Genetics, genomics, and breeding of black gram [Vigna mungo (L.) Hepper]

Black gram [Vigna mungo (L.) Hepper] is a highly nutritious grain legume crop, mainly grown in South and Southeast Asia, with the largest area in India, where the crop is challenged by several biotic and abiotic stresses leading to significant yield losses. Improving genetic gains to increase on-farm yields is the primary goal of black gram breeding programs. This could be achieved by developing varieties resistant to major diseases like mungbean yellow mosaic disease, urdbean leaf crinkle virus, Cercospora leaf spot, anthracnose, powdery mildew, and insect pests such as whitefly, cowpea aphids, thrips, stem flies, and bruchids. Along with increasing on-farm yields, incorporating market-preferred traits ensures the adoption of improved varieties. Black gram breeding programs rely upon a limited number of parental lines, leading to a narrow genetic base of the developed varieties. For accelerating genetic gain, there is an urgent need to include more diverse genetic material for improving traits for better adaptability and stress resistance in breeding populations. The present review summarizes the importance of black gram, the major biotic and abiotic stresses, available genetic and genomic resources, major traits for potential crop improvement, their inheritance, and the breeding approaches being used in black gram for the development of new varieties.

Urdbean Leaf Crinkle Virus: A Mystery Waiting to Be Solved

Urdbean leaf crinkle disease (ULCD) affects mainly the urdbean or blackgram (Vigna mungo (L.) Hepper) causing distinct symptoms that often result in serious yield losses. It has been known to occur for more than five decades and is considered to be of viral etiology. The identity of the causal agent, often referred to as the urdbean leaf crinkle virus, is not unequivocally proved. There are few attempts to characterize the causal agent of ULCD; however, there is no unanimity in the results. Recent attempts to characterize the causal agent of ULCD using next-generation sequencing of the virome of ULCD-affected urdbean plants indicated the involvement of cowpea mild mottle virus; however, without conforming through Koch's postulates, the etiology of ULCD remains inconclusive. Claims of different insect vectors involved in the transmission of ULCD make this disease even more mysterious. The information available so far indicates that either two different viruses are causing ULCD or a mixture of viruses is involved. The identity of the virus/es causing ULCD still remains to be unambiguously ascertained. In this review, we attempt to analyze information on the various aspects of ULCD.

Phytoremediation efficiency of Vigna mungo with the amalgamation of indigenous metal tolerant bacterial strain on metal polluted agriculture soil

This research was performed to evaluate physico-chemical properties of farmland soil nearby the magnesite mine site. Unexpectedly, few physico-chemical properties were crossing the acceptable limits. Particularly, the quantities of Cd (112.34 ± 3.25), Pb (386.42 ± 11.71), Zn (854.28 ± 3.53), and Mn (2538 ± 41.11) were crossing the permissible limits. Among 11 bacterial cultures isolated from the metal contaminated soil, 2 isolates names as SS1 and SS3 showed significant multi-metal tolerance up to the concentration of 750 mg L^-1. Furthermore, these strains also showed considerable metal mobilization as well as absorption ability on metal contaminated soil under in-vitro conditions. In a short duration of treatment, these isolates effectively mobilize and absorb the metals from the polluted soil. The results obtained from the greenhouse investigation with Vigna mungo revealed that the among various treatment (T1 to T5) groups, the T3 (V.mungo + SS1+SS3) showed remarkable phytoremediation potential (Pb: 50.88, Mn: 152, Cd: 14.54, and Zn: 67.99 mg kg^-1) on metal contaminated soil. Furthermore, these isolates influence the growth as well as biomass of V.mungo under greenhouse conditions on metal contaminated soil. These findings suggest that combining multi-metal tolerant bacterial isolates can improve the phytoextraction efficiency of V.mungo on metal-contaminated soil.

