Disruption of the Arabidopsis SMC4 gene, AtCAP-C, compromises gametogenesis and embryogenesis

In higher eukaryotes, the condensin complex is a multisubunit apparatus that plays a pivotal role in the coordinated condensation of chromatin during mitosis. The catalytic subunits, CAP-E and CAP-C, members of the SMC family of ATPases, form a heterodimer, the activity of which is controlled by the non-SMC subunits CAP-D2, CAP-G and CAP-H. Here, we report the characterization of a T-DNA insertion mutant of the Arabidopsis CAP-C gene. Analysis of the progeny of selfed heterozygotes revealed that the homozygous null genotype is embryo lethal, with arrest occurring at or before the globular stage of development. Patterning defects associated with altered planes of cytokinesis were found in both the embryo and the suspensor. Crosses of heterozygotes with wild type plants revealed both male and female gametophytic defects. Stretched chromatin was observed between segregating mitotic chromosomes in pollen produced by selfed heterozygotes. Additionally, some plants heterozygous for the T-DNA insertion exhibited loss of apical dominance and mild fasciation, indicating a semi-dominant effect of the mutation. These results reveal a critical role for AtCAP-C during cell division and, unlike our previous studies on the AtCAP-E genes, suggest that no redundant factors for AtCAP-C exist in the Arabidopsis genome.