Horse gram -An ideal candidate plant for mining genes for abiotic stress tolerance and therapeutic values
Authors: Dinesh Chand1, N. Dikshit1 and J.C.Rana2
1 ICAR-National Bureau of Plant Genetic Resources, Regional Station, Akola 444104, Maharashtra, India
2 ICAR-National Bureau of Plant Genetic Resources, Germplasm Evaluation Division, New Delhi-110012, India

Introduction

Macrotyloma uniflorum (Lam.) Verd. commonly known as horse gram (Kulthi) belongs to family Fabaceae and is an important crop of rich protein and are capable of nitrogen fixation. (Shirsat, 2010). It is cultivated in Asia viz. (India, Malaysia, Mauritius, Myanmar, Nepal, and Sri Lanka) for food purposes and fodder purposes in Africa and Australia. It is native to India (Bogdan, 1977) and is an important minor legume crop in the peninsular region. Horse gram contains 23% protein and rich in lysine content compared to chick pea and pigeon pea (Prakash, et al., 2010) besides its use as green manure for improving soil fertility tremendously (Prakash et al., 2008). Abitoic stress is one of the greatest constraints to crop production world-wide and among the abiotic stresses, drought is a major limiting factors for reduction in yields of crops (Somerville and Biscoe, 2000) and (Chaves et al., 2003). Yield reduction up to 70% has been reported due to abiotic stresses by Acquaah 2007. Horse gram can best be described as a reddish brown legume which is having a number of health benefits and can help alleviate number of health problems as it contains a rich amount of vitamins, proteins, iron and helps in reduction of extra fat from the body leading to weight loss.

- Economic importance: The crop is highly suitable for rainfed and marginal agriculture. The plant grows very fast, and becomes dense in a short period of time, thus it prevents soil erosion. It is a valuable plant on sloping land with poor mineral content. Sprouted seed, or whole meal of horse gram is used by large populations in hilly regions and rural areas of southern India. High protein content, antioxidant activity (Reddy et al., 2005), and antimicrobial activity and various medicinal properties make it an interesting pulse crop and potential food source of the future. In cultivated horse gram, protein content varies from 16.9-30.4%. Horse gram is rich in iron, phosphorus, and vitamins, viz., carotene, niacin, riboflavin, thiamine, and vitamin C (Sodani et al., 2004) and has high lysine content, an essential amino acid (Gopalan et al,. 1989).

- Source of Medicine and health benefits of horse gram: The seeds contain the richest vegetarian sources of protein, iron, calcium, protein and B-complex vitamin. High carbohydrate content, low lipid, sodium content, and slow digestible starch makes it ideal for diabetic and obesity patients.Raw horse gram is particularly rich in polyphenols, flavonoids and proteins are the major anti-oxidants. The health benefit of horse gram in traditional medicine describes its use for asthma, bronchitis, leucoderma, urinary discharge, and heart disease. Eating plenty of horse gram can actually help for obesity due to its phenol content and thus helps in reduction of extra fat from the body leading to weight loss. Kulthi also has the ability to generate heat and energy in our system and therefore on a cold winter time it keeps our body warm. It cures the kidney stones, gall stones and reduces high blood pressure. Patients suffering from weak liver, spleen enlargement are also highly benefited from horse gram. It helps to relieve in menstrual problems and prevents arthritis. The presence of a good amount of dietary fiber in the horse gram helps in maintaining balance in sugar, glucose and protects against diabetes and blood pressure levels.

Desirable Traits:

Horse gram has number of desirable traits like drought tolerance (Reddy et al.1990), heavy metal stress tolerance (Sudhakar et al., 1992), high protein content, antioxidant activity (Reddy et al., 2005), and antimicrobial activity and various medicinal properties make it a crop of interest and potential food source of the future. Horse gram is remarkably tough and drought-resistant. It is capable of withstanding extended periods of drought with little access to technology or irrigation and often the preferred crop by the farmers. It is also grown in low fertility regions where other crop species may have failed. It is a great candidate for land reclamation programs.All these factors combined makes it a great cost-effective source of food, fodder. Desirable characters viz. high number of pods per plant, high seed yield from Macrotyloma axillare can be incorporated into the cultivated form for tolerance to cold and resistance to diseases (Dikshit et al., 2014).

Mining Genes for Abiotic Stress Tolerance

There is a tremendous amount of biological diversity among different plant species for adaptation to drought stress. All stress adaptive mechanisms may not be operating in all plants to the same extent. There is a great emphasis on identifying novel stress physiology of crop plants to improve the tolerance of stress susceptible crops. Tolerant species may have specific adaptive physiological mechanisms and can express novel stress response. The mechanism can be popularized by the use of less water taken by plants in different cultivars and identify novel genes for maintaining more and more yields when challenged with drought.

Plants sense and respond to drought stress at the molecular and cellular levels as well as at the physiological and biochemical levels, thus enabling them to survive (Shinozaki et al., 2000) and ( Bartles and Ramanjulu, 2005). Valliyodan and Nguyen (2006) reported that multiple genes are induced during drought stress by the plants to develop drought tolerance capability.

The products of the stress-inducible genes can be broadly classified into two groups. The gene products of the first group directly protect cells against stress (e.g. chaperons, LEA, proteins, osmo-protectans, detoxifying enzymes, the radical scavengers and various proteases Bray (2002) and (Shinozaki and Yamaguchi-Shinozaki, 2007), and the second group advocates the role of transcription factors, secondary messengers, phosphatases and kinases such as mitozen-activated kinases , calcium dependent protein kinases etc. (Ludwig et al., 2004).

