Overexpression of MdSOS2L1, a CIPK protein kinase, increases the antioxidant metabolites to enhance salt tolerance in apple and tomato

Soil salinity hinders the growth of most higher plants and becomes a gradually increasing threat to the agricultural production of such crops as the woody plant apple. In this study, a calcineurin B-like protein (CBL)-interacting protein kinase, MdCIPK24-LIKE1 (named as MdSOS2L1), was identified. Quantitative real-time polymerase chain reaction (qRT-PCR) assay revealed that the expression of MdSOS2L1 was upregulated by CaCl2. Yeast two-hybrid (Y2H) assay and transiently transgenic analysis demonstrated that the MdSOS2L1 protein kinase physically interacted with MdCBL1, MdCBL4 and MdCBL10 proteins to increase salt tolerance in apple. Furthermore, iTRAQ proteome combined with liquid chromatography-tandem mass spectrometry (LC/MS) analysis found that several proteins, which are involved in reactive oxygen species (ROS) scavenging, procyanidin biosynthesis and malate metabolism, were induced in MdSOS2L1-overexpressing apple plants. Subsequent studies have shown that MdSOS2L1 increased antioxidant metabolites such as procyanidin and malate to improve salt tolerance in apple and tomato. In summary, our studies provide a mechanism in which SOS2L1 enhances the salt stress tolerance in apple and tomato.