Genetic transformation of tropical maize inbred lines using aldose reductase (ald1) gene for enhancement of drought tolerance
Luasi, Wycliffe Wanjala
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Maize is a cereal crop that is grown widely throughout the world in a range of agro-ecological environments. Maize is ranked third after wheat and rice in terms of production and is a staple food in many regions of the world. However, maize yields in the sub Saharan Africa, will decrease due to drought as majority of farmers in this region depend on rain-fed farming. As such, the future of maize production and livelihoods of a great population of smallholder farmers in this region of climate vulnerability, are based to a great extent on access to climate resilient cultivars. Researchers are working on the development of maize that can tolerate the effects of drought. Conventional breeding has been used in the development of drought tolerant crops but often brings along undesirable agronomic characteristics from the donor parents hence, genetic engineering by identifying and inserting genes only involved in stress tolerance in plants is being explored to complement efforts of this classical approach of improving crop varieties. The Xerophyta viscosa aldose reductase (XvALDI) gene isolated from the resurrection plant Xerophyta viscosa has been postulated to be involved in the synthesis of osmoprotectants and in the maintaining of the structural integrity of macromolecules under abiotic stress. Over-expression of XvALDI gene in model plants has been shown to increase drought tolerance. In this study, the gene construct with its T-DNA harboring XvALDlgene driven by a stress inducible plant promoter, XvPSAP 1 and phosphomannose-isomerase gene as a selectable marker was used to transform CML 144 and CML 216 maize inbred lines through Agrobacterium-mediated transformation. Putatively transformed calli were selected on selection medium containing 5g/1 mannose supplemented with 25g/1 sucrose. The surviving putative transformed events were regenerated to whole plants. The resultant putative transgenic maize plants were analysed by PCR and detected presence of XvALDIgene and the XvPSAPI in three events of CML 144 maize line. The transformation frequencies of 41.3% and 39.7% for CML 144 and CML 216 were obtained, respectively. One way ANOV A analysis at 95% confidence interval, indicated that CML 144 and CML 216 had no significant difference in transformation frequency and regeneration frequency. Further molecular analysis and drought stress assay is recommended, before any potential application of XvALDI gene either singly or in combination for maize drought tolerance.