Ethylene is a central plant hormone that regulates growth, development, senescence and stress responses. Because it is gaseous, it cannot be stored and must be synthesised on demand. However, the catalytic and regulatory mechanisms of its biosynthetic enzyme, 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), remain poorly understood. In this talk, I will describe how we combine structural biology, biophysical and computational analyses to dissect the mechanism and regulation of ACO. Our work reveals how conformational dynamics and redox-dependent oligomerisation modulate enzyme activity, providing a molecular basis for how ethylene production is tuned in response to cellular conditions. Given ethylene’s central role in crop productivity and stress resilience, understanding these regulatory principles provides a foundation for more precise control of hormone biosynthesis in agriculture and biotechnology.