value for improving the biological and economic value of tartary buckwheat.

Effects of exogenous sulfur on alleviating cadmium stress in tartary buckwheat.

Supplying exogenous sulfur-rich compounds increases the content of glutathione(GSH) and phytochelatins(PCs) in plant tissues, enabling plants to enhance their cellular defense capacity and/or compartmentalize Cadmium(Cd) into vacuoles. However, the mechanism by which surplus S modulates tolerance to Cd stress in different tissues need further investigation. In the present study, we found that supplementing the tartary buckwheat(Fagopyrum tararicum) exposed to Cd with surplus S reversed Cd induced adverse effects, and increased Cd concentrations in roots, but decreased in leaves. Further analysis revealed that exogenous S significantly mitigated Cd-induced oxidative stress with the aids of antioxidant enzymes and agents both in leaves and roots, including peroxidase(POD), ascorbate peroxidase(APX), glutathione peroxidase(GPX), glutathione S-transferase(GST), ascorbic acid(AsA), and GSH, but not superoxide dismutase(SOD) and catalase(CAT). The increased Cd uptake in root vacuoles and decreased translocation in leaves of exogenous S treated plants could be ascribed to the increasing Cd binding on cell walls, chelation and vacuolar sequestration with helps of non-protein thiols(NPT), PCs and heavy metal ATPase 3(FtHMA3) in roots, and inhibiting expression of FtHMA2, a transporter that helps Cd translocation from roots to shoots. Results provide the fundamental information for the application of exogenous S in reversal of heavy metal stress.

Genome-wide analysis of the NAC transcription factor family in Tartary buckwheat (Fagopyrum tataricum).

BACKGROUND: The NAC (NAM, ATAF1/2, and CUC2) transcription factor family represents a group of large plant-specific transcriptional regulators, participating in plant development and response to external stress. However, there is no comprehensive study on the NAC genes of Tartary buckwheat (Fagopyrum tataricum), a large group of extensively cultivated medicinal and edible plants. The recently published Tartary buckwheat genome permits us to explore all the FtNAC genes on a genome-wide basis. RESULTS: In the present study, 80 NAC (FtNAC) genes of Tartary buckwheat were obtained and named uniformly according to their distribution on chromosomes. Phylogenetic analysis of NAC proteins in both Tartary buckwheat and Arabidopsis showed that the FtNAC proteins are widely distributed in 15 subgroups with one subgroup unclassified. Gene structure analysis found that multitudinous FtNAC genes contained three exons, indicating that the structural diversity in Tartary buckwheat NAC genes is relatively low. Some duplication genes of FtNAC have a conserved structure that was different from others, indicating that these genes may have a variety of functions. By observing gene expression, we found that FtNAC genes showed abundant differences in expression levels in various tissues and at different stages of fruit development. CONCLUSIONS: In this research, 80 NAC genes were identified in Tartary buckwheat, and their phylogenetic relationships, gene structures, duplication, global expression and potential roles in Tartary buckwheat development were studied. Comprehensive analysis will be useful for a follow-up study of functional characteristics of FtNAC genes and for the development of high-quality Tartary buckwheat varieties.

[Screening genotypes and identifying indicators of different Fagopyrum tataricum varieties with low phosphorus tolerance.] / è‹¦èžè€ä½Žç£·åŸºå› åž‹ç­›é€‰åŠè¯„ä»·æŒ‡æ ‡çš„é‰´å®š.

