Cyclin-dependent protein kinase (CDK) inhibitor that restricts cell proliferation and cooperates with SIM and SMR1 to promote endoreplication during leaf development (PubMed:26546445). Interacts with CYCD2-1 (PubMed:17098811). Interacts with CDKB1-1 (PubMed:20706207). Expressed at low levels in roots and stems (PubMed:17098811). Expressed in the root vascular tissue (PubMed:24399300). Larger leaves with an increased cell number.