Functional Characterization of Tea Plant (Camellia sinensis L.) CsCBF2 Gene Involved in Multiple Abiotic Stress Response in Tobacco (Nicotiana tabacum L.)

Abstract

C-repeat binding factors/dehydration responsive element binding factors 1 (CBFs/DREB1s) are a small family of transcription factors that play important roles in plant resistance to various external stresses. However, functional characterization of tea plant (Camellia sinensis L.) CBF gene (CsCBF) was still seldom reported. Here, functional study of the cold-responsive CBF gene (CsCBF2) was done. Results showed that CsCBF2 had conserved AP2 DNA-binding domain and the typical PKK/RPAGRxKFxETRHP and DSAWR signature sequences of CBF/DREB1. Yeast one-hybrid and transcription activation assays revealed that the activation domain of CsCBF2 could activate the reporter gene expression, and the N terminal of CsCBF2 displayed an inhibitory effect. Although CsCBF2 was conserved to bind the C-repeat/dehydration-responsive element (CRT/DRE), intact CsCBF2 protein preferred the CRT cis element. Under normal growth conditions, CsCBF2-overexpressing tobacco plants (CsCBF2-OX) exhibited lighter green leaf color, growth retardation, and dwarfism. Smaller leaf of CsCBF2-OX was only seen in eight weeks after been sown in soil. Under cold, salinity, or drought stress, CsCBF2-OX displayed better growing with longer roots, heavier fresh weight, higher germination rate, and accumulated more proline and sugar contents, but lower electrolyte leakage. The results demonstrated that CsCBF2 enhanced plant tolerance to multiple abiotic stresses.