TdCBL6, a calcineurin B-like gene from wild emmer wheat (Triticum dicoccoides), is involved in response to salt and low-K⁺ stresses

The calcineurin B-like proteins (CBLs), a unique family of calcium sensors in plants, have been shown to be involved in abiotic stresses, such as salt, drought and cold. Although extensive studies and remarkable progress have been made in Arabidopsis (Arabidopsis thaliana) CBLs, very little is known about the role of CBL genes in wheat. In this study, a CBL gene, designated TdCBL6, was cloned and characterized from wild emmer wheat (Triticum dicoccoides), the progenitor of cultivated wheat. Sequence alignment revealed that TdCBL6 shares high sequence homology with rice OsCBL6. Phylogenetic analysis also revealed that TdCBL6 protein has the closest evolutionary relationship with rice OsCBL6 protein. TdCBL6 transcription was induced by NaCl, polyethylene glycol and abscisic acid. Further differential expression analysis revealed that TdCBL6 expression was much higher in the salt-tolerant line than in the salt-sensitive line when they were subjected to salt treatment. Transgenic Arabidopsis ectopic expression of the TdCBL6 gene displayed higher levels of photosynthetic efficiency (Fv/Fm) and lower ion leakage (EL) than wild-type (WT) plants under NaCl stress conditions. Moreover, TdCBL6-overexpressing lines showed low-K⁺ (LK)-sensitive phenotypes compared with WT plants. Further experiments revealed that ectopic expression of TdCBL6 resulted in reduction of H₂O₂ content, and affected expression of K⁺-responsive/H₂O₂-regulated genes under LK stress. Taken together, we demonstrated that heterologous expression of TdCBL6 in Arabidopsis confers salt tolerance by reducing membrane injury and improving photosynthetic efficiency, and that the TdCBL6 gene may be involved in response to LK stress by regulating the reactive oxygen species-mediated LK signaling pathway.