Expression of wheat expansin driven by the RD29 promoter in tobacco confers water-stress tolerance without impacting growth and development.

Expansins are the key regulators of cell wall extension during plant growth. Previously, we produced transgenic tobacco plants with increased tolerance to water stress by overexpressing the wheat expansin gene TaEXPB23 driven by the constitutive 35S cauliflower mosaic virus (CaMV) promoter. However, the growth and development of 35S::TaEXPB23 transgenic tobacco plants were altered under normal growth conditions, with a faster growth rate at the seedling stage, earlier flowering and maturation, and a shorter plant height compared to WT. In the current study, we determined that cellular characteristics and carbohydrate metabolism were altered in 35S::TaEXPB23 transgenic tobacco plants. We also generated transgenic Arabidopsis plants using the same vector. The transgenic Arabidopsis plants had the same phenotype as the transgenic tobacco plants, which may have resulted from the altered expression of several flowering-related genes. We then produced TaEXPB23 transgenic tobacco plants using the stress-inducible RD29A promoter. The use of this promoter reduced the negative effects of TaEXPB23 on plant growth and development. The RD29A::TaEXPB23 transgenic tobacco plants had greater tolerance to water stress than WT, as determined by examining physiological and biochemical parameters. Therefore, the use of stress-inducible promoters, such as RD29A, may minimize the negative effects of constitutive transgene expression and improve the water-stress tolerance of plants.