Dioscorea composita WRKY3 positively regulates salt-stress tolerance in transgenic Arabidopsis thaliana

Dioscorea composita (D. composita) is a perennial dioecious herb with strong biotic and abiotic stress tolerance. However, what roles WRKY transcription factors might play in regulating abiotic stress responses in this medicinal plant is unknown. Here, we isolated DcWRKY3 from D. composita and analyzed its role in stress tolerance. DcWRKY3 is a group I WRKY transcription factor that localized to the nucleus and specifically bound to the W-box cis-elements, but lacked transcriptional activation activity in yeast cells. The expression of DcWRKY3 was strongly affected by salt stress. The heterologous expression of DcWRKY3 strongly enhanced the seed germination rate and root length of Arabidopsis thaliana under salt stress. The DcWRKY3-expressing transgenic lines (DcWRKY3-OEs) also showed higher proline content and antioxidant enzyme activity but lower malondialdehyde and reactive oxygen (ROS) levels compared with the wild type. Moreover, these plants showed upregulated expression of genes related to the salt-stress response and ROS clearance. These findings indicate that DcWRKY3 plays a positive role in the salt-stress response by improving the ROS scavenging ability and maintaining the balance of osmotic pressure in plants. Further studies showed that DcWRKY3 binds to the promoter of AtP5CS1, but not AtSOD and AtRD22, suggesting that DcWRKY3 improves salt tolerance in plants by directly or indirectly regulating the expression of downstream genes. This functional characterization of DcWRKY3 provides new insight into the molecular mechanism underlying the response of D. composita to salt stress.