A plant cyclin B2 is degraded early in mitosis and its ectopic expression shortens G2-phase and alleviates the DNA-damage checkpoint

Author:

Weingartner Magdalena12,Pelayo Helvia R.3,Binarova Pavla4,Zwerger Karin1,Melikant Balázs1,de la Torre Consuelo3,Heberle-Bors Erwin1,Bögre László2

Affiliation:

1. Institute of Microbiology and Genetics, University of Vienna, Vienna Biocenter, Dr Bohrgasse 9, A-1030 Vienna, Austria

2. School of Biological Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK

3. Centro de Investigaciones Biológicas CSIC, Velázquez 144,E-28006-Madrid, Spain

4. Institute of Microbiology, Academy of Sciences of the Czech Republic,Vídeňská 1083, 142 20 Prague 4, Czech Republic

Abstract

Mitotic progression is timely regulated by the accumulation and degradation of A- and B-type cyclins. In plants, there are three classes of A-, and two classes of B-type cyclins, but their specific roles are not known. We have generated transgenic tobacco plants in which the ectopic expression of a plant cyclin B2 gene is under the control of a tetracycline-inducible promoter. We show that the induction of cyclin B2 expression in cultured cells during G2 phase accelerates the entry into mitosis and allows cells to override the replication checkpoint induced by hydroxyurea in the simultaneous presence of caffeine or okadaic acid, drugs that are known to alleviate checkpoint control. These results indicate that in plants, a B2-type cyclin is a rate-limiting regulator for the entry into mitosis and a cyclin B2-CDK complex might be a target for checkpoint control pathways. The cyclin B2 localization and the timing of its degradation during mitosis corroborate these conclusions: cyclin B2 protein is confined to the nucleus and during mitosis it is only present during a short time window until mid prophase, but it is effectively degraded from this timepoint onwards. Although cyclin B2 is not present in cells arrested by the spindle checkpoint in metaphase, cyclin B1 is accumulating in these cells. Ectopic expression of cyclin B2 in developing plants interferes with differentiation events and specifically blocks root regeneration, indicating the importance of control mechanisms at the G2- to M-phase transition during plant developmental processes.

Publisher

The Company of Biologists

Subject

Cell Biology

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