Two-dimensional RFLP analyses reveal megabase-sized clusters of rRNA gene variants in Arabidopsis thaliana, suggesting local spreading of variants as the mode for gene homogenization during concerted evolution
Two-dimensional RFLP analyses reveal megabase-sized clusters of rRNA gene variants in Arabidopsis thaliana, suggesting local spreading of variants as the mode for gene homogenization during concerted evolution
复制标题
DOI：
10.1046/j.1365-313x.1996.09020273.x
复制
发表时间：
1996-02-01
期刊：
影响因子：
7.2
通讯作者：
Pikaard, CS
中科院分区：
文献类型：
--
作者：
Copenhaver, GP;Pikaard, CS
编码185、5.8S和25 S核糖体RNA前体的真核基因（rRNA基因或rDNA）在一个物种内实际上是相同的，但它们在物种之间迅速进化，这种现象称为协同进化。基因组内序列均一化和新rRNA基因变异体固定的机制尚不清楚。在二倍体拟南芥中，大约1500个rRNA基因串联排列在两个核仁组织者区域，一个位于2号染色体（NOR 2），另一个位于4号染色体（NOR 4）。本文表明，NOR 2和NOR 4的大小相似，每个跨度约为3.5-4.0 Mbp。使用二维映射技术，涉及脉冲场和常规凝胶电泳的组合，在NOR 2和NOR 4的四个不同的rRNA基因变异的分布已被确定。NOR 4处的rRNA基因相对于每个基因出现一次的HindIII位点是同质的。相比之下，在NOR 2的rRNA基因中少于10%是携带HindIII的变体。一个单一的基因间的间隔区长度被发现在rRNA基因在NOR 2，但三个类的间隔区长度的变体是存在于NOR 4。NOR 4变体彼此不混合;相反，它们在1.5 Mbp的距离上高度聚集。这些数据表明，在rRNA基因的协同进化中，均质化是新rRNA基因变体局部扩散的结果。
Eukaryotic genes encoding the precursor of 185, 5.8S and 25S ribosomal RNA (rRNA genes or rDNA) are virtually identical within a species, yet they evolve rapidly between species, a phenomenon known as concerted evolution. The mechanisms by which sequence homogenization and fixation of new rRNA gene variants occurs within a genome are not clear. In diploid Arabidopsis thaliana, approximately 1500 rRNA genes are tandemly arrayed at two nucleolus organizer regions, one on chromosome 2 (NOR2), the other on chromosome 4 (NOR4). This paper shows that NOR2 and NOR4 are similar in size, each spanning approximately 3.5-4.0 Mbp. Using two-dimensional mapping techniques involving a combination of pulsed-field and conventional gel electrophoresis, the distributions of four distinct rRNA gene variants at NOR2 and NOR4 have been determined. rRNA genes at NOR4 are homogeneous with respect to a Hindlll site occurring once per gene. In contrast, fewer than 10% of the rRNA genes at NOR2 are Hindlll-bearing variants. A single intergenic spacer length is found among rRNA genes at NOR2 but three classes of spacer length variants are present at NOR4. The NOR4 variants are not intermingled with one another; instead, they are highly clustered over distances as large as 1.5 Mbp. These data suggest that in the concerted evolution of rRNA genes, homogenization is a consequence of local spreading of new rRNA gene variants.