Soil phosphorus (P) deficiency is one of the main factors that diminish the yield of crops on the Loess Plateau. Fagopyrum tataricum is a dominant cereal plant on the Loess Plateau, whose responses to low-P stress are significantly different and dependent on its genotypes. Therefore, screening genotypes with efficient P utilization is an important approach to increase the yield of F. tataricum and promote the sustainable development of local agriculture. With fourteen F. tataricum genotypes, the agronomic traits, physiology and biochemical characters of F. tataricum at seedling stage under normal (2 mmol·L-1) and low-P treatment (0.2 mmol·L-1) were studied by using sand culture. By examining the characters of selected F. tataricum at seedling stage, the varieties of F. tataricum with low-P tolerance were screened out and their evaluation indices were assessed to provide theoretical basis for the breeding of F. tataricum with high P-efficiency and the infertile soil cultivation on the Loess Plateau. The results showed that under low-P stress, the shoots of all genotypes were more affected than roots, with the decline of shoot aboveground index, average root diameter, root surface area and root volume, whereas the length of main root was elongated. Root activity and soluble protein content were decreased. In contrast, other physiological and biochemical indicators were increased. Moreover, plant total phosphorus content and plant phosphorus accumulation reduced, but phosphorus use efficiency increased. The principal component analysis divided the 22 individual indicators into four mutually independent comprehensive indicators (cumulative contribution rate of 90.1%). Cluster analysis divided 14 kinds of F. tataricum into three categories: Low phosphorus tolerant, intermediate and phosphorus sensitive. In order to investigate the index of low-P tolerance of F. tataricum at seedling stage, the optimal regression equation was established with the comprehensive evaluation value of low-P tolerance (D value) as the dependent variable and the low-P tolerance index of each indicator as the independent variables. Seven indicators of root surface area, root length, plant height, aboveground dry mass, acid phosphatase, phosphorus accumulation and POD activity were examined, which could be used for the rapid identification of low-P tolerance of F. tataricum at seedling stage.

Biochemical constituents of buckwheat (Fagopyrum esculentum Moench) collected from different geographical regions of Himachal Pradesh.

Buckwheat (Fagopyrum esculentum), one of the major traditional, underexploited crop having good nutritional value, can be grown in poor agroclimatic regions requires low inputs for its cultivation. Variability in biochemical parameters were observed in biotypes of buckwheat collected from different geographical regions. 1000 seed weight was varied from 9.48 to 15.22 g. Buckwheat biotypes contains high amount of protein (7.69-15.47%). Rutin, the most important ingredient of buckwheat was also varies (3.74-6.53%) in different biotypes. It was also found that many essential amino acids are also found in buckwheat. Variations among almost all estimated parameters were found to be highly significant.

Insights into the correlation between Physiological changes in and seed development of tartary buckwheat (Fagopyrum tataricum Gaertn.).

BACKGROUND: Tartary buckwheat (Fagopyrum tataricum Gaertn.) is a widely cultivated medicinal and edible crop with excellent economic and nutritional value. The development of tartary buckwheat seeds is a very complex process involving many expression-dependent physiological changes and regulation of a large number of genes and phytohormones. In recent years, the gene regulatory network governing the physiological changes occurring during seed development have received little attention. RESULTS: Here, we characterized the seed development of tartary buckwheat using light and electron microscopy and measured phytohormone and nutrient accumulation by using high performance liquid chromatography (HPLC) and by profiling the expression of key genes using RNA sequencing with the support of the tartary buckwheat genome. We first divided the development of tartary buckwheat seed into five stages that include complex changes in development, morphology, physiology and phytohormone levels. At the same time, the contents of phytohormones (gibberellin, indole-3-acetic acid, abscisic acid, and zeatin) and nutrients (rutin, starch, total proteins and soluble sugars) at five stages were determined, and their accumulation patterns in the development of tartary buckwheat seeds were analyzed. Second, gene expression patterns of tartary buckwheat samples were compared during three seed developmental stages (13, 19, and 25 days postanthesis, DPA), and 9 765 differentially expressed genes (DEGs) were identified. We analyzed the overlapping DEGs in different sample combinations and measured 665 DEGs in the three samples. Furthermore, expression patterns of DEGs related to phytohormones, flavonoids, starch, and storage proteins were analyzed. Third, we noted the correlation between the trait (physiological changes, nutrient changes) and metabolites during seed development, and discussed the key genes that might be involved in the synthesis and degradation of each of them. CONCLUSION: We provided abundant genomic resources for tartary buckwheat and Polygonaceae communities and revealed novel molecular insights into the correlations between the physiological changes and seed development of tartary buckwheat.

