Plant ERD2s self-interact and interact with GTPase-activating proteins and ADP-ribosylation factor 1.

ERD2s (ER luminal protein receptors)-mediated retrograde transport is one of the most substantial processes to maintain the endoplasmic reticulum (ER) homeostasis. It is completed by the recognition of the escaped ER luminal proteins, the gathering into COP I vesicle, and the fusion and releasing into the ER. ERD2s can recognize HDEL/KDEL motifs at the C-terminal of the escaped ER luminal proteins at the Golgi to initiate the retrograde transport. However, these mechanisms remain largely unknown in plants. We recently found that two Nicotiana benthamiana homologs, ERD2a and ERD2b, functioned as ER luminal protein receptors, were required for both HDEL/KDEL motifs-mediated ER retrieval and participated in cell death triggered by ER stress and nonhost pathogens. Here, we provide a set of new data that ERD2a/2b can form homo- or hetero-oligomerization and interact with both the ADP-ribosylation factor 1 (ARF1) and its potential GTPase-activating proteins (GAP) indicated by the firefly luciferase complementation imaging assay (LCI). These evidences further support the ER luminal protein receptor function of ERD2a/2b in plants and suggest their evolutionarily conserved mechanism during the retrograde trafficking. We also analyze the characteristics of ERD2s within a species and among different species.