Cloning and Functional Characterization of a Cation-chloride Cotransporter Gene OsCCC1

Potassium (K+) and chloride (Cl-) are two essential elements for plant growth and development. While it is known that plants possess specific membrane transporters for transporting K+ and Cl-, it remains unclear if they actively use K+-coupled Cl- cotransporters (KCC), as used in animals, to transport K+ and Cl-. We have cloned an Oryza sativa cDNA encoding for a member of the cation-Cl- cotransporter (CCC) family. Phylogenetic analysis revealed that plant CCC proteins are highly conserved and that they have greater sequence similarity to the sub-family of animal K--Cl- cotransporters than to other cation-Cl- cotransporters. Real-time PCR revealed that the O. sativa cDNA, which was named OsCCC1, can be induced by KCl in the shoot and root and that the expression level was higher in the leaf and root tips than in any other part of the rice plant. The OsCCC1 protein was located not only in onion plasma membrane but also in O. sativa plasma membrane. The OsCCC1 gene-silenced plants grow more slowly than wild-type (WT) plants, especially under the KCl treatment regime. After 1 month of KCl treatment, the leaf tips of the gene-silenced lines were necrosed. In addition, seed germination, root length, and fresh and dry weight were distinctly lower in the gene-silenced lines than in WT plants, especially after KCl treatment. Analysis of Na+, K+, and Cl- contents of the gene-silenced lines and WT plants grown under the NaCl and KCl treatment regimes revealed that the former accumulated relatively less K+ and Cl- than the latter but that they did not differ in terms of Na+ contents, suggesting OsCCC1 may be involved in K+ and Cl- transport. Results from different tests indicated that the OsCCC1 plays a significant role in K+ and Cl- homeostasis and rice plant development.