Thirty Years of Mungbean Genome Research: Where Do We Stand and What Have We Learned?

A panomics-driven framework for the improvement of major food legume crops: advances, challenges, and future prospects

Food legume crops, including common bean, faba bean, mungbean, cowpea, chickpea, and pea, have long served as vital sources of energy, protein, and minerals worldwide, both as grains and vegetables. Advancements in high-throughput phenotyping, next-generation sequencing, transcriptomics, proteomics, and metabolomics have significantly expanded genomic resources for food legumes, ushering research into the panomics era. Despite their nutritional and agronomic importance, food legumes still face constraints in yield potential and genetic improvement due to limited genomic resources, complex inheritance patterns, and insufficient exploration of key traits, such as quality and stress resistance. This highlights the need for continued efforts to comprehensively dissect the phenome, genome, and regulome of these crops. This review summarizes recent advances in technological innovations and multi-omics applications in food legumes research and improvement. Given the critical role of germplasm resources and the challenges in applying phenomics to food legumes-such as complex trait architecture and limited standardized methodologies-we first address these foundational areas. We then discuss recent gene discoveries associated with yield stability, seed composition, and stress tolerance and their potential as breeding targets. Considering the growing role of genetic engineering, we provide an update on gene-editing applications in legumes, particularly CRISPR-based approaches for trait enhancement. We advocate for integrating chemical and biochemical signatures of cells ('molecular phenomics') with genetic mapping to accelerate gene discovery. We anticipate that combining panomics approaches with advanced breeding technologies will accelerate genetic gains in food legumes, enhancing their productivity, resilience, and contribution to sustainable global food security.

A robust in-vitro and ex-vitro Agrobacterium rhizogenes-mediated hairy root transformation system in mungbean for efficient visual screening of transformants using the RUBY reporter

BACKGROUND

Mungbean is one of the most economically important grain legume crops in Asia. Functional genomics studies in mungbean are necessary to understand the molecular mechanisms behind agronomic traits, to advance the crop improvement. However, this progress is significantly impeded by the absence of effective and extensive genetic analysis tools. Agrobacterium rhizogenes-mediated hairy root transformation has become a powerful tool for studying gene function and an efficient alternative for investigating root-specific interactions and processes in different species, due to its quick and simple methodology. Agrobacterium-mediated plant transformation, however, is known to be difficult in legumes, especially in mungbean.

RESULTS

In this report, we developed an Agrobacterium rhizogenes-mediated mungbean transformation system using both in-vitro and ex-vitro approaches, with RUBY employed as a reporter gene. We optimized various parameters, including mungbean genotypes, explant age, optical density of the bacterial culture, co-cultivation medium, and acetosyringone concentration. Our findings indicated that in-vitro transformation was more efficient than ex-vitro in terms of hairy root induction percentage and the proportion of transformed hairy roots expressing the RUBY reporter gene. However, the ex-vitro transformation technique was faster and less complex than the in-vitro method. The highest transformation efficiency for RUBY expression was achieved using 5-day-old cotyledonary nodal explants of cv. K-851, inoculated for 30 min with A4 Agrobacterium cells resuspended in full-strength MS medium at an OD₆₀₀ of 0.5 and supplemented with 100 µM acetosyringone. A total of 60 composite plants were generated and evaluated through PCR, resulting in a transformation efficiency of 6.13%. These optimized parameters also led to the highest percentage of RUBY expression using the two-step ex-vitro hairy root transformation method.

CONCLUSION

We have developed a simple, rapid, low-cost, and labor-efficient Agrobacterium rhizogenes-mediated mungbean transformation protocol using both in-vitro and ex-vitro approaches, with RUBY as a reporter gene. This method enables the generation of composite mungbean plants that are easier to handle, exhibit higher transformation efficiency, and can be effectively used for root specific functional genomics studies. We expect this technology to be widely adopted for investigating root-related processes in mungbean and other plant species.