Two Genes Encoding a Bacterial-Type ATP-Binding Cassette Transporter are Implicated in Aluminum Tolerance in Buckwheat.

Buckwheat (Fagopyrum esculentum Moench) shows high tolerance to aluminum (Al) toxicity, but the molecular mechanisms underlying its high Al tolerance are poorly understood. Here, we functionally characterized two genes (FeSTAR1 and FeSTAR2), which encode a nucleotide-binding domain and a membrane domain, respectively, of a bacterial-type ATP-binding cassette (ABC) transporter. The expression of FeSTAR1 and FeSTAR2 was induced by Al in both roots and leaves with higher expression in the roots. Spatial and tissue-specific expression analysis showed that the Al-induced expression of these two genes was found in both the root tips and basal root regions with higher expression in the root outer cell layers. The expression was neither induced by other metals including Cd and La nor by low pH and phosphorus-deficiency. FeSTAR1 and FeSTAR2 were present in a single copy in the genome, but the Al-induced transcript copy number of FeSTAR1 and FeSTAR2 was much higher than their homologous genes in rice and Arabidopsis. FeSTAR1 and FeSTAR2 form a complex when co-expressed in onion epidermal cells. Introduction of FeSTAR1 and FeSTAR2 into Arabidopsis mutants atstar1 and als3/atstar2, respectively, rescued the sensitivity of the mutants to Al. Taken together, our results indicate that FeSTAR1 and FeSTAR2 are involved in Al tolerance and that their high expression level may contribute to high Al tolerance in buckwheat.

Heterostyly promotes compatible pollination in buckwheats: Comparisons of intraflower, intraplant, and interplant pollen flow in distylous and homostylous Fagopyrum.

PREMISE OF THE STUDY: Heterostyly, the reciprocal positioning of stigmas and anthers in different floral morphs, has long been thought to promote intermorph pollination. However, extensive intramorph pollination occurs commonly in heterostylous species, leading to recurrent questions about the functional and evolutionary significance of heterostyly. METHODS: To identify the sources of stigmatic pollen (autogamous [intraflower], geitonogamous [intraplant], vs. interplant), we emasculated either one flower or entire plants in experimental populations of the two closely related buckwheat species, distylous Fagopyrum esculentum and homostylous F. tataricum. Differences in pollen size allowed unambiguous identification of pollen on stigmas. RESULTS: Only 2.4% of F. tataricum pollen and 1.5% of F. esculentum pollen arrived successfully on compatible stigmas of other plants. In the former (homostylous) species, 71.3% of the pollen load on stigmas was autogamous, 10.8% was geitonogamous, and 17.9% was interplant. In the latter (distylous) species, 37.45% of the pollen on stigmas was autogamous, 13.8% was geitonogamous, 17.0% was intramorph, and 31.75% was intermorph. The amount of incompatible pollen arriving on stigmas was greatly decreased by both one-flower and whole-plant emasculations, and thus, the proportion of compatible pollen deposited increased with one-flower emasculation and increased even more with whole-plant emasculation. CONCLUSIONS: Our quantification of pollen-donor sources in these two species indicated that heterostyly in Fagopyrum esculentum provided a nearly 2-fold fitness advantage (in terms of compatible pollination) over expected (random) pollen transfers between morphs. Because of reduced herkogamy, the homostylous F. tataricum was highly autogamous.

The Tartary Buckwheat Genome Provides Insights into Rutin Biosynthesis and Abiotic Stress Tolerance.

