Low temperature is among the most significant abiotic stresses, restricting the habitats of sessile plants and reducing crop productivity. Cold regulated (COR) genes are low temperature-responsive genes expressing under regulation of a specific signal transduction pathway, which is designated C-repeat-binding-factor (CBF) signaling pathway. In the present article, cold bioassay showed that the transcript level of cold regulated gene CbCOR15b from shepherd's purse (Capsella bursa-pastoris) was obviously elevated under cold treatments. Reverse transcription-PCR (RT-PCR) and GUS report system revealed that unlike AtCOR15b, CbCOR15b expressed not only in leaves but also in stems and maturation zone of roots. When transgenic tobacco plants ectopically expressing CbCOR15b were exposed to chilling and freezing temperatures, they displayed more cold tolerance compared to control plants. According to the electrolyte leakage, the relative water content, the glucose content and the phenotype observation, CbCOR15b transformants suffered less damage under cold stress. Further investigation of the subcellular localization of CbCOR15b by transient expression of fusion protein CbCOR15b-GFP revealed that it was localized exclusively in the chloroplasts of tobacco mesophyll cells and in the cytoplasm of onion epidermal cells. It can be concluded that CbCOR15b which located in the chloroplasts and in the cytoplasm of cells without chloroplasts was involved in cold response of C. bursa-pastoris and conferred enhanced cold tolerance in transgenic tobacco plants.
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