A chromosome-scale reference assembly of Vigna radiata enables delineation of centromeres and telomeres

Vigna radiata (L.) R. Wilczek var. radiata (mungbean) is a pulse crop important for both the global protein security and sustainable crop production. Here, to facilitate genomics-assisted breeding programs in mungbean, we present a high-quality reference genome originating from the crop's centre of origin, India. In this study, we present a significantly continuous genome assembly of V. radiata Indian cultivar, achieved through a combination of long-read PacBio HiFi sequencing and Hi-C sequencing. The total assembled genome size is ~596 Mb equating to ~98% of the predicted genome size complemented by a contig N50 value of 10.35 Mb and a BUSCO score of 98.5%. Around 502 Mb of the assembled genome is anchored on 11 pseudochromosomes conforming to the chromosome count in the crop with distinctly identified telomeres and centromeres. We predicted a total of 43,147 gene models of which 39,144 protein coding genes were functionally annotated. The present assembly was able to resolve several gaps in the genome and provides a high-quality genomic resource for accelerating mungbean breeding programs.

Identifcation and fine mapping of qHSW1, a major QTL for hundred-seed weight in mungbean

Mung bean, an important economic crop, is considered a crop with relatively high levels of plant protein constituents and is consumed as both a vegetable and a grain. Among various yield-related traits, hundred-seed weight (HSW) is crucial in determining mung bean production. This study employed a recombinant inbred line (RIL) population of 200 lines that were genotyped via whole-genome resequencing to exploit genetic potential in the identification of HSW-associated quantitative trait loci (QTLs) across four environments. We identified 5 QTLs for HSW, each explaining 2.46-26.15% of the phenotypic variance. Among these, qHSW1 was mapped on chromosome 1 in all four environments, explaining 16.65-26.15% of the phenotypic variation. Fine mapping and map-based cloning procedures, along with progeny testing of recombinants, aided in narrowing the candidate interval for qHSW1 to 506 kb. This identification of the qHSW1 genomic interval and closely linked markers to qHSW1 could prove valuable in breeding efforts for improved mung bean cultivars with higher seed weight.

A chromosome-scale genome assembly of mungbean (Vigna radiata)

Background

Mungbean (Vigna radiata) is one of the most socio-economically important leguminous food crops of Asia and a rich source of dietary protein and micronutrients. Understanding its genetic makeup is crucial for genetic improvement and cultivar development.

Methods

In this study, we combined single-tube long-fragment reads (stLFR) sequencing technology with high-throughput chromosome conformation capture (Hi-C) technique to obtain a chromosome-level assembly of V. radiata cultivar 'KUML4'.

Results

The final assembly of the V. radiata genome was 468.08 Mb in size, with a scaffold N50 of 40.75 Mb. This assembly comprised 11 pseudomolecules, covering 96.94% of the estimated genome size. The genome contained 253.85 Mb (54.76%) of repetitive sequences and 27,667 protein-coding genes. Our gene prediction recovered 98.3% of the highly conserved orthologs based on Benchmarking Universal Single-Copy Orthologs (BUSCO) analysis. Comparative analyses using sequence data from single-copy orthologous genes indicated that V. radiata diverged from V. mungo approximately 4.17 million years ago. Moreover, gene family analysis revealed that major gene families associated with defense responses were significantly expanded in V. radiata.

Conclusion

Our chromosome-scale genome assembly of V. radiata cultivar KUML4 will provide a valuable genomic resource, supporting genetic improvement and molecular breeding. This data will also be valuable for future comparative genomics studies among legume species.