Tartary buckwheat (Fagopyrum tataricum) is an important pseudocereal crop that is strongly adapted to growth in adverse environments. Its gluten-free grain contains complete proteins with a well-balanced composition of essential amino acids and is a rich source of beneficial phytochemicals that provide significant health benefits. Here, we report a high-quality, chromosome-scale Tartary buckwheat genome sequence of 489.3 Mb that is assembled by combining whole-genome shotgun sequencing of both Illumina short reads and single-molecule real-time long reads, sequence tags of a large DNA insert fosmid library, Hi-C sequencing data, and BioNano genome maps. We annotated 33 366 high-confidence protein-coding genes based on expression evidence. Comparisons of the intra-genome with the sugar beet genome revealed an independent whole-genome duplication that occurred in the buckwheat lineage after they diverged from the common ancestor, which was not shared with rosids or asterids. The reference genome facilitated the identification of many new genes predicted to be involved in rutin biosynthesis and regulation, aluminum stress resistance, and in drought and cold stress responses. Our data suggest that Tartary buckwheat's ability to tolerate high levels of abiotic stress is attributed to the expansion of several gene families involved in signal transduction, gene regulation, and membrane transport. The availability of these genomic resources will facilitate the discovery of agronomically and nutritionally important genes and genetic improvement of Tartary buckwheat.

An Aluminum-Inducible IREG Gene is Required for Internal Detoxification of Aluminum in Buckwheat.

Buckwheat (Fagopyrum esculentum Moench) is able to detoxify aluminum (Al) both externally and internally, but the molecular mechanisms underlying its high Al tolerance are not understood. We functionally characterized a gene (FeIREG1) belonging to IRON REGULATED/ferroportin in buckwheat, which showed high expression in our previous genome-wide transcriptome analysis. FeIREG1 was mainly expressed in the roots, and its expression was up-regulated by Al, but not by other metals and low pH. Furthermore, in contrast to AtIREG1 and AtIREG2 in Arabidopsis, the expression of FeIREG1 was not induced by Fe deficiency. Spatial expression analysis showed that the Al-induced expression of FeIREG1 was found in the root tips and higher expression was detected in the outer layers of this part. Immunostaining also showed that FeIREG1 was localized at the outer cell layers in the root tip. A FeIREG1-green fluorescent protein (GFP) fusion protein was localized to the tonoplast when transiently expressed in onion epidermal cells. Overexpression of FeIREG1 in Arabidopsis resulted in increased Al tolerance, but did not alter the tolerance to Cd, Co and Fe. The tolerance to Ni was slightly enhanced in the overexpression lines. Mineral analysis showed that the accumulation of total root Al and other essential mineral elements was hardly altered in the overexpression lines. Taken together, our results suggest that FeIREG1 localized at the tonoplast plays an important role in internal Al detoxification by sequestering Al into the root vacuoles in buckwheat.

Identification, isolation and expression analysis of eight stress-related R2R3-MYB genes in tartary buckwheat (Fagopyrum tataricum).

KEY MESSAGE: Eight R2R3 - MYB genes in tartary buckwheat were identified, and their expression patterns were comprehensively analyzed, which reveals role in plant response to abiotic stresses. The proteins of the R2R3-MYB superfamily play key roles in the growth and development processes as well as defense responses in plants. However, their characteristics and functions have not been fully investigated in tartary buckwheat (Fagopyrum tataricum), a strongly abiotic resistant coarse cereal. In this article, eight tartary buckwheat R2R3-MYB genes were isolated with full-length cDNA and DNA sequences. Phylogenetic analysis of the members of the R2R3-MYB superfamily between Arabidopsis and tartary buckwheat revealed that the assumed functions of the eight tartary buckwheat R2R3-MYB proteins are divided into five Arabidopsis functional subgroups that are involved in abiotic stress. Expression analysis during abiotic stress and exogenous phytohormone treatments identified that the eight R2R3-MYB genes responded to one or more treatments. This study is the first comprehensive analysis of the R2R3-MYB gene family in tartary buckwheat under abiotic stress.

