Ragupathy Raja, Naeem Hamid A, Reimer Elsa, Lukow Odean M, Sapirstein Harry D, Cloutier Sylvie
Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, Manitoba, Canada, R3T 2M9.
Theor Appl Genet. 2008 Jan;116(2):283-96. doi: 10.1007/s00122-007-0666-2. Epub 2007 Nov 6.
Sequencing of a BAC clone encompassing the Glu-B1 locus in Glenlea, revealed a 10.3 Kb segmental duplication including the Bx7 gene and flanking an LTR retroelement. To better understand the evolution of this locus, two collections of wheat were surveyed. The first consisted of 96 diploid and tetraploid species accessions while the second consisted of 316 Triticum aestivum cultivars and landraces from 41 countries. The genotypes were first characterized by SDS-PAGE and a total of 40 of the 316 T. aestivum accessions were found to display the overexpressed Bx7 phenotype (Bx7OE). Three lines from the 96 diploid/tetraploid collection also displayed the stronger intensity staining characteristic of the Bx7(OE) subunit. The relative amounts of the Bx7 subunit to total HMW-GS were quantified by RP-HPLC for all Bx7OE accessions and a number of checks. The entire collection was assessed for the presence of four DNA markers namely an 18 bp indel of the coding region of Bx7 variant alleles, a 43 bp indel of the 5'-region and the left and right junctions of the LTR retrotransposon borders and the duplicated segment. All 43 accessions found to have the Bx7OE subunit by SDS-PAGE and RP-HPLC produced the four diagnostic PCR amplicons. None of the lines without the Bx7OE had the LTR retroelement/duplication genomic structure. However, the 18 and 43 bp indel were found in accessions other than Bx7OE. These results indicate that the overexpression of the Bx7 HMW-GS is likely the result of a single event, i.e., a gene duplication at the Glu-B1 locus mediated by the insertion of a retroelement. Also, the 18 and 43 bp indels pre-date the duplication event. Allelic variants Bx7*, Bx7 with and without 43 bp insert and Bx7OE were found in both tetraploid and hexaploid collections and shared the same genomic organization. Though the possibility of introgression from T. aestivum to T. turgidum cannot be ruled out, the three structural genomic changes of the B-genome taken together support the hypothesis of multiple polyploidization events involving different tetraploid progenitors.
对包含Glenlea中Glu - B1位点的一个BAC克隆进行测序，发现了一个10.3 Kb的片段重复，其中包括Bx7基因并侧翼有一个LTR反转录元件。为了更好地理解该位点的进化，对两个小麦群体进行了调查。第一个群体由96个二倍体和四倍体物种的种质组成，而第二个群体由来自41个国家的316个普通小麦品种和地方品种组成。首先通过SDS - PAGE对基因型进行表征，在316个普通小麦种质中，共发现40个表现出Bx7过表达表型（Bx7OE）。96个二倍体/四倍体群体中的三个品系也表现出Bx7（OE）亚基更强的染色强度特征。通过RP - HPLC对所有Bx7OE种质和一些对照品系中Bx7亚基相对于总高分子量谷蛋白的相对含量进行了定量。对整个群体进行了四种DNA标记的检测，即Bx7变异等位基因编码区的一个18 bp插入缺失、5' - 区域的一个43 bp插入缺失以及LTR反转录转座子边界和重复片段的左右连接区。通过SDS - PAGE和RP - HPLC发现具有Bx7OE亚基的所有43个种质都产生了四个诊断性PCR扩增产物。没有Bx7OE的品系均没有LTR反转录元件/重复基因组结构。然而，在非Bx7OE的种质中发现了18和43 bp的插入缺失。这些结果表明Bx7高分子量谷蛋白的过表达可能是单一事件的结果，即由一个反转录元件插入介导的Glu - B1位点的基因重复。此外，18和43 bp的插入缺失早于重复事件。在四倍体和六倍体群体中都发现了等位变异Bx7*、有和没有43 bp插入的Bx7以及Bx7OE，并且它们具有相同的基因组结构。虽然不能排除从普通小麦渗入到硬粒小麦的可能性，但B基因组的这三个结构基因组变化共同支持了涉及不同四倍体祖先的多次多倍体化事件的假设。
