Warm temperature activates the TCP15-HDA4 module to suppress shoot branching by promoting auxin biosynthesis and signaling in tomato

Shoot branching, an important agronomic trait, is environmentally and developmentally regulated. Epigenetic modifications play a pivotal role in regulating transcriptional responses to light and temperature cues that control plant growth. Nevertheless, the roles of epigenetic modifiers in regulating shoot branching under varying temperatures remain elusive. In this study, we reveal that elevated temperature suppresses lateral bud outgrowth in tomato (Solanum lycopersicum), accompanied by increased HISTONE DEACETYLASE 4 (HDA4) levels. Loss of function of SlHDA4 augments lateral bud outgrowth, resulting from a reduced auxin response. Notably, increased lateral bud outgrowth observed in slhda4 mutants is insensitive to elevated temperature but can be restored by SlHDA4 overexpression. Furthermore, we found that the histone deacetylase SlHDA4 interacts with the transcription factor SlTCP15 to suppress the expression of genes encoding the light receptor SlPHYB1 and auxin signaling repressor SlIAA12 by decreasing the H3K9ac levels at their promoters. In summary, our work demonstrates that the SlTCP15-SlHDA4 module participates in the regulation of lateral bud outgrowth at warm temperatures by enhancing auxin biosynthesis and signaling in tomato.