The Vigna Genome Server, 'VigGS': A Genomic Knowledge Base of the Genus Vigna Based on High-Quality, Annotated Genome Sequence of the Azuki Bean, Vigna angularis (Willd.) Ohwi & Ohashi

Taxonomic history, morphology, evolution, gene pool and stress tolerances of azuki bean and its related wild Vigna genetic resources

This review compiles information on the morphology, historical taxonomic treatments, species origin, gene pool concept, geographical and ecological habitats, and stress tolerance of the azuki bean (Vigna angularis) and related species. Willdenow (1802) first described the azuki bean in the genus Dolichos, and Ohwi and Ohashi (1969) finally transferred it to the genus Vigna. The genus Vigna is currently divided into five subgenera: Ceratotropis, Haydonia, Lasiospron, Plectrotropis, and Vigna. The subgenus Ceratotropis includes the moth bean in section Aconitifoliae; the mungbean and black gram in section Ceratotropis; and the azuki bean, rice bean, and creole bean in section Angulares. The wild species in section Angulares generally possess larger standard petal with more prominent appendage, keel petal with longer pocket, pistil with longer style beak compared with those of species in sections Aconitifoliae and Ceratotropis, and characterized by glabrous mature pod, smooth seed coat, hypogeal germination seed, and cordate primary leaves with petiole. Section Angulares currently consists of 13 species. The taxa that cross readily with the azuki beans included in the primary genepool are the wild azuki bean V. angularis var. nipponensis, V. nepalensis, V. tenuicaulis, V. hirtella, V. minima, V. nakashimae, and V. riukiuensis. These wild species are expected to be used as breeding material against biotic and abiotic stresses.

Single candidate gene for salt tolerance of Vigna nakashimae (Ohwi) Ohwi & Ohashi identified by QTL mapping, whole genome sequencing and triplicated RNA-seq analyses

Salt tolerance has been an important issue as a solution for soil salinization and groundwater depletion. To challenge this issue, genetic diversity of wild plants must be harnessed. Here we report a discovery of a candidate gene for salt tolerance in Vigna nakashimae, one of the coastal species in the genus Vigna. Using intraspecific variation, we performed a forward genetic analysis and identified a strong QTL region harboring ~200 genes. To further narrow down the candidate genes, we performed a comparative transcriptome analysis, using the genome sequence of azuki bean (V. angularis) as a reference. However the detected differentially-expressed genes (DEGs) did not include those related to salt tolerance. As we suspected that the target gene in V. nakashimae is missing in V. angularis, we sequenced the whole genome sequence of V. nakashimae with long-reads. By re-analyzing the transcriptome data with the new reference genome, we successfully identified POCO1 as a candidate gene, which was missing not only in V. angularis but also in the salt-sensitive accession of V. nakashimae. Further comparative analysis revealed that the tolerant genotypes conserved the ancestral form of the locus, while the sensitive genotypes did not. We also emphasize the pitfalls in our study, such as position effect in a growth chamber, missing important genes in the reference genome, and limited reproducibility of RNA-seq experiments.

Progress in Adzuki Bean Seed Coat Colour Studies

Seed coat colour is an important quality trait, domestication trait, and morphological marker, and it is closely associated with flavonoid and anthocyanin metabolism pathways. The seed coat colour of the adzuki bean, an important legume crop, influences the processing quality, the commodity itself, and its nutritional quality. In this review, a genetic analysis of different seed coat colours, gene mapping, metabolite content determination, and varietal improvement in adzuki bean are summarized. It provides further insight into gene mapping and cloning of seed coat colour genes and varietal improvements in adzuki beans.