Alternative splicing shapes the transcriptome complexity in blackgram [Vigna mungo (L.) Hepper]

Vigna mungo, a highly consumed crop in the pan-Asian countries, is vulnerable to several biotic and abiotic stresses. Understanding the post-transcriptional gene regulatory cascades, especially alternative splicing (AS), may underpin large-scale genetic improvements to develop stress-resilient varieties. Herein, a transcriptome based approach was undertaken to decipher the genome-wide AS landscape and splicing dynamics in order to establish the intricacies of their functional interactions in various tissues and stresses. RNA sequencing followed by high-throughput computational analyses identified 54,526 AS events involving 15,506 AS genes that generated 57,405 transcripts isoforms. Enrichment analysis revealed their involvement in diverse regulatory functions and demonstrated that transcription factors are splicing-intensive, splice variants of which are expressed differentially across tissues and environmental cues. Increased expression of a splicing regulator NHP2L1/SNU13 was found to co-occur with lower intron retention events. The host transcriptome is significantly impacted by differential isoform expression of 1172 and 765 AS genes that resulted in 1227 (46.8% up and 53.2% downregulated) and 831 (47.5% up and 52.5% downregulated) transcript isoforms under viral pathogenesis and Fe²⁺ stressed condition, respectively. However, genes experiencing AS operate differently from the differentially expressed genes, suggesting AS is a unique and independent mode of regulatory mechanism. Therefore, it can be inferred that AS mediates a crucial regulatory role across tissues and stressful situations and the results would provide an invaluable resource for future endeavours in V. mungo genomics.

Phenolic Profiles and Bioactivities of Ten Original Lineage Beans in Thailand

Legumes and pulses are important food components with various phytochemicals and health benefits. However, the health-related bioactivities of some underutilized species remain uninvestigated. To breed a new bean lineage with particular health-related properties, this study investigated phenolics (specifically, isoflavones) and the in vitro inhibitory activities of the enzyme relevant to some non-communicable diseases in underutilized cultivars of Phaseolus lunatus (lima beans), compared to the commonly consumed P. vulgaris (red kidney bean) and beans in the Glycine and Vigna genera. The results indicated that soybeans in the Glycine genus contained the highest isoflavone contents, especially glycitein (1825-2633 mg/100 g bean) and daidzein (1153-6471 mg/100 g bean), leading to potentially higher enzyme inhibitory activities (25-26% inhibition against α-amylase, 54-60% inhibition against α-glucosidase, 42-46% inhibition against dipeptidyl peptidase IV, 12-19% inhibition against acetylcholinesterase and 20-23% inhibition against butyrylcholinesterase) than those from other genera. Interestingly, lima beans with low isoflavone content (up to 2 mg/100 g bean) still possessed high inhibitory activities against lipase (12-21% inhibition) and β-secretase (50-58% inhibition), suggesting that bioactive compounds other than the isoflavones might be responsible for these activities. Isoflavone contents and enzyme inhibitory activities in Vigna beans were diverse, depending on the particular cultivars. The information gained from this study can be used for further investigation of bioactive components and in-depth health properties, as well as for future breeding of a new lineage of bean with specific health potentials.

Morpho-Physiological Traits and Functional Markers Based Molecular Dissection of Heat-Tolerance in Urdbean

Urdbean (Vigna mungo L. Hepper) is one of the important pulse crops. Its cultivation is not so popular during summer seasons because this crop is unable to withstand excessive heat stress beside lack of humidity in the atmosphere. Therefore, a panel of 97 urdbean diverse genotypes was assessed for yield under stress and non-stress conditions with an aim to identify heat tolerant genotypes. This study identified 8 highly heat tolerant and 35 highly heat sensitive genotypes based on heat susceptibility index. Further, physiological and biochemical traits-based characterization of a group of six highly heat sensitive and seven highly heat tolerant urdbean genotypes showed genotypic variability for leaf nitrogen balance index (NBI), chlorophyll (SPAD), epidermal flavnols, and anthocyanin contents under 42/25°C max/min temperature. Our results showed higher membrane stability index among heat tolerant genotypes compared to sensitive genotypes. Significant differences among genotypes for ETR at different levels of PAR irradiances and PAR × genotypes interactions indicated high photosynthetic ability of a few genotypes under heat stress. Further, the most highly sensitive genotype PKGU-1 showed a decrease in different fluorescence parameters indicating distortion of PS II. Consequently, reduction in the quantum yield of PS II was observed in a sensitive one as compared to a tolerant genotype. Fluorescence kinetics showed the delayed and fast quenching of Fm in highly heat sensitive (PKGU 1) and tolerant (UPU 85-86) genotypes, respectively. Moreover, tolerant genotype (UPU 85-86) had high antioxidant activities explaining their role for scavenging superoxide radicals (ROS) protecting delicate membranes from oxidative damage. Molecular characterization further pinpointed genetic differences between heat tolerant (UPU 85-86) and heat sensitive genotypes (PKGU 1). These findings will contribute to the breeding toward the development of heat tolerant cultivars in urdbean.

