SlERF.H6 mediates the orchestration of ethylene and gibberellin signaling that suppresses bitter-SGA biosynthesis in tomato

Steroidal glycoalkaloids (SGAs) constitute a characteristic class of antinutritional metabolites that are found in certain Solanum species. Despite the considerable studies on SGA biosynthesis, the mechanisms of crosstalk between hormone signaling pathways that regulate SGA content still remain to be elucidated. Here, we performed a metabolic genome-wide association study (mGWAS) based on the levels of SGA metabolites and identified SlERF.H6 as a negative regulator of bitter-SGA biosynthesis. SlERF.H6 repressed the expression of SGA biosynthetic glycoalkaloid metabolism (GAME) genes and caused a subsequent decrease in the abundance of bitter SGAs. Furthermore, SlERF.H6 were shown to act downstream of GAME9, a regulator of SGA biosynthesis in tomato. We also uncovered the interplay between ethylene and gibberellin (GA) signaling in regulating SGA biosynthesis. SlERF.H6, acting as a downstream component in ethylene signaling, modulated GA content by inhibiting SlGA2ox12 expression. Increasing levels of endogenous GA₁₂ and GA₅₃ in SlERF.H6-OE could inhibit of GA on SGA biosynthesis. Additionally, 1-aminocyclopropane-1-carboxylic acid (ACC) treatment decreased the stability of SlERF.H6, weakening its inhibition on GAME genes and SlGA2ox12, and caused bitter-SGA accumulation. Our findings reveal a key role of SlERF.H6 in the regulation of SGA biosynthesis through the coordinated ethylene-gibberellin signaling.