ELONGATED HYPOCOTYL 5 regulates steroidal glycoalkaloids biosynthesis and bitterness removal in tomato fruit

Steroidal glycoalkaloids (SGAs) are a class of important secondary metabolites in tomato fruit development and ripening, which enhance fruit disease resistance but also act as antinutritional factors for human health. Although previous studies have reported that SGAs metabolism is influenced by light, the specific regulatory mechanisms remain insufficiently explored. This study demonstrates that light enhances the expression of the light-responsive transcription factor ELONGATED HYPOCOTYL 5 (HY5) and promotes the accumulation of bitter glycoalkaloids, whereas HY5 mutation suppresses this pathway and increases the synthesis of the non-bitter compound esculeoside A during fruit ripening. Further investigation reveals that HY5 directly binds to light-responsive elements in the promoters of glycoalkaloid biosynthesis genes, coordinating the metabolic shift from glycoalkaloid biosynthesis to detoxification metabolism. This provides a molecular basis for balancing tomato defense capability and fruit palatability.