Unique Salt-Tolerance-Related QTLs, Evolved in Vigna riukiuensis (Na+ Includer) and V. nakashimae (Na+ Excluder), Shed Light on the Development of Super-Salt-Tolerant Azuki Bean (V. angularis) Cultivars

Wild relatives of crops have the potential to improve food crops, especially in terms of improving abiotic stress tolerance. Two closely related wild species of the traditional East Asian legume crops, Azuki bean (Vigna angularis), V. riukiuensis "Tojinbaka" and V. nakashimae "Ukushima" were shown to have much higher levels of salt tolerance than azuki beans. To identify the genomic regions responsible for salt tolerance in "Tojinbaka" and "Ukushima", three interspecific hybrids were developed: (A) azuki bean cultivar "Kyoto Dainagon" × "Tojinbaka", (B) "Kyoto Dainagon" × "Ukushima" and (C) "Ukushima" × "Tojinbaka". Linkage maps were developed using SSR or restriction-site-associated DNA markers. There were three QTLs for "percentage of wilt leaves" in populations A, B and C, while populations A and B had three QTLs and population C had two QTLs for "days to wilt". In population C, four QTLs were detected for Na+ concentration in the primary leaf. Among the F2 individuals in population C, 24% showed higher salt tolerance than both wild parents, suggesting that the salt tolerance of azuki beans can be further improved by combining the QTL alleles of the two wild relatives. The marker information would facilitate the transfer of salt tolerance alleles from "Tojinbaka" and "Ukushima" to azuki beans.

Domesticating Vigna stipulacea: Chromosome-Level genome assembly reveals VsPSAT1 as a candidate gene decreasing hard-seededness

To increase food production under the challenges presented by global climate change, the concept of de novo domestication-utilizing stress-tolerant wild species as new crops-has recently gained considerable attention. We had previously identified mutants with desired domestication traits in a mutagenized population of the legume Vigna stipulacea Kuntze (minni payaru) as a pilot for de novo domestication. Given that there are multiple stress-tolerant wild legume species, it is important to establish efficient domestication processes using reverse genetics and identify the genes responsible for domestication traits. In this study, we identified VsPSAT1 as the candidate gene responsible for decreased hard-seededness, using a Vigna stipulacea isi2 mutant that takes up water from the lens groove. Scanning electron microscopy and computed tomography revealed that the isi2 mutant has lesser honeycomb-like wax sealing the lens groove than the wild-type, and takes up water from the lens groove. We also identified the pleiotropic effects of the isi2 mutant: accelerating leaf senescence, increasing seed size, and decreasing numbers of seeds per pod. While doing so, we produced a V. stipulacea whole-genome assembly of 441 Mbp in 11 chromosomes and 30,963 annotated protein-coding sequences. This study highlights the importance of wild legumes, especially those of the genus Vigna with pre-existing tolerance to biotic and abiotic stresses, for global food security during climate change.

Diversity of Na+ allocation in salt-tolerant species of the genus Vigna

Wild species in the genus Vigna are a great resource of tolerance to various stresses including salinity. We have previously screened the genetic resources of the genus Vigna and identified several accessions that have independently evolved salt tolerance. However, many aspects of such tolerance have remained unknown. Thus, we used autoradiography with radioactive sodium (²²Na⁺) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to visualize and compare Na⁺ allocation in Vigna angularis (Willd.) Ohwi & H.Ohashi (azuki bean), Vigna nakashimae (Ohwi) Ohwi & H.Ohashi, Vigna riukiuensis (Ohwi) Ohwi & H.Ohashi, Vigna luteola (Jacq.) Benth. and Vigna marina (Burm.) Merr.. The results indicated: 1) Tolerant accessions suppress Na⁺ accumulation compared to azuki bean. 2) V. nakashimae and V. marina does so by accumulating higher amount of K⁺, whereas V. riukiuensis and V. luteola does so by other mechanisms. 3) V. luteola avoids salt-shedding by allocating excess Na⁺ to newly expanded leaves. As the mechanisms of the tolerant species were different, they could be piled up in a single crop via classical breeding or by genetic engineering or genome editing.