QTL-seq and QTL mapping identify a new locus for Cercospora leaf spot (Cercospora canescens) resistance in mungbean (Vigna radiata) and a cluster of Receptor-like protein 12 (RLP12) genes as candidate genes for the resistance

KEY MESSAGE

QTL-seq, linkage mapping, and whole-genome resequencing revealed a new locus (qCLS5.1) controlling Cercospora canescens resistance in mungbean and Receptor-like protein 12 (RLP12) genes as candidate genes for the resistance. Cercospora leaf spot (CLS) disease, caused by Cercospora canescens, is a common disease of mungbean (Vigna radiata). In this study, the genetics of CLS resistance was investigated in a new source of resistance (accession V2817) and the resistance was finely mapped to identify candidate genes. F2 and F2:3 populations of the cross V1197 (susceptible) × V2718 and a BC1F1 population of the cross V1197 × (V1197 × V2817) were used in this study. Segregation analysis suggested that the resistance is controlled by a single dominant gene. QTL-seq using F2 individuals revealed that a single QTL (designated qCLS5.1) on chromosome 5 controlled the resistance. The qCLS5.1 was confirmed in the F2:3 and BC1F1 populations by QTL analysis. Fine mapping using 978 F2 individuals localized qCLS5.1 to a 48.94 Kb region containing three tandemly duplicated Receptor-like protein 12 (RLP12) genes. Whole-genome resequencing and alignment of V1197 and V2817 revealed polymorphisms causing amino acid changes and premature stop codons in the three RLP12 genes. Collectively, these results show that qCLS5.1 is a new locus for CLS resistance in mungbean, and a cluster of RLP12 genes are candidate genes for the resistance. The new locus qCLS5.1 will be useful for molecular breeding of durable CLS-resistant mungbean cultivars.

Variations of Major Flavonoids, Nutritional Components, and Antioxidant Activities in Mung Beans (Vigna radiate L.) of Different Seed Weights

This study examined the levels of major flavonoids, nutritional components, total secondary metabolite contents, and antioxidant activities in 136 mung bean accessions and statistically analyzed the effect of seed weight difference on each. Vitexin and isovitexin were detected in all the mung bean accessions, with isovitexin being in a higher concentration regardless of seed weight difference. The contents of total protein and total starch were in the ranges of 22.01-28.96 and 32.62-49.03 g/100 g, respectively. Five fatty acids were detected by GC-FID analysis in all mung bean accessions, with linoleic acid being the most dominant (37.96-50.71 g/100 g). Total saponin content (TSC), total phenol content (TPC), DPPH• scavenging activity, ABTS•+ scavenging activity, and ferric reducing antioxidant power (FRAP) showed more than five-fold differences. Analysis of variance supported by multivariate analysis demonstrated that seed weight difference had a significant effect on total starch, all individual fatty acids except for stearic acid and oleic acid, TSC, and all antioxidant activities except for ABTS•+ scavenging activity. On the other hand, vitexin, isovitexin, total protein, total phenol, and total fatty acid contents remained unaffected by seed weight difference. Overall, this study showed the diversity of key flavonoids, nutritional components, total secondary metabolite contents, and antioxidant activities in mung bean genetic materials. Moreover, the study unveiled how seed weight affects the analyzed parameters in mung beans for the first time. These findings could maximize the use of mung beans in food industries and breeding programs as well as lead to more studies in metabolomics and genomics.

Genetic variation for tolerance to pre-harvest sprouting in mungbean (Vigna radiata) genotypes

Pre-harvest sprouting (PHS) is one of the important abiotic stresses in mungbean which significantly reduces yield and quality of the produce. This study was conducted to evaluate the genetic variability for tolerance to pre-harvest sprouting in diverse mungbean genotypes while simultaneously deciphering the association of yield contributing traits with PHS. Eighty-three diverse mungbean genotypes (23 released varieties, 23 advanced breeding lines and 37 exotic germplasm lines) were investigated for tolerance to PHS, water imbibition capacities by pods, pod and seed physical traits. Wide variation in PHS was recorded which ranged between 17.8% to 81% (mean value 54.34%). Germplasm lines exhibited higher tolerance to PHS than the high-yielding released varieties. Correlation analysis revealed PHS to be positively associated with water imbibition capacity by pods (r = 0.21) and germinated pod % (r = 0.78). Pod length (r = -0.13) and seeds per pod (r = -0.13) were negatively influencing PHS. Positive associations between PHS and water imbibition capacity by pods, germinated pod % and 100-seed weight was further confirmed by multivariate analysis. Small-seeded genotypes having 100-seed weight <3 g exhibited higher tolerance to PHS compared to bold-seeded genotypes having 100-seed weight more than 3.5 g. Fresh seed germination among the selected PHS tolerant and susceptible genotypes ranged from 42% (M 204) to 98% (Pusa 1131). A positive association (r = 0.79) was recorded between fresh seed germination and PHS. Genotypes M 1255, M 145, M 422, M 1421 identified as potential genetic donors against PHS could be utilized in mungbean breeding programs.

