OsCCD1, a novel small calcium-binding protein with one EF-hand motif, positively regulates osmotic and salt tolerance in rice

•OsCCD1 is a small calcium-binding protein with one EF-hand motif in rice.•OsCCD1 can bind calcium ion in the in vitro EMSA and fluorescence staining calcium-binding assays.•OsCCD1 is localized in the nucleus and cytosol of rice cells.•OsCCD1 transcript levels are transiently induced by osmotic stress, salt stress and calcium-mediated ABA signal.•OsCCD1 can enhance the tolerances to osmotic and salt stress via the enhanced transcription levels of OsDREB2B, OsAPX1 and OsP5CS genes in rice seedlings.

Calcium-binding proteins play key roles in the signal transduction in the growth and stress response in eukaryotes. However, a subfamily of proteins with one EF-hand motif has not been fully studied in higher plants. Here, a novel small calcium-binding protein with a C-terminal centrin-like domain (CCD1) in rice, OsCCD1, was characterized to show high similarity with a TaCCD1 in wheat. As a result, OsCCD1 can bind Ca2+ in the in vitro EMSA and the fluorescence staining calcium-binding assays. Transient expression of green fluorescent protein (GFP)-tagged OsCCD1 in rice protoplasts showed that OsCCD1 was localized in the nucleus and cytosol of rice cells. OsCCD1 transcript levels were transiently induced by osmotic stress and salt stress through the calcium-mediated ABA signal. The rice seedlings of T-DNA mutant lines showed significantly less tolerance to osmotic and salt stresses than wild type plants (p < 0.01). Conversely, its overexpressors can significantly enhance the tolerance to osmotic and salt stresses than wild type plants (p < 0.05). Semi-quantitative RT-PCR analysis revealed that, OsDREB2B, OsAPX1 and OsP5CS genes are involved in the rice tolerance to osmotic and salt stresses. In sum, OsCCD1 gene probably affects the DREB2B and its downstream genes to positively regulate osmotic and salt tolerance in rice seedlings.