Tobacco BY-2 cells expressing fission yeast cdc25 bypass a G2/M block on the cell cycle |
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Authors: | Orchard Craig B Siciliano Ilario Sorrell David A Marchbank Angela Rogers Hilary J Francis Dennis Herbert Robert J Suchomelova Petra Lipavska Helena Azmi Abdelkrim Van Onckelen Harry |
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Institution: | School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK. |
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Abstract: | The mitotic inducer gene from Schizosaccharomyces pombe, Spcdc25, was used as a tool to investigate regulation of G2/M in higher plants using the BY-2 (Nicotiana tabacum) cell line as a model. Spcdc25-expressing BY-2 cells exhibited a reduced mitotic cell size through a shortening of the G2 phase. The cells often formed isodiametric double files both in BY-2 cells and in cell suspensions derived from 35S::Spcdc25 tobacco plants. In Spcdc25-expressing cells, the tobacco cyclin-dependent kinase, NtCDKB1, showed high activity in early S phase, S/G2 and early M phase, whereas in empty vector cells CDKB1 activity was transiently high in early S phase but thereafter remained lower. Spcdc25-expressing cells also bypassed a block on G2/M imposed by the cytokinin biosynthetic inhibitor lovastatin (LVS). Surprisingly, cytokinins were at remarkably low levels in Spcdc25-expressing cells compared with the empty vector, explaining why these cells retained mitotic competence despite the presence of LVS. In conclusion, synchronised Spcdc25-expressing BY-2 cells divided prematurely at a small cell size, and they exhibited premature, but sustained, CDKB1 activity even though endogenous cytokinins were virtually undetectable. |
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Keywords: | Nicotiana tabacum cell size cytokinins BY-2 cell line CDKA/B plant cell cycle |
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