Improvement in drought tolerance and biomass of transgenic wheat ectopically expressing E.coli glutamate dehydrogenase (gdhA) gene

Abstract

Drought stress is the major limiting environmental factor in wheat yield. It is thought to be the most crucial factor that hinders crop productivity and poses problems to meet the increasing food demands. So, need is to develop drought tolerant and high yielding varieties to feed the ever increasing population. Wheat is highly calcitrant and poor responsive to tissue culture like other cereal crops. Recent study was conducted with the aims to establish an efficient regeneration protocol for development of transgenic wheat with improved drought tolerance and increased biomass. gdhA is a multifunctional gene reported to improve nitrogen and carbon metabolism, drought and herbicide tolerance and biomass. Regeneration protocol for wheat commercial cultivar Faisalabad-2008 was optimized using different combinations of 2,4-D, carbon source and age of calli. Better regeneratuion response was observed in 3 weeks old calli using 2 mg/L 2,4-D and maltose as carbon source. gdhA of E. coli was transformed using Agrobacterium mediated transformation method. Drought tolerance of putative transgenics calli was evaluated in vitro using different levels of PEG6000. Molecular analysis for presence and expression of transgene was performed. Transgenics alongwith control plants were subjected to different levels of drought stress. Transgenic plants showed 6.2, 13 and 10.1% more RWC and 5.6, 13.4 and 15.4% less saturation water deficit than control plants at moderate, medium, and high level of drought stress respectively. gdhA transgenic plants also showed 10.8% more excised leaf water retention and quick recovery from drought than non-transgenic controls. About 52.2 and 29.73% and 16.47 % more chlorophyll a, b and X+C contents were estimated in transgenic plants than controls. Effect of different levels of drought stress on plant pigments was also measured. Non-transgenic control plants showed 5.71, 20.39 and 15.89% more decrease in chlorophyll A and B contents at medium, mild and high level of drought stress. In control plants 44.74 and 67.39 % more increase in X+C contents in comparison to transgenics at low and medium level of drought stress while 70.98 % decrease was estimated at high level of drought stress. Regarding biomass related parameters were studied. Transgenic plants showed 10, 8.39, 9.69 and 8.02 % increase in number of fertile tillers, spikelets/spike, grains/spike and 1000 grain weight respectively than non-transgenic control plants. The ectopic expression of gdhA gene in transgenic plants resulted in improved drought tolerance and biomass.