One Crop Disease, How Many Pathogens? Podosphaera xanthii and Erysiphe vignae sp. nov. Identified as the Two Species that Cause Powdery Mildew of Mungbean (Vigna radiata) and Black Gram (V. mungo) in Australia

Powdery mildew is a significant threat to mungbean (Vigna radiata) and black gram (V. mungo) production across Australia and overseas. Although they have been present in Australia for at least six decades and are easily recognized in the field, the precise identification of the pathogens causing this disease has remained unclear. Our goal was to identify the powdery mildew species infecting mungbean, black gram, and wild mungbean (V. radiata ssp. sublobata) in Australia. The internal transcribed spacer (ITS) and large subunit sequences of the ribosomal DNA and/or morphology of 57 Australian specimens were examined. Mungbean and black gram were infected by two species: Podosphaera xanthii and a newly recognized taxon, Erysiphe vignae sp. nov. Wild mungbean was infected only with P. xanthii. Mungbean and black gram powdery mildew ITS sequences from China, India, and Taiwan revealed the presence of only P. xanthii on these crops despite controversial reports of an Erysiphe species on both crops in India. Sequence analyses indicated that the closest relative of E. vignae is E. diffusa, which infects soybean (Glycine max) and other plants. E. vignae did not infect soybean in cross-inoculation tests. In turn, E. diffusa from soybean infected black gram and provoked hypersensitive response in mungbean. The recognition of a second species, E. vignae, as another causal agent of mungbean and black gram powdery mildew in Australia may complicate plant breeding efforts and control of the disease with fungicide applications.

Bruchid beetle ovipositioning mediated defense responses in black gram pods

BACKGROUND

Black gram [Vigna mungo (L)] seeds are a rich source of digestible protein and dietary fibre, both for human and animal consumption. However, the quality and quantity of the Vigna seeds are severely affected by bruchid beetles during storage. Therefore, analyses of the expression of the bruchid induced transcript dynamics in black gram pods would be helpful to understand the underlying defense mechanism against bruchid oviposition.

RESULTS

We used the RNAseq approach to survey the changes in transcript profile in the developing seeds of a moderately resistant cultivar IC-8219 against bruchid oviposition using a susceptible cultivar T-9 as a control. A total of 96,084,600 and 99,532,488 clean reads were generated from eight (4 each) samples of IC-8219 and T-9 cultivar, respectively. Based on the BLASTX search against the NR database, 32,584 CDSs were generated of which 31,817 CDSs were significantly similar to Vigna radiata, a close relative of Vigna mungo. The IC-8219 cultivar had 630 significantly differentially expressed genes (DEGs) of which 304 and 326 genes up and down-regulated, respectively. However, in the T-9 cultivar, only 168 DEGs were identified of which 142 and 26 genes up and down-regulated, respectively. The expression analyses of 10 DEGs by qPCR confirmed the accuracy of the RNA-Seq data. Gene Ontology and KEGG pathway analyses helped us to better understand the role of these DEGs in oviposition mediated defense response of black gram. In both the cultivars, the most significant transcriptomic changes in response to the oviposition were related to the induction of defense response genes, transcription factors, secondary metabolites, enzyme inhibitors, and signal transduction pathways. It appears that the bruchid ovipositioning mediated defense response in black gram is induced by SA signaling pathways and defense genes such as defensin, genes for secondary metabolites, and enzyme inhibitors could be potential candidates for resistance to bruchids.

