JXB Advance Access originally published online on October 22, 2004
Journal of Experimental Botany 2005 56(409):123-134; doi:10.1093/jxb/eri001
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RESEARCH PAPER |
Ectopic expression of Arabidopsis CYCD2 and CYCD3 in tobacco has distinct effects on the structural organization of the shoot apical meristem
1Université Pierre et Marie Curie, site Ivry-le Raphaël, Laboratoire CEMV-EA3494, case 150, 4 place Jussieu, F-75252 Paris Cedex 05, France
2Graduate School of Biology Sciences, Nara Institute of Science and Technology, Takayam 8916-5, Ikoma, Nara 630-01, Japan
3Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QT, UK
4University of Antwerp, Department of Biology, Universiteitsplein1, B-2610 Wilrijk, Belgium
* To whom correspondence should be addressed. Fax: +33 1 44 27 45 82. E-mail: dominique.chriqui{at}snv.jussieu.fr
Transgenic tobacco lines expressing Arath-CYCD2 or Arath-CYCD3 genes under a cauliflower mosaic virus 35S promoter are modified in the timing of their development, but not in the phenotype of their vegetative organs. They display an increased rate of leaf initiation, which is shown to be associated with distinct changes in the structural organization of their shoot apical meristem (SAM). Constitutive expression of Arath-CYCD2 leads to a progressive modification of the SAM structural organization with predominant periclinal divisions in the L3 layer and to the loss of the classical cytophysiological zonation, the central zone being reduced to the central cells of the L1 and L2 layers. These changes reveal a particular sensitivity of the corpus cells (L3) to Arath-CYCD2 over-expression and suggest a role for CYCD2 in controlling the planes of cell division in these cells. The SAM structural modifications in the Arath-CYCD3 over-expressing lines are less drastic; only an increased cell number together with a reduced cell size, particularly in the L1 layer, characterizes the peripheral zones. This could be related to the shortening of the G1-phase duration that renders cell growth incomplete between successive mitoses. Cell proliferation continues beyond the SAM in the developing internodes and confers a delayed senescence to Arath-CYCD3 over-expressing juvenile tissues. In addition, the ploidy levels of mature stem tissues in both types of transgenic lines are unaffected, suggesting that the studied G1 to S cell-cycle genes have no effect on the extent of endoreduplication in tobacco stem tissues.
Key words: D-type cyclins, morphogenesis, plant cell cycle, shoot meristem, tobacco
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