Sergeeva Ekaterina M, Shcherban Andrey B, Adonina Irina G, Nesterov Michail A, Beletsky Alexey V, Rakitin Andrey L, Mardanov Andrey V, Ravin Nikolai V, Salina Elena A
The Federal Research Center "Institute of Cytology and Genetics SB RAS", Novosibirsk, Russia.
The Federal Research Center "Fundamentals of Biotechnology RAS", Moscow, Russia.
BMC Plant Biol. 2017 Nov 14;17(Suppl 1):183. doi: 10.1186/s12870-017-1120-5.
The multigene family encoding the 5S rRNA, one of the most important structurally-functional part of the large ribosomal subunit, is an obligate component of all eukaryotic genomes. 5S rDNA has long been a favored target for cytological and phylogenetic studies due to the inherent peculiarities of its structural organization, such as the tandem arrays of repetitive units and their high interspecific divergence. The complex polyploid nature of the genome of bread wheat, Triticum aestivum, and the technically difficult task of sequencing clusters of tandem repeats mean that the detailed organization of extended genomic regions containing 5S rRNA genes remains unclear. This is despite the recent progress made in wheat genomic sequencing. Using pyrosequencing of BAC clones, in this work we studied the organization of two distinct 5S rDNA-tagged regions of the 5BS chromosome of bread wheat.
Three BAC-clones containing 5S rDNA were identified in the 5BS chromosome-specific BAC-library of Triticum aestivum. Using the results of pyrosequencing and assembling, we obtained six 5S rDNA- containing contigs with a total length of 140,417 bp, and two sets (pools) of individual 5S rDNA sequences belonging to separate, but closely located genomic regions on the 5BS chromosome. Both regions are characterized by the presence of approximately 70-80 copies of 5S rDNA, however, they are completely different in their structural organization. The first region contained highly diverged short-type 5S rDNA units that were disrupted by multiple insertions of transposable elements. The second region contained the more conserved long-type 5S rDNA, organized as a single tandem array. FISH using probes specific to both 5S rDNA unit types showed differences in the distribution and intensity of signals on the chromosomes of polyploid wheat species and their diploid progenitors.
A detailed structural organization of two closely located 5S rDNA-tagged genomic regions on the 5BS chromosome of bread wheat has been established. These two regions differ in the organization of both 5S rDNA and the neighboring sequences comprised of transposable elements, implying different modes of evolution for these regions.
编码5S rRNA的多基因家族是大核糖体亚基最重要的结构功能部分之一，是所有真核生物基因组的必需组成部分。由于其结构组织的固有特性，如重复单元的串联阵列及其高度的种间差异，5S rDNA长期以来一直是细胞学和系统发育研究的热门靶点。普通小麦（Triticum aestivum）基因组的复杂多倍体性质以及串联重复序列簇测序的技术难题意味着，包含5S rRNA基因的扩展基因组区域的详细组织情况仍不清楚。尽管最近小麦基因组测序取得了进展，但情况依然如此。在这项工作中，我们使用BAC克隆的焦磷酸测序技术，研究了普通小麦5BS染色体上两个不同的5S rDNA标记区域的组织情况。
在普通小麦5BS染色体特异性BAC文库中鉴定出三个含有5S rDNA的BAC克隆。利用焦磷酸测序和组装结果，我们获得了六个含有5S rDNA的重叠群，总长度为140,417 bp，以及两组属于5BS染色体上不同但位置紧密的基因组区域的单个5S rDNA序列（池）。这两个区域的特征都是存在大约70 - 80个5S rDNA拷贝，然而，它们的结构组织完全不同。第一个区域包含高度分化的短型5S rDNA单元，这些单元被转座元件的多次插入打断。第二个区域包含更保守的长型5S rDNA，组织为单个串联阵列。使用针对两种5S rDNA单元类型的特异性探针进行荧光原位杂交，显示了多倍体小麦物种及其二倍体祖先染色体上信号分布和强度的差异。
已经确定了普通小麦5BS染色体上两个位置紧密的5S rDNA标记基因组区域的详细结构组织。这两个区域在5S rDNA和由转座元件组成的相邻序列的组织上都有所不同，这意味着这些区域的进化模式不同。
