Expression and stability of Arabidopsis CDC6 are associated with endoreplication.
Studies on the CDC6 protein, which is crucial to the control of DNA replication in yeast and animal cells, are lacking in plants. We have isolated an Arabidopsis cDNA encoding the AtCDC6 protein and studied its possible connection to the occurrence of developmentally regulated endoreplication cycles. The AtCDC6 gene is expressed maximally in early S-phase, and its promoter contains an E2F consensus site that mediates the binding of a plant E2F/DP complex. Transgenic plants carrying an AtCDC6 promoter-beta-glucuronidase fusion revealed that it is active in proliferating cells and, interestingly, in endoreplicating cells. In particular, the extra endoreplication cycle that occurs in dark-grown hypocotyl cells is associated with upregulation of the AtCDC6 gene. This was corroborated using ctr1 Arabidopsis mutants altered in their endoreplication pattern. The ectopic expression of AtCDC6 in transgenic plants induced endoreplication and produced a change in the somatic ploidy level. AtCDC6 was degraded in a ubiquitin- and proteosome-dependent manner by extracts from proliferating cells, but it was degraded poorly by extracts from dark-grown hypocotyl endoreplicating cells. Our results indicate that endoreplication is associated with expression of the AtCDC6 gene and, most likely, the stability of its product; it also apparently requires activation of the retinoblastoma/E2F/DP pathway. These conclusions may apply to endoreplicating cells in other tissues of the plant and to endoreplicating cells in other eukaryotes.
Castellano
M M
MM
Centro de Biologia Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
del Pozo
J C
JC
Ramirez-Parra
E
E
Brown
S
S
Gutierrez
C
C
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D002940:Circadian Rhythm; D004261:DNA Replication / Q000235:genetics*; D004268:DNA-Binding Proteins; D003624:Darkness; D050684:E2F Transcription Factors; D018506:Gene Expression Regulation, Plant; D006801:Humans; D008027:Light; D051379:Mice; D008938:Mitosis; D008969:Molecular Sequence Data; D010802:Phylogeny; D011003:Ploidies; D011401:Promoter Regions, Genetic; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; C066503:CDC6 protein, S cerevisiae; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors