Multivariate biochemical characterization of rice bean (Vigna umbellata) seeds for nutritional enhancement

Farmers' preferences for rice bean production traits in western Kenya

Rice bean (Vigna umbellata) is an important legume for food and nutritional security. However, the level of its cultivation in western Kenya, where there is a serious malnutrition challenge, is still low due to a lack of insights into its attributes. Hence, to bridge this knowledge gap, this study analyzed smallholder farmers' preferences for production traits. We collected data from 204 farmers through a choice experiment (CE) approach in upper and lower midland agro-ecological zones. Subsequently, we used the random parameter logit (RPL) model to analyze the data. Results showed that farmers preferred all attribute levels presented except 61 % or more pest resistance. The lower midland farmers preferred compensation of Kenya shillings (Ksh) 34.93 for yields of 9 or more bags per acre; Ksh 52.22 for 61 to 79 maturity days and; Ksh 20.24 for 40 %-60 % pest resistance level. In comparison, upper midland farmers preferred compensation of Ksh 66.44 for 6 to 8 bags per acre; Ksh 53.82 for 9 or more bags per acre; no compensation for 50 to 60 maturity days; and Ksh 132.98 for 40 %-60 % pest resistance. However, farmers preferred no compensation for intact pods. The observed differences in farmers' preferences for rice bean attributes are explained by heterogeneity in the agroecological conditions, farmers' socio-economic characteristics, and risk perceptions. The findings should inform targeted extension and breeding programs that fit farmers' diverse environments and resource endowments.

De Novo Transcriptome Assembly of Rice Bean (Vigna umbellata) and Characterization of WRKY Transcription Factors Response to Aluminum Stress

Rice bean is an underutilized legume crop cultivated in Asia, and it is a good source of protein, minerals, and essential fatty acids for human consumption. Moreover, the leaves left over after harvesting rice bean seeds contain various biological constituents beneficial to humans and animals. In our study, we performed a de-novo transcriptome assembly of rice bean, characterized the WRKY transcription factors, and studied their response to aluminum stress. A total of 46.6 million clean reads, with a GC value of 43%, were generated via transcriptome sequencing. De novo assembly of the clean reads resulted in 90,933 transcripts and 74,926 unigenes, with minimum and maximum lengths of 301 bp and 24,052 bp, and N50 values of 1801 bp and 1710 bp, respectively. A total of 27,095 and 28,378 unigenes were annotated and subjected to GO and KEGG analyses. Among the unigenes, 15,593, 20,770, and 15,385 unigenes were identified in the domains of biological process, molecular function, and cellular component, respectively. A total of 16,132 unigenes were assigned to 188 pathways, including metabolic pathways (5500) and secondary metabolite biosynthesis (2858). Transcription factor analysis revealed 4860 unigenes from 98 different transcription factor families. For WRKY, a total of 95 unigenes were identified. Further analysis revealed the diverse response of WRKY transcription factors to aluminum stress. Collectively, the results of this study boost genomic resources and provide a baseline for further research on the role of WRKY transcription factors in aluminum tolerance in rice bean.

Exploiting genetic and genomic resources to enhance productivity and abiotic stress adaptation of underutilized pulses

Underutilized pulses and their wild relatives are typically stress tolerant and their seeds are packed with protein, fibers, minerals, vitamins, and phytochemicals. The consumption of such nutritionally dense legumes together with cereal-based food may promote global food and nutritional security. However, such species are deficient in a few or several desirable domestication traits thereby reducing their agronomic value, requiring further genetic enhancement for developing productive, nutritionally dense, and climate resilient cultivars. This review article considers 13 underutilized pulses and focuses on their germplasm holdings, diversity, crop-wild-crop gene flow, genome sequencing, syntenic relationships, the potential for breeding and transgenic manipulation, and the genetics of agronomic and stress tolerance traits. Recent progress has shown the potential for crop improvement and food security, for example, the genetic basis of stem determinacy and fragrance in moth bean and rice bean, multiple abiotic stress tolerant traits in horse gram and tepary bean, bruchid resistance in lima bean, low neurotoxin in grass pea, and photoperiod induced flowering and anthocyanin accumulation in adzuki bean have been investigated. Advances in introgression breeding to develop elite genetic stocks of grass pea with low β-ODAP (neurotoxin compound), resistance to Mungbean yellow mosaic India virus in black gram using rice bean, and abiotic stress adaptation in common bean, using genes from tepary bean have been carried out. This highlights their potential in wider breeding programs to introduce such traits in locally adapted cultivars. The potential of de-domestication or feralization in the evolution of new variants in these crops are also highlighted.

