Cytological characterization of the tandem repetitive sequences and their methylation status in the Antirrhinum majus genome.
Tandem repetitive sequences are DNA motifs common in the genomes of eukaryotic species and are often embedded in heterochromatic regions. In most eukaryotes, ribosomal genes, as well as centromeres and telomeres or subtelomeres, are associated with abundant tandem arrays of repetitive sequences and typically represent the final barriers to completion of whole-genome sequencing. The nature of these repeats makes it difficult to estimate their actual sizes. In this study, combining the two cytological techniques DNA fiber-FISH and pachytene chromosome FISH allowed us to characterize the tandem repeats distributed genome wide in Antirrhinum majus and identify four types of tandem repeats, 45S rDNA, 5S rDNA, CentA1, and CentA2, representing the major tandem repetitive components, which were estimated to have a total length of 18.50 Mb and account for 3.59% of the A. majus genome. FISH examination revealed that all the tandem repeats correspond to heterochromatic knobs along the pachytene chromosomes. Moreover, the methylation status of the tandem repeats was investigated in both somatic cells and pollen mother cells from anther tissues using an antibody against 5-methylcytosine combined with sequential FISH analyses. Our results showed that these repeats were hypomethylated in anther tissues, especially in the pollen mother cells at pachytene stage.
State Key Laboratory of Plant Genomics and Center for Plant Gene Research, Beijing 100101, China.
Dongfen
D
Zhang
Qiuying
Q
Yang
Yong
Y
Ding
Xiaofeng
X
Cao
Yongbiao
Y
Xue
Zhukuan
Z
Cheng
D032161:Antirrhinum / Q000235:genetics*; D032461:Chromosomes, Plant / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D003596:Cytosine / Q000378:metabolism; D019175:DNA Methylation; D005456:Fluorescent Dyes / Q000737:chemistry; D018745:Genome, Plant; D006570:Heterochromatin / Q000378:metabolism / Q000648:ultrastructure; D017404:In Situ Hybridization, Fluorescence; D007211:Indoles / Q000737:chemistry; D020080:Tandem Repeat Sequences
D005456:Fluorescent Dyes; D006570:Heterochromatin; D007211:Indoles; C007293:DAPI; D003596:Cytosine