CONCLUSION

We generated a transcript profile of immature black gram pods upon bruchid ovipositioning by de novo assembly and studied the underlying defense mechanism of a moderately resistant cultivar.

The Genome and Transcriptome Analysis of the Vigna mungo Chloroplast

Vigna mungo is cultivated in approximately 5 million hectares worldwide. The chloroplast genome of this species has not been previously reported. In this study, we sequenced the genome and transcriptome of the V. mungo chloroplast. We identified many positively selected genes in the photosynthetic pathway (e.g., rbcL, ndhF, and atpF) and RNA polymerase genes (e.g., rpoC2) from the comparison of the chloroplast genome of V. mungo, temperate legume species, and tropical legume species. Our transcriptome data from PacBio isoform sequencing showed that the 51-kb DNA inversion could affect the transcriptional regulation of accD polycistronic. Using Illumina deep RNA sequencing, we found RNA editing of clpP in the leaf, shoot, flower, fruit, and root tissues of V. mungo. We also found three G-to-A RNA editing events that change guanine to adenine in the transcripts transcribed from the adenine-rich regions of the ycf4 gene. The edited guanine bases were found particularly in the chloroplast genome of the Vigna species. These G-to-A RNA editing events were likely to provide a mechanism for correcting DNA base mutations. The V. mungo chloroplast genome sequence and the analysis results obtained in this study can apply to phylogenetic studies and chloroplast genome engineering.

A chromosome-scale assembly of the black gram (Vigna mungo) genome

Black gram (Vigna mungo) is an important short duration grain legume crop. Black gram seeds provide an inexpensive source of dietary protein. Here, we applied the 10X Genomics linked-read technology to obtain a de novo whole genome assembly of V. mungo cultivated variety Chai Nat 80 (CN80). The preliminary assembly contained 12,228 contigs and had an N50 length of 5.2 Mb. Subsequent scaffolding using the long-range Chicago and HiC techniques yielded the first high-quality, chromosome-level assembly of 499 Mb comprising 11 pseudomolecules. Comparative genomics analyses based on sequence information from single-copy orthologous genes revealed that black gram and mungbean (Vigna radiata) diverged about 2.7 million years ago . The transversion rate (4DTv) analysis in V. mungo revealed no evidence supporting a recent genome-wide duplication event observed in the tetraploid créole bean (Vigna reflexo-pilosa). The proportion of repetitive elements in the black gram genome is slightly lower than the numbers reported for related Vigna species. The majority of long terminal repeat retrotransposons appeared to integrate into the genome within the last five million years. We also examined alternative splicing events in V. mungo using full-length transcript sequences. While intron retention was the most prevalent mode of alternative splicing in several plant species, alternative 3' acceptor site selection represented the majority of events in black gram. Our high-quality genome assembly along with the genomic variation information from the germplasm provides valuable resources for accelerating the development of elite varieties through marker-assisted breeding and for future comparative genomics and phylogenetic studies in legume species.

Soluble and Cross-Linked Aggregated Forms of α-Galactosidase from Vigna mungo Immobilized on Magnetic Nanocomposites: Improved Stability and Reusability

α-Galactosidases hold immense potential due to their biotechnological applications in various industrial and functional food sectors. In the present study, soluble and covalently cross-linked aggregated forms of a low molecular weight, thermo-labile α-galactosidase from Vigna mungo (VM-αGal) seeds were immobilized onto chitosan-coated magnetic nanoparticles for improved stability and repeated usage by magnetic separation. Parameters like precipitants (type, amount, and ratio), glutaraldehyde concentration, and enzyme load were optimized for the preparation of chitosan-coated magnetic nanocomposites of cross-linked VM-αGal (VM-αGal-MC) and VM-αGal (VM-αGal-M) resulted in 100% immobilization efficiency. Size and morphology of VM-αGal-M were studied through dynamic light scattering (DLS) and scanning electron microscopy (SEM), while Fourier transform infrared spectroscopy (FTIR) was used to study the chemical composition of VM-αGal-MC and VM-αGal-M. VM-αGal-MC and VM-αGal-M were found more active in a broad range of pH (3-8) and displayed optimal temperatures up to 25 °C higher than VM-αGal. Addition of non-ionic detergents (except Tween-40) improved VM-αGal-MC activity by up to 44% but negatively affected VM-αGal-M activity. Both VM-αGal-MC (15% residual activity after 21 min at 85 °C, E_d 92.42 kcal/mol) and VM-αGal-M (69.0% residual activity after 10 min at 75 °C, E_d 39.87 kcal/mol) showed remarkable thermal stability and repeatedly hydrolyzed the substrate for 10 cycles.

