Chapter 1
Exploring Genomics Research in the Context of Some Underutilized Legumes-A Review
Patrush Lepcha, Pittala Ranjith Kumar and N. Sathyanarayana*
Department of Botany, Sikkim University, Gangtok, East Sikkim, India
*Corresponding author: nsathyanarayana@cus.ac.in
Abstract
Broadening legume resource base is imperative to meet the ever-increasing demand for protein-rich diet in the developing world. Many legumes species considered to be minor on a global scale have now been investigated and found to possess excellent nutritional value. Some of them are even a storehouse of rare drug molecules. Till date, their large-scale adoption for cultivation has remained unmet owing to poor research investments in these crops. Many of them have skipped genomics revolution and lack targeted genetic improvement programs. Recently, there has been renewed interest in these crops, and progress in genetic and genomics resources development is catching up, fueling greater promise toward molecular breeding and gene discovery programs in the near future. This review focuses on providing nutritional potential and prospects of genomic research in four lesser-known legume species: velvet bean, winged bean, rice bean, and lablab bean, which are grown as minor crops across the Indian subcontinent.
Keywords: Genomics, legumes, genomic resources, transcriptome, nutritional potential, segregant population, genetic map
1.1 Introduction
Trends in human population growth and pattern of consumption imply that the global demand for food will continue to grow for the next 40 years. This, along with depleting land and water resources in addition to climate change, poses serious threats to food security, particularly in the developing countries [1]. The burgeoning problem may attain serious dimensions in future years as the current yield-increase trends in major food crops may not be adequate in dealing with the growing demand [2, 3]. The grain legumes provide humans with important sources of food, fodder, oil, and fodder products [4]. They are also the vital source of dietary protein, vitamins, minerals, as well as omega-3 fatty acids [5] and can supply rare pharmaceuticals [6]. Even though quite a few proteinaceous edible legumes are available on the market, their production rate vis-à-vis consumption in most instances has remained unachieved and an ever-rising demand has been witnessed [7]. Also, a rising penchant for protein-rich vegetarian-based diet in world population has created unusual scarcity to plant resources [8]. There are several minor food legumes whose potential is untapped and underexploited. Bambara groundnut (Vigna subterranean L.), adzuki bean [Vigna angularis], faba bean (Vicia faba L.), velvet bean (Mucuna spp.), grass pea (Lathyrus sativus L.), horse gram [Macrotyloma uniflorum], hyacinth bean (Lablab purpureus L.), moth bean [Vigna aconitifolia], rice bean [Vigna umbellata], and winged bean [Psophocarpus tetragonolobus (L.) DC.] are important members of this grouping [6]. They possess excellent nutritional value and can offer a vital source of protein, vitamins, and minerals in LIFDC (low-income-food-deficit) countries. Since many of them are well adapted to marginal conditions, they may also be a warehouse of important genes associated with biotic and abiotic stress tolerance. However, to varying extents, almost all these crops have suffered from scantily developed resources for genetic and genomic research, thus limiting use of enabling biotechnologies for their improvement. In this review, we have focused on the nutritional potential and the accessibility and deployment of advanced genetic and genomic tools for diversity assessment, trait mapping, and molecular breeding in four underutilized legume species cultivated in and around the Indian subcontinent (Table 1.1). Further, an insight based on newly emerging biological approaches for early deployment of molecular breeding and development of improved cultivars has been provided, though many of these methods are yet to be tested for improving quality, nutritional abundance, and productivity in these legume species.
Table 1.1 Comparison of genomic resources in four lesser-known legume species.