LSAP: A Machine Learning Method for Leaf-Senescence-Associated Genes Prediction

Plant leaves, which convert light energy into chemical energy, serve as a major food source on Earth. The decrease in crop yield and quality is caused by plant leaf premature senescence. It is important to detect senescence-associated genes. In this study, we collected 5853 genes from a leaf senescence database and developed a leaf-senescence-associated genes (SAGs) prediction model using the support vector machine (SVM) and XGBoost algorithms. This is the first computational approach for predicting SAGs with the sequence dataset. The SVM-PCA-Kmer-PC-PseAAC model achieved the best performance (F1score = 0.866, accuracy = 0.862 and receiver operating characteristic = 0.922), and based on this model, we developed a SAGs prediction tool called “SAGs_Anno”. We identified a total of 1,398,277 SAGs from 3,165,746 gene sequences from 83 species, including 12 lower plants and 71 higher plants. Interestingly, leafy species showed a higher percentage of SAGs, while leafless species showed a lower percentage of SAGs. Finally, we constructed the Leaf SAGs Annotation Platform using these available datasets and the SAGs_Anno tool, which helps users to easily predict, download, and search for plant leaf SAGs of all species. Our study will provide rich resources for plant leaf-senescence-associated genes research.

Flowering Date1, a major photoperiod sensitivity gene in adzuki bean, is a soybean floral repressor E1 ortholog

Adzuki bean is an important legume crop originating in temperate regions, with photoperiod in sensitivity being a key factor in its latitudinal adaptation. The Flowering Date1 (FD1) gene has a large effect on the photoperiodic response of flowering time, but the molecular basis for the effect of this locus is undetermined. The present study delimited the FD1 locus to a 17.1 kb sequence, containing a single gene, an E1 ortholog (VaE1). A comparison between Vigna angularis 'Shumari' (photoperiod insensitive) and 'Acc2265' (photoperiod sensitive) identified 29 insertions/deletions and 178 SNPs upstream of VaE1 in the FD1 locus. VaE1 expression in 'Acc2265' was greater under long-day than short-day conditions, whereas VaE1 expression in 'Shumari' was lower regardless of day length. These findings suggested that responsible gene of FD1 is a VaE1, which acts as a floral repressor by being upregulated in response to long-day conditions. The inability to upregulate VaE1 under long-day conditions was linked to its ability to flower under these conditions. These results provide greater understanding of the molecular control of a flowering date and clues enabling the breeding of adzuki bean at higher latitudes.

Interindividual Differences in In Vitro Human Intestinal Microbial Conversion of 3-Acetyl-DON and 15-Acetyl-DON

In order to evaluate the potential differences between 3-Ac-DON and 15-Ac-DON in the human intestinal microbial metabolism, human fecal samples were anaerobically cultured in vitro. Quantitative fecal microbiota characteristics were obtained by 16S rRNA sequencing, and the data revealed several genera that may be relevant for the transformation of the acetylated DONs. Significant differences in the level of 3-Ac-DON and 15-Ac-DON conversion were observed among microbiota from different human individuals. 3-Ac-DON could be rapidly hydrolyzed; a ten-fold difference was observed between the highest and lowest in vitro conversion after 4 h. However, 15-Ac-DON was not fully transformed in the 4 h culture of all the individual samples. In all cases, the conversion rate of 3-Ac-DON was higher than that of 15-Ac-DON, and the conversion rate of 3-Ac-DON into DON varied from 1.3- to 8.4-fold that of 15-Ac-DON. Based on in vitro conversion rates, it was estimated that 45–452 min is required to convert all 3-Ac-DON to DON, implying that deacetylation of 3-Ac-DON is likely to occur completely in all human individuals during intestinal transit. However, for conversion of 15-Ac-DON, DON formation was undetectable at 4 h incubation in 8 out of the 25 human samples, while for 7 of these 8 samples conversion to DON was detected at 24 h incubation. The conversion rates obtained for these seven samples indicated that it would take 1925–4805 min to convert all 15-Ac-DON to DON, while the other 17 samples required 173–734 min. From these results it followed that for eight of the 25 individuals, conversion of 15-Ac-DON to DON was estimated to be incomplete during the 1848 min intestinal transit time. The results thus indicate substantial interindividual as well as compound specific differences in the deconjugation of acetylated DONs. A spearman correlation analysis showed a statistically significant relationship between deconjugation of both acetyl-DONs at 4 h and 24 h incubation. Based on the in vitro kinetic parameters and their scaling to the in vivo situation, it was concluded that for a substantial number of human individuals the deconjugation of 15-Ac-DON may not be complete upon intestinal transit.

