Involved in the control of the cell cycle at the G2/M (mitosis) transition. May activate CDKB2-1 kinase. Interacts with CDKB2-1. Expressed in the intercalary meristem and the elongation zone of internodes. Expressed in adventitious roots at all nodes under submergence conditions. Expressed in the G2/M phases and disappears at the anaphase of mitosis. By gibberellic acid (GA3), ethylene and submergence. May be involved in rapid internodal growth of deepwater rice under submergence. Belongs to the cyclin family. Cyclin AB subfamily.