Binds and inhibits CYCD2-1/CDKA-1 kinase complex activity. Regulates cell division which is crucial for plant growth, development and morphogenesis. Functions in turning cells from a mitotic to an endoreplicating cell cycle mode. Acts cell- and non-cell-autonomously to regulate endoreduplication by allowing S phase progression, but blocking entry into mitosis. Keeps on the one hand the plant cell cycle locally controlled, and on the other hand provides a possibility of linking cell cycle control in single cells with the supracellular organization of a tissue or an organ. May target specifically CDKA-1. Specifically interacts with CDKA-1, but not with CDKB1-1. Interacts with CYCD2-1 and CYCD3-1. Distributed in a ponctuate pattern and in heterochromatic chromocenters. Expressed at low levels in roots, stems, leaves and flowers. Highly expressed in root pericycle and cell suspension culture during cell cycle arrest. Expressed early in the G1 phase, disappears quickly and starts to increase again to reach a peak before mitosis. By abscisic acid (ABA). Ubiquitinated independently by RKP and SCF (SKP1-CUL1-FBL5/SKP2B) protein ligase complex, leading to proteasomal degradation. No visible phenotype. Plants overexpressing ICK1/KRP1 show altered morphology (including flowers) with a reduction in plant size, cell numbers, pollen germination, seed production and CDK kinase activity. Trichome cells misexpressing ICK1/KRP1 show reduced endoreduplication and cell size, and undergo cell death. ICK1/KRP1 degradation is regulated by the AXR1-dependent RUB conjugation pathway that is required for the function of the SCF complexes. Belongs to the CDI family. ICK/KRP subfamily.