The sweet potato transcription factor IbbHLH33 enhances chilling tolerance in transgenic tobacco

Chilling is an important abiotic stress in plants. Sweet potato is sensitive to cold damage due to its tropical origin. In this study, we identified a basic helix-loop-helix (bHLH) gene, IbbHLH33, from our cold-tolerance-related transcriptomic data. Further analyses revealed that IbbHLH33 encoded a nuclear protein and was most closely related to AtbHLH33. RT-qPCR analysis showed that IbbHLH33 was expressed at the highest level in the roots, and its expression was strongly induced by low temperature (4 °C), H2O2 and abscisic acid (ABA) treatments. Transgenic tobacco plants overexpressing IbbHLH33 were obtained by Agrobacterium-mediated transformation, which enhanced the chilling resistance of tobacco. At low temperatures, the proline content, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content increased significantly, while the relative conductivity decreased significantly. At the same time, the expression of proline synthesis related genes and antioxidant activity related genes increased, while the expression of ABA synthesis related genes decreased. The results showed that IbbHLH33 is a transcription factor encoding a gene of the bHLH family that regulates chilling tolerance. In conclusion, these data suggest that IbbHLH33 has the potential to improve chilling tolerance in tobacco and other plants.