title: Condensin and cohesin knockouts in Arabidopsis exhibit a titan seed phenotype.
abstract: The titan (ttn) mutants of Arabidopsis exhibit striking alterations in chromosome dynamics and cell division during seed development. Endosperm defects include aberrant mitoses and giant polyploid nuclei. Mutant embryos differ in cell size, morphology and viability, depending on the locus involved. Here we demonstrate that three TTN genes encode chromosome scaffold proteins of the condensin (SMC2) and cohesin (SMC1 and SMC3) classes. These proteins have been studied extensively in yeast and animal systems, where they modulate chromosome condensation, chromatid separation, and dosage compensation. Arabidopsis contains single copies of SMC1 and SMC3 cohesins. We used forward genetics to identify duplicate T-DNA insertions in each gene. These mutants (ttn7 and ttn8) have similar titan phenotypes: giant endosperm nuclei and arrested embryos with a few small cells. A single SMC2 knockout (ttn3) was identified and confirmed by molecular complementation. The weak embryo phenotype observed in this mutant may result from expression of a related gene (AtSMC2) with overlapping functions. Further analysis of titan mutants and the SMC gene family in Arabidopsis should provide clues to chromosome mechanics in plants and insights into the regulation of nuclear activity during endosperm development.
authors.affiliation: Department of Botany, Oklahoma State University, Stillwater, OK 74078, USA.
authors.forename: Chun-ming
authors.initials: CM
authors.lastname: Liu Cm
authors.forename: John
authors.initials: J
authors.lastname: McElver
authors.forename: Iris
authors.initials: I
authors.lastname: Tzafrir
authors.forename: Ronny
authors.initials: R
authors.lastname: Joosen
authors.forename: Peter
authors.initials: P
authors.lastname: Wittich
authors.forename: David
authors.initials: D
authors.lastname: Patton
authors.forename: Andre A M
authors.initials: AA
authors.lastname: Van Lammeren
authors.forename: David
authors.initials: D
authors.lastname: Meinke
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000502:physiology; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins / Q000235:genetics*; D005656:Fungal Proteins; D015870:Gene Expression; D005816:Genetic Complementation Test; D008938:Mitosis / Q000235:genetics; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D010641:Phenotype; D010802:Phylogeny; D011123:Polyploidy; D012639:Seeds / Q000235:genetics* / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D000097722:Cohesins
chemical_list: D000251:Adenosine Triphosphatases; D029681:Arabidopsis Proteins; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D000097722:Cohesins; C108312:condensin complexes