African Journal of Biotechnology Vol. 10(55), pp. 11340-11344, 21 September, 2011 Available online at http://www.academicjournals.org/AJB ISSN 1684–5315 © 2011 Academic Journals Review Potentials of molecular based breeding to enhance drought tolerance in wheat (Triticum aestivum L.) Mueen Alam Khan1*, Muhammad Iqbal1, Moazzam Jameel1, Wajad Nazeer2, Sara Shakir1, Muhammad Tabish Aslam1 and Bushra Iqbal1 1 College of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur, Pakistan. 2 Cotton Research Station, Multan, Pakistan. Accepted 22 July, 2011 The ability of plant to sustain itself in limited water conditions is crucial in the world of agriculture. To breed for drought tolerance in wheat, it is essential to clearly understand drought tolerant mechanisms. Conventional breeding is time consuming and labor intensive being inefficient with low heritability traits like drought tolerance. Recent progress made in the field of genomics enabling us to access genes linked with drought tolerance has enhanced our understanding of this complex phenomenon. The purpose of this review paper was to briefly overview the accomplishments in molecular breeding for drought tolerance in wheat. Thus, by knowing the genetics of drought tolerance and identifying quantitative trait loci (QTLs) linked with DNA markers will help wheat breeders to develop high yielding drought tolerant cultivars. Key words: Triticum aestivum L, drought tolerance, QTLs, marker assisted selection (MAS). INTRODUCTON Wheat (Triticum aestivum L) is a cereal of choice in most countries of the world. Constant efforts are therefore needed to boost its production to keep the pace with ever increasing population. But unfortunately, these efforts are seriously being hampered by a number of abiotic stresses among which is drought (Boyer, 1982). According to Pfeiffer et al. (2005), 50% of wheat production area is affected due to drought worldwide. Drought leads to abnormal germination and poor crop stand (Harris et al., 2002; Kaya et al., 2006). Furthermore, drought prevailing at various critical growth stages like flowering and grain filling greatly reduce crop yield and due to that reason, its importance have been realized at the global level. Thus, developing drought resistant cultivars has been the objective of plant breeders and plant biotechnologists. Considerable efforts have been made in the past to develop drought tolerant cultivars of wheat through conventional breeding. But with little success due to quantitative (polygenic) nature of drought tolerance which *Corresponding author. E-mail: mueen_1981@yahoo.com Tel: +92-62-9255531. is more influenced by external environmental conditions than by the genetic component (El-Jaafari, 1999; Krishnamurthy et al., 1996; Ingrams and Bartels, 1996; Zhang, 2004). The recent progress in the field of genomics is astonishing providing breeders new tools for crop genetic improvement with reference to drought tolerance (Cattivelli et al., 2008) This review paper therefore analyses how genomic based approaches can contribute to the accelerating release of drought tolerant wheat cultivars. DROUGHT TOLERANT MECHANISMS Drought tolerance is the ability of plant to sustain itself in limited water supply (Ashley, 1993). As aforementioned, drought tolerance is a complex polygenic trait, therefore a number of factors come in to play making the plant to sustain drought. Drought affects the plant at the cellular, tissue and organ levels (Beck et al., 2007) and drought tolerant plants tackle the injurious effects of drought by initiating various defense mechanisms which should be understood in order to breed for drought tolerant cultivars Khan et al. (Chaves and Oliveira, 2004; Zhou et al., 2007). Drought tolerant mechanisms can be morphological, physiological or molecular (Bohnert et al., 