Probable cyclin-dependent protein kinase (CDK) inhibitor that functions as a repressor of mitosis in the endoreduplication cell cycle (PubMed:26546445). Acts as a potent cell cycle inhibitor, regulating a hydroxyurea-dependent checkpoint in leaves (PubMed:24399300). Essential to activate a high-light-dependent cell cycle checkpoint (PubMed:24399300). Interacts with CDKA-1 and D-type cyclins (PubMed:20706207). Expressed in columella cells in the roots and in root meristems after induction. Up-regulated by double-stranded DNA breaks-inducing treatments (PubMed:17227549). Up-regulated by zeocin treatment (PubMed:21613568). Up-regulated by DNA damage and oxidative stress (PubMed:24399300). Directly regulated by the transcription factor SOG1 (PubMed:24399300). Down-regulated by iron excess treatment (PubMed:25624148).