QTL Mapping for Agronomic and Adaptive Traits Confirmed Pleiotropic Effect of mog Gene in Black Gram [Vigna mungo (L.) Hepper]

Organ size and architecture of plants are important traits affecting crop yield and agronomic practices. An induced mutant, multiple-organ gigantism (MOG), of black gram (Vigna mungo) has been obtained, which shows gigantic leaves, fruit, seed, and architecture (plant height) but lower number of pods per plant. These traits are a pleiotropic effect of a single recessive gene, mog. In this study, we investigated variation of 16 agronomic and adaptive traits in a recombinant inbred line (RIL) population derived from a cross between the MOG mutant (V. mungo var. mungo) and wild black gram (V. mungo var. silvestris) accession TC2210 and identified quantitative trait loci (QTLs) controlling those traits to gain a better understanding of the effect of the mog gene on breeding. The results showed that most of the traits (100-seed weight, leaf size, and plant height) showed moderate narrow-sense heritability (h ²) (45-65%), while pod size and seed length (SDL) showed high h ² (>75%) and pod dehiscence (shattering), and seed width (SDW) and days to flowering showed low h ² (<35%). The QTLs for the traits were mapped onto a high-density linkage map developed for the RIL population. Inclusive composite interval mapping identified 42 QTLs in total for the 16 traits with number of QTLs per trait ranging from one to six. Major QTLs for the MOG phenotypes were clustered on linkage group (LG) 6, confirming the pleiotropic effect of the mog gene. Effect of the mog gene/QTL for the MOG phenotypic variations was not high, ranging from about 15% in plant height to 40% in leaf size. For 100-seed weight, which is the most interesting trait, the mog gene/QTL contributed about 30% of the total trait variation and showed an additive effect of only 0.51 g, which is only about 1.5-fold higher than that of the other five QTLs detected for this trait. These results indicated that mog gene expression is highly affected by environment and the effect of the gene toward organ size and plant height is not extraordinarily high. Implications of the findings of this study and exploiting of the MOG mutant in breeding were also discussed.

Identification of Bradyrhizobium elkanii USDA61 Type III Effectors Determining Symbiosis with Vigna mungo

Bradyrhizobium elkanii USDA61 possesses a functional type III secretion system (T3SS) that controls host-specific symbioses with legumes. Here, we demonstrated that B. elkanii T3SS is essential for the nodulation of several southern Asiatic Vigna mungo cultivars. Strikingly, inactivation of either Nod factor synthesis or T3SS in B. elkanii abolished nodulation of the V. mungo plants. Among the effectors, NopL was identified as a key determinant for T3SS-dependent symbiosis. Mutations of other effector genes, such as innB, nopP2, and bel2-5, also impacted symbiotic effectiveness, depending on host genotypes. The nopL deletion mutant formed no nodules on V. mungo, but infection thread formation was still maintained, thereby suggesting its pivotal role in nodule organogenesis. Phylogenetic analyses revealed that NopL was exclusively conserved among Bradyrhizobium and Sinorhizobium (Ensifer) species and showed a different phylogenetic lineage from T3SS. These findings suggest that V. mungo evolved a unique symbiotic signaling cascade that requires both NFs and T3Es (NopL).