1995; Farooq et al, 2009). Morphological mechanisms include; drought escape which is the ability of plant to complete its life cycle before the onset of drought season (Mitra, 2001), drought avoidance which is the plant’s ability to retain the water by increasing the uptake of water and reducing its loss through reduced transpiration which is made possible by long and thick root network as well as leaf and stomatal characteristics (Blum, 1988; Turner et al., 2001; Izanloo et al., 2008; Agbicodo et al., 2009). Among the physiological mechanisms, osmotic adjustment (OA) is perhaps the most crucial factor which allows the cell to decrease osmotic potential and maintain the turgor and the plant is able to sustain itself in decreased water supply (Blum, 2005; Farooq et al., 2009; Taiz and Zeiger, 2006). The role of abscisic acid (ABA) a stress hormone cannot be overlooked. Under water deficit environment, ABA induces the closure of stomata and thus reducing water transpiration (Turner et al. 2001). Glucousness (a waxy covering over the cuticle) is also considered to be a reliable parameter leading to increase in water use of efficiency in wheat plant thus providing a mechanism of drought tolerance (Richards et al; 1986). The molecular mechanisms involve activation of a cascade of genes which ultimately make the plant desiccation tolerant (Agarwal et al., 2006; Umezawa et al., 2006) 11341 MAPPING QTLS THROUGH MARKER ASSISTED SELECTION (MAS) IN WHEAT Marker assisted selection (MAS) refers to selection based on DNA markers linked to QTLs. The DNA markers are very powerful. Once these are identified, their mapping on the chromosome in relation to QTLs is carried out. Thus, presence of QTLs for drought tolerance can then be tracked by careful monitoring of these DNA markers (Thoday, 1961; Everson and Schaller, 1955). Various DNA markers like restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), and simple sequence repeat (SSR) have been used to tag QTLs for drought stress in wheat (Quarrie et al., 2005). Application of microsettalite markers in wheat for tagging QTLs for disease resistance, grain protein contents, and yield have also been documented by a number of scientists (Fahima et al., 1998; Huang et al., 2000; Del Blanco et al., 2003; Huang et al., 2003; Prasad et al., 2003). Kirigwi et al. (2007) used simple sequence repeat (SST)/expressed sequence tag (EST) marker for mapping QTL on chromosome 4A for grain yield and yield components in wheat. The markers associated with the QTL were XBE637912, Xwmc89, and Xwmc420. Thus, the DNA markers closely linked with QTLs conferring drought tolerance would greatly enhance the selection efficiency (Cattivelli et al., 2008). CANDIDATE GENES AND FUNCTIONAL GENOMICS MAPPING QTLS FOR DROUGHT TOLERANCE IN WHEAT As aforementioned, conventional breeding strategies like selection and hybridization have met with little success in breeding for drought tolerance in wheat. The genomic based approaches provide excellent opportunities to search and map quantitative trait loci (QTLs) for drought tolerance. This is due to our increased understanding of gene structure and function at the cellular and molecular level (Gosal et al., 2009). Various QTLs for drought tolerance in wheat are summarized in Table 1. Earlier, Quarrie et al. (2005) conducted mapping of QTLs for drought tolerance in hexaploid wheat which were located on chromosomes 1A, 1B, 2A, 2B, 2D, 3D, 5A, 5B, 7A, and 7B. Double haploid populations serve as a permanent source of mapping QTLs. Dashti et al. (2007) used 96 doubled haploid lines of wheat to analyze QTLs for drought tolerance. They found drought tolerant indices for QTL effects ranged from 13 to 36%. Recombinant inbred lines developed from crossing drought resistant and drought susceptible lines were used to produce mapping