Structural Basis of Nidovirus Replication Organelle Evolution Revealed by the Arterivirus DMV Pore Complex

Positive-strand RNA viruses of the order Nidovirales - which include coronaviruses and arteriviruses - remodel host membranes into double-membrane vesicles (DMVs) as replication organelle to shield viral RNA synthesis from immune sensors. In coronaviruses, newly synthesized RNA is exported to the cytoplasm through a massive DMV pore complex formed by viral non-structural proteins (nsps). However, it remains unknown whether this elaborate architecture is unique to large-genome coronaviruses or a universal hallmark of the order. Here, we integrate in situ cryo-electron tomography and single-particle cryo-electron microscopy to resolve the atomic structure of DMV pore complex within its native membrane environment, from Equine Arteritis Virus (EAV), a prototype arterivirus with small genome. Despite lacking obvious sequence homology, the minimal EAV pore shares conserved architectural principles with its elaborate coronavirus counterpart. EAV pore complex is formed by a 12:12 stoichiometry of nsp2 and nsp3 protomers organized into four stacked concentric rings on double-membrane, yet generating pronounced structure symmetry mismatch. Functionally, the complex displays a distinct pore profile while preserving a positively charged central channel, essential for viral replication and transport. These findings demonstrate that, despite diversity in genome size and virion morphology, nidovirus replication organelles exhibit striking evolutionary conservation at the atomic structural level. Collectively, we propose that the order Nidovirales can be unified at the ultrastructural level by this conserved signature pore complex on the DMV-based replication organelle.