An archaebacterial topoisomerase homolog not present in other eukaryotes is indispensable for cell proliferation of plants.
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.
Hartung
Frank
F
Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466 Gatersleben, Germany.
Angelis
Karel J
KJ
Meister
Armin
A
Schubert
Ingo
I
Melzer
Michael
M
Puchta
Holger
H
D017360:Arabidopsis / Q000166:cytology* / Q000254:growth & development; D001105:Archaea / Q000201:enzymology*; D002455:Cell Division / Q000502:physiology*; D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D004251:DNA Transposable Elements; D020043:Genes, Essential; D016296:Mutagenesis; D010641:Phenotype; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism
D004251:DNA Transposable Elements; D021122:Protein Subunits; D004264:DNA Topoisomerases, Type I