A maize calcineurin B‐like interacting protein kinase ZmCIPK42 confers salt stress tolerance

Calcineurin B‐like (CBL) and CBL‐interacting protein kinase (CIPK) play a crucial role in biotic and abiotic stress responses. However, the roles of different CIPKs in biotic and abiotic stress responses are less well characterized. In this study, we identified a mutation leading to an early protein termination of the maize CIPK gene ZmCIPK42 that undergoes a G to A mutation at the coding region via searching for genes involved in salt stress tolerance and ion homeostasis from maize with querying the EMS mutant library of maize B73. The mutant zmcipk42 plants have less branched tassel and impaired salt stress tolerance at the seedling stage. Quantitative real‐time PCR analysis revealed that ZmCIPK42was expressed in diverse tissues and was induced by NaCl stress. A yeast two‐hybrid screen identified a proteinase inhibitor (ZmMPI) as well as calcineurin B‐like protein 1 and protein 4 (ZmCBL1, ZmCBL4) as interaction partners of ZmCIPK42. These interactions were further confirmed by bimolecular fluorescence complementation in plant cells. Moreover, over‐expressing ZmCIPK42 resulted in enhanced tolerance to high salinity in both maize and Arabidopsis. These findings suggest that ZmCIPK42 is a positive regulator of salt stress tolerance and is a promising candidate gene to improve salt stress tolerance in maize through genetic manipulation.     

The phosphorylation of an actin depolymerizing factor by a calcium-dependent protein kinase regulates cotton fiber elongation

A cotton fiber is a single and highly elongated ovule epidermal cell. However, the mechanism that governs the development of fiber traits remains unclear. In this study, we cloned a calcium-dependent protein kinase (GhCPK1) and an actin depolymerizing factor (GhADF1) from Gossypium hirsutum. Real-time PCR analyses indicated that the expression of GhCPK1 and GhADF1 correlated with the elongation pattern of cotton fibers. Yeast two-hybrid assays using full-length GhCPK1 and truncated forms of GhCPK1 as baits identified GhADF1 as an interactor of GhCPK1. Furthermore, GhCPK1 is capable of phosphorylating GhADF1 in vitro in a calcium-dependent manner, and the phosphorylation of GhADF1 by GhCPK1 occurs on the Ser-6 of GhADF1. In addition, we observed that the heterologous expression of the GhCPK1 gene induced longitudinal growth of the host cells by 3.18-fold, with no apparent effect on other aspects of the host cells. The results strongly suggest that GhCPK1 may regulate the function of GhADF1 by phosphorylating this protein during cotton fiber elongation.