GsCLC-c2 from wild soybean confers chloride/salt tolerance to transgenic Arabidopsis and soybean composite plants by regulating anion homeostasis

The responses of the GsCLC-c2 gene and its promoter to NaCl stress, as well as the Cl-/salt tolerance of GsCLC-c2-transgenic Arabidopsis and overexpressed or RNAi wild soybean hairy root composite plants, were investigated. Results showed that both GsCLC-c2 and its promoter display enhanced induction under salt stress. In the transgenic Arabidopsis WT-GsCLC-c2 and atclc-c-GsCLC-c2 seedlings, the salt-induced growth reduction was markedly ameliorated; plant fresh weight, leaf area, and relative water content (RWC) increased; relative electrolytic leakage (REL), and malondialdehyde (MDA) content in shoots decreased significantly. In addition, accumulation of Cl- and K+, especially Cl-, increased markedly in roots to minimize Cl- transport to shoots and maintain higher and lower Cl-/NO3- ratios in roots and shoots, respectively. When compared to GsCLC-c2-RNAi wild soybean composite plants under salt stress, clear advantages, such as growth appearance, plant height, and leaf area, were displayed by GsCLC-c2-overexpressing composite plants. Moreover, their REL values in roots and leaves declined significantly. The accumulation of absorbed Cl- and Na+ in the roots increased, as the transportation to the stems and leaves decreased, the NO3- content in roots, stems, and leaves significantly increased, and the changes in K+ contents were small, which resulted in the maintenance of a low Cl-/NO3- ratio in all plant parts and low Na+/K+ ratio in stems and leaves. Taken together, these results highlight the role of GsCLC-c2 in regulating anionic homeostasis in NaCl-stressed transgenic Arabidopsis and soybean composite plants to maintain lower Cl-/NO3- ratios in shoots, thus conferring enhanced Cl-/salt tolerance.