Salinity and drought tolerant OsACA6 enhances cold tolerance in transgenic tobacco by interacting with stress-inducible proteins.

Plant Ca(2+)ATPases regulate many signalling pathways which are important for plant growth, development and abiotic stress responses. Our previous work identified that overexpression of OsACA6 confers salinity and drought tolerance in tobacco. In the present work we report, the function of OsACA6 in cold stress tolerance in transgenic tobacco plants. The expression of OsACA6 was induced by cold stress. The promoter-GUS fusion analyses in the different tissues of transgenic tobacoco confirmed that OsACA6 promoter is cold stress-inducible. Transgenic tobacco plants overexpressing OsACA6 exhibited cold tolerance compared to the wild type (WT) controls. The enhanced tolerance was confirmed by phenotypic analyses as well as by measuring germination, survival rate, chlorophyll content, cell membrane stability, malondialdehyde and proline content. Compared to the WT, the expression of catalase, ascorbate peroxidase and superoxide dismutase increased in the OsACA6 overexpressing plants, which was inversely correlated with the levels of H2O2 in the transgenic lines. We also identified interacting proteins of OsACA6 by using yeast two-hybrid screening assay. Most of the interacting partners of OsACA6 are associated with the widespread biological processes including plant growth, development, signalling and stress adaptation. Furthermore, we also confirmed that OsACA6 is able to self-interact. Overall, these results suggest that OsACA6 plays an important role in cold tolerance at least in part, by regulating antioxidants-mediated removal of reactive oxygen species or by interacting with different calcium signal decoders including calmodulin-like proteins (CaM) calcium/calmodulin dependent protein kinases (CDPKs) and receptor-like protein kinases (RLKs).