Binds and inhibits CYCD2-1/CDKA-1 complex kinase activity. Regulates cell division which is crucial for plant growth, development and morphogenesis. May inhibit CDK kinases specifically involved in the G1/S phase transition. Down-regulated by KIN10 under a phosphorylation-dependent manner. Specifically interacts with CDKA-1, but not with CDKB1-1. Interacts with CYCD1-1, CYCD4-1 and RHF1A. Binds to FBL17. Interacts with KIN10 (PubMed:23617622). Interacts with CYCD3-1 (PubMed:23617622). Homogeneously distributed. Present in microspores and accumulates strongly in vegetative cell nuclei immediately after asymmetric division and disappears later. Expressed in newly formed organs such as the shoot apex. Expressed in cotyledon, primary root and marginal region of the leaves as well as in developing pollen. Expressed in both ovules and anthers during meiosis and disappears before gametophytic mitosis. Present in uninucleate microspore and bicellular pollen, and, to a lower extent, in immature tricellular pollen and mature tricellular pollen. Ubiquitinated by RHF1A and SCF(FBL17). Ubiquitination leads to its subsequent degradation, thus controlling cell cycle progression. The phosphorylation at Thr-152 by KIN10 represses its activity. Belongs to the CDI family. ICK/KRP subfamily.