Rice OsCIPK17-OsCBL2/3 module enhances shoot Na+ exclusion and plant salt tolerance in transgenic Arabidopsis

Soil salinity is detrimental to plant growth and remains a major threat to crop productivity of the world. Plants employ various physiological and molecular mechanisms to maintain growth under salt stress. Identification of genes and genetic loci underlying plant salt tolerance holds the key to breeding salt tolerant crops. CIPK-CBL pathways regulate adaptive responses of plants (especially ion transport) to abiotic stresses via fine-tuned Ca²⁺ signal transduction. In this study, we showed that over-expression of OsCIPK17 in Arabidopsis enhanced primary root elongation under salt stress, which is in a Ca²⁺ dependent manner. Further investigation revealed that, under salt stress, OsCIPK17 transcript level was significantly induced and its protein moved from the cytosol to the tonoplast. Using both Y2H and BiFC, tonoplast-localised OsCBL2 and OsCBL3 were shown to interact with OsCIPK17. Interestingly, over-expressing salt-induced OsCBL2 or OsCBL3 in Arabidopsis led to enhanced primary root elongation under salt stress. In this process, OsCIPK17 was shown recruited to the tonoplast (similar to the effect of salt stress). Furthermore, transgenic Arabidopsis lines individually over-expressing OsCIPK17, OsCBL2 and OsCBL3 all demonstrated larger biomass and less Na ⁺ accumulation in the shoot under salt stress. All data combined suggest that OsCIPK17- OsCBL2/3 module is a major component of shoot Na⁺ exclusion and therefore plant salt tolerance, which is through enhanced Na ⁺ compartmentation into the vacuole in the root. OsCIPK17 and OsCBL2/3 are therefore potential genetic targets that can be used for delivering salt tolerant rice cultivars.