Heat-inducible SlWRKY3 confers thermotolerance by activating the SlGRXS1 gene cluster in tomato

High temperature stress is one of the major environmental factors that affect the growth and development of plants. Although WRKY transcription factors play a critical role in stress responses, there are few studies on the regulation of heat stress by WRKY transcription factors, especially in tomato. Here, we identified a group I WRKY transcription factor, SlWRKY3, involved in thermotolerance in tomato. First, SlWRKY3 was induced and upregulated under heat stress. Accordingly, overexpression of SlWRKY3 led to an increase, whereas knock-out of SlWRKY3 resulted in decreased tolerance to heat stress. Overexpression of SlWRKY3 accumulated less reactive oxygen species (ROS), whereas knock-out of SlWRKY3 accumulated more ROS under heat stress. This indicated that SlWRKY3 positively regulates heat stress in tomato. In addition, SlWRKY3 activated the expression of a range of abiotic stress-responsive genes involved in ROS scavenging, such as a SlGRXS1 gene cluster. Further analysis showed that SlWRKY3 can bind to the promoters of the SlGRXS1 gene cluster and activate their expression. Collectively, these results imply that SlWRKY3 is a positive regulator of thermotolerance through direct binding to the promoters of the SlGRXS1 gene cluster and