Steroidal Alkaloids Defense Metabolism and Plant Growth are Modulated by the Joint Action of Gibberellin and Jasmonate Signaling

●Steroidal glycoalkaloids (SGAs) are protective metabolites constitutively produced by Solanaceae species. Genes and enzymes generating the vast structural diversity of SGAs have been largely identified. Yet, mechanisms of hormone pathways coordinating defense (jasmonate; JA) and growth (gibberellin; GA) controlling SGAs metabolism remain unclear. ●We used tomato to decipher the hormonal regulation of SGAs metabolism during growth vs defense tradeoff. This was performed by genetic and biochemical characterization of different JA and GA pathways components, coupled with in-vitro experiments to elucidate the crosstalk between these hormone pathways mediating SGAs metabolism. ●We discovered that reduced active JA results in decreased SGAs production, while low levels of GA or its receptor led to elevated SGAs accumulation. We showed that MYC1 and MYC2 transcription factors mediate the JA/GA crosstalk by transcriptional activation of SGA biosynthesis and GA catabolism genes. Furthermore, MYC1 and MYC2 transcriptionally regulate the GA signaling suppressor DELLA that by itself interferes in JA-mediated SGAs control by modulating MYCs activity through protein-protein interaction. Chemical and fungal pathogen treatments reinforced the concept of JA/GA crosstalk during SGAs metabolism. ●These findings reveal the mechanism of JA/GA interplay in SGAs biosynthesis to balance the cost of chemical defense with growth.