Redox regulation of membrane-associated processes mediated by chloroplastic thioredoxins

Plant chloroplasts are complex organelles that house a plethora of redox-controlled metabolic processes. However, our understanding of membrane-level redox signalling remains limited. In order to expand our knowledge of redox regulation in these photosynthetic subcellular compartments, we carried out in vitro and in vivo experimental approaches focused on the analysis of processes taking place at the membrane level. In addition to the classic stromal localization, these approaches have revealed that chloroplastic thioredoxins (TRXs) from Arabidopsis thaliana are also membrane-associated proteins, having a network of non-stromal interactors. We have identified 185 putative chloroplastic targets, with 80 % predicted to be located at the envelope or thylakoid membranes, and classified into 18 functional categories, with the most prevalent one being related to photosynthesis and, notably, metabolite/ion transport, a novel finding in redox regulation. Direct in vivo interactions between TRXs m and three integral proteins involved in protein import and metabolite transport, as well as one thylakoid membrane-bound protein that regulates proteolytic processes, were confirmed. Moreover, the role of TRXs m appears to extend beyond the regulation of the primary process of photosynthesis, such as during the establishment of greening cotyledons and the protection against high-light intensities. These findings provide a novel perspective on the function of TRXs as multifaceted regulators. The present study aims to address a current knowledge gap by exploring redox signalling in the membranes of plant chloroplasts.