title: Tobacco BY-2 cells expressing fission yeast cdc25 bypass a G2/M block on the cell cycle.
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.
authors.affiliation: School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK.
authors.forename: Craig B
authors.initials: CB
authors.lastname: Orchard
authors.forename: Ilario
authors.initials: I
authors.lastname: Siciliano
authors.forename: David A
authors.initials: DA
authors.lastname: Sorrell
authors.forename: Angela
authors.initials: A
authors.lastname: Marchbank
authors.forename: Hilary J
authors.initials: HJ
authors.lastname: Rogers
authors.forename: Dennis
authors.initials: D
authors.lastname: Francis
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Herbert
authors.forename: Petra
authors.initials: P
authors.lastname: Suchomelova
authors.forename: Helena
authors.initials: H
authors.lastname: Lipavska
authors.forename: Abdelkrim
authors.initials: A
authors.lastname: Azmi
authors.forename: Harry
authors.initials: H
authors.lastname: Van Onckelen
mesh_terms: D016590:Aphidicolin / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D048429:Cell Size; D002478:Cells, Cultured; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D016195:G2 Phase / Q000187:drug effects; D018506:Gene Expression Regulation, Plant; D008148:Lovastatin / Q000494:pharmacology; D010940:Plant Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified; D012568:Schizosaccharomyces; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014026:Nicotiana / Q000166:cytology* / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D020666:ras-GRF1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D010940:Plant Proteins; D029702:Schizosaccharomyces pombe Proteins; D020666:ras-GRF1; D016590:Aphidicolin; D008148:Lovastatin; C434264:CdkB1 protein, Nicotiana tabacum; D018844:Cyclin-Dependent Kinases