Plantlet Regeneration of Tartary Buckwheat (Fagopyrum tataricum Gaertn.) in Vitro Tissue Cultures.

Tartary buckwheat is an ancient annual dicotyledonous herb, which is widely distributed around the world, specifically in the high altitude area of southwestern China and in the hill region of Himalayan. The plantlet regeneration of tartary buckwheat via somatic embryogenesis or multiple shoot induction was investigated in two different tartary buckwheats, Yuanzi and Xichang. The regeneration ability of Yuanzi was better than Xichang tartary buckwheat, and the hypocotyls were better than cotyledons as tartary buckwheat plantlet regeneration explants via somatic embryogenesis. The most suitable medium for callus induction was Murashige and Skoog basal medium added 2 mg/L 2, 4- dichlorophenoxyacetic acid and 1 mg/L Kinetin, which could reach up to 98.96% callus induction percentage. The plantlet regeneration percentage from callus of tartary buckwheat could reach up to 55.77%, which induced on 2.0 mg/L Benzyladenine and 1.0 mg/L KT in MS basal medium. In addition, maximum of multiple shoot induction percentage was 69.05%, which was observed in case of Yuanzi tartary buckwheat in MS basal medium with added 3.0 mg/L 6-BA and 1.0 mg/L Thidiazuron. Roots induction of regenerated plants were achieved on 1/2 MS basal medium with added 1mg/L Indole-3-Butytric acid, which has 75% survival after transferred regenerated plants to soil under field conditions.

Characterization of FeDREB1 promoter involved in cold- and drought-inducible expression from common buckwheat (Fagopyrum esculentum).

C-repeat-binding factor (CBF)/dehydration-responsive element (DREB) transcription factors play key roles in plant stress responses. However, little information is available on the regulation of CBF/DREB expression. In this study, we isolated and characterized the FeDREB1 promoter sequence from the common buckwheat accession Xinong 9976. To identify the upstream region of the FeDREB1 gene required for promoter activity, we constructed a series of FeDREB1 promoter deletion derivatives. Each deletion construct was analyzed through Agrobacterium-mediated transient transformation in tobacco leaves treated with 4°C cold or drought stress. Promoter-beta-glucuronidase fusion assays revealed that the pCD1 (-270 bp) deletion in the upstream region of FeDREB1 could activate expression of the GUS gene at 4°C. The pCD1 (-270 bp), pCD2 (-530 bp), and pCD3 (-904 bp) deletion induced low-level GUS expression under drought stress. However, the pCD4 (-1278 bp) deletion clearly activated GUS gene expression. Our results suggest that sections pCD1 (-270 bp) and pCD4 (-1278 bp) in the FeDREB1 gene promoter are new sources of induced promoters for adversity-resistance breeding in plant genetic engineering.

Genome-wide transcriptomic and phylogenetic analyses reveal distinct aluminum-tolerance mechanisms in the aluminum-accumulating species buckwheat (Fagopyrum tataricum).

BACKGROUND: Similar to common buckwheat (Fagopyrum esculentum), tartary buckwheat (Fagopyrum tataricum) shows a high level of aluminum (Al) tolerance and accumulation. However, the molecular mechanisms for Al detoxification and accumulation are still poorly understood. To begin to elucidate the molecular basis of Al tolerance and accumulation, we used the Illumina high-throughput mRNA sequencing (RNA-seq) technology to conduct a genome-wide transcriptome analysis on both tip and basal segments of the roots exposed to Al. RESULTS: By using the Trinity method for the de novo assembly and cap3 software to reduce the redundancy and chimeras of the transcripts, we constructed 39,815 transcripts with an average length of 1184 bp, among which 20,605 transcripts were annotated by BLAST searches in the NCBI non-redundant protein database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that expression of genes involved in the defense of cell wall toxicity and oxidative stress was preferentially induced by Al stress. Our RNA-seq data also revealed that organic acid metabolism was unlikely to be a rate-limiting step for the Al-induced secretion of organic acids in buckwheat. We identified two citrate transporter genes that were highly induced by Al and potentially involved in the release of citrate into the xylem. In addition, three of four conserved Al-tolerance genes were found to be duplicated in tartary buckwheat and display diverse expression patterns. CONCLUSIONS: Nearly 40,000 high quality transcript contigs were de novo assembled for tartary buckwheat, providing a reference platform for future research work in this plant species. Our differential expression and phylogenetic analysis revealed novel aspects of Al-tolerant mechanisms in buckwheat.

