This domain corresponds to the C-terminal intermembrane space (IMS) region from protein accumulation and replication of chloroplasts 6 (ARC6) and its paralogue PARC6 [1]. ARC6 and PARC6 are components of the plastid division machinery which are essential for the chloroplast replication process [1,2], which implies the assembly and constriction of the tubulin-like FtsZ ring on the stromal surface of the inner envelope membrane (IEM) and the dynamin-like ARC5 ring on the cytosolic surface of the outer envelope membrane (OEM). ARC6 is evolutionarily related to the cyanobacterial cell division protein Ftn2/ZipN [1], having similar structures. This domain from ARC6 and PARC6 interacts with PDV2 and PDV1 respectively. PDV proteins recruit dynamin-like ARC5 ring to the chloroplast surface and mediates its constriction. ARC6/PARC6 are key to connect and coordinate Fst and ARC5 rings during fission [3,4].

1: Crystal structure of a conserved domain in the intermembrane space region of the plastid division protein ARC6. Kumar N, Radhakrishnan A, Su CC, Osteryoung KW, Yu EW; Protein Sci. 2016;25:523-529. PMID:26452626

2: Roles of Arabidopsis PARC6 in Coordination of the Chloroplast Division Complex and Negative Regulation of FtsZ Assembly. Zhang M, Chen C, Froehlich JE, TerBush AD, Osteryoung KW; Plant Physiol. 2016;170:250-262. PMID:26527658

3: Arabidopsis ARC6 coordinates the division machineries of the inner and outer chloroplast membranes through interaction with PDV2 in the intermembrane space. Glynn JM, Froehlich JE, Osteryoung KW; Plant Cell. 2008;20:2460-2470. PMID:18812496

4: Arabidopsis PARC6 Is Critical for Plastid Morphogenesis in Pavement, Trichome, and Guard Cells in Leaf Epidermis. Ishikawa H, Yasuzawa M, Koike N, Sanjaya A, Moriyama S, Nishizawa A, Matsuoka K, Sasaki S, Kazama Y, Hayashi Y, Abe T, Fujiwara MT, Itoh RD; Front Plant Sci. 2020;10:1665. PMID:32010156