Discussion

Horse gram is a low-profile legume. It serves as a good crop in plantations in southern India and hilly regions of India. It requires relatively low levels of light, and grown out quietly under the trees, and when plants die it enhances the quality of the soil. Its stalks and stems provide high quality forage to animals as it contains 30-40% nutrients. Nutritionally, horse gram contains about 23% protein and high lysine content as compared to pigeon pea and chickpea. It is also used for a number of medicinal and therapeutic applications in Ayurvedic medicine such as curing piles, renal stones etc. It is a potential crop for future as it possesses desirable traits like tolerance to drought, heavy metal stress, nitrogen fixation ability, protein content, antimicrobial, antioxidant activity and medicinal properties etc. Keeping this in mind, there is need to undertake an extensive hybridization program to incorporate useful variability from diverse parents and related species. Broadening of genetic base can be accomplished through collection of indigenous and exotic sources. In addition, desirable characters of

Macrotyloma axillare ( high number of pods per plant, high seed yield ) can be incorporated into the cultivated form through wide hybridization and embryo rescue technique. Further, emphasis needs to be given to prevent loss of genetic material, diversity in wild relatives in view of the invaluable genes for abiotic stress and therapeutic values.

References

1. Acquaah G (2007). Principles of Plant genetics and breeding. Blackwell, Oxford.
2. Bartles, D., S. Ramanjulu (2005). Drought and salt tolerance in plants. Crit. Rev. Plant Sci. 24: 23-58.
3. Bogdan, A. V. (1977). Tropical pastures and fodder plants. Pp.475. Longman, London.
4. Bray, E. A. (2002). Classification of genes differentially expressed during water- deficit stress in Arabidopsis thaliana: an analysis using microarray and differential expression data. Ann. Bot. 89: 803-811.
5. Chaves,M. M., JV. Maroco, JS. Pereira. (2003) Understanding plant responses to drought: from genes to the whole plant. Funct. Plant Biol. 30: 239-264.
6. Dikshit, N., C.S. Mohanty, G. Katna, N. Sivaraj and A. B. Das (2014).Horse gram In: Mohar Singh, IS Bisht and M.Dutta edited book “Broadening the Genetic Base in Grain legumes”. Pp 209-215. DOI 10.1007/978-81-322-2023-7-10,@Springer India 2014.
7. Gopalan C, Ramashastri BV, Balasubramanyan SC. (1989). Nutritive value of Indian foods. National Institute of Nutration, ICMR, Hyderabad.
8. Ludwig, A., T. Romeis, J. D. Jones (2004). CDPK- mediated signaling pathways: specificity and cross talk. J. Exp. Bot. 55: 181-188.
9. Prakash, BG., Guled, MB. And Asha, MB. (2008). Identification of suitable horse gram varieties for northern dry zone of Karnataka. Karnataka J. Agri. Sci. 21: 343-345.
10. Prakash, BG., Channayya, P. Hiremath., Devarnavdgi, SB. and Salimath, PM. (2010). Assessment of genetic diversity among germplasm lines of horse gram (Macrotyloma uniflorum L.) at Bijapur. Electronic J. plant breeding. 1: 414-419.
11. Reddy, A. M., Kumar SG, Kumari GJ, Thimmanaik S, Sudhakar C (2005). Lead induced changes in antioxidant metabolism of horsegram (Macrotyloma uniflorum (Lam.) verdc.) and bengalgram (Cice rarietinum L.). Chemosphere 60: 97-104.
12. Reddy, P.S., Sudhakar C, Veeranjaneyulu K (1990). Water stressed induced changes in enzymes of nitrogen metabolism in horse gram. (Macrotylom auniflorum (Lam.) seedlings .Indian J Exp Biol. 28:273-276.
13. Shinozaki, K., K.Yamaguchi-Shinozaki (2000). Molecular responses to dehydration and low temperature: differences and cross-talk between two stress signaling pathways. Curr.Opin. Plant Biol. 3: 217-223.
14. Shinozaki, K., K.Yamaguchi-Shinozaki (2007). Gene networks involved in drought stress response and tolerance. J. Exp. Bot. 58: 221-227.
15. Shirsat, RK (2010). Induced mutations in horse gram: Mutagenic efficiency and effectiveness.Recent Res. Sci. Tech. 2: 20-23.
16. Sodani, S. N., Paliwal RV, Jain LK (2004). Phenotypic stability for seed yield in rainfed horse gram (Macrotyloma uniflorum (Lam.) Verdc.) In: Proceedings of the national symposium on arid legumes for sustainable agriculture and trade, Central Arid Zone Research Institute, Jodhpur, Rajasthan, India 5-7 Nov.
17. Somerville, C., J. Briscoe. Genetic engineering and water Science 292 (2000). 2217-2226.
18. Sudhakar, C, Bai, LS, Veeranjaneyulu K (1992). Lead tolerance of certain legume crops grown on lead oretailings. AgricEcosyst. Environ 41: 253-261.
19. Valliyodan, B., H. T. Nguyen. (2006). Understanding regulatory networks and engineering for enhanced drought tolerance in plants. Curr. Opin. Plant Biol. 2: 189-195.



About Author / Additional Info:
Currently I am working as Senior Scientist (Economic Botany & PGR) at ICAR- National Bureau of Plant Genetic Resources, Regional Station, Akola, Maharashtra, India in the field of Plant Genetic Resources, acquisition, characterization , maintenance, regeneration and conservation.