Mucuna pruriens Psophocarpus tetragonolobus Vigna umbellata Lablab purpureus Chromosome number 2n = 2x = 22 [10] 2n = 2x = 18 [27] 2n = 2x = 22 [44, 45] 2n = 2x = 22 or 24 [58] Genome size ~1,361 Mbp [6] 1.22 Gbp [28] 367 Mb [59] RAPD Padmesh
et al., [21], Patil
et al., [23] Mohanty
et al., [39] Kaga
et al., [49],
Shafiqul
et al., [50],
Muthusamy
et al., [52] Rai
et al., [69],
Biswas
et al., [70] AFLP Capo-chichi
et al., [19, 20], Sathyanarayana
et al., [22] - - Maass
et al., [71],
Venkatesha
et al., [72] ISSR Patil
et al., [23] Mohanty
et al., [39], Chen
et al., [40] Muthusamy
et al., [51] SSR Sathyanarayana
et al., [24] Chen
et al., [52],
Wang
et al., [53],
Ingrai
et al., [54],
Thakur
et al., [55]
Wang
et al., [73],
Yao
et al., [74],
Shivakumar
et al., [75],
Guwen
et al., [76] Transcriptome Sathyanarayana
et al., [24] Vatanparast
et al., [28],
Wong
et al., [41, 43], Chen
et al., [52] Chapman [42] Genetic mapping Capo-chichi
et al., [25],
Mahesh
et al., [26] - Kaga
et al., [49],
Ismura
et al., [57] Kondur
et al., [77],
Humphry
et al., [78],
Yuan [79, 80]
1.2 Velvet Bean [Mucuna pruriens (L.) DC. var. utilis (Wall. ex Wight)] Baker ex Burck
Common Names: Velvet bean, Bengal velvet bean, Florida velvet bean.
Description: Self-pollinated tropical species [9] belonging to phaseoloid clade of leguminosae. Chromosome number of 2n = 2x = 22 [10] and genome size is ~1,361 Mbp [6]. The plant is a climber bearing large white or purple flowers; seeds (3-6/pod) are black/mottled/white in color and highly variable in color, size, and texture (Figure 1.1). Pods are non-itching. Matured seeds, immature pods, and leaves are consumed as food and used as supplement for ruminant livestock feed in several parts of the Asia and Africa [11-13]. Different plant parts are used in traditional Ayurvedic system of medicine for the treatment of diabetes, gout, tuberculosis, and nervous disorders and also as an aphrodisiac [14]. Most importantly, Mucuna spp. are a chief source of 3,4-dihydroxy-L-phenylalanine (L-Dopa, 1-9%)-a precursor of the dopamine widely used in the treatment of Parkinson's disease [15].
Figure 1.1 Variability for seed characters in M. pruriens germplasm.
Nutritional potential: Good source of protein (28%), carbohydrates (33%), lipids (7%), fibers (8%), moisture (8%), ash (6%), and minerals such as sodium, potassium, calcium, magnesium, phosphorus, manganese, iron, zinc, and amino acids [16, 17]. Presence of antinutritional factors such as saponins, phytic acids, phenolic compounds, tannins, hemagglutinins, as well as protease inhibitors such as trypsin inhibitors and chymotrypsin inhibitors are also reported [17, 18].
Genetic and genomic resources: The first-ever marker study on velvet bean was reported by Capo-chichi et al., [19] who studied genetic diversity among 40 US landraces using amplified fragment length polymorphism (AFLP) markers, which revealed narrow genetic base (3-13%). An extended study by the same authors on 64 accessions [20] revealed enhanced genetic diversity (0-0.32%). In India, Padmesh et al., [21] carried out the first diversity study using six accessions of M. pruriens comprising both wild (var. pruriens) and cultivated (var. utilis) varieties from Kerala using 15 randomly amplified polymorphic DNA (RAPD) primers. The results found overall good diversity (10-61%) with var. pruriens genetically more diverse vis-à-vis var. utilis. Later, similar results were reported in other germplasm collections using AFLP and inter simple sequence repeat (ISSR) markers [22, 23]. Recently, de novo transcriptome assembly comprising 67,561 assembled transcripts with N50 length of 987 bp and a mean transcript length of 641 bp has been reported [24]. From a total of 7,493 SSR motifs accounted from this work, 134 SSRs have been validated, offering an important resource for genetic studies and ongoing breeding programs. Linkage map based on AFLP markers has been developed, in addition to segregation analysis of pod color and pod pubescence in F2 population [25]. Recently, another genetic map has been reported...