populations for QTL analysis regulating yield under drought (Tuberosa et al., 2002). A candidate gene is one which is associated with the function and development of any trait. There has been a growing interest to map and sequence the candidate genes with known or proposed function determining QTLs associated with drought tolerance (Byrne and McMullen, 1996; Gutterson and Zhang, 2004; Nguyen et al., 2004). The technologies of microarrays and DNA chips are being successfully employed to quickly monitor or predict the expression of millions of genes and search the genomes of target crops (Schena et al., 1996; Lemieux et al., 1998). The technology of microarray becomes more useful when coupled with EST analysis (Sreenivasulu et al., 2007). EST markers are available for rice and efforts for developing EST markers for wheat are in progress (Goff, 1999). In short a dedicated effort is what is required to isolate and develop EST markers for drought tolerance to be able to get full potential of microarray technology. TRANSGENIC DROUGHT TOLERANT WHEAT In recent years, introducing drought tolerant genes from different sources into drought susceptible plants has 11342 Afr. J. Biotechnol. Table 1. Summary of QTLs associated with drought tolerance in wheata QTL Mapping DHL* RIL* Number of QTL 1 1 Yield interaction with water supply and hot conditions DHL 1 Kuchel et al. (2007) Durum x Wild emmer Various morphophysiological traits RIL many Peleg et al. (2009) Seri M82 x Babax Various productivity and physiological traits RIL many McIntyre et al. 2010; Suzuky Pinto et al., 2010. Cross Trait Chinese Spring x Ciano 67 Songlen x Cobdor 4/3Ag14 ABA concentration Osmoregulation under drought Trident x Molineux Reference Quarrie et al. (1994) Morgan and Tan (1996) a *DHL= doubled haploid; RIL= recombinant inbred lines; Similar studies reported in the text were not included in this table. Table 2. List of recently produced transgenic wheat with drought tolerant genes. Gene DREB1A HVA1 mtlD P5CS TaLTP1 Mechanism of tolerance Regulatory control Protective proteins Mannitol as osmoprotectant Osmoprotectant Lipid transfer protein become one of the promising avenues for plant genetic engineers. A transgenic approach involves the structural modification in traits by transferring genes from one species to another (Ashraf, 2010). A number of genes conferring drought tolerance from different sources have been incorporated in wheat making it transgenic (Table 2). Most of these transgenic lines have been tested in the laboratory. Their full scale utilization in the field would provide important information for continued exploitation of transgenic work. Nonetheless it is expected that transgenic approach will have an increased role in the future as far as the mapping and engineering of QTLs for drought tolerance is concerned (Cattivelli et al., 2008; Ashraf, 2010). CONCLUSION Drought is a major cause of yield losses of wheat in the world. Applications of conventional selection based breeding are limited due to complex nature of drought stress and drought tolerance. The molecular based tools would ultimately help us to identify potential candidate genes and valuable QTLs for drought tolerance and their effective utility in marker assisted breeding (Tuberosa Reference Pellegrineschi et al. (2004). Sivamani et al., 2000; Bahieldin et al., 2005 Abebe et al. (2003) Kavi Kishor et al., 1995; Sawahel and Hassan, 2002; Jang et al. (2004). and Silvio, 2006; Taishi et al., 2006; Fleury et al., 2010). The integration of these novel approaches with conventional system of crop genetic improvement should provide exciting results to breed for drought tolerance in wheat in the near future (Khan and Iqbal, 2011). REFERENCES Abebe T, Guenzi AC, Martin, B, Chushman, JC (2003). Tolerance of mannitol-accumulating transgenic