A calcium-dependent protein kinase gene SpCPK33 from Solanum pennellii associated with increased cold tolerance in tomato

Calcium-dependent protein kinases (CDPKs, CPKs) represent a vital class of calcium sensors, which play a crucial role in plant growth, development and adaption to complex environmental stresses. Wild species tend to exhibit greater tolerance than cultivated species under environmental stress. Here, we isolated a calcium-dependent protein kinase gene SpCPK33 located primarily on the plasma membrane of abiotic-resistant species (Solanum pennellii LA0716). It was highly expressed in stems and leaves and was also induced by cold stress. Compared with WT plants, the overexpression of SpCPK33 in cultivated tomato (cv M82) enhanced its tolerance to cold stress. Transgenic lines demonstrated strong vitality under low temperature treatment. Moreover, the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) were decreased in SpCPK33-overexpressing plants. The activities of antioxidant enzymes and the levels of osmotic regulatory substances were higher. The transcript levels of cold stress-related genes were up-regulated. In summary, the results indicate that SpCPK33-overexpressing transgenic plants experience less severe chilling injury under cold stress, and improved tomato cold tolerance by scavenging ROS accumulation and modulating the expression of stress-related genes.