E3 ubiquitin ligases play crucial roles in plant growth and development, as well as in responses to various stresses. However, the specific regulatory mechanisms of E3 ligases under heat stress remain largely unexplored. In this study, we investigated two homologous E3 ubiquitin ligases, SlXERICO1 and SlXERICO3 (SlXERICO1/3), which were significantly responsive to heat stress in tomato (Solanum lycopersicum L.). Our results showed that the slxerico1 and slxerico3 mutants had lower heat tolerance compared with wild-type plants. A yeast two-hybrid screen identified the heat shock factor (Hsf) transcription factor SlHsfB3b as interacting with SlXERICO1/3. We found that SlHsfB3b was degraded via SlXERICO1/3-mediated ubiquitination under heat stress, negatively regulating tomato thermotolerance. Interestingly, SlHsfB3b specifically interacted with the HsfA subfamily member SlHsfA6a, which positively regulates thermotolerance by transcriptionally activating the expression of SlHsfA2, SlHSP17.6A, and SlHSP70-18. Furthermore, SlHsfB3b interfered with the transcriptional activity of SlHsfA6a. The heat-sensitive phenotypes observed in slhsfa6a slhsfb3b double and slhsfa6a single mutant plants revealed that SlHsfA6a functions downstream of SlHsfB3b in regulating heat tolerance in tomato plants. Taken together, the current findings provide evidence that SlXERICO1/3 enhances thermotolerance in tomato by modulating the SlHsfB3b-SlHsfA6a molecular module.
Zhu et al. (2026) studied this question.