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 <i>SlHsfC1</i>, 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 (<i>SlKO</i>, <i>SlKAO</i>, <i>SlGA20ox3</i>, and <i>SlGA20ox4</i>) were upregulated, whereas GA metabolic pathway genes (<i>SlGA2ox1</i> and <i>SlGA2ox2</i>) were downregulated, leading to the accumulation of bioactive gibberellins. However, GA signal transduction pathway genes (<i>SlGAI2</i> and <i>SlGAI3</i>) were also upregulated, thereby impairing gibberellin signaling in these lines. Protein-DNA interaction assays confirmed that <i>SlHsfC1</i> directly binds the <i>SlGAI3</i> promoter and activates its expression. Thus, <i>SlHsfC1</i> regulates plant height by modulating key genes in the gibberellin signaling pathway.