Redox-controlled dimerisation regulates ethylene biosynthesis

Ethylene is a central plant hormone that orchestrates growth, development, senescence, and stress responses. Because it is gaseous, ethylene must be synthesised on demand, yet the catalytic and regulatory mechanisms of its biosynthetic enzyme, 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), remain poorly understood. Here, using structural, biophysical, and computational analyses, we uncovered two principles: ACO catalysis relies on an induced-fit mechanism, and disulfide-mediated dimerisation via a conserved cysteine acts as a redox switch toggling ACO between active monomer and inactive dimer. This previously unrecognised regulatory layer positions ACO as a redox sensor in plant cells, revealing a fundamental control point in ethylene biosynthesis. Given ethylenes pivotal role in crop productivity and stress resilience, these findings open new opportunities for precise manipulation of hormone signalling in agriculture and biotechnology.