Genetic engineering of finger millet (Eleusine coracana) with aldose reductase gene isolated from Xerophyta viscosa to enhance drought and salinity tolerance

Abstract

Finger millet is chief food crop for millions of people in the world. It is ranked third in cereal production in semi-arid regions after sorghum and pearl millet. It is generally grown all over the world especially the developing countries with stable yield and strong adaptability to a number of agro-ecological environments. Despite its importance, finger millet increase in production is limited by abiotic stresses especially drought and salinity which affects the plant in the field during seed germination and early phases of seedling development. Unique plants such as Xerophyta viscosa, (a resurrection plant) that uses a number of physiological and molecular responses in order to survive under extreme stress conditions, are valuable sources of useful genes for crop improvement. Accordingly, XvAld1gene that encodes aldose reductase has previously been isolated from X. Viscosa under dehydration stress. The objective of this study was to establish a direct regeneration protocol of Kenyan finger millet varieties and develop transgenic drought and salinity tolerant finger millet plants expressing XvAld1 gene via Agrobacterium- mediated transformation. Six finger millet varieties GBK043137, GBK043128, GBK043124, GBK043122, GBK043094 and GBK043050 were used. As a prerequisite, a rapid and reproducible direct regeneration protocol was established using shoot apical meristems. The study established that the highest shoot induction was obtained in MS media supplemented with 1.75mg/l BAP while highest rooting events was obtained in MS media supplemented with 4.0 µM. In order to produce drought and salinity tolerant finger millet plants, XvAld1 gene controlled by stress-inducible XvPsap1 promoter was introduced into finger millet via Agrobacterium-mediated transformation and the transgenic events regenerated through direct organogenesis. The polymerase chain reaction (PCR) and the reverse transcription PCR (RT-PCR) confirmed the integration and the expression of XvAld1 gene with 1 positive event recorded in each finger millet line. In order to evaluate the drought and salinity tolerance, the rate of germination, number of green leaves and the total chlorophyll content of the transgenic compared to the wildtype plants was examined under simulated drought and salinity stress using mannitol and sodium chloride respectively. The study established that transgenic plants were more tolerant to drought and salinity stresses than the wildtype plants. The results of this study demonstrate a rapid, adoptable and effective system to transform and regenerate finger millet plant. Genetic enhancement of finger millet will improve yield and ensure food security even during crop failure due to hostile weather conditions associated with climate change.