SlMAPK3-SlWRKY5-SlGR1 Module Mediates Thermotolerance Response in Tomato via Transcriptional and Post-Translational Mechanisms.

Heat stress severely impairs crop growth and production. WRKY transcription factors are key regulators of plant responses to abiotic stresses, but the mechanisms by which these transcription factors respond to heat stress in tomato are poorly understood. In this study, we identified a transcription factor SlWRKY5, which was significantly induced at high temperature (42°C). Phenotypic analyses showed that overexpression of SlWRKY5 positively regulated thermotolerance but suppressed growth of tomato plants, while its knockout exhibited opposite effects. Transcriptome analysis further demonstrated that SlWRKY5 activated a series of heat responsive genes. Notably, SlWRKY5 positively regulated the expression of glutathione reductase gene SlGR1 by binding W-box elements on SlGR1 promoter, thereby increasing glutathione reductase (GR) activity and enhancing the reactive oxygen species (ROS) scavenging ability of tomato plants under heat stress. In addition, SlWRKY5 interacted with SlMAPK3 (a negative regulator of thermotolerance) and was phosphorylated by SlMAPK3, ultimately inhibiting SlWRKY5 activity. However, heat stress downregulates SlMAPK3 expression, which alleviates the SlMAPK3-mediated phosphorylation of SlWRKY5, allowing tomato plants to mount a rapid heat stress response. Overall, this study found that SlMAPK3, SlWRKY5, and SlGR1 formed a complex interacting module, thereby facilitating a rapid response to heat stress and maintains normal growth of tomato plants through transcriptional and post-translational mechanisms. The identification of SlWRKY5 as a positive regulator of thermotolerance and revelation of related mechanisms lay a theoretical and practical foundation for genetic engineering of thermotolerant tomato cultivars.