The First Genetic Linkage Map of Winged Bean [Psophocarpus tetragonolobus (L.) DC.] and QTL Mapping for Flower-, Pod-, and Seed-Related Traits

Winged bean [Psophocarpus tetragonolobus (L.) DC.] (2n = 2× = 18) is a tropical legume crop with multipurpose usages. Recently, the winged bean has regained attention from scientists as a food protein source. Currently, there is no breeding program for winged bean cultivars. All winged bean cultivars are landraces or selections from landraces. Molecular markers and genetic linkage maps are pre-requisites for molecular plant breeding. The aim of this study was to develop a high-density linkage map and identify quantitative trait loci (QTLs) for pod and seed-related traits of the winged bean. An F2 population of 86 plants was developed from a cross between winged bean accessions W054 and TPT9 showing contrasting pod length, and pod, flower and seed colors. A genetic linkage map of 1384 single nucleotide polymorphism (SNP) markers generated from restriction site-associated DNA sequencing was constructed. The map resolved nine haploid chromosomes of the winged bean and spanned the cumulative length of 4552.8 cM with the number of SNPs per linkage ranging from 36 to 218 with an average of 153.78. QTL analysis in the F2 population revealed 31 QTLs controlling pod length, pod color, pod anthocyanin content, flower color, and seed color. The number of QTLs per trait varied between 1 (seed length) to 7 (banner color). Interestingly, the major QTLs for pod color, anthocyanin content, and calyx color, and for seed color and flower wing color were located at the same position. The high-density linkage map QTLs reported in this study will be useful for molecular breeding of winged beans.

Biodiversity and Geographic Distribution of Rhizobia Nodulating With Vigna minima

Vigna minima is a climbing annual plant widely distributed in barren wilderness, grass land, and shrub bush of China and other countries such as Japan. However, the rhizobia nodulating with this plant has never been systematically studied. In order to reveal the biodiversity of nodulating rhizobia symbiosis with V. minima, a total of 874 rhizobium isolates were obtained from root nodules of the plant spread in 11 sampling sites of Shandong Peninsula, China, and they were designated as 41 haplotypes in the genus Bradyrhizobium based upon recA sequence analyses. By multilocus sequence analysis (MLSA) of five housekeeping genes (dnaK, glnII, gyrB, recA, and rpoB), the 41 strains representing different recA haplotypes were classified into nine defined species and nine novel genospecies. Bradyrhizobium elkanii, Bradyrhizobium ferriligni, and Bradyrhizobium pachyrhizi were the predominant and universally distributed groups. The phylogeny of symbiotic genes of nodC and nifH showed similar topology and phylogenetic relationships, in which all the representative strains were classified into two clades grouped with strains nodulating with Vigna spp., demonstrating that Vigna spp. shared common nodulating groups in the natural environment. All the representative strains formed nodules with V. minima in a nodulation test performed in green house conditions. The correlation between V. minima nodulating rhizobia and soil characteristics analyzed by CANOCO indicates that available nitrogen, total nitrogen, and organic carbon in the soil samples were the main factors affecting the distribution of rhizobia isolated in this study. This study systematically uncovered the biodiversity and distribution characteristics of V. minima nodulating rhizobia for the first time, which provided novel information for the formation of the corresponding rhizobium community.

