Tvp38/DedA Family Protein mediates biogenesis of chloroplast peripheral reticulum and envelope-to-thylakoid contacts in Arabidopsis

Abstract

Chloroplasts of land plants are dynamic organelles essential for photosynthesis, metabolism, and plant adaptation to changing environmental conditions. Within chloroplasts, the inner envelope and thylakoid membranes are spatially separated but functionally interconnected. The inner envelope harbors enzymes involved in lipid synthesis for internal membranes and controls the exchange of metabolites and proteins, whereas the thylakoid membranes accommodate the machinery of the photosynthetic electron transport chain responsible for converting light energy into chemical energy. Therefore, efficient communication between these membrane systems is essential for maintaining chloroplast homeostasis and sustaining photosynthetic activity. In this study we have characterized the role of Tvp38/DedA Family Protein (TVPFP) in mediating inner envelope-to-thylakoid communication in Arabidopsis thaliana. Despite exhibiting wild-type-like growth and similar accumulation of the major thylakoid-anchored photosynthetic complexes, tvpfp mutants displayed reduced photosynthetic activity and increased abundance of photorespiration- and pigment-related proteins. Our results revealed that TVPFP localizes to the chloroplast envelope and undergoes post-translational modification when localized to the thylakoids. The unmodified form of TVPFP is enriched in high-molecular-weight complexes, suggesting that TVPFP oligomers are partially dissolved upon thylakoid relocation. Transmission electron microscopy data showed reduced abundance of vesicles as well as chloroplast peripheral reticulum (CPR) structures connecting the envelope and thylakoids in tvpfp mutants. Together, our results demonstrate that TVPFP fine-tunes photosynthesis by regulating vesicle abundance and biogenesis of CPR structures. Our findings shed light on the importance of envelope-to-thylakoid communication and the role of CPR structures in land plants.