Ascorbate oxidase: The unexpected involvement of a 'wasteful enzyme' in the symbioses with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi

► AO catalyzes the oxidation of ascorbate and the reduction of O2 to water. ► The expression of a Lotus japonicus AO is induced in the symbiosis with rhizobia and AM fungi. ► AO could be involved in the control of oxygen diffusion and in redox signaling modules.