Nutritional and nutraceutical potential of rice bean (Vigna umbellata) -a legume with hidden potential

In the recent years there has been paradigm shift in global agriculture for the exploration of different underutilized crops as future potential crops. Rice bean [Vigna umbellata (Thunb.) Ohwi and Ohashi] one of the lesser known pulses among Vigna species has gained attention during last decade as food and nutritional security crop. Rice bean seeds are well-balanced source of beneficial constituents such as protein, carbohydrates, minerals, vitamins, polyunsaturated fatty acids (PUFAs) and anti-oxidants for health benefits and combating malnourishment in human. In the present investigation, seeds of 15 diverse rice bean accessions from north-western Himalayan region were analyzed for nutrients, anti-nutrients and nutraceutical traits. Significant differences were observed among genotypes for different traits. The rice bean genotypes revealed variation for major quality traits including total carbohydrates (50.56-56.87%), crude protein content (22.56-25.97%) and lipid content (1.87 to 3.17%) with the higher proportion of linolenic acid followed by linoleic acid which are nutritionally desirable PUFAs. The genotype IC-548758 revealed higher proportion of desirable quality traits. Among protein fractions, globulins and albumins constituted major seed storage protein fraction in rice bean seeds. The wide range variation was also observed for anti-nutrients like including raffinose family oligosaccharides (RFOs), phenolics, tannins, trypsin inhibitor (TI), phytic acid, lipoxygenase activity and saponin content among genotypes. Insignificant correlation among iron, zinc, magnesium and manganese revealed good selection accuracy for genetic biofortification program in rice bean. In summary, the genotype IC-548757, IC-548760 and IC-548770 revealed lower proportion of anti-nutrients, whereas, the genotype IC-548759 and IC-548757 revealed higher level of free radical scavenging activity indicating nutritional and nutraceutical superiority of these genotypes. Overall, the study revealed nutritional superiority of genotype IC-548770, IC-548758 and IC-548760 with balanced proportions of nutrients and anti-nutrients. Rice bean legume has the potential to support more sustainable and resilient food and nutritional security in future. Our study highlights the potential of different rice bean genotypes as functional ingredients for future food and nutritional security programmes.

Nutritional, functional, and bioactive properties of african underutilized legumes

Globally, legumes are vital constituents of diet and perform critical roles in maintaining well-being owing to the dense nutritional contents and functional properties of their seeds. While much emphasis has been placed on the major grain legumes over the years, the neglected and underutilized legumes (NULs) are gaining significant recognition as probable crops to alleviate malnutrition and give a boost to food security in Africa. Consumption of these underutilized legumes has been associated with several health-promoting benefits and can be utilized as functional foods due to their rich dietary fibers, vitamins, polyunsaturated fatty acids (PUFAs), proteins/essential amino acids, micro-nutrients, and bioactive compounds. Despite the plethora of nutritional benefits, the underutilized legumes have not received much research attention compared to common mainstream grain legumes, thus hindering their adoption and utilization. Consequently, research efforts geared toward improvement, utilization, and incorporation into mainstream agriculture in Africa are more convincing than ever. This work reviews some selected NULs of Africa (Adzuki beans (Vigna angularis), African yam bean (Sphenostylis stenocarpa), Bambara groundnut (Vigna subterranea), Jack bean (Canavalia ensiformis), Kidney bean (Phaseolus vulgaris), Lima bean (Phaseolus lunatus), Marama bean (Tylosema esculentum), Mung bean, (Vigna radiata), Rice bean (Vigna Umbellata), and Winged bean (Psophocarpus tetragonolobus)), and their nutritional, and functional properties. Furthermore, we highlight the prospects and current challenges associated with the utilization of the NULs and discusses the strategies to facilitate their exploitation as not only sources of vital nutrients, but also their integration for the development of cheap and accessible functional foods.