Development of transcriptome based web genomic resources of yellow mosaic disease in Vigna mungo

Vigna mungo (Urdbean) is cultivated in the tropical and sub-tropical continental region of Asia. It is not only important source of dietary protein and nutritional elements, but also of immense value to human health due to medicinal properties. Yellow mosaic disease caused by Mungbean Yellow Mosaic India Virus is known to incur huge loss to crop, adversely affecting crop yield. Contrasting genotypes are ideal source for knowledge discovery of plant defence mechanism and associated candidate genes for varietal improvement. Whole genome sequence of this crop is yet to be completed. Moreover, genomic resources are also not freely accessible, thus available transcriptome data can be of immense use. V. mungo Transcriptome database, accessible at http://webtom.cabgrid.res.in/vmtdb/ has been developed using available data of two contrasting varieties viz., cv. VM84 (resistant) and cv. T9 (susceptible). De novo assembly was carried out using Trinity and CAP3. Out of total 240,945 unigenes, 165,894 (68.8%) showed similarity with known genes against NR database, and remaining 31.2% were found to be novel. We found 22,101 differentially expressed genes in all datasets, 44,335 putative genic SSR markers, 4105 SNPs and Indels, 64,964 transcriptional factor, 546 mature miRNA target prediction in 703 differentially expressed unigenes and 137 pathways. MAPK, salicylic acid-binding protein 2-like, pathogenesis-related protein and NBS-LRR domain were found which may play an important role in defence against pathogens. This is the first web genomic resource of V. mungo for future genome annotation as well as ready to use markers for future variety improvement program.

Molecular and biochemical characterization of a Vigna mungo MAP kinase associated with Mungbean Yellow Mosaic India Virus infection and deciphering its role in restricting the virus multiplication

Yellow Mosaic Disease caused by the begomovirus Mungbean Yellow Mosaic India Virus (MYMIV) severely affects many economically important legumes. Recent investigations in Vigna mungo - MYMIV incompatible interaction identified a MAPK homolog in the defense signaling pathway. An important branch of immunity involves phosphorylation by evolutionary conserved Mitogen-activated protein kinases (MAPK) that transduce signals of pathogen invasion to downstream molecules leading to diverse immune responses. However, most of the knowledge of MAPKs is derived from model crops, and functions of these versatile kinases are little explored in legumes. Here we report characterization of a MAP kinase (VmMAPK1), which was induced upon MYMIV-inoculation in resistant V. mungo. Phylogenetic analysis revealed that VmMAPK1 is closely related to other plant-stress-responsive MAPKs. Both mRNA and protein of VmMAPK1 were accumulated upon MYMIV infection. The VmMAPK1 protein localized in the nucleus as well as cytoplasm and possessed phosphorylation activity in vitro. A detailed biochemical characterization of purified recombinant VmMAPK1 demonstrated an intramolecular mechanism of autophosphorylation and self-catalyzed phosphate incorporation on both threonine and tyrosine residues. The V_max and K_m values of recombinant VmMAPK1 for ATP were 6.292nmol/mg/min and 0.7978μM, respectively. Furthermore, the ability of VmMAPK1 to restrict MYMIV multiplication was validated by its ectopic expression in transgenic tobacco. Importantly, overexpression of VmMAPK1 resulted in the considerable upregulation of defense-responsive marker PR genes. Thus, the present data suggests the critical role of VmMAPK1 in suppressing MYMIV multiplication presumably through SA-mediated signaling pathway and inducing PR genes establishing the significant implications in understanding MAP kinase gene function during Vigna-MYMIV interaction; and hence paves the way for introgression of resistance in leguminous crops susceptible to MYMIV.

High throughput sequencing reveals modulation of microRNAs in Vigna mungo upon Mungbean Yellow Mosaic India Virus inoculation highlighting stress regulation