Unequal contribution of two paralogous CENH3 variants in cowpea centromere function

In most diploids the centromere-specific histone H3 (CENH3), the assembly site of active centromeres, is encoded by a single copy gene. Persistance of two CENH3 paralogs in diploids species raises the possibility of subfunctionalization. Here we analysed both CENH3 genes of the  diploid dryland crop cowpea. Phylogenetic analysis suggests that gene duplication of CENH3 occurred independently during the speciation of Vigna unguiculata. Both functional CENH3 variants are transcribed, and the corresponding proteins are intermingled in subdomains of different types of centromere sequences in a tissue-specific manner together with the kinetochore protein CENPC. CENH3.2 is removed from the generative cell of mature pollen, while CENH3.1 persists. CRISPR/Cas9-based inactivation of CENH3.1 resulted in delayed vegetative growth and sterility, indicating that this variant is needed for plant development and reproduction. By contrast, CENH3.2 knockout individuals did not show obvious defects during vegetative and reproductive development. Hence, CENH3.2 of cowpea is likely at an early stage of pseudogenization and less likely undergoing subfunctionalization.

Same Locus for Non-shattering Seed Pod in Two Independently Domesticated Legumes, Vigna angularis and Vigna unguiculata

Loss of pod shattering is one of the most important domestication-related traits in legume crops. The non-shattering phenotypes have been achieved either by disturbed formation of abscission layer between the valves, or by loss of helical tension in sclerenchyma of endocarp, that split open the pods to disperse the seeds. During domestication, azuki bean (Vigna angularis) and yard-long bean (Vigna unguiculata cv-gr. Sesquipedalis) have reduced or lost the sclerenchyma and thus the shattering behavior of seed pods. Here we performed fine-mapping with backcrossed populations and narrowed the candidate genomic region down to 4 kbp in azuki bean and 13 kbp in yard-long bean. Among the genes located in these regions, we found MYB26 genes encoded truncated proteins in azuki bean, yard-long bean, and even cowpea. As such, our findings indicate that independent domestication on the two legumes has selected the same locus for the same traits. We also argue that MYB26 could be a target gene for improving shattering phenotype in other legumes, such as soybean.

Narrowing Down a Major QTL Region Conferring Pod Fiber Contents in Yardlong Bean (Vigna unguiculata), a Vegetable Cowpea

Yardlong bean (Vigna unguiculata (L.) Walp. ssp. sesquipedalis), a subgroup of cowpea, is an important vegetable legume crop of Asia where its young pods are consumed in both fresh and cooked forms. Pod fiber contents (cellulose, hemicellulose and lignin) correlates with pod tenderness (softness/hardness) and pod shattering. In a previous study using populations derived from crosses between yardlong bean and wild cowpea (V. unguiculata ssp. unguiculata var. spontanea), three major quantitative trait loci (QTLs), qCel7.1, qHem7.1 and qLig7.1, controlling these fibers were identified on linkage group 7 (cowpea chromosome 5) and are co-located with QTLs for pod tenderness and pod shattering. The objective of this study was to identify candidate gene(s) controlling the pod fiber contents. Fine mapping for qCel7.1, qHem7.1 and qLig7.1 was conducted using F₂ and F_2:3 populations of 309 and 334 individuals, respectively, from the same cross combination. New DNA markers were developed from cowpea reference genome sequence and used for fine mapping. A QTL analysis showed that in most cases, each pod fiber content was controlled by one major and one minor QTLs on the LG7. The major QTLs for cellulose, hemicellulose and lignin in pod were always mapped to the same regions or close to each other. In addition, a major QTL for pod shattering was also located in the region. Although there were several annotated genes relating to pod fiber contents in the region, two genes including Vigun05g266600 (VuBGLU12) encoding a beta glucosidase and Vigun05g273500 (VuMYB26b) encoding a transcription factor MYB26 were identified as candidate genes for the pod fiber contents and pod shattering. Function(s) of these genes in relation to pod wall fiber biosynthesis and pod shattering was discussed.

