Assessment of the Insular Organization of the Wheat D Genome by Physical Mapping

小麦（Triticum aestivum）是由三种二倍体小麦（Triticum urartu, Aegilops speltoides, Ae）种间杂交而成。tauschii。因此小麦细胞核包含三对基因组，分别命名为AA、BB和DD。小麦基因组的一个特性是，与模式植物拟南芥和水稻的基因组相比，它们的基因组更大。在小基因组中，基因被长度一致的基因间DNA分开。拟南芥的基因组测序已经直接证明了这一点。在大型基因组中，分离基因的非编码DNA片段可能会发生变化。间接证据表明，在小麦中，可能存在基因丰富的岛屿（基因孤岛），其中基因被基因间DNA的短片段分开。据推测，这些基因绝缘层是由缺乏基因或没有基因的空间分隔开的。为了获得小麦D基因组中基因分布的详细图像，从Ae。tauschii(伊蚊基因组；在细菌人工染色体（BACs）中克隆出与小麦D基因组完全相同的陶氏体，并按其在小麦染色体中的排列顺序进行排序。这些有序的DNA片段被称为contigs。总共30万个BAC克隆将通过全球指纹识别方法进行特征化，并在克隆间指纹共享的基础上组装成contigs。大量BAC克隆的指纹识别及其组装将通过指纹识别过程的自动化和基于计算机的基因组组装来完成。每个染色体上的位置将被确定，相邻的染色体将被识别并连接，从而生成七条d基因组染色体的物理图谱。数千个小麦基因的cDNA克隆将被放置在d -基因组物理图谱上，以整合现有的d -基因组连锁和缺失图谱与其物理图谱，并绘制出每个d -基因组染色体上基因分布的详细图。这些cDNA克隆的核苷酸序列正在由NSF植物基因组计划资助的另一个项目中确定。比较小麦d型基因组（大基因组）、玉米基因组（中等基因组）和水稻基因组（小基因组）物理图谱上相应基因的位置，将提供禾本科植物基因组结构随基因组大小增加而变化的信息。小麦D基因组中insule基因的鉴定和定位具有重要的现实意义，因为这将有助于小麦基因组中最相关区域的基因发现和分离，并最终测序。

Common wheat, Triticum aestivum, originated by interspecific hybridization of three diploid species, Triticum urartu, Aegilops speltoides and Ae. tauschii. The wheat nucleus therefore contains three pairs of genomes, designated AA, BB, and DD, respectively. One of the attributes of wheat genomes is that they are large compared to the genomes of the model plants Arabidopsis thaliana and rice. In small genomes, genes are separated by intergenic DNA of a uniform length. This has been shown directly by sequencing the genome of Arabidopsis thaliana. In large genomes, stretches of noncoding DNA separating the genes are likely to vary. Indirect evidence suggests that in wheat, there may be gene-rich islands (gene insulae) in which genes are separated by short stretches of intergenic DNA. These gene insulae are speculated to be separated by gene-poor or gene-empty space. To obtain a detailed picture of gene distribution in the wheat D genome, DNA fragments isolated from Ae. tauschii (the genome of Ae. tauschii is completely equivalent to the D genome of wheat) will be cloned in bacterial artificial chromosomes (BACs) and ordered as they are in wheat chromosomes. These groups of ordered DNA fragments are called contigs. A total of 300,000 BAC clones will be characterized by the global fingerprinting method and assembled into contigs on the basis of fingerprint sharing among the clones. Fingerprinting of this large number of BAC clones and their assembly into contigs will be accomplished by automation of the fingerprinting process and computer-based contig assembly. The position of each contig on the chromosome will be determined and neighboring contigs identified and joined to generate the physical map of each of the seven D-genome chromosomes. Thousands of cDNA clones of wheat genes will be placed on the D-genome physical map to integrate the existing D-genome linkage and deletion maps with its physical map and to chart a detailed picture of gene distribution across each D-genome chromosome. The nucleotide sequences of these cDNA clones are being determined in another project funded by the NSF Plant Genome Program. Comparisons of the positions of corresponding genes on the physical maps of the wheat D-genome (large genome), the maize genome (medium-size genome) and the genome sequence of the rice genome (small genome) will provide information on changes in genome structure as a function of genome size increase in the grass family. The identification of gene insulae in the wheat D genome and their mapping will have great practical significance since it will facilitate gene discovery and isolation and, ultimately, the sequencing of the most relevant regions of wheat genomes.