Large-scale dissociation and sequential reassembly of pericentric heterochromatin in dedifferentiated Arabidopsis cells.
Chromocenters in Arabidopsis thaliana are discrete nuclear domains of mainly pericentric heterochromatin. They are characterized by the presence of repetitive sequences, methylated DNA and dimethylated histone H3K9. Here we show that dedifferentiation of specialized mesophyll cells into undifferentiated protoplasts is accompanied by the disruption of chromocenter structures. The dramatic reduction of heterochromatin involves the decondensation of all major repeat regions, also including the centromeric 180 bp tandem repeats. Only the 45S rDNA repeat remained in a partly compact state in most cells. Remarkably, the epigenetic indicators for heterochromatin, DNA methylation and H3K9 dimethylation, did not change upon decondensation. Furthermore, the decondensation of pericentric heterochromatin did not result in transcriptional reactivation of silent genomic elements. The decondensation process was reversible upon prolonged culturing. Strikingly, recondensation of heterochromatin into chromocenters is a stepwise process. Compaction of the tandemly arranged 45S rDNA regions occurs first, followed by the centromeric 180 bp and the 5S rDNA repeats and finally the dispersed repeats, including transposons. The sequence of reassembly seems to be correlated to the size of the repeat domains. Our results indicate that different types of pericentromeric repeats form different types of heterochromatin, which subsequently merge to form a chromocenter.
Tessadori
Federico
F
Nuclear Organization Group, Swammerdam Institute for Life Sciences, University of Amsterdam, BioCentrum Amsterdam, Kruislaan 318, 1098SM Amsterdam, The Netherlands.
Chupeau
Marie-Christine
MC
Chupeau
Yves
Y
Knip
Marijn
M
Germann
Sophie
S
van Driel
Roel
R
Fransz
Paul
P
Gaudin
Valérie
V
D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D015139:Blotting, Southern; D015153:Blotting, Western; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002503:Centromere / Q000378:metabolism*; D019175:DNA Methylation; D004251:DNA Transposable Elements / Q000502:physiology; D018744:DNA, Plant; D004275:DNA, Ribosomal / Q000032:analysis; D005456:Fluorescent Dyes; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D007211:Indoles; D018515:Plant Leaves / Q000166:cytology; D011523:Protoplasts / Q000166:cytology / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020080:Tandem Repeat Sequences / Q000502:physiology; D013997:Time Factors
D004251:DNA Transposable Elements; D018744:DNA, Plant; D004275:DNA, Ribosomal; D005456:Fluorescent Dyes; D006570:Heterochromatin; D006657:Histones; D007211:Indoles; C007293:DAPI