Molecular Basis of C-30 Product Regioselectivity of Legume Oxidases Involved in High-Value Triterpenoid Biosynthesis

The triterpenes are structurally diverse group of specialized metabolites with important roles in plant defense and human health. Glycyrrhizin, with a carboxyl group at C-30 of its aglycone moiety, is a valuable triterpene glycoside, the production of which is restricted to legume medicinal plants belonging to the Glycyrrhiza species. Cytochrome P450 monooxygenases (P450s) are important for generating triterpene chemodiversity by catalyzing site-specific oxidation of the triterpene scaffold. CYP72A154 was previously identified from the glycyrrhizin-producing plant Glycyrrhiza uralensis as a C-30 oxidase in glycyrrhizin biosynthesis, but its regioselectivity is rather low. In contrast, CYP72A63 from Medicago truncatula showed superior regioselectivity in C-30 oxidation, improving the production of glycyrrhizin aglycone in engineered yeast. The underlying molecular basis of C-30 product regioselectivity is not well understood. Here, we identified two amino acid residues that control C-30 product regioselectivity and contribute to the chemodiversity of triterpenes accumulated in legumes. Amino acid sequence comparison combined with structural analysis of the protein model identified Leu149 and Leu398 as important amino acid residues for C-30 product regioselectivity. These results were further confirmed by mutagenesis of CYP72A154 homologs from glycyrrhizin-producing species, functional phylogenomics analyses, and comparison of corresponding residues of C-30 oxidase homologs in other legumes. These findings could be combined with metabolic engineering to further enhance the production of high-value triterpene compounds.

Genome sequence analysis of the fairy ring-forming fungus Lepista sordida and gene candidates for interaction with plants

Circular patterns called "fairy rings" in fields are a natural phenomenon that arises through the interaction between basidiomycete fungi and plants. Acceleration or inhibition of plant vegetative growth and the formation of mushroom fruiting bodies are both commonly observed when fairy rings form. The gene of an enzyme involved in the biosynthesis of these regulators was recently isolated in the fairy ring-forming fungus, Lepista sordida. To identify other genes involved in L. sordida fairy ring formation, we used previously generated sequence data to produce a more complete draft genome sequence for this species. Finally, we predicted the metabolic pathways of the plant growth regulators and 29 candidate enzyme-coding genes involved in fairy-ring formation based on gene annotations. Comparisons of protein coding genes among basidiomycete fungi revealed two nitric oxide synthase gene candidates that were uniquely encoded in genomes of fairy ring-forming fungi. These results provide a basis for the discovery of genes involved in fairy ring formation and for understanding the mechanisms involved in the interaction between fungi and plants. We also constructed a new web database F-RINGS ( http://bioinf.mind.meiji.ac.jp/f-rings/ ) to provide the comprehensive genomic information for L. sordida.

Development of an SNP-based high-density linkage map and QTL analysis for bruchid (Callosobruchus maculatus F.) resistance in black gram (Vigna mungo (L.) Hepper)

Black gram (Vigna mungo var. mungo) is an important pulse crop in Asia. The cowpea weevil (Callosobruchus maculatus) is a stored-seed insect pest (seed weevil/bruchid) that causes serious postharvest losses in pulse crops, including black gram. In this study, we constructed a high-density linkage map for black gram and identified quantitative trait loci (QTLs) for C. maculatus resistance. A recombinant inbred line (RIL) population of 150 lines from a cross between BC48 [cultivated black gram (var. mungo); bruchid-susceptible] and TC2210 [wild black gram (var. silvestris); bruchid-resistant] were used to construct a linkage map of 3,675 SNP markers from specific-locus amplified fragment sequencing. The map comprised 11 linkage groups spanning 1,588.7 cM with an average distance between adjacent markers of 0.57 cM. Seeds of the RIL population grown in 2016 and 2017 were evaluated for C. maculatus resistance through two traits; the percentage of damaged seeds (PDS) and infestation severity progress (AUDPS). Inclusive composite interval mapping identified three QTLs each for PDS and AUDPS. Two QTLs, qVmunBr6.1 and qVmunBr6.2, mapped about 10 cM apart on linkage group 6 were common between PDS and AUDPS. Comparative genome analysis revealed that qVmunBr6.1 and qVmunBr6.2 are new loci for C. maculatus resistance in Vigna species and that genes encoding a lectin receptor kinase and chitinase are candidates for qVmunBr6.2. The high-density linkage map constructed and QTLs for bruchid resistance identified in this study will be useful for molecular breeding of black gram.

