Overexpressing IbCBF3 increases low temperature and drought stress tolerance in transgenic sweetpotato

Dehydration-responsive element-binding/C-repeat-binding factor (DREB/CBF) proteins regulate the transcription of genes involved in cold acclimation in several species. However, little is known about the physiological functions of CBF proteins in the low temperature-sensitive crop sweetpotato. We previously reported that the DREB1/CBF-like sweetpotato gene SwDREB1/IbCBF3 is involved in responses to diverse abiotic stresses. In this study, we confirmed that IbCBF3 is localized to the nucleus and binds to the C-repeat/dehydration-responsive elements (CRT/DRE) in the promoters of cold-regulated (COR) genes. We generated transgenic sweetpotato plants overexpressing IbCBF3 under the control of the CaMV 35S promoter (referred to as SC plants) and evaluated their responses to various abiotic stresses. IbCBF3 expression was dramatically induced by cold and drought but much less strongly induced by high salinity and ABA. We further characterized two SC lines (SC3 and SC6) with high levels of IbCBF3 transcript. The SC plants displayed enhanced tolerance to cold, drought, and oxidative stress on the whole-plant level. Under cold stress treatment (4 °C for 48 h), severe wilting and chilling injury were observed in the leaves of wild-type (WT) plants, whereas SC plants were not affected by cold stress. In addition, the COR genes were significantly upregulated in SC plants compared with the WT. The SC plants also showed significantly higher tolerance to drought stress than the WT, which was associated with higher photosynthesis efficiency and lower hydrogen peroxide levels. These results indicate that IbCBF3 is a functional transcription factor involved in the responses to various abiotic stresses in sweetpotato.