Involved in cell cycle regulation. May be a regulatory subunit of CDKD-1/CAK-R2. Interacts specifically with CDKD-1/CAK-R2. Expressed in roots, nodes and internodes, and at lower levels in shoots and leaves. Expressed in the intercalary meristem of internodes and at lower levels in the elongation zone and differentiation zone. Expressed in the S and G2 phases. By submergence in the meristematic zone of internodes. Belongs to the cyclin family. Cyclin F subfamily.