Cloning And Functional Analysis Of Salt Inducible Protein Kinase Genes ZmPtil, ZmSPK1 And ZmASK1 In Maize

Protein kinase plays an important role in plant salt resistance pathway. We cloned three protein kinase genes induced by salt stress from maize with the probe sequences involved in salt stress pathwany from Arabidopsis and rice, and analyzed their protein sequences and roles in salt resistance pathway.One full-length cDNA encoding a Pti1 homologue was isolated from maize by RT-PCR and named as ZmPti1. The ZmPti1 protein was expressed in Saccharomyces cereviciae, purified by ProBond Resin and examined for its autophosphorylation ability. The phosphorylation assay in vitro showed that ZmPti1 had a kinase activity. RT-PCR analysis showed that the ZmPti1 expression was induced by salicylic acid (SA), low-temperature, mannitol and salt but not by abscisic acid (ABA). Furthermore, in different tissues the ZmPti1 showed different expression patterns. These results demonstrated that ZmPti1 represented a new Pti1-like gene and might play multiple roles in both plant biotic and abiotic resistant pathways, as well as in plant development process.In order to analyzed the biological function of ZmPti1, we overexpressed ZmPti1 gene in Arabidopsis. The followed analysises showed that the transgenic plants can enhance the salt resistance, but have no obvious effect on enhancing the resistance to pathogen, cold and drought comparing to control plants. The transgenic plants can increase the relative biomass and yield under salt stress. Furthermore, the SOD activity of transgenic plants can keep to a high level when treated with high salt. The MDA content and relative electric conductivity of transgenic plants can keep to a relative low level under salt treatment.Another full-length cDNA encoding a SnRK2b homologue was isolated from maize by RT-PCR and named as ZmSPK1 (for stress-induced protein kinase). The ZmSPK1 protein has 364 amino acids with an estimated molecular mass of 41.8 KD and an isoelectric point of 5.8. The deduced protein sequence has the closest identities to the members of SnRK2b group. The ZmSPK1 protein was expressed in Saccharomyces cereviciae, purified by ProBond Resin and examined for its phosphorylation ability. The phosphorylation assay in vitro showed that ZmSPK1 had a kinase activity. RT-PCR analysis showed that the ZmSPK1 expression was induced by mannitol, salt and abscisic acid (ABA). Furthermore, in different tissues the ZmSPK1 showed different expression patterns and was most abundant in reproductive organs. These results suggested that ZmSPK1 might play multiple...