Sandhu Devinder, Gill Kulvinder S
Department of Agronomy and Horticulture, 362H Plant Science, P.O. Box 830915, University of Nebraska, Lincoln, Nebraska 68583-0915, USA.
Plant Physiol. 2002 Mar;128(3):803-11. doi: 10.1104/pp.010745.
Deletion line-based high-density physical maps revealed that the wheat (Triticum aestivum) genome is partitioned into gene-rich and -poor compartments. Available deletion lines have bracketed the gene-containing regions to about 10% of the genome. Emerging sequence data suggest that these may further be partitioned into "mini" gene-rich and gene-poor regions. An average of about 10% of each gene-rich region seem to contain genes. Sequence analyses in various species suggest that uneven distribution of genes may be a characteristic of all grasses and perhaps all higher organisms. Comparison of the physical maps with genetic linkage maps showed that recombination in wheat and barley (Hordeum vulgare) is confined to the gene-containing regions. Number of genes, gene density, and the extent of recombination vary greatly among the gene-rich regions. The gene order, relative region size, and recombination are highly conserved within the tribe Triticeae and moderately conserved within the family. Gene-poor regions are composed of retrotransposon-like non-transcribing repeats and pseudogenes. Direct comparisons of orthologous regions indicated that gene density in wheat is about one-half compared with rice (Oryza sativa). Genome size difference between wheat and rice is, therefore, mainly because of amplification of the gene-poor regions. Presence of species-, genera-, and family-specific repeats reveal a repeated invasion of the genomes by different retrotransposons over time. Preferential transposition to adjacent locations and presence of vital genes flanking a gene-rich region may have restricted retrotransposon amplification to gene-poor regions, resulting into tandem blocks of non-transcribing repeats. Insertional inactivation by adjoining retro-elements and selection seem to have played a major role in stabilizing genomes.
基于缺失系的高密度物理图谱显示，小麦（Triticum aestivum）基因组被划分为基因丰富和基因贫乏的区域。现有的缺失系已将含基因区域定位到基因组的约10%。新出现的序列数据表明，这些区域可能进一步被划分为“微型”基因丰富和基因贫乏区域。每个基因丰富区域平均约10%似乎包含基因。对各种物种的序列分析表明，基因的不均匀分布可能是所有禾本科植物甚至所有高等生物的一个特征。物理图谱与遗传连锁图谱的比较表明，小麦和大麦（Hordeum vulgare）中的重组仅限于含基因区域。基因丰富区域之间的基因数量、基因密度和重组程度差异很大。基因顺序、相对区域大小和重组在小麦族内高度保守，在科内中度保守。基因贫乏区域由类反转录转座子的非转录重复序列和假基因组成。直系同源区域的直接比较表明，小麦的基因密度约为水稻（Oryza sativa）的二分之一。因此，小麦和水稻之间的基因组大小差异主要是由于基因贫乏区域的扩增。物种、属和科特异性重复序列的存在揭示了随着时间的推移，不同反转录转座子对基因组的反复入侵。优先转座到相邻位置以及基因丰富区域两侧存在重要基因可能将反转录转座子的扩增限制在基因贫乏区域，从而形成非转录重复序列的串联块。相邻反转元件的插入失活和选择似乎在稳定基因组方面发挥了主要作用。
