Increased salt stress tolerance and modified sugar content of bread wheat stably expressing the mtlD gene

Abstract

The bacterial E. coli mtlD gene (encoding mannitol-1-phosphate dehydrogenase) under the control of maize ubiquitin promoter was used in transforming bread wheat cv. Giza 163 via biolistic device. The presence and expression of the transgene in two selected T0 transgenic lines were confirmed at the molecular level. The tolerance of transgenic T<inf>2</inf> families to salt (8 g/l, 3 NaCl: 1 CaCl<inf>2</inf>) stress was evaluated at the greenhouse over two consecutive seasons. In either season, grain yield per plant of transgenic family 235/3 was significantly the highest under salt stress, while that of the wild-type control was the lowest. These results coincided with the rate of mtlD transgene expression of the two T<inf>1</inf> transgenic lines. The results of mean total biomass per plant and plant height perfectly contradicted those of grain yield per plant across treatment and seasons. Differences in total seed storage protein concentrations among different genotypes were non-significant within or across environmental conditions. Mannitol was detected in grains and plantlets of the two transgenic families. The soluble sugars significantly increased in the transgenic plantlets and grains as compared to the wild-type control. On the contrary, the total sugar level significantly decreased in the transgenic plantlets. Fructose, glucose and galactronic acid highly increased in the transgenic plantlets and grains, while sorbitol, mannose and galactose decreased. In conclusion, the results indicated that mtlD gene confers salt stress protection in transgenic wheat through the induction of mannitol and reducing sugars accumulation in plant tissues.