Stress-induced expression of IPT gene in transgenic wheat reduces grain yield penalty under drought

Background The heterologous expression of isopentenyl transferase (IPT) under the transcriptional control of the senescence-associated receptor-like kinase (SARK) promoter delayed cellular senescence and, through it, increased drought tolerance in plants. To evaluate the effect of pSARK::IPT expression in bread wheat, six independent transgenic events were obtained through the biolistic method and evaluated transgene expression, phenology, grain yield and physiological biomass components in plants grown under both drought and well-irrigating conditions. Experiments were performed at different levels: (i) pots and (ii) microplots inside a biosafety greenhouse, as well as under (iii) field conditions. Results Two transgenic events, called TR1 and TR4, outperformed the wild-type control under drought conditions. Transgenic plants showed higher yield under both greenhouse and field conditions, which was positively correlated to grain number (given by more spikes and grains per spike) than wild type. Interestingly, this yield advantage of the transgenic events was observed under both drought and well-watered conditions. Conclusions The results obtained allow us to conclude that the SARK promoter-regulated expression of the IPT gene in bread wheat not only reduced the yield penalty produced by water stress but also led to improved productivity under well-watered conditions.

Genetic engineering of sweet potatoes (Ipomoea batatas) using isopentenyl transferase gene for enhanced drought tolerance

Nawiri SO, Oduor RO, Jalemba AM. 2017. Genetic engineering of sweet potatoes (Ipomoea batatas) using isopentenyl transferase gene for enhanced drought tolerance. Asian J Agric 1: 85-99. Approximately 70% of yield crop reduction worldwide is caused by drought. Due to severe drought which happened many times as a result of climate change, substantial yield deprivation is usual among the major cereals such as maize, wheat, and barley.. Therefore, drought tolerant crops that still yield amidst erratic climatic phenomenon are greatly needed. Due to its capability to produce high yield in a short period, sweet potato is suitable for cultivation in regions with limited or erratic rain water supply where other food crops cannot grow easily. Nevertheless, its sensitivity to water deficit may lead to the adverse crop growth and yield. By conventional hybridization method, sweet potato is tried to be improved, but it gives unsatisfied results due to its high male sterility, sexual incompatibility and hexaploid nature of its genome.The aim of this study, therefore, is to develop new varieties of sweet potato with improved tolerance to water-deficit stress for sustainable production of sweet potato under water-limited conditions. Three sweet potato genotypes: Jewel, Kemb36, and Ksp36 were transformed using isopentenyl transferase gene (IPT) that delays drought-induced senescence via up-regulation of cytokinin biosynthesis, under the control of a waterdeficit responsive and maturation specific promoter (PSARK). The PNOV-IPT gene construct was introduced into sweet potato to evaluate their transformability and regenerability. It is done 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 KSP36. Calli were cultured on media supplemented with various mannose concentrations to evaluate the suitability of mannose as a selectable marker for sweet potato, and it was figured out that 30 g/L concentration was optimal for selection of transformed events. At the time of PCR analysis, Jewel had the highest transformation efficiency followed by Kemb36. At the time for evaluation on drought tolerance under controlled conditions, the sweet potato showed delayed senescence and greater drought tolerance under water deficit conditions in the glasshouse. These plants exhibited better growth, higher yield, higher water status maintenance, higher chlorophyll content, and thus higher photosynthetic rates under reduced water conditions in comparison to wild-type. These results, therefore, indicated that expression of isopentenyl transferase gene in sweet potato 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.