Okra WRKY Transcription Factor AeWRKY32 and AeWRKY70 Are Involved in Salt Stress Response

Soil salinization is one of the abiotic stresses that inhibit plant growth and development, which seriously restricts global crop production. WRKY transcription factors play an important role in regulating plant responses to stress such as salt stress. In our previous study, two WRKY family genes from okra, <i>AeWRKY32</i> and <i>AeWRKY70</i>, were significantly up-regulated and down-regulated, respectively, in response to salt stress. In this study, subcellular localization showed that they were localized to the nucleus. The down-regulation of <i>AeWRKY32</i> and <i>AeWRKY70</i> via whole plant virus-induced gene silencing (VIGS) increased and decreased plant sensitivity to salt stress, respectively. Ectopic expression of <i>AeWRKY32</i> and <i>AeWRKY70</i> led to promoted and reduced salt tolerance in transgenic <i>Arabidopsis</i>, respectively. There was no significant difference between transgenic plants and wild type (WT) without salt treatment. Salt stress significantly inhibited plant growth. The decrease of chlorophyll content and the increase of anthocyanin content in <i>AeWRKY32</i>-overexpressed transgenic plants were lower than those in the WT, while <i>AeWRKY70</i>-overexpressed plants had the opposite effect. Under salt stress, the <i>AeWRKY70</i>-overexpressed plants had the highest malondialdehyde (MDA) content, followed by the WT, and the lowest in <i>AeWRKY32</i>-overexpressed plants. The hydrogen peroxide (H₂O₂) content and superoxide anion (O₂^•-) generation rate were only slightly increased. Moreover, salt stress significantly increased plant proline content and antioxidant enzyme activities, which was highest in <i>AeWRKY70</i>-overexpressed plants except superoxide dismutase (SOD). Taken together, these results suggest that AeWRKY32 and AeWRKY70 play positive and negative roles in plant in response to salt stress, respectively.