The transcription factor ThDof8 binds to a novel cis-element and mediates molecular response to salt stress in Tamarix hispida.

Salt stress is a commom abiotic factor that restricts plant growth and development. As a halophyte plant, it is of great significance to explore the salt tolerance genes and regulatory mechanisms of Tamarix hispida. Dof (DNA-bining with one finger), as an important transcription factor (TF), influences and controls various signaling substances involved in diverse biological processes related to plant growth and development. However, the regulatory mechanisms of Dof TFs, in response to salt stress, are largely unknown in T. hispida. In the present study, ThDof8, a new Dof gene, was cloned from T. hispida, and ThDof8 gene expression was induced by salt stress. Transient overexpression of the ThDof8 enhanced T. hispida salt tolerance by enhancing proline levels, and the activities of antioxidant enzymes, superoxide dismutase (SOD) and peroxidase (POD). These results were also verified in stably transformed Arabidopsis thaliana. The results of a TF-Centered Yeast One-Hybrid (TF-centered Y1H) assay and electrophoretic mobility shift assay (EMSA) showed that ThDof8 bound to a new cis-element (TGCG). Expression profile gene chip analysis identified four potential direct gene targets of ThDof8, CRK10, CRK26, GAD41 and GAD42, which were also verified by chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR), EMSA, yeast one hybrid (Y1H) assays, and beta-glucuronidase (GUS) enzyme activity assays. ThDof8 can bind to the TGCG element in the promoter regions of downstream target genes. Transient overexpression of ThCRK10 also enhanced T. hispida salt tolerance. In brief, a new regulatory mechanism model of ThDof8 was founded that ThDof8 binds to the TGCG cis-element in the promoter of the downstream gene CRK10 to regulate its expression and improve salt tolerance in T. hispida. This study provides a basis for further understanding the role of the Dof TFs and identifying other downstream candidate genes for improving plant salt tolerance via molecular breeding.