Overexpression of BrCIPK1 Gene Enhances Abiotic Stress Tolerance by Increasing Proline Biosynthesis in Rice

The calcineurin B-like protein (CBL)-CBL-interacting protein kinase (CIPK) pathway is emerging as a major signaling pathway in plants. To understand the function of CIPK, the gene named BrCIPK1 from Brassica rapa were introduced into rice. Characterization of BrCIPK1 gene showed a 1982 bp, containing 1509 bp coding region and 502 amino acids. Green fluorescent protein (GFP)-tagged BrCIPK1 was observed exclusively in the cytoplasmic and peripheral regions in the plant cell. Gene expression showed that its messenger RNA (mRNA) transcription in B. rapa was differentially accumulated in the presence of cold, salinity, and drought, indicating its biological roles in multiple stress response pathways in plants. Furthermore, Ubi-1::BrCIPK1 rice lines showed significantly higher biomass, water content, and proline and free sugar content relative to those in the wild-type Gopum. The BrCIPK1 interacted with rice calcineurin B-like protein 1 and 5 (OsCBL1, OsCBL5), suggesting that it is activated by Ca2+-bound CBLs in the cytosol by calcium spiking and regulates its downstream target proteins in these regions to increase abiotic stress tolerance. The results imply that BrCIPK1 gene may be involved in stress adaptations through the activation of pyrroline-5-carboxylate synthase in the proline biosynthetic pathway. In this paper, a hypothetical mechanism of elevated tolerance to cold, drought, and salinity is presented.