Required for chloroplast division (PubMed:29967285, PubMed:23936263). Together with MIND1 and ARC3, regulates FtsZ ring positioning in chloroplasts in an ARC6-dependent manner (PubMed:29967285). Determines the site of chloroplast division in concert with MIND1 (PubMed:29967285). Not directly involved in ring formation, but required for MIND1 and MINE1 localization to regulate FtsZ ring formation during plastidial constriction (PubMed:29967285). Interacts with MIND1 (PubMed:19135368). Interacts with ARC6 in the chloroplast stroma and binds to FtsZ2-1 in an ARC6-dependent manner (PubMed:29967285). Localizes at the chloroplast to a ring structure at the constriction site and on the punctate structures of the envelope membrane throughout the chloroplast division. Heterogeneous population of chloroplasts with variable size and multiple division sites (PubMed:19135368, PubMed:23936263). Abnormal subplastidial localization of the key plastid division proteins FTSZ1 forming multiple rings (PubMed:29967285). Normal shape and number of etioplasts in cotyledons (PubMed:23936263). The double mutant mcd1 arc6 exhibits similar chloroplast defect than the single mutant arc6, including the abnormal localization of FTSZ1 to short filaments and dots within chloroplasts (PubMed:29967285).