Member of the pre-replication complex. Component of the plastid division machinery. Promotes polyloidization and regulates endoreduplication. Involved in the coordination of cell and plastid division. Binds to ARC6. Expressed in proliferating (e.g. shoot and root apical meristems, organ primordia) and endoreplicating cells (e.g. guard cells and stomatal lineage, developing trichomes). Repressed by abscisic acid (ABA) and ABAP1. Degraded by the proteasome. Phosphorylated by cyclin D- and cyclin A-containing CDKA-1, and thus targeted to proteasome-mediated proteolysis. Belongs to the Cdt1 family.