Originally published as Genetics Published Articles Ahead of Print on September 12, 2005.

Genetics, Vol. 172, 467-475, January 2006, Copyright © 2006
doi:10.1534/genetics.105.048363

Sister Chromatids Are Often Incompletely Aligned in Meristematic and Endopolyploid Interphase Nuclei of Arabidopsis thaliana

Institute of Plant Genetics and Crop Plant Research (IPK), D-06466 Gatersleben, Germany

2 Corresponding author: Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, D-06466 Gatersleben, Germany.
E-mail: schubert{at}ipk-gatersleben.de

We analyzed whether sister chromatids are continuously aligned in meristematic and endopolyploid Arabidopsis interphase nuclei by studying sister-chromatid alignment at various chromosomal positions. FISH with individual BACs to flow-sorted 4C root and leaf nuclei frequently yielded more than two hybridization signals, indicating incomplete or absent sister-chromatid alignment. Up to 100% of 8C, 16C, and 32C nuclei showed no sister-chromatid alignment at defined positions. Simultaneous FISH with BACs from different chromosomal positions revealed more frequent sister-chromatid alignment in terminal than in midarm positions. Centromeric positions were mainly aligned up to a ploidy level of 16C but became separated or dispersed in 32C nuclei. DNA hypomethylation (of the whole genome) and transcriptional activity (at FWA gene position) did not impair sister-chromatid alignment. Only 6.1% of 4C leaf nuclei showed sister-chromatid separation of the entire chromosome 1 top arm territories. Homozygous transgenic tandem repeat (lac operator) arrays showing somatic homologous pairing more often than average euchromatic loci did not promote an increased frequency of sister-chromatid alignment. The high frequency of separated sister-chromatid arm positions in ≥4C nuclei suggests that sister-chromatid cohesion is variable, dynamic, and not obligatory along the entire chromosome arm in meristematic and differentiated Arabidopsis nuclei.




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