Effect of selected physical and chemical modifications on physicochemical, pasting, and morphological properties of underutilized starch from rice bean (Vigna umbellata)

Starch was extracted from the rice bean which is largely underutilized and modified by physical (i.e. heat moisture treatment and retrogradation) and chemical (i.e. esterification and acid alcohol modification) methods. Both, physical and chemical modifications significantly (p < 0.05) affected the physicochemical, pasting, particle size and morphological properties of rice bean starch. Both amylose content and swelling power reduced after physical and chemical modifications. Among modified starches, retrograded starch showed higher solubility (8.56%) at 90 °C. Retrogradation also resulted in higher values of water (251%) and oil absorption (106%) capacities in comparison to other modified starches. Physical modifications greatly influenced the pasting properties in comparison to chemical modifications. The particle size distribution followed the order: native starch (659.8 nm) > heat moisture treated (434.3 nm) > retrograded (355.4 nm) > esterified (218 nm) > acid alcohol treated starch (234.5 nm). The study revealed that the particle size of rice bean starch was reduced by both physical and chemical modifications. FE-Scanning electron microscopy was used to study the morphological characteristics of starches and it was observed that retrogradation had a pronounced effect on the starch granules morphology.

Cloning, Characterization, Expression Analysis, and Agglutination Studies of Novel Gene Encoding β-D-Galactose, N-Acetyl-D-Glucosamine and Lactose-Binding Lectin from Rice Bean (Vigna umbellata)

Lectins are glycoproteins and known for their peculiar carbohydrate-binding activity and their insect-pest-resistant properties. Earlier we have published our research finding on novel gene encoding Bowman-Birk type protease inhibitor with insecticidal properties from rice bean. This paper presents first report on cloning, sequencing, and expression of RbL ORF of 843 bp encoding 280 amino acids long lectin precursor from rice bean (Vigna umbellata) seeds. Blast analysis revealed more than 90% similarity of RbL protein with Vigna aconitifolia and Vigna angularis lectins. Phylogenetic analysis also revealed a close relationship between RbL and other legume lectins. Sequence analysis of genomic DNA revealed intronless nature of RbL gene (GenBank accession No. MT043160). The isolated RbL ORF was expressed in E. coli BL-21(DE3) cells and maximum expression was recorded with 0.5 mM IPTG after 4 h incubation at 37 °C. Western blotting confirmed RbL protein expression in E. coli. Recombinant protein (His₆-RbL) of ~ 35 kDa m.wt was purified using Ni-NTA affinity chromatography to the extent of 0.26 mg/ml. In silico analysis characterized RbL protein as acidic, stable, hydrophobic, and secretary protein with one signal peptide cleavage site (A₂₆-A₂₇) and four N-glycosylation sites. Template-based 3D model of RbL was structured using MODELLER tool and validated as good quality model. Structural analysis revealed dominance of β-pleated sheets and β-turns in RbL protein structure. β-D-galactose, N-acetyl-D-glucosamine, and lactose were predicted as putative ligands for RbL protein. Hydrogen bonding and hydrophobic forces were the major interactions between the predicted ligands and RbL protein. Agglutination and agglutination inhibition assays confirmed the binding specificity of RbL protein with the trypsinized rabbit erythrocytes and with the predicted ligands, respectively. Gene ontology analysis functionally annotated RbL protein as a plant defense protein. The novel information generated in the study is not mere pre-experimental findings but could also lay foundation for future research on exploring RbL gene and encoding protein for different biomedical and biotechnological applications.