Molecular Organization of Constitutive Heterochromatinin Allium cepa

摘要

The constitutive heterochromatin of Allium cepa has been characterized using PCR, C-banding and fluorescence in situ hybridization (FISH) techniques. Three kinds of repeated DNA sequences (named pAc072, pAc073 and pAc074) were characterized in Allium cepa by FISH analyses using random amplified fragment as probe. Especially, the 314-bp tandemly repeated DNA sequence of the clone pAc074 is partially homologous to the satellite DNA sequences, ACSAT1, ACSAT2, and ACSAT3, of A. cepa with 81%, 81% and 78% similarity, respectively. Our sequential C-banding and FISH with pAc074 probe also clearly showed a close relation between C-heterochromatin at telomeric region and pAc074 sequences on all the chromosomes except on chromosome 6. On the long arm of chromosome 7, pAc074 sequences appeared as interstitial band which did not correspond to C-heterochromatin bands. Instead, the C-heterochromatin bands corresponded with the 5S rDNA signals. This is the first simultaneous evidence on the relation between the 5S rDNA and C-band in A. cepa . FISH analysis was carried out using pAc074 clone as a probe in A. cepa, A. fistulosum and A. wakegi. A. fistulosum revealed stronger hybridization signals which were positioned at the terminal heterochromatic regions of all chromosome ends than signals of A. cepa. In the karyotype of A. wakegi, eight chromosomes from A. fistulosum showed stronger signals than those from A. cepa. The pAc074 probe is useful for understanding the genomic composition of A. wakegi derived from A. cepa and A. fistulosum.