Genetic engineering of sweetpotatoes (Ipomoea batata (L.) LAM) using isopentenyltransferase gene for enhanced drought tolerance
Nawiri, Sylvia Obinda
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Drought adversely affects crop production worldwide leading to approximately 70% of yield reduction. Significant yield loss is common among the major cereals such as maize, wheat and barley due to frequent and severe drought as a result of climate change. Therefore, there is a great need for drought tolerant or escaping crops that still yield amidst erratic climatic manifestation. Sweetpotato is capable of producing high yield in a short period of time making it suitable for cultivation in regions with limited or erratic rain water supply where other food crops grow with difficulty. However, it is sensitive to water deficit which adversely affects crop growth and yield. Sweetpotato improvement by conventional hybridization is limited because of its high male sterility, sexual incompatibility and hexaploid nature of its genome. This study therefore aimed at developing sweetpotato varieties with improved tolerance to water-deficit stress for sustainable production under water-limited conditions. Three sweetpotato genotypes: Jewel, Kemb36 and Ksp36 were transformed using isopentenyltransferase gene (IPT) that delays drought-induced senescence via up-regulation of cytokinin biosynthesis, under the control of a water-deficit responsive and maturation specific promoter (PSARK). To evaluate their transformability and regenerability, the PNOV-IPT gene construct was introduced into sweetpotato via Agrobacterium tumefaciens strain EHA101 and the plants subsequently regenerated via somatic embryogenesis. Jewel genotype recorded the highest transformation and regeneration frequency followed by Kemb36 and finally KSP36. To evaluate the suitability of mannose as a selectable marker for sweetpotato, calli were cultured on media supplemented with various mannose concentrations where 30g/L concentration was found to be optimal for selection of transformed events. The transgenic plants when analyzed via PCR, Jewel had the highest transformation efficiency followed by Kemb36. When transgenic sweetpotato plants were evaluated for drought tolerance under controlled conditions, they displayed delayed senescence and greater drought tolerance under water deficit conditions in the glasshouse. These plants exhibited better growth, higher yield, maintained higher water status, chlorophyll content, and thus higher photosynthetic rates under reduced water conditions in comparison to wild-type. These results therefore indicate that expression of isopentenyltransferase gene in sweetpotato significantly improves drought tolerance. Therefore, IPT gene should be used to transform other economically important food crops to delay drought induced senescence and enhance drought tolerance.