Overexpression of Glycine soja WRKY20 enhances drought tolerance and improves plant yields under drought stress in transgenic soybean

Drought stress is a major constraint to the production and yield stability of soybean ( Glycine max L. Merrill). Transgenic breeding offers new opportunities for developing drought-resistant varieties. However, soybean is much more difficult to transform than other species; so in our previous studies, several drought-related genes, which were identified from the transcriptome profiles of Glycine soja , were first heterologous expressed in Arabidopsis or alfalfa ( Medicago sativa L. ) for function characterization. Among these genes, GsWRKY20 shows effective roles in drought tolerance. In this study, to breed high drought-tolerant soybean cultivar, GsWRKY20 was overexpressed in soybean under the control of the cauliflower mosaic virus 35S promoter. We found that transgenic soybean overexpressing GsWRKY20 showed greatly enhanced tolerance to drought stress compared with the non-transformed plants. Under drought stress conditions, lower relative membrane permeability and malondialdehyde (MDA) content were observed in transgenic soybean, indicating a less degree of membrane injury of transgenic plants. Higher antioxidant enzyme activity and more free proline content were observed in transgenic soybean, which help plants to resist drought stress. GsWRKY20 overexpressing soybean plants have lower stomatal density, faster stomatal closure and so exhibited lower stomatal conductance, which reduced water loss under drought stress conditions. GsWRKY20 overexpressing soybean plants exhibited higher yields under drought stress conditions, with higher plant height, longer root, and higher seed yield at the adult developmental stage. In conclusion, the transgenic soybean generated in this study could be used for farming in arid and semi-arid areas that are prone to extremely severe drought stress.