TaEXPB7-B, a β-expansin gene involved in low-temperature stress and abscisic acid responses, promotes growth and cold resistance in Arabidopsis thaliana.

Low temperature is one of the primary causes of economic loss in agricultural production, and in this regard, expansin proteins are known to play important roles in plant growth and responses to various abiotic stresses and plant hormones. In order to elucidate the roles of expansin genes in the response of Dongnongdongmai 2 (D2), a highly cold-resistant winter wheat variety, to low-temperature stress, we exposed plants to a temperature of 4℃ and analysed the transcriptome of tillering nodes. Expression levels of TaEXPB7-B were significantly increased in response to both low-temperature stress and abscisic acid (ABA) treatment. To further confirm these observations, we transformed Arabidopsis plants with the β-glucuronidase (GUS) gene driven by the TaEXPB7-B promoter. GUS staining results revealed that TaEXPB7-B showed similar responses to low-temperature and ABA treatments. Our transcriptome data indicated that the AREB/ABF transcription factor gene TaWABI5 was also induced by low temperature in D2. Yeast one-hybrid experiments demonstrated that TaWABI5 binds to an ABRE cis-element in the TaEXPB7-B promoter, and overexpression of TaWABI5 in wheat protoplasts enhanced the expression of endogenous TaEXPB7-B by 7.7-fold, implying that TaWABI5 plays important roles in regulating the expression of TaEXPB7-B. Cytological data obtained from the transient expression of 35S::TaEXPB7-B-eYFP in onion epidermal cells indicated that TaEXPB7-B is cell wall localised. Overexpression of TaEXPB7-B in Arabidopsis promoted a significant increase in plant growth and increased lignin and cellulose contents. Moreover, TaEXPB7-B conferred enhanced antioxidant and osmotic regulation in transgenic Arabidopsis, thereby increasing the tolerance and survival of plants under conditions of low-temperature stress.