Calcineurin B-like protein ZmCBL8-1 promotes salt stress resistance in Arabidopsis

Calcineurin B-like proteins (CBLs) as plant-specific calcium sensors have been explored for their roles in the regulation of abiotic stress tolerance. Further, the functional variations in ZmCBL8, encoding a component of the salt overly sensitive pathway, conferred the salt stress tolerance in maize. ZmCBL8-1 is a transcript of ZmCBL8 found in maize, but its function in the salt stress response is still unclear. The present study aimed to characterize the protein ZmCBL8-1 that was determined to be composed of 194 amino acids (aa) with three conserved EF hands responsible for binding Ca2+. However, a 20-aa fragment was found to be missing from its C-terminus relative to another transcript of ZmCBL8. Results indicated that it harbored a dual-lipid modification motif MGCXXS at its N-terminus and was located on the cell membrane. The accumulation of ZmCBL8-1 transcripts was high in the roots but relatively lower in the leaves of maize under normal condition. In contrast, its expression was significantly decreased in the roots, while increased in the leaves under NaCl treatment. The overexpression of ZmCBL8-1 resulted in higher salt stress resistance of transgenic Arabidopsis in a Ca2+-dependent manner relative to that of the wild type (WT). In ZmCBL8-1-overexpressing plants exposed to NaCl, the contents of malondialdehyde and hydrogen peroxide were decreased in comparison with those in the WT, and the expression of key genes involved in the antioxidant defense system and Na+/H+ antiporter were upregulated. These results suggested that ZmCBL8-1 played a positive role in the response of leaves to salt stress by inducing the expression of Na+/H+ antiporter genes and enhancing the antioxidant system to neutralize the accumulation of reactive oxygen species. These observations further indicate that ZmCBL8-1 confers salt stress tolerance, suggesting that transcriptional regulation of the ZmCBL8 gene is important for salt tolerance.