The SlDREBA4-SlASIL2 module mediates tomato thermotolerance by regulating the expression of SlHSP20/90.

SlASIL2 can regulate tomato heat tolerance by suppressing the expression of SlHSP20/SlHSP90 and forming protein complexes with SlDREBA4. Tomato (Solanum lycopersicum) is an important vegetable crop with substantial economic value. High-temperature stress severely impacts tomato yield and quality, making it a major constraint on the development of the tomato industry. The DREBA4 transcription factor is thought to play a key role in the high-temperature stress response pathway; however, its regulatory mechanism remains to be fully elucidated. In this study, a combination of genetic and biochemical approaches was used to elucidate the roles of SlDREBA4 and SlASIL2 in regulating the transcription of SlHSP20 and SlHSP90. Further analysis were performed to investigate the function of the SlASIL2 gene using overexpression and silencing systems. Additionally, SlASIL2 was found to suppress the reactive oxygen species (ROS) scavenging system, thereby negatively regulating tomato heat tolerance. Moreover, SlASIL2 directly binds to the promoters of SlHSP20 and SlHSP90, repressing their expression and thereby reducing tomato heat tolerance. Importantly, the interaction between SlDREBA4 and SlASIL2 mitigated the inhibitory effect of SlASIL2 on SlHSP20 and SlHSP90, contributing to the establishment of a stable physiological state in tomatoes under high-temperature conditions. These results indicate that the transcriptional regulation of SlHSP20 and SlHSP90 by SlDREBA4 and SlASIL2, together with the modulation of the ROS scavenging system, collectively fine-tune the tomato response to short-term heat stress. Our findings further expand the understanding of the molecular regulatory network involved in plant heat stress responses.