Narrowing down a major QTL region reveals Phytochrome E (PHYE) as the candidate gene controlling flowering time in mungbean (Vigna radiata)

Flowering time is an important agronomic trait that is highly correlated with plant height, maturity time and yield in mungbean. Up to present, however, molecular basis of flowering time in mungbean is poorly understood. Previous studies demonstrated that flowering time in mungbean is largely controlled by a major QTL on linkage group 2 (LG2). In this study, the QTL on the LG2 in mungbean was investigated using F2 and F2:3 populations derived from a cross between mungbean cultivar Kamphaeng Saen 2 (KPS2) and wild mungbean accession ACC41. The QTL was narrowed down to a genome region of 164.87 Kb containing a phytochrome gene, designated VrPHYE, encoding phytochrome E (phyE), a known photoreceptor modulating flowering time. Compared to VrPHYE of the wild ACC41, VrPHYE of KPS2 contained several single nucleotide polymorphisms (SNPs) causing amino acid changes. Those SNPs were also found in other mungbean cultivars. Some amino acid changes were predicted to occur in the regulatory region of phytochromes. Gene expression analysis revealed that VrPHYE in KPS2 was expressed significantly higher than that in ACC41. These results showed that VrPHYE is the candidate gene controlling flowering time in the mungbean.

Combining GWAS and comparative genomics to fine map candidate genes for days to flowering in mung bean

BACKGROUND

Mung bean (Vigna radiata (L.) Wilczek), is an important pulse crop in the global south. Early flowering and maturation are advantageous traits for adaptation to northern and southern latitudes. This study investigates the genetic basis of the Days-to-Flowering trait (DTF) in mung bean, combining genome-wide association studies (GWAS) in mung bean and comparisons with orthologous genes involved with control of DTF responses in soybean (Glycine max (L) Merr) and Arabidopsis (Arabidopsis thaliana).

RESULTS

The most significant associations for DTF were on mung bean chromosomes 1, 2, and 4. Only the SNPs on chromosomes 1 and 4 were heavily investigated using downstream analysis. The chromosome 1 DTF association is tightly linked with a cluster of locally duplicated FERONIA (FER) receptor-like protein kinase genes, and the SNP occurs within one of the FERONIA genes. In Arabidopsis, an orthologous FERONIA gene (AT3G51550), has been reported to regulate the expression of the FLOWERING LOCUS C (FLC). For the chromosome 4 DTF locus, the strongest candidates are Vradi04g00002773 and Vradi04g00002778, orthologous to the Arabidopsis PhyA and PIF3 genes, encoding phytochrome A (a photoreceptor protein sensitive to red to far-red light) and phytochrome-interacting factor 3, respectively. The soybean PhyA orthologs include the classical loci E3 and E4 (genes GmPhyA3, Glyma.19G224200, and GmPhyA2, Glyma.20G090000). The mung bean PhyA ortholog has been previously reported as a candidate for DTF in studies conducted in South Korea.

CONCLUSION

The top two identified SNPs accounted for a significant proportion (~ 65%) of the phenotypic variability in mung bean DTF by the six significant SNPs (39.61%), with a broad-sense heritability of 0.93. The strong associations of DTF with genes that have orthologs with analogous functions in soybean and Arabidopsis provide strong circumstantial evidence that these genes are causal for this trait. The three reported loci and candidate genes provide useful targets for marker-assisted breeding in mung beans.