Physiological characterization of aluminum tolerance and accumulation in tartary and wild buckwheat.

Ionic aluminum (Al) is toxic for plant growth, but some plant species are able to accumulate Al at high concentrations without showing toxicity symptoms. In order to determine whether other species in the genus Fagopyrum are able to accumulate Al like common buckwheat (Fagopyrum esculentum), we investigated the external and internal detoxification mechanisms of Al in two self-compatible species: tartary (Fagopyrum tataricum) and wild buckwheat (Fagopyrum homotropicum). Both tartary and wild buckwheat showed high Al tolerance comparable to common buckwheat. Furthermore, these two species also secreted oxalate rapidly from the roots in response to Al in a time-dependent manner. Both tartary and wild buckwheat accumulated > 1 mg g(-1) Al in the leaves after short-term exposure to Al. Analysis with (27) Al-nuclear magnetic resonance (NMR) revealed that Al was present in the form of Al-oxalate (1 : 3 ratio) in the roots and leaves, but in the form of Al-citrate (1 : 1 ratio) in the xylem sap in both species. These results indicate that similar to common buckwheat, both tartary and wild buckwheat detoxify Al externally and internally, respectively, by secreting oxalate from the roots and by forming the Al-oxalate complex, which is a nonphytotoxic form. These features of Al response and accumulation may be conserved in genus Fagopyrum.

Global transcriptome analysis of Al-induced genes in an Al-accumulating species, common buckwheat (Fagopyrum esculentum Moench).

Buckwheat (Fagopyrum esculentum Moench) is a species with high aluminum (Al) tolerance and accumulation. Although the physiological mechanisms for external and internal detoxification of Al have been well studied, the molecular mechanisms responsible are poorly understood. Here, we conducted a genome-wide transcriptome analysis of Al-responsive genes in the roots and leaves using RNA sequencing (RNA-Seq) technology. RNA-Seq generated reads ranging from 56×10(6) to 93×10(6). A total of 148,734 transcript contigs with an average length of 1,014 bp were assembled, generating 84,516 unigenes. Among them, 31,730 and 23,853 unigenes were annotated, respectively, in the NCBI plant database and TAIR database for Arabidopsis. Of the annotated genes, 4,067 genes in the roots and 2,663 genes in the leaves were up-regulated (>2-fold) by Al exposure, while 2,456 genes in the roots and 2,426 genes in the leaves were down-regulated (<2-fold) A few STOP1/ART1 (SENSITIVE TO PROTON RHIZOTOXICITY1/AL RESISTANCE TRANSCRIPTION FACTOR1)-regulated gene homologs including FeSTAR1, FeALS3 (ALUMINUM SENSITIVE3), FeALS1 (ALUMINUM SENSITIVE1), FeMATE1 and FeMATE2 (MULTIDRUG AND TOXIC COMPOUND EXTRUSION1 and 2) were also up-regulated in buckwheat, indicating some common Al tolerance mechanism across the species, although most STOP1/ART1-regulated gene homologs were not changed. Most genes involved in citric and oxalic acid biosynthesis were not significantly altered. Some transporter genes were highly expressed in the roots and leaves and responded to Al stress, implicating their role in Al tolerance and accumulation. Overall, our data provide a platform for further characterizing the functions of genes involved in Al tolerance and accumulation in buckwheat.