SUMO E3 Ligase SlSIZ1 Facilitates Heat Tolerance in Tomato.

High temperature has become a major abiotic stress that limits crop productivity. Heat shock transcription factors (HSFs) and heat shock proteins (HSPs) play important roles in enhancing thermotolerance of plants. SUMOylation is an important post-translational modification in regulating cellular functions in eukaryotes. SIZ1, a well-characterized SUMO E3 ligase, mediates the process of SUMOylation. In this study, SUMO conjugations were clearly induced by high temperature. Overexpression of SIZ1 SUMO E3 ligase (SlSIZ1) in tomato could enhance the tolerance to heat stress in tomato. The RNA interference (RNAi) plants were more wilted than the wild type with heat treatment. Under heat stress, SlSIZ1 could decrease the accumulation of reactive oxygen species (ROS) and induce some genes of HSF and HSP transcription. Furthermore, overexpression of SlSIZ1 could increase the level of Hsp70 under high temperature. Yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays showed that SlSIZ1 could interact with SlHsfA1 to mediate the SUMOylation of SlHsfA1 and consequently enhance thermotolerance of tomato. In conclusion, overexpression of SlSIZ1 enhanced heat tolerance by regulating the activities of HsfA1 and increasing the content Hsp70.