Role of the Arabidopsis calcineurin B-like protein-interacting protein kinase CIPK21 in plant cold stress tolerance

The Arabidopsis calcineurin B-like protein-interacting protein kinase CIPK21 gene (AtCIPK21) plays important roles in cell metabolism, plant development, and abiotic stress responses. However, the function of the AtCIPK21 gene in cold stress tolerance in plant cells is not fully understood. In this study, we use cell cultures of three plant species including rice (Oryza sativa L.), cotton (Gossypium hirsutum L.), and white pine (Pinus strobus L.), as well as Agrobacterium tumefaciens strain GV3101 harboring pBI-AtCIPK21 to generate transgenic cell lines. After confirmation of integration of the AtCIPK21 gene into the genome by polymerase chain reaction (PCR), southern blotting, and northern blotting analyses, the rice, cotton, and pine AtCIPK21 transgenic cell lines were used to examine cold stress tolerance. The experimental results demonstrated that overexpression of the AtCIPK21 gene enhanced cold stress tolerance of transgenic cells by increasing cell viability and cell growth rate, decreasing lipid peroxidation and ion leakage, increasing the content of polyamines, as well as elevating the activity of antioxidative enzymes. In rice cells, AtCIPK21 increases expression of Ca2+-dependent protein kinase (CPK) genes and mitogen-activated protein kinase (MAPK) genes under cold stress. These results indicated that overexpression of the AtCIPK21 gene in plant cells improved cold stress tolerance by elevating polyamines content, antioxidative enzyme activity, and expression of CPK genes and MAPK genes. Overexpression of the AtCIPK21 gene may be a valuable approach for engineering plant cold stress tolerance.