Domesticating Vigna Stipulacea: A Potential Legume Crop With Broad Resistance to Biotic Stresses

Though crossing wild relatives to modern cultivars is a usual means to introduce alleles of stress tolerance, an alternative is de novo domesticating wild species that are already tolerant to various kinds of stresses. As a test case, we chose Vigna stipulacea Kuntze, which has fast growth, short vegetative stage, and broad resistance to pests and diseases. We developed an ethyl methanesulfonate-mutagenized population and obtained three mutants with reduced seed dormancy and one with reduced pod shattering. We crossed one of the mutants of less seed dormancy to the wild type and confirmed that the phenotype was inherited in a Mendelian manner. De novo assembly of V. stipulacea genome, and the following resequencing of the F2 progenies successfully identified a Single Nucleotide Polymorphism (SNP) associated with seed dormancy. By crossing and pyramiding the mutant phenotypes, we will be able to turn V. stipulacea into a crop which is yet primitive but can be cultivated without pesticides.

Comparative genome-wide analysis of WRKY transcription factors in two Asian legume crops: Adzuki bean and Mung bean

The seminal participation of WRKY transcription factors in plant development, metabolism and in the governance of defense mechanism implicated their gaining importance for genomic and functional studies. The recent release of draft genome sequences of two legume crops, Adzuki bean (Vigna angularis) and Mung bean (Vigna radiata) has paved the way for characterization of WRKY gene family in these crops. We found 84 WRKY genes in Adzuki bean (VaWRKY) and 85 WRKY genes in Mung bean (VrWRKY). Based on the phylogenetic analysis, VaWRKY genes were classified into three groups with 15 members in Group I, 56 members in Group II, and 13 members in Group III, which was comparable to VrWRKY distribution in Mung bean, 16, 56 and 13 members in Group I, II and III, respectively. The few tandem and segmental duplication events suggested that recent duplication plays no prominent role in the expansion VaWRKY and VrWRKY genes. The illustration of gene-structure and their encoded protein-domains further revealed the nature of WRKY proteins. Moreover, the identification of abiotic or biotic stress-responsive cis-regulatory elements in the promoter regions of some WRKY genes provides fundamental insights for their further implementation in stress-tolerance and genetic improvement of agronomic traits.

Heap: a highly sensitive and accurate SNP detection tool for low-coverage high-throughput sequencing data

Recent availability of large-scale genomic resources enables us to conduct so called genome-wide association studies (GWAS) and genomic prediction (GP) studies, particularly with next-generation sequencing (NGS) data. The effectiveness of GWAS and GP depends on not only their mathematical models, but the quality and quantity of variants employed in the analysis. In NGS single nucleotide polymorphism (SNP) calling, conventional tools ideally require more reads for higher SNP sensitivity and accuracy. In this study, we aimed to develop a tool, Heap, that enables robustly sensitive and accurate calling of SNPs, particularly with a low coverage NGS data, which must be aligned to the reference genome sequences in advance. To reduce false positive SNPs, Heap determines genotypes and calls SNPs at each site except for sites at the both ends of reads or containing a minor allele supported by only one read. Performance comparison with existing tools showed that Heap achieved the highest F-scores with low coverage (7X) restriction-site associated DNA sequencing reads of sorghum and rice individuals. This will facilitate cost-effective GWAS and GP studies in this NGS era. Code and documentation of Heap are freely available from https://github.com/meiji-bioinf/heap (29 March 2017, date last accessed) and our web site (http://bioinf.mind.meiji.ac.jp/lab/en/tools.html (29 March 2017, date last accessed)).

