HbCIPK2, a novel CBL-interacting protein kinase from halophyte Hordeum brevisubulatum, confers salt and osmotic stress tolerance

Protein kinases play an important role in regulating the response to abiotic stress in plant. CIPKs are plant-specific signal transducers, and some members have been identified. However, the precise functions of novel CIPKs still remain unknown. Here we report that HbCIPK2 is a positive regulator of salt and osmotic stress tolerance. HbCIPK2 was screened out of the differentially expressed fragments from halophyte Hordeum brevisubulatum by cDNA-AFLP technique, and was a single-copy gene without intron. Expression of HbCIPK2 was increased by salt, drought and ABA treatment. HbCIPK2 is mainly localized to the plasma membrane and nucleus. Ectopic expression of 35S:HbCIPK2 not only rescued the salt hypersensitivity in Arabidopsis mutant sos2-1, but also enhanced salt tolerance in Arabidopsis wild type, and exhibited tolerance to osmotic stress during germination. The HbCIPK2 contributed to the ability to prevent K+ loss in root and to accumulate less Na+ in shoot resulting in K+/Na+ homeostasis and protection of root cell from death, which is consistent with the gene expression profile of HbCIPK2-overexpressing lines. These findings imply possible novel HbCIPK2-mediated salt signalling pathways or networks in H. brevisubulatum.