Visualization of the ribosomal DNA (45S rDNA) of Indica rice with FISH on some phases of cell cycle and extended DNA fibers

Zong Yun Li ,Shu Feng Huang ,Fang Hu ,Mei Li Fu ,Yun Song

doi:10.32604/biocell.2006.30.027

Abstract

The ribosomal DNA (45S rDNA) behaviors during the cell cycle were analyzed on interphase nuclei, prophases, metaphases, pachytene chromosomes and extended DNA fibers in rice (Oryza, sativa ssp. indica cv. Guangluai No.4) by using high-resolution fluorescent in situ hybridization (FISH). The results show that 45S rDNA is located at the ends of short arms of chromosomes 9 and 10. But the signals are much more intense on chromosome 9 than on chromosome 10 in metaphase. Pachytene chromosome has rDNA signal arrays on chromosome 9. Different phases are described and discussed. These results indicate that the activity ofrDNA at individual loci may also vary through the cell cycle in rice. On extended DNA fibers, 45S rDNA signals appear as strings of numerous red spots, but some signals are missed in some regions, probably result from weak signals or intergenic spacers.

Highlights

Genome sizes differ greatly in plants due to the presence of different amounts of repeat DNA sequences (Bennetzen, 1996; Graham, 1995)
In metaphase the rDNA loci are located at the ends of short arms of chromosomes 9 and 10, consistent with the previous study (Fukui et al, 1994; Gong et al, 2002).The rice chromosome 9 and 10 were identified by their unique characters, such as chromosome 9 is the second smallest chromosome in rice, and chromosome 10 contains considerable heterochromatin on the entire short arm, which were described by Fukui and Gong (Fukui et al, 1994; Gong et al, 2002)
It is very interesting that the signals on pachytene chromosomes are contracted in pre-pachytene (Fig. 5) and appear as array beads, 3 to 6 signals are arranged clearly in late-pachytene (Fig. 6), like the signals detected with fiber-Fluorescence in situ hybridization (FISH) (Fig. 7)

Summary

Introduction

Genome sizes differ greatly in plants due to the presence of different amounts of repeat DNA sequences (Bennetzen, 1996; Graham, 1995). The length observed for the rDNA repeating unit range from 7.8kb to 18.5kb in plants (Lapitan, 1992). Numbers of rDNA loci range from 1 to 3 among the species tested in rice (Fukui et al, 1994; Shishido et al, 2000).

Results

Conclusion