MicroRNAs (miRNAs) are 20-24 nucleotides long non-coding RNAs known to play important regulatory roles during biotic and abiotic stresses by controlling gene expression. Blackgram (Vigna mungo), an economically important grain legume is highly susceptible to pathogenic begomovirus Mungbean Yellow Mosaic India Virus (MYMIV) and resulting in high yield loss. In this study two different leaf-small-RNA libraries were prepared from the pooled RNA at three different time points of resistant V. mungo inbred line VM84 inoculated either with viruliferous or non-viruliferous whiteflies carrying MYMIV and performed high-throughput Illumina sequencing. Sequencing followed by bioinformatics analysis of the small RNA reads indicated that the expression patterns of most of the known and novel miRNAs were altered in resistant line over mock-inoculated sample during the plant virus incompatible interaction. Highly altered miRNAs belong to the families of miR156, miR159, miR160, miR166, miR398, miR1511, miR1514, miR2118 and novel vmu-miRn7, vmu-miRn8, vmu-miRn13 and vmu-miRn14. These results were validated using qPCR, and most of the miRNAs showed similar pattern of expression like that of Illumina reads. The expression patterns of some selected known and novel miRNAs were also compared between the infected MYMIV-resistant and -susceptible genotypes and most of these were modulated after MYMIV-inoculation. Target transcripts like NB-LRR, NAC, MYB, Zinc finger, CCAAT-box transcription factor, fructose 2-6 bisphosphate, HDZIP protein that confers immune response were predicted as targets amongst identified miRNAs using psRNATarget server. Some selected target transcripts including NB-LRR, ARF, SOD, SPB, Basic blue copper protein were validated and their differential expression were demonstrated between MYMIV-resistant and -susceptible V. mungo by qPCR data analyses. In the present study we have identified miRNAs that implicate in the regulation of MYMIV-induced stress response in V. mungo; and generated genomic resources for a non-model legume with the aid of bioinformatics tools supplemented by experimental validation.

Multiple abiotic stress tolerance in Vigna mungo is altered by overexpression of ALDRXV4 gene via reactive carbonyl detoxification

Vigna mungo (blackgram) is an important leguminous pulse crop, which is grown for its protein rich edible seeds. Drought and salinity are the major abiotic stresses which adversely affect the growth and productivity of crop plants including blackgram. The ALDRXV4 belongs to the aldo-keto reductase superfamily of enzymes that catalyze the reduction of carbonyl metabolites in the cells and plays an important role in the osmoprotection and detoxification of the reactive carbonyl species. In the present study, we developed transgenic plants of V. mungo using Agrobacterium mediated transformation. The transgene integration was confirmed by Southern blot analysis whereas the expression was confirmed by RT-PCR, Western blot and enzyme activity. The T1 generation transgenic plants displayed improved tolerance to various environmental stresses, including drought, salt, methyl viologen and H2O2 induced oxidative stress. The increased aldose reductase activity, higher sorbitol content and less accumulation of the toxic metabolite, methylglyoxal in the transgenic lines under non-stress and stress (drought and salinity) conditions resulted in increased protection through maintenance of better photosynthetic efficiency, higher relative water content and less photooxidative damage. The accumulation of reactive oxygen species was remarkably decreased in the transgenic lines as compared with the wild type plants. This study of engineering multiple stress tolerance in blackgram, is the first report to date and this strategy for trait improvement is proposed to provide a novel germplasm for blackgram production on marginal lands.

Analyses of MYMIV-induced transcriptome in Vigna mungo as revealed by next generation sequencing

Mungbean Yellow Mosaic Virus (MYMIV) is the viral pathogen that causes yellow mosaic disease to a number of legumes including Vigna mungo. VM84 is a recombinant inbred line resistant to MYMIV, developed in our laboratory through introgression of resistance trait from V. mungo line VM-1. Here we present the quality control passed transcriptome data of mock inoculated (control) and MYMIV-infected VM84, those have already been submitted in Sequence Read Archive (SRX1032950, SRX1082731) of NCBI. QC reports of FASTQ files generated by ‘SeqQC V2.2’ bioinformatics tool.

Proteomics approach combined with biochemical attributes to elucidate compatible and incompatible plant-virus interactions between Vigna mungo and Mungbean Yellow Mosaic India Virus

Background

Vigna mungo, a tropical leguminous plant, highly susceptible to yellow mosaic disease caused by Mungbean Yellow Mosaic India Virus (MYMIV) resulting in high yield penalty. The molecular events occurring during compatible and incompatible interactions between V. mungo and MYMIV pathosystem are yet to be explored. In this study biochemical analyses in conjunction with proteomics of MYMIV-susceptible and -resistant V. mungo genotypes were executed to get an insight in the molecular events during compatible and incompatible plant-virus interactions.

