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Free Content The first zygotic division in Arabidopsis requires de novo transcription of thymidylate kinase

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Re-activation of cell division after fertilization involves the specific regulation of a set of genes. To identify genes involved in the gametophytic to sporophytic transition, we screened Arabidopsis T-DNA insertion lines for early seed abortion at the zygote (zeus) or one-cell embryo stages (cyclops), and characterized a sporophytic zygote-lethal mutation, zeus1. ZEUS1 encodes a thymidylate kinase (AtTMPK) that synthesizes dTDP and is involved in the regulation of DNA replication. Unlike in yeast and animals, the single AtTMPK gene is capable of producing two proteins by alternative splicing; the longer isoform is targeted to the mitochondria, the shorter to the cytosol. Transcription of AtTMPK is activated during the G1/S-phase transition of the cell cycle, similarly to yeast and mammalian orthologues. In AtTMPK:GUS plants, the reporter gene was preferentially expressed in cells undergoing division, but was not detected during the male and female gametophytic mitoses. GUS expression was observed in mature embryo sacs prior to fertilization, and this expression may indicate the time of synchronization of the gamete cell-cycle phases. Identification of ZEU1 emphasizes the importance of control of the metabolism of DNA in the regulation of the G1/S-phase transition at fertilization.
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Keywords: Arabidopsis; G1/S-phase transition; cell cycle; embryogenesis; fertilization; thymidylate kinase

Document Type: Research Article

Affiliations: 1: Laboratoire Génome et Développement des Plantes, UMR-CNRS-IRD-Université 5096, 52 Avenue Paul Alduy, 66 860 Perpignan-cedex, France 2: Institut de Biologie Moléculaire des Plantes du CNRS, 12 rue du Général Zimmer, 67 084 Strasbourg-cedex, France 3: Station de Génétique et Amélioration des Plantes, INRA, Route de Saint-Cyr, 78 026 Versailles-cedex, France

Publication date: March 1, 2008

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