wheat to water stress and salinity. Plant Physiol., 131: 1748-1755. Agarwal PK, Agarwal P, Reddy MK, Sopory SK (2006). Role of DREB transcription factors in abiotic and biotic stress tolerance in plants. Plant Cell Rep., 25: 1263-1274. Agbicodo EM, Fatokun, ECA, Muranaka ES, Visser RGF, Linden van der CG (2009). Breeding drought tolerant cowpea: constraints, accomplishments, and future prospects. Euphytica, 167: 353-370. Ashley J (1993). Drought and crop adaptation. In: Rowland JRJ (ed) Dryland farming in Africa. Macmillan Press Ltd, UK, pp. 46-67. Ashraf M (2010). Inducing drought tolerance in plants: recent advances. Biotechnol. Adv., 28(1):169-183. Bahieldin A, Mahfouz HT, Eissa HF, Saleh OM, Ramadan AM, Ahmed IA, Dyer WE, El-Itriby HA, Madkour MA (2005). Field evaluation of transgenic wheat plants stably expressing the HVA1 gene for drought tolerance. Physiol. Plant, 123: 421-427. Beck EH, Fettig S, Knake C, Hartig K, Bhattarai T (2007). Specific and unspecific responses of plants to cold and drought stress. J. Biosci., 32: 501-510. Blum A (1988). Plant breeding for stress environments. CRC Press Inc., Boca Raton, Florida, USA. Khan et al. Blum A (2005). Drought resistance, water use efficiency and yield potential- are they compatible, dissonant, or mutually exclusive? Aust. J. Agric. Res., 56: 1159-11680. Bohnert HJ, Nelson DE, Jensen RG (1995). Adaptations to environmental stresses. Plant Cell, 7: 1099-1111. Boyer JS (1982). Plant productivity and environment. Science, 218: 443-448. Byrne PF, McMullen MD (1996). Defining genes for agricultural traits: QTL analysis and the candidate gene approach. Probe, 7: 24-27. Cattivelli L, Rizza F, Badeck FW, Mazzucotelli E, Mastrangelo AM, Francia E, Mare C, Tondelli A, Stanca AM (2008) Drought tolerance improvement in crop plants: An integrative view from breeding to genomics. Field Crop. Res., 105: 1-14. Chaves MM, Oliveira MM (2004) Mechanisms underlying plant resilience to water deficits: prospects for water-saving agriculture, J. Exp. Bot. 55: 2365–2384. Dashti H, Yazdi-samadi B, Ghannadha M, Naghavi MR, Quarri S (2007). QTL analysis for drought resistance in wheat using doubled haploid lines. Int. J. Agric. Biol. 9(1): 98-102. Del Blanco IA, Frohberg RC, Stack RW, Berzonsky WA, Kianian SF (2003). Detection of QTL linked to Fusarium head blight resistance in Sumai 3-derived North Dakota bread wheat lines. Theor. Appl. Genet., 106: 1027-1031. El Jaafari S (1999). Morphophysiological tools for cereals breeding for abiotic stresses resistance. In: The Fourth International Crop Science Conference for Africa Sustainable Crop Production: Management, Protection, and Rehabilitation, 11-14 October 1999, Casablanca, Morocco. Everson E, Schaller CW (1955). The genetics of yield differences associated with awn barbing in the barley hybrid (‘Lion’ x ‘Atlas 10’) x ‘Atlas’. Agron. J., 47: 276-280. Fahima T, Röder MS, Grama A, Nevo E (1998). Microsatellite DNA polymorphism divergence in Triticum dicoccoides accessions highly resistant to yellow rust. Theor. Appl. Genet., 96: 187-195. Farooq M, Wahid A, Kobayashi N, Fujita D, Basra SMA (2009). Plant drought stress: effects, mechanisms and management Agron. Sustain. Dev., 29: 185–212. Fleury D, Stephen Jefferies S, Kuchel H, Langridge P (2010). Genetic and genomic tools to improve drought tolerance in wheat. J. Exp. Bot. 61(12): 3199-3210. Goff SA (1999). Rice as a model for cereal genomics, Curr. Opin. Plant Biol., 2: 86–89. Gosal SS, Wani SH, Kang MS (2009). Biotechnology and Drought Tolerance. J. Crop Improvement, 23: 19–54. Gutterson N, Zhang JZ (2004). Genomics applications to biotech traits: A revolution in progress? Curr. Opin. Plant Biol., 7: 226–230. Harris D, Tripathi RS, Joshi A (2002). On-farm seed priming to improve crop establishment and yield in dry direct-seeded rice, in: Pandey S, Mortimer M, Wade L, Tuong TP, Lopes K, Hardy B (Eds.), Direct seeding: Research Strategies and Opportunities, International Research Institute, Manila, Philippines, pp. 231–240 Huang XQ, Hsam SLK, Zeller FJ, Wenzel G, Mohler V (2000). Molecular mapping of the wheat powdery mildew resistance gene Pm24 and marker validation for molecular breeding. Theor. Appl. Genet., 101: 407-414. Huang XQ, Wang, LX, Xu MX, Röder MS (2003). Microsatellite mapping of the powdery mildew resistance gene Pm5e in common wheat (Triticum aestivum L.). Theor. Appl. Genet. 