Results

Biochemical analysis revealed an increase in phenolics, hydrogen peroxide and carbohydrate contents in both compatible and incompatible interactions; but the magnitudes were higher during incompatible interaction. In the resistant genotype the activities of superoxide dismutase and ascorbate peroxidase increased significantly, while catalase activity decreased. Comparative proteome analyses using two-dimensional gel electrophoresis coupled with mass spectrometry identified 109 differentially abundant proteins at 3, 7 and 14 days post MYMIV-inoculation. Proteins of several functional categories were differentially changed in abundance during both compatible and incompatible interactions. Among these, photosynthesis related proteins were mostly affected in the susceptible genotype resulting in reduced photosynthesis rate under MYMIV-stress. Differential intensities of chlorophyll fluorescence and chlorophyll contents are in congruence with proteomics data. It was revealed that Photosystem II electron transports are the primary targets of MYMIV during pathogenesis. Quantitative real time PCR analyses of selected genes corroborates with respective protein abundance during incompatible interaction. The network of various cellular pathways that are involved in inducing defense response contains several conglomerated cores of nodal proteins, of which ascorbate peroxidase, rubisco activase and serine/glycine hydroxymethyl transferase are the three major hubs with high connectivity. These nodal proteins play the crucial role of key regulators in bringing about a coordinated defense response in highly orchestrated manner.

Conclusions

Biochemical and proteomic analyses revealed early accumulation of the defense/stress related proteins involved in ROS metabolism during incompatible interaction. The robustness in induction of defense/stress and signal transduction related proteins is the key factor in inducing resistance. The mechanism of MYMIV-resistance in V. mungo involves redirection of carbohydrate flux towards pentose phosphate pathway. Some of these identified, differentially regulated proteins are also conferring abiotic stress responses illustrating harmony amongst different stress responses. To the best of our knowledge, this is the lone study deciphering differential regulations of V. mungo leaf proteome upon MYMIV infection elucidating the mode of resistance response at the biochemical level.

Transcriptome Profiling Identifies Candidate Genes Associated with the Accumulation of Distinct Sulfur γ-Glutamyl Dipeptides in Phaseolus vulgaris and Vigna mungo Seeds

Common bean (Phaseolus vulgaris) and black gram (Vigna mungo) accumulate γ-Glutamyl-S-methylcysteine and γ-Glutamyl-methionine in seed, respectively. Transcripts were profiled by 454 pyrosequencing data at a similar developmental stage coinciding with the beginning of the accumulation of these metabolites. Expressed sequence tags were assembled into Unigenes, which were assigned to specific genes in the early release chromosomal assembly of the P. vulgaris genome. Genes involved in multiple sulfur metabolic processes were expressed in both species. Expression of Sultr3 members was predominant in P. vulgaris, whereas expression of Sultr5 members predominated in V. mungo. Expression of the cytosolic SERAT1;1 and -1;2 was approximately fourfold higher in P. vulgaris while expression of the plastidic SERAT2;1 was twofold higher in V. mungo. Among BSAS family members, BSAS4;1, encoding a cytosolic cysteine desulfhydrase, and BSAS1;1, encoding a cytosolic O-acetylserine sulphydrylase were most highly expressed in both species. This was followed by BSAS3;1 encoding a plastidic β-cyanoalanine synthase which was more highly expressed by 10-fold in P. vulgaris. The data identify BSAS3;1 as a candidate enzyme for the biosynthesis of S-methylcysteine through the use of methanethiol as substrate instead of cyanide. Expression of GLC1 would provide a complete sequence leading to the biosynthesis of γ-Glutamyl-S-methylcysteine in plastids. The detection of S-methylhomoglutathione in P. vulgaris suggested that homoglutathione synthetase may accept, to some extent, γ-Glutamyl-S-methylcysteine as substrate, which might lead to the formation of S-methylated phytochelatins. In conclusion, 454 sequencing was effective at revealing differences in the expression of sulfur metabolic genes, providing information on candidate genes for the biosynthesis of distinct sulfur amino acid γ-Glutamyl dipeptides between P. vulgaris and V. mungo.