title: The genes encoding Arabidopsis ORC subunits are E2F targets and the two ORC1 genes are differently expressed in proliferating and endoreplicating cells.
abstract: Initiation of eukaryotic DNA replication depends on the function of pre-replication complexes (pre-RC), one of its key component being the six subunits origin recognition complex (ORC). In spite of a significant degree of conservation among ORC proteins from different eukaryotic sources, the regulation of their availability varies considerably in different model systems and cell types. Here, we show that the six ORC genes of Arabidopsis thaliana are regulated at the transcriptional level during cell cycle and development. We found that Arabidopsis ORC genes, except AtORC5, contain binding sites for the E2F family of transcription factors. Expression of AtORC genes containing E2F binding sites peaks at the G1/S-phase. Analysis of AtORC gene expression in plants with reduced E2F activity, obtained by expressing a dominant negative version of DP, the E2F heterodimerization partner, and with increased E2F activity, obtained by inactivation of the retinoblastoma protein, led us to conclude that all AtORC genes, except AtORC5 are E2F targets. Interestingly, Arabidopsis contains two AtORC1 (a and b) genes, highly conserved at the amino acid level but with unrelated promoter sequences. AtORC1b expression is restricted to proliferating cells. However, AtORC1a is preferentially expressed in endoreplicating cells based on our analysis in endoreplicating tissues and in a mutant with altered endocycle pattern. This suggests a differential expression of the two ORC1 genes in Arabidopsis.
authors.affiliation: Centro de Biologia Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid Cantoblanco, 28049 Madrid, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Diaz-Trivino
authors.forename: María
authors.initials: M
authors.lastname: del Mar Castellano
authors.forename: María
authors.initials: M
authors.lastname: de la Paz Sanchez
authors.forename: Elena
authors.initials: E
authors.lastname: Ramirez-Parra
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Desvoyes
authors.forename: Crisanto
authors.initials: C
authors.lastname: Gutierrez
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics*; D001665:Binding Sites; D002453:Cell Cycle / Q000235:genetics; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D049109:Cell Proliferation; D002478:Cells, Cultured; D004261:DNA Replication; D018076:DNA, Complementary / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D050684:E2F Transcription Factors; D018506:Gene Expression Regulation, Plant; D051738:Origin Recognition Complex; D010940:Plant Proteins; D011401:Promoter Regions, Genetic; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D018797:Cell Cycle Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C417206:DP transcription factor, plant; D050684:E2F Transcription Factors; C504720:ORC1a protein, Arabidopsis; C504721:ORC1b protein, Arabidopsis; D051738:Origin Recognition Complex; D010940:Plant Proteins; D021122:Protein Subunits; D014157:Transcription Factors