Genome resources for climate-resilient cowpea, an essential crop for food security

Cowpea (Vigna unguiculata L. Walp.) is a legume crop that is resilient to hot and drought-prone climates, and a primary source of protein in sub-Saharan Africa and other parts of the developing world. However, genome resources for cowpea have lagged behind most other major crops. Here we describe foundational genome resources and their application to the analysis of germplasm currently in use in West African breeding programs. Resources developed from the African cultivar IT97K-499-35 include a whole-genome shotgun (WGS) assembly, a bacterial artificial chromosome (BAC) physical map, and assembled sequences from 4355 BACs. These resources and WGS sequences of an additional 36 diverse cowpea accessions supported the development of a genotyping assay for 51 128 SNPs, which was then applied to five bi-parental RIL populations to produce a consensus genetic map containing 37 372 SNPs. This genetic map enabled the anchoring of 100 Mb of WGS and 420 Mb of BAC sequences, an exploration of genetic diversity along each linkage group, and clarification of macrosynteny between cowpea and common bean. The SNP assay enabled a diversity analysis of materials from West African breeding programs. Two major subpopulations exist within those materials, one of which has significant parentage from South and East Africa and more diversity. There are genomic regions of high differentiation between subpopulations, one of which coincides with a cluster of nodulin genes. The new resources and knowledge help to define goals and accelerate the breeding of improved varieties to address food security issues related to limited-input small-holder farming and climate stress.

Orchidstra 2.0-A Transcriptomics Resource for the Orchid Family

Orchidaceae, the orchid family, encompasses more than 25,000 species and five subfamilies. Due to their beautiful and exotic flowers, distinct biological and ecological features, orchids have aroused wide interest among both researchers and the general public. We constructed the Orchidstra database, a resource for orchid transcriptome assembly and gene annotations. The Orchistra database has been under active development since 2013. To accommodate the increasing amount of orchid transcriptome data and house more comprehensive information, Orchidstra 2.0 has been built with a new database system to store the annotations of 510,947 protein-coding genes and 161,826 noncoding transcripts, covering 18 orchid species belonging to 12 genera in five subfamilies of Orchidaceae. We have improved the N50 size of protein-coding genes, provided new functional annotations (including protein-coding gene annotations, protein domain/family information, pathways analysis, Gene Ontology term assignments, orthologous genes across orchid species, cross-links to the database of model species, and miRNA information), and improved the user interface with better website performance. We also provide new database functionalities for database searching and sequence retrieval. Moreover, the Orchidstra 2.0 database incorporates detailed RNA-Seq gene expression data from various tissues and developmental stages in different orchid species. The database will be useful for gene prediction and gene family studies, and for exploring gene expression in orchid species. The Orchidstra 2.0 database is freely accessible at http://orchidstra2.abrc.sinica.edu.tw.

Label-free Proteomic Reveals that Cowpea Severe Mosaic Virus Transiently Suppresses the Host Leaf Protein Accumulation During the Compatible Interaction with Cowpea (Vigna unguiculata [L.] Walp.)

Viruses are important plant pathogens that threaten diverse crops worldwide. Diseases caused by Cowpea severe mosaic virus (CPSMV) have drawn attention because of the serious damages they cause to economically important crops including cowpea. This work was undertaken to quantify and identify the responsive proteins of a susceptible cowpea genotype infected with CPSMV, in comparison with mock-inoculated controls, using label-free quantitative proteomics and databanks, aiming at providing insights on the molecular basis of this compatible interaction. Cowpea leaves were mock- or CPSMV-inoculated and 2 and 6 days later proteins were extracted and analyzed. More than 3000 proteins were identified (data available via ProteomeXchange, identifier PXD005025) and 75 and 55 of them differentially accumulated in response to CPSMV, at 2 and 6 DAI, respectively. At 2 DAI, 76% of the proteins decreased in amount and 24% increased. However, at 6 DAI, 100% of the identified proteins increased. Thus, CPSMV transiently suppresses the synthesis of proteins involved particularly in the redox homeostasis, protein synthesis, defense, stress, RNA/DNA metabolism, signaling, and other functions, allowing viral invasion and spread in cowpea tissues.