Novel DnaJ Protein Facilitates Thermotolerance of Transgenic Tomatoes.

DnaJ proteins, which are molecular chaperones that are widely present in plants, can respond to various environmental stresses. At present, the function of DnaJ proteins was studied in many plant species, but only a few studies were conducted in tomato. Here, we examined the functions of a novel tomato () DnaJ protein (SlDnaJ20) in heat tolerance using sense and antisense transgenic tomatoes. Transient conversion assays of protoplasts showed that SlDnaJ20 was targeted to chloroplasts. Expression analysis showed that expression was induced by chilling, NaCl, polyethylene glycol, and H₂O₂, especially via heat stress. Under heat stress, sense plants showed higher fresh weights, chlorophyll content, fluorescence (Fv/Fm), and D1 protein levels, and a lower accumulation of reactive oxygen species (ROS) than antisense plants. These results suggest that overexpression can reduce the photoinhibition of photosystem II (PSII) by relieving ROS accumulation. Moreover, higher expression levels of and were observed under heat stress in sense plants, indicating that overexpression contributes to expression. The yeast two-hybrid system proved that SlDnaJ20 can interact with the chloroplast heat-shock protein 70. Our results indicate that overexpression enhances the thermotolerance of transgenic tomatoes, whereas suppression of increases the heat sensitivity of transgenic tomatoes.