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Examines the regulation of mitotic progression regulated by the accumulation and degradation of A- and B-type cyclins. Classification of A- and B-type cyclins; Induction of the cyclin B2 expression in cultured cells; Presence of caffeine or akadaic acid.

The rapidly proliferating cells in plant meristems must be protected from genome damage. Here, we show that the regulatory role of the Arabidopsis RETINOBLASTOMA RELATED ( RBR) in cell proliferation can be separated from a novel function in safeguarding genome integrity. Upon DNA damage, RBR and its binding partner E2 FA are recruited to heterochromatic γH2 AX-labelled DNA damage foci in an ATM- and ATR-dependent manner. These γH2 AX-labelled DNA lesions are more dispersedly occupied by the conserved repair protein, At BRCA1, which can also co-localise with RBR foci. RBR and At BRCA1 physically interact in vitro and in planta. Genetic interaction between the RBR-silenced ami RBR and Atbrca1 mutants suggests that RBR and At BRCA1 may function together in maintaining genome integrity. Together with E2 FA, RBR is directly involved in the transcriptional DNA damage response as well as in the cell death pathway that is independent of SOG1, the plant functional analogue of p53. Thus, plant homologs and analogues of major mammalian tumour suppressor proteins form a regulatory network that coordinates cell proliferation with cell and genome integrity. [ABSTRACT FROM AUTHOR]

In plants after the disassembly of mitotic spindle, a specific cytokinetic structure called the phragmoplast is built, and after cytokinesis, microtubules populate the cell cortex in an organized orientation that determines cell elongation and shape. Here, we show that impaired cyclin B1 degradation, resulting from a mutation within its destruction box, leads to an isodiametric shape of epidermal cells in leaves, stems, and roots and retarded growth of seedlings. Microtubules in these misshaped cells are grossly disorganized, focused around the nucleus, whereas they were entirely missing or abnormally organized along the cell cortex. A high percentage of cells expressing nondestructible cyclin B1 had doubled DNA content as a result of undergoing endomitosiso During anaphase the cytokinesis-specific syntaxin KNOLLE could still localize to the midplane of cell division, whereas NPK1-activating kinesin-like protein 1, a cytokinetic kinesin-related protein, was unable to do so, and instead of the formation of a phragmoplast, the midzone microtubules persisted between the separated nuclei, which eventually fused. In summary, our results show that the timely degradation of mitotic cyclins in plants is required for the reorganization of mitotic microtubules to the phragmoplast and for proper cytokinesis. Subsequently, the presence of nondegradable cyclin B1 leads to a failure in organizing properly the cortical microtubules that determine cell elongation and shape. [ABSTRACT FROM AUTHOR]

Presents evidence that γ-tubulin is present in protein complexes of various sizes and different subcellular locations in Arabidopsis and fava bean. Background on the γ-tubulin; Association of γ-tubulin with microtubules and membranes; Subcellular localization of γ-tubulin in mitotic cells.