106: 858-865. Ingram J, Bartels D (1996). The molecular basis of dehydration tolerance in plants. Annual review of Plant Physiology. Plant Mol. Biol., 47: 377-403. Izanloo A, Condon AG, Langridge P, Tester M, Schnurbusch T (2008). Different mechanisms of adaptation to cyclic water stress in two South Australian bread wheat cultivars. J. Exp. Bot., 59(12): 3327– 3346. Jang CS, Lee HJ, Chang SJ, Seo YW (2004). Expression and promoter analysis of the TaLTP1 gene induced by drought and salt stress in wheat (Triticum aestivum L.). Plant Sci., 167: 995–1001 Kavi KPB, Hong Z, Miao GH, Hu CAA, Verma DPS (1995). Overexpression of d-pyrroline-5-carboxylate synthetase increases praline production and confers osmotolerance in transgenic plants. Plant Physiol., 25: 1387–1394. 11343 Kaya MD, Okçub G, Ataka M, Çıkılıc Y, Kolsarıcıa Ö (2006). Seed treatments to overcome salt and drought stress during germination in sunflower (Helianthus annuus L.). Eur. J. Agron., 24: 291-295. Kirigwi FM, Van Ginkel M, Brown-Guedira G, Gill BS, Paulsen GM, Fritz AK (2007). Markers associated with a QTL for grain yield in wheat under drought, Mol. Breed., 20: 401–413. Khan MA, Iqbal M (2011). Breeding for drought tolerance in wheat (Triticum aestivum L.): constraints and future prospects. Front. Agric. China, 5(1): 31–34. DOI 10.1007/s11703-010-1054-2. Krishnamurthy LC, Johansen C, Ito O (1996). Genotypic variation in root system development and its implication for drought resistance in Chickpea. In: Ito O, Johansen C, Adu-Gyamfi JJ, Katayama K, Kumar Rao JVK, Rego TJ (eds) Roots and nitrogen in cropping systems of the semiarid tropics. JIRCAS and ICRISAT, Hyderabad, pp. 235-250. Kuchel H, Williams K, Langridge P, Eagles HA, Jefferies SP (2007). Genetic dissection of grain yield in bread wheat. II. QTL-byenvironment interaction. Theor. Appl. Genet. 115: 1015-1027. Lemieux B, Aharoni A, Schena M (1998). Overview of DNA chip technology. Mol. Breed., 4: 277–289. McIntyre CL, Mathews Ky L, Rattey A, Chapman SC, Drenth J, Ghaderi M, Reynolds M, Shorter R (2010). Molecular detection of genomic regions associated with grain yield and yield-related components in an elite bread wheat cross evaluated under irrigated and rainfed conditions. Theor. Appl. Genet., 120: 527-541 Mitra J (2001). Genetics and genetic improvement of drought resistance of crop plants. Curr. Sci., 80: 758–763. Morgan JM, Tan MK (1996). Chromosomal location of a wheat osmoregulation gene using RFLP analysis. Aust. J. Plant Physiol., 23: 803-806. Nguyen TTT, Klueva N, Chamareck V, Aarti A, Magpantay G, Millena ACM, Pathan MS, Nguyen HT (2004). Saturation mapping of QTL regions and identification of putative candidate genes for drought tolerance in rice. Mol. Genet. Genomics, 272: 35-46 Peleg Z, Fahima T, Krugman T, Abbo S, Yakir D, Korol AB, Saranga Y (2009). Genomic dissection of drought resistance in durum wheat x wild emmer wheat recombinant inbreed line population. Plant Cell Environ.32: 758-779. Pellegrineschi A, Reynolds M, Paceco M, Brito RM, Almeraya R, Yamaguchi-Shinozaki K, Hoisington D (2004). Stress-induced expression in wheat of the Arabidopsis thaliana DREB1A gene delays water stress symptoms under greenhouse conditions. Genome, 47: 493-500. Pfeiffer WH, Trethowan RM, Van