LAUSR

The plastid terminal oxidase (PTOX) is a plastohydroquinone:oxygen oxidoreductase that shares structural similarities with alternative oxidases (AOX). Multiple roles have been attributed to PTOX, such as involvement in carotene desaturation, a safety valve function, participation in the processes of chlororespiration and setting the redox poise for cyclic electron transport. PTOX activity has been previously shown to depend on its localization at the thylakoid membrane. Here we investigated the dynamics of PTOX localization in dependence on the proton motive force. Infiltrating illuminated leaves with uncouplers led to a partial dissociation of PTOX from the thylakoid membrane. In vitro reconstitution experiments showed that the attachment of purified recombinant MBP-OsPTOX to liposomes and isolated thylakoid membranes was strongest at slightly alkaline pH values in the presence of lower millimolar concentrations of KCl or MgCl2. In A. thaliana overexpressing GFP-PTOX, confocal microscopy images showed that PTOX formed distinct spots in chloroplasts of dark-adapted or uncoupler-treated leaves while the protein was more equally distributed in a network-like structure in the light. We propose a dynamic PTOX association with the thylakoid membrane depending on the presence of a proton motive force.