Acts on the G1 phase of the cell cycle to control cell division rate in both shoot and root meristems. The complex formed with CDKA-1 phosphorylates plant retinoblastoma protein. Interacts with KRP1/ICK1 and with the C-terminal domain of CDKA-1. A number of isoforms are produced. According to EST sequences. Expressed in roots and leaves. Expressed throughout the cell cycle. By sucrose and glucose. Belongs to the cyclin family. Cyclin D subfamily.