An Archaebacterial Topoisomerase Homolog Not Present in Other Eukaryotes Is Indispensable for Cell Proliferation of Plants

Curr Biol. 2002 Oct 15;12(20):1787-91. doi: 10.1016/s0960-9822(02)01218-6.


Plants, in contrast to other eukaryotes, possess not only homologs of subunit A (AtSPO11-1, 2, 3) but also of subunit B (AtTOP6B) of the archaebacterial topoisomerase VI. AtTOP6B and AtSPO11-3 are strongly expressed in somatic tissue of Arabidopsis and are able to interact with each other in vitro. A T-DNA insertion in AtTOP6B results in deficient cell proliferation; plants stop growing at the rosette stage, have small crinkled leaves, and die about 4 weeks after germination. Cultured root cells die after a limited number of cell divisions. The mitotic index of the root meristems is strongly reduced. Flow cytometric analysis demonstrates that endoreplication in mutant plants is stopped at the 8C stage; the last cycle is not completed in most cases. Mutant plants show a significant increase in nuclear DNA strand breaks. A T-DNA insertion mutant of AtSPO11-3 has a phenotype that is almost to that of AtTOP6B and the double mutant. Thus, both genes seem to act in vivo as subunits of a functional entity. A loss of this function most likely results in a defect in DNA replication, leading directly, or via the activation of a DNA damage checkpoint, to an arrest of cell division and endoreduplication. The dependence on an archaebacterial topoisomerase VI homolog distinguishes plants from the other eukaryotic kingdoms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / cytology*
  • Arabidopsis / growth & development
  • Archaea / enzymology*
  • Cell Division / physiology*
  • DNA Damage
  • DNA Topoisomerases, Type I / genetics
  • DNA Topoisomerases, Type I / metabolism*
  • DNA Transposable Elements
  • Genes, Essential
  • Mutagenesis
  • Phenotype
  • Protein Subunits / genetics
  • Protein Subunits / metabolism


  • DNA Transposable Elements
  • Protein Subunits
  • DNA Topoisomerases, Type I