Cyclin-dependent kinase activity maintains the shoot apical meristem cells in an undifferentiated state.

As the shoot apex produces most of the cells that comprise the aerial part of the plant, perfect orchestration between cell division rates and fate specification is essential for normal organ formation and plant development. However, the inter-dependence of cell-cycle machinery and meristem-organizing genes is still poorly understood. To investigate this mechanism, we specifically inhibited the cell-cycle machinery in the shoot apex by expression of a dominant negative allele of the A-type cyclin-dependent kinase (CDK) CDKA;1 in meristematic cells.

Atypical E2F activity restrains APC/CCCS52A2 function obligatory for endocycle onset.

The endocycle represents an alternative cell cycle that is activated in various developmental processes, including placental formation, Drosophila oogenesis, and leaf development. In endocycling cells, mitotic cell cycle exit is followed by successive doublings of the DNA content, resulting in polyploidy. The timing of endocycle onset is crucial for correct development, because polyploidization is linked with cessation of cell division and initiation of terminal differentiation.