Transcriptomic and Proteomic Research To Explore Bruchid-Resistant Genes in Mungbean Isogenic Lines

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

Mungbean is a socioeconomically important legume crop in Asia that is currently in high demand by consumers and industries both as dried beans and in plant-based protein foods. Marker-assisted and genomics-assisted breeding are promising approaches to efficiently and rapidly develop new cultivars with improved yield, quality, and resistance to biotic and abiotic stresses. Although mungbean was at the forefront of research at the dawn of the plant genomics era 30 years ago, the crop is a "slow runner" in genome research due to limited genomic resources, especially DNA markers. Significant progress in mungbean genome research was achieved only within the last 10 years, notably after the release of the VC1973A draft reference genome constructed using next-generation sequencing technology, which enabled fast and efficient DNA marker development, gene mapping, and identification of candidate genes for complex traits. Resistance to biotic stresses has dominated mungbean genome research to date; however, research is on the rise. In this study, we provide an overview of the past progress and current status of mungbean genomics research. We also discuss and evaluate some research results to provide a better understanding of mungbean genomics.

Genome-Wide Analysis of HSP70 Family Protein in Vigna radiata and Coexpression Analysis Under Abiotic and Biotic Stress

Heat shock protein 70 (Hsp70), a 70-kDa protein, also known as a molecular chaperone, is highly conserved. It plays a major role in cellular functions such as protein folding, regulation of protein degradation, translocation of proteins across membranes, receptor signaling, and protein assembly or disassembly. Vigna radiata is an important legume crop with available whole-genome sequence, but no such study on the HSP70 family is reported. A total of 32 V. radiate HSP70s (Vr-HSP70s) were identified and described. They are phylogenetically clustered into four subgroups. Vr-HSP70s show variations in intron/exon organization. This indicates that introns may play an essential role in gene regulating. The coexpression analysis of Vr-HSP70s revealed that these genes were involved in both abiotic and biotic stresses. Three cytoplasmic hub genes namely Vr-HSP70-C-14, Vr-HSP70-C-29, and Vr-HSP70-C-30 were found common in both stresses. Our findings provide directions for future studies to dissect functional analysis of Vr-HSP70s in response to abiotic and biotic stresses.

Towards Exploitation of Adaptive Traits for Climate-Resilient Smart Pulses

Pulses are the main source of protein and minerals in the vegetarian diet. These are primarily cultivated on marginal lands with few inputs in several resource-poor countries of the world, including several in South Asia. Their cultivation in resource-scarce conditions exposes them to various abiotic and biotic stresses, leading to significant yield losses. Furthermore, climate change due to global warming has increased their vulnerability to emerging new insect pests and abiotic stresses that can become even more serious in the coming years. The changing climate scenario has made it more challenging to breed and develop climate-resilient smart pulses. Although pulses are climate smart, as they simultaneously adapt to and mitigate the effects of climate change, their narrow genetic diversity has always been a major constraint to their improvement for adaptability. However, existing genetic diversity still provides opportunities to exploit novel attributes for developing climate-resilient cultivars. The mining and exploitation of adaptive traits imparting tolerance/resistance to climate-smart pulses can be accelerated further by using cutting-edge approaches of biotechnology such as transgenics, genome editing, and epigenetics. This review discusses various classical and molecular approaches and strategies to exploit adaptive traits for breeding climate-smart pulses.

Mechanism of Resistance in Mungbean [Vigna radiata (L.) R. Wilczek var. radiata] to bruchids, Callosobruchus spp. (Coleoptera: Bruchidae)

Mungbean [Vigna radiata (L.) R. Wilczek var. radiata] is an important pulse crop in Asia, and is consumed as dry seeds and as bean sprouts. It is an excellent source of digestible protein. Bruchids [Callosobruchus chinensis (L.) and Callosobruchus maculatus (F.)] are the important pests of mungbean and cause damage in the field and in storage. Bruchid infestation reduces the nutritional and market value of the grain and renders seeds unfit for human consumption, agricultural and commercial uses. These pests are controlled mainly by fumigation with highly toxic chemicals such as carbon disulfide, phosphene, and methyl bromide, or by dusting with several other insecticides, which leave residues on the grain, thus, threatening food safety. Some plant-based extracts have been found useful in controlling bruchids, but are not fully successful due to their short-term activity, rapid degradability, and potentially negative effect on seed germination. Although some wild sources of bruchid resistance in mungbean have been reported, which have been used to develop bruchid- resistant lines, undesirable genetic linkages threaten the proper exploitation of genetic diversity from wild germplasm into commercial cultivars. Further, biotype variation in bruchids has rendered some mungbean lines susceptible that otherwise would have been resistant to the pest. Host plant resistance is a cost-effective and a safe alternative to control bruchids in mungbean and is associated with morphological, biochemical, and molecular traits. These traits affect insect growth and development, thereby, reduce the yield losses by the pests. Understanding the defense mechanisms against insect pests could be utilized in exploiting these traits in crop breeding. This review discusses different traits in mungbean involved in defense against bruchids and their utility in pest management. We also highlight the breeding constraints for developing bruchid-resistant mungbean and how can these constraints be minimized. We further highlight the importance of supporting conventional breeding techniques by molecular techniques such as molecular markers linked to bruchid resistance.

Novel Alleles of Two Tightly Linked Genes Encoding Polygalacturonase-Inhibiting Proteins (VrPGIP1 and VrPGIP2) Associated with the Br Locus That Confer Bruchid (Callosobruchus spp.) Resistance to Mungbean (Vigna radiata) Accession V2709

Nearly all mungbean cultivars are completely susceptible to seed bruchids (Callosobruchus chinensis and Callosobruchus maculatus). Breeding bruchid-resistant mungbean is a major goal in mungbean breeding programs. Recently, we demonstrated in mungbean (Vigna radiata) accession V2802 that VrPGIP2, which encodes a polygalacturonase inhibiting protein (PGIP), is the Br locus responsible for resistance to C. chinensis and C. maculatus. In this study, mapping in mungbean accession V2709 using a BC₁₁F₂ population of 355 individuals revealed that a single major quantitative trait locus, which controlled resistance to both C. chinensis and C. maculatus, was located in a 237.35 Kb region of mungbean chromosome 5 that contained eight annotated genes, including VrPGIP1 (LOC106760236) and VrPGIP2 (LOC106760237). VrPGIP1 and VrPGIP2 are located next to each other and are only 27.56 Kb apart. Sequencing VrPGIP1 and VrPGIP2 in "V2709" revealed new alleles for both VrPGIP1 and VrPGIP2, named VrPGIP1-1 and VrPGIP2-2, respectively. VrPGIP2-2 has one single nucleotide polymorphism (SNP) at position 554 of wild type VrPGIP2. This SNP is a guanine to cystine substitution and causes a proline to arginine change at residue 185 in the VrPGIP2 of "V2709". VrPGIP1-1 has 43 SNPs compared with wild type and "V2802", and 20 cause amino acid changes in VrPGIP1. One change is threonine to proline at residue 185 in VrPGIP1, which is the same as in VrPGIP2. Sequence alignments of VrPGIP2 and VrPGIP1 from "V2709" with common bean (Phaseolus vulgaris) PGIP2 revealed that residue 185 in VrPGIP2 and VrPGIP1 contributes to the secondary structures of proteins that affect interactions between PGIP and polygalacturonase, and that some amino acid changes in VrPGIP1 also affect interactions between PGIP and polygalacturonase. Thus, tightly linked VrPGIP1 and VrPGIP2 are the likely genes at the Br locus that confer bruchid resistance in mungbean "V2709".