Ginkel M, Ortiz MI, Rajaram S (2005) Breeding for abiotic stress tolerance in wheat. In Abiotic Stresses: Plant Resistance through Breeding and Molecular Approaches (eds Ashraf M & Harris PJC), The Haworth Press, New York, NY, USA, pp. 401-489. Prasad M, Kumar N, Kulwal PL, Röder MS, Balyan HS, Dhaliwal HS, Gupta PK (2003). QTL analysis for grain protein content using SSR markers and validation studies using NILs in bread wheat. Theor. Appl. Genet., 106: 659-667. Quarrie SA, Gulli M, Calestani C, Steed A, Marmaroli N (1994). Location of a gene regulating drought-induced abscisic acid production on the long arm of chromosome 5A of wheat. Theor. Appl. Genet., 89: 794-800. Quarrie SA, Steed A, Calestani C, Semikhodskii A, Lebreton C, Chinoy C, Steele N, Pljevljakusic D, Waterman E, Weyen J, Schondelmaier J, Habash DZ, Farmer P, Saker L, Clarkson DT, Abugalieva A, the Yessimbekova M, Turuspekov Y, Abugalieva S, Tuberosa R, Sanguineti MC, Hollington PA, Aragues R, Royo R, Dodig D (2005). A high-density genetic map of hexaploid wheat (Triticum aestivum L.) from cross Chinese Spring x SQ1 and its use to compare QTLs for grain yield across a range of environments. Theor. Appl. Genet., 110: 865-880. Richards RA, Rawson HM, Johnson DA (1986). Glaucousness in wheat: Its development and effect on water-use efficiency, gas exchange and photosynthetic tissue temperatures. Aust. J. Plant Physiol., 13: 465-473. Sawahel WA, Hassan AH (2002). Generation of transgenic wheat plants producing high levels of the osmoprotectant proline. Biotechnol. Lett., 24: 721-725. Schena MD, Shalon D, Heller R, Chai A, Brown PO, Davis RW (1996). 11344 Afr. J. Biotechnol. Parallel human genome analysis: microarray-based expression monitoring of 1000 genes. Proc. Natl. Acad. Sci. USA, 93: 1061410619. Sivamani E, Bahieldin A, Wraith JM, Al-Niemi T, Dyer, WE, Ho THD, Qu R (2000). Improved biomass productivity and water use efficiency under water deficit conditions in transgenic wheat constitutively expressing the barley HVA1 gene, Plant Sci.,155: 1–9. Sreenivasulu N, Sopory SK, Kishor PBK (2007). Deciphering the regulatory mechanisms of abiotic stress tolerance in plants by genomic approaches. Gene, 388: 1-13. Suzuky PR, Reynolds MP, Mathews KYL, Lynne McIntyre C, Juan-Jose Olivares-Villegas, Chapman SC (2010). Heat and drought adaptive QTL in a wheat population designed to minimize confounding agronomic effects. Theor. Appl. Genet., 121: 1001-1021. Taishi U, Fujita M, Fujita Y, Kazuko YS, Kazuo S (2006). Engineering drought tolerance in plants: discovering and tailoring genes to unlock the future. Curr. Opin. Biotechnol. 17: 113-122. Taiz L, Zeiger E (2006) Plant Physiology, 4th Ed., Sinauer Associates Inc. Publishers, Massachusetts. Thoday JM (1961). Location of polygenes. Nature, 191: 368-370. Tuberosa R, Silvio S (2006). Genomics-based approaches to improve drought tolerance of crops. Trends Plant Sci., 11: 405-412. Tuberosa R, Salvi S, Sanguineti MC, Landi P, Maccaferri M, Conti S (2002). Mapping QTLs regulating morpho-physiological traits and yield: Case studies, shortcomings and perspectives in drought stressed maize. Ann. Bot., 89: 941-963 Turner NC, Wright GC, Siddique KHM (2001). Adaptation of grain legumes (pulses) to water-limited environments, Adv. Agron., 71: 123-231. Umezawa T, Fujita M, Fujita Y, Yamguchi-Shinozaki K and Shinozaki K (2006). Engineering drought tolerance in plants: discovering and tailoring genes to unlock the future. Curr. Opin. Biotechnol., 17: 113122 Zhang JZ (2004). From laboratory to field. Using information from Arabidopsis to engineer salt, cold, and drought tolerance in crops. Plant Physiol., 135: 615-621. Zhou Y, Lam HM, Zhang J (2007). Inhibition of photosynthesis and energy dissipation induced by water and high light stresses in rice. J. Exp. Bot., 58: 1207-1217.