Stupar Robert M, Song Junqi, Tek Ahmet L, Cheng Zhukuan, Dong Fenggao, Jiang Jiming
Department of Horticulture, University of Wisconsin, Madison 53706, USA.
Genetics. 2002 Nov;162(3):1435-44. doi: 10.1093/genetics/162.3.1435.
The heterochromatin in eukaryotic genomes represents gene-poor regions and contains highly repetitive DNA sequences. The origin and evolution of DNA sequences in the heterochromatic regions are poorly understood. Here we report a unique class of pericentromeric heterochromatin consisting of DNA sequences highly homologous to the intergenic spacer (IGS) of the 18S.25S ribosomal RNA genes in potato. A 5.9-kb tandem repeat, named 2D8, was isolated from a diploid potato species Solanum bulbocastanum. Sequence analysis indicates that the 2D8 repeat is related to the IGS of potato rDNA. This repeat is associated with highly condensed pericentromeric heterochromatin at several hemizygous loci. The 2D8 repeat is highly variable in structure and copy number throughout the Solanum genus, suggesting that it is evolutionarily dynamic. Additional IGS-related repetitive DNA elements were also identified in the potato genome. The possible mechanism of the origin and evolution of the IGS-related repeats is discussed. We demonstrate that potato serves as an interesting model for studying repetitive DNA families because it is propagated vegetatively, thus minimizing the meiotic mechanisms that can remove novel DNA repeats.
真核生物基因组中的异染色质代表基因贫乏区域，并包含高度重复的DNA序列。人们对异染色质区域DNA序列的起源和进化了解甚少。在此，我们报告了一类独特的着丝粒周围异染色质，其由与马铃薯18S.25S核糖体RNA基因的基因间隔区（IGS）高度同源的DNA序列组成。从二倍体马铃薯物种 Solanum bulbocastanum中分离出一个5.9 kb的串联重复序列，命名为2D8。序列分析表明，2D8重复序列与马铃薯rDNA的IGS相关。该重复序列在几个半合子位点与高度浓缩的着丝粒周围异染色质相关。2D8重复序列在茄属植物中结构和拷贝数高度可变，表明其在进化上具有动态性。在马铃薯基因组中还鉴定出了其他与IGS相关的重复DNA元件。讨论了与IGS相关重复序列的起源和进化的可能机制。我们证明，马铃薯是研究重复DNA家族的一个有趣模型，因为它通过无性繁殖，从而最大限度地减少了可能去除新DNA重复序列的减数分裂机制。
