Genetic engineering of soybean using candidate genes to improve drought tolerance
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Drought is one of the major abiotic stresses which affect productivity in soybean. Plants respond and adapt to drought stress through various biochemical and physiological processes, and they induce several stress-responsive genes including osmolyte biosynthesis genes and transcription factors. To date, most of the abiotic stress-related genes have been constitutively expressed. Constitutive overexpression of a transgene requires additional building blocks and energy, which may affect the normal growth of transgenic plants. The use of stress-inducible promoters can help express the gene under stress conditions and can also protect transgenic plants from growth suppression under non-stress conditions. Arabidopsis thaliana dehydration response element binding transcription factor (DREB1D) and three osmolyte genes driven by a constitutive, ABAinducible and stress-inducible promoters were introduced in soybean through Agrobacterium tumefaciens-mediated gene transfer. Several transgenic lines were generated and molecular analysis was performed to confirm transgene integration. Transgenic plants overexpressing the AtDREB1D transcription factor showed reduced total leaf area and shoot biomass compared to non-transgenic plants under well-watered conditions. No significant difference in root length or root biomass was observed between transgenic and nontransgenic plants under well-watered conditions. When subjected to gradual water-deficit, transgenic plants maintained higher relative water content because the transgenic lines used water more slowly due to reduced total leaf area, which caused them to wilt slowler than nontransgenic plants. The transgenic plants showed improved drought tolerance by maintaining 17- 24% higher leaf cell membrane stability compared to non-transgenic plants. The results demonstrate the feasibility of engineering soybean for increased drought tolerance by expressing stress-responsive genes.
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