Characterization of rDNAs and tandem repeats in the heterochromatin of Brassica rapa.
We describe the morphology and molecular organization of heterochromatin domains in the interphase nuclei, and mitotic and meiotic chromosomes, of Brassica rapa, using DAPI staining and fluorescence in situ hybridization (FISH) of rDNA and pericentromere tandem repeats. We have developed a simple method to distinguish the centromeric regions of mitotic metaphase chromosomes by prolonged irradiation with UV light at the DAPI excitation wavelength. Application of this bleached DAPI band (BDB) karyotyping method to the 45S and 5S rDNAs and 176 bp centromere satellite repeats distinguished the 10 B. rapa chromosomes. We further characterized the centromeric repeat sequences in BAC end sequences. These fell into two classes, CentBr1 and CentBr2, occupying the centromeres of eight and two chromosomes, respectively. The centromere satellites encompassed about 30% of the total chromosomes, particularly in the core centromere blocks of all the chromosomes. Interestingly, centromere length was inversely correlated with chromosome length. The morphology and molecular organization of heterochromatin domains in interphase nuclei, and in mitotic and meiotic chromosomes, were further characterized by DAPI staining and FISH of rDNA and CentBr. The DAPI fluorescence of interphase nuclei revealed ten to twenty conspicuous chromocenters, each composed of the heterochromatin of up to four chromosomes and/or nucleolar organizing regions.
Lim
Ki-Byung
KB
Brassica Genomics Team, National Institute of Agricultural Biotechnology, Rural Development Administration, Suwon 441-707, Korea.
de Jong
Hans
H
Yang
Tae-Jin
TJ
Park
Jee-Young
JY
Kwon
Soo-Jin
SJ
Kim
Jung Sun
JS
Lim
Myung-Ho
MH
Kim
Jin A
JA
Jin
Mina
M
Jin
Yong-Moon
YM
Kim
Seog Hyung
SH
Lim
Yong Pyo
YP
Bang
Jae-Wook
JW
Kim
Ho-Il
HI
Park
Beom-Seok
BS
D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D029741:Brassica rapa / Q000235:genetics*; D032461:Chromosomes, Plant / Q000648:ultrastructure; D004275:DNA, Ribosomal / Q000032:analysis*; D006570:Heterochromatin / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D020080:Tandem Repeat Sequences
D004275:DNA, Ribosomal; D006570:Heterochromatin