Publications by authors named "Riou-Khamlichi C"

Two APETALA2 domain transcription factors were characterized first in angiosperms, and, recently, in several gymnosperms. These proteins are involved in several processes, from flowering to embryogenesis in Arabidopsis thaliana. We extrapolated this result to hybrid larch (Larixxmarschlinsii Coaz) resulting from a cross between European (Larix decidua) and Japanese (Larix kaempferi) larches.

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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.

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In plants, Lewisa type N-glycans may be involved in cell-to-cell communication and recognition. N-glycoproteins harboring Lewisa glycotopes are mainly found in plasma membranes and cell walls. Some can be also involved in cell wall synthesis or the loosening process, and subsequently in cell elongation.

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CYCD3;1 expression in Arabidopsis is associated with proliferating tissues such as meristems and developing leaves but not with differentiated tissues. Constitutive overexpression of CYCD3;1 increases CYCD3;1-associated kinase activity and reduces the proportion of cells in the G1-phase of the cell cycle. Moreover, CYCD3;1 overexpression leads to striking alterations in development.

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Tuber explants of Jerusalem artichoke (Helianthus tuberosus L.) are a model system for cell-cycle re-entry from a quiescent state, involving the activation of division of tuber parenchyma cells in response to exogenous auxin. To enable molecular studies of this system, two cyclin (Heltu;CYCD1;1 and Heltu; CYCD3;1) and two cyclin-dependent kinase (Heltu; CDKA;1 and Heltu;CDKB1;1) genes have been isolated from a Jerusalem artichoke cDNA library and their expression demonstrated during the activation of cell division.

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The basic pattern of controls that operate during the G1 phase of the plant cell cycle shows much closer similarity to animals than to the yeasts and other fungi. The activity of D-type cyclin (CycD) kinases is induced in response to stimulatory signals, and these phosphorylate the plant homologue of the retinoblastoma tumour susceptibility (Rb) protein. It is likely that Rb phosphorylation results in the activation of genes under the control of E2F transcription factors, including those required for S phase entry.

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alpha4-Fucosylation represents a final step of protein N- glycosylation. alpha4-fucosylated N-glycans are thought to be involved in cell-to-cell communication and recognition in primates and plants. Nevertheless, in the plant life cycle, the function of alpha4-fucosylation remains largely unknown.

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Plant development requires stringent controls between cell proliferation and cell differentiation. Proliferation is positively regulated by cyclin dependent kinases (CDKs). Acting in opposition to CDKs are CDK inhibitors (CKIs).

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In most plants, sucrose is the major transported carbon source. Carbon source availability in the form of sucrose is likely to be a major determinant of cell division, and mechanisms must exist for sensing sugar levels and mediating appropriate control of the cell cycle. We show that sugar availability plays a major role during the G(1) phase by controlling the expression of CycD cyclins in Arabidopsis.

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Three D-cyclin genes are expressed in the apical meristems of snapdragon (Antirrhinum majus). The cyclin D1 and D3b genes are expressed throughout meristems, whereas cyclin D3a is restricted to the peripheral region of the meristem, especially the organ primordia. During floral development, cyclin D3b expression is: (a) locally modulated in the cells immediately surrounding the base of organ primordia, defining a zone between lateral organs that may act as a developmental boundary; (b) locally modulated in the ventral petals during petal folding; and (c) is specifically repressed in the dorsal stamen by the cycloidea gene.

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Cytokinins are plant hormones that regulate plant cell division. The D-type cyclin CycD3 was found to be elevated in a mutant of Arabidopsis with a high level of cytokinin and to be rapidly induced by cytokinin application in both cell cultures and whole plants. Constitutive expression of CycD3 in transgenic plants allowed induction and maintenance of cell division in the absence of exogenous cytokinin.

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