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The dynamic trans-Golgi network/early endosome (TGN/EE) facilitates cargo sorting and trafficking and plays a vital role in plant development and environmental response. Transport protein particles (TRAPPs) are multi-protein complexes acting as guanine nucleotide exchange factors (GEFs) and possibly as tethers, regulating intracellular trafficking. TRAPPs are essential in all eukaryotic cells and are implicated in a number of human diseases. It has been proposed that they also play crucial roles in plants; however, our current knowledge about the structure and function of plant TRAPPs is very limited. We identified and characterized AtTRAPPC11/Response to Oligogalacturonide-2 (AtTRAPPC11/ROG2), a TGN/EE-associated, evolutionarily conserved TRAPP protein in Arabidopsis. AtTRAPPC11/ROG2 regulates TGN integrity, as evidenced by altered TGN/EE association of several residents, including SYP61, and altered TGN vesicle morphology in attrappc11/rog2 mutants. Further, endocytic traffic and BFA body formation are perturbed in attrappc11/rog2, suggesting a role of AtTRAPPC11/ROG2 in regulation of endosomal function. Proteomic analysis showed that AtTRAPPC11/ROG2 defines a hitherto uncharacterized TRAPPIII complex in plants. In addition, attrappc11/rog2 mutants are hypersensitive to salinity, indicating an undescribed role of TRAPPs in stress responses. Overall, our study illustrates the plasticity of the endomembrane system through TRAPP protein functions and opens new avenues exploring this dynamic network.