CBL4-CIPK5 pathway confers salt but not drought and chilling tolerance by regulating ion homeostasis

Calcineurin B-like protein (CBL) and CBL-interacting protein kinase (CIPK) play an important role in regulation on plant abiotic stress tolerance. It is unknown whether CBL-CIPK pathway regulates abiotic stress tolerance in bermudagrass. In the present study, CdtCBL4 and CdtCIPK5 from triploid bermudagrass were characterized. CdtCBL4 and CdtCIPK5 transcripts were induced by dehydration and salt. In addition, low temperature induced CdtCIPK5 transcript, but inhibited CdtCBL4 transcript; ABA induced CdtCIPK5 transcript, but had no influence on CdtCBL4 transcript. Yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assay demonstrated CdtCIPK5 interacted with CdtCBL4. Overexpression of CdtCIPK5 and CdtCBL4 improved salt tolerance in transgenic rice compared with wild type, based on measurements on relative water content (RWC), chlorophyll content and F-v/F-m. CdtCIPK5 and CdtCBL4 overexpressing transgenic lines had a lower Na+ accumulation and a higher K+/Na+ ratio under salt stress. The higher transcript levels of OsNHX3, OsHKT1;1, OsHKT1;4, OsHKT1;5 were observed in CdtCIPK5 overexpressing plants than in WT. It is suggested that CdtCBL4-CdtCIPK5 pathway confers salinity tolerance by upregulating OsNHX3, OsHKT1;1, OsHKT1;4, OsHKT1;5 expression for maintenance of Na+/K+ homeostasis during salt stress.