Orchestration of ethylene and gibberellin signals determines root growth and K+ uptake in tomato

Ethylene plays an important role in regulating root growth; however, its role in root growth under low potassium (LK) stress remains unclear. Here, we report that ethylene inhibits gibberellin (GA) and enhances root growth and potassium (K+) uptake in tomato (Solanum lycopersicum) under LK stress. Previously, we identified an LK-tolerant phospholipase Dδ, SlPLDδ, which interacts with 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase 1 (SlACO1) to negatively regulate ethylene content. Ethylene treatment induces expression of the ethylene response transcription factor SlERN1 under LK stress, and SlERN1 plays a negative role in root growth and K+ uptake in tomatoes. Further investigation revealed that SlERN1 represses the expression of the GA biosynthesis genes GIBBERELLIN 20–OXIDASE 1 (SlGA20ox1) and SlGA2ox3, decreasing GA activity and gradually inhibiting root growth and K+ uptake. Silencing SlGA20ox1/3 reduced the ethylene sensitivity in root growth and K+ uptake. Additionally, SlERN1 represses the expression of voltage–gated K+ channel (SlLKT1) to regulate K+ and magnesium ion (Mg2+) transport. Genetic analysis revealed that SlGA20ox1/3 and SlLKT1 function downstream of SlERN1. Overall, we identified a molecular pathway affected by ethylene during LK stress in tomatoes and provided insights into the coordination of ethylene and GA signals during LK-inhibited root growth and K+ uptake.