The SlHsfC1–SlGAI3 Module Controls Tomato Growth and Development via the Gibberellin Signaling Pathway

In agricultural production, plants commonly suppress their growth and development under abiotic stresses. We identified the heat shock transcription factor SlHsfC1, and overexpression (OE) lines resulted in a dwarf phenotype. Overexpression lines exhibited reduced cell size and elevated levels of bioactive gibberellins (GAs). However, applying external GA3 did not restore the dwarf phenotype. Gene expression analysis showed that GA biosynthesis pathway genes (SlKO, SlKAO, SlGA20ox3, and SlGA20ox4) were upregulated, whereas GA metabolic pathway genes (SlGA2ox1 and SlGA2ox2) were downregulated, leading to the accumulation of bioactive gibberellins. However, GA signal transduction pathway genes (SlGAI2 and SlGAI3) were also upregulated, thereby impairing gibberellin signaling in these lines. Protein–DNA interaction assays confirmed that SlHsfC1 directly binds the SlGAI3 promoter and activates its expression. Thus, SlHsfC1 regulates plant height by modulating key genes in the gibberellin signaling pathway.