Allopolyploidy - a shaping force in the evolution of wheat genomes
Allopolyploidy - a shaping force in the evolution of wheat genomes
复制标题
DOI：
10.1159/000082407
复制
发表时间：
2005-01-01
影响因子：
1.7
通讯作者：
Levy, AA
中科院分区：
文献类型：
--
作者：
Feldman, M;Levy, AA
最近的研究表明，异源多倍体以两种方式加速小麦基因组的进化：（1）异源多倍体化通过瞬时产生各种主要遗传和表观遗传改变而引发快速的基因组变化（革命性变化），以及（2）异源多倍体条件促进物种生活期间的零星基因组变化（进化变化），这在二倍体水平上是无法实现的。革命性的变化包括（1）编码和非编码DNA序列的非随机消除，（2）表观遗传变化，例如编码和非编码DNA的DNA甲基化，导致基因沉默等，（3）基因和逆转录元件的激活，这反过来又改变了邻近基因的表达。这些高度可重复的变化发生在F-1杂种或新生异源多倍体的第一代中，并且与自然界中发生的两次变化相似：第一次是异源四倍体小麦的形成（类似于50万年前），第二次是六倍体小麦的形成（类似于1万年前）。四倍体小麦中两对同源异源染色体中的一对和六倍体小麦中两对同源异源染色体中的非编码序列的去除，增强了同源异源染色体在多倍体水平上的分化，从而为异源多倍体小麦的类二倍体减数分裂行为提供了物理基础。基因表达的调节可能导致基因组间相互作用的改善。基因失活导致快速二倍化，而通过去甲基化或通过逆转录因子的转录激活来激活基因，改变相邻基因的表达，导致新的表达模式。进化变化包括（1）组成基因组之间染色体片段的水平基因组间转移，（2）通过不同异源多倍体物种之间或更罕见的异源多倍体和二倍体之间的杂交和渐渗产生重组基因组，以及（3）突变。这些现象强调了基因组在结构和功能方面的可塑性，可能会提高新形成的异源多倍体的适应性，并促进它们在自然界中的快速和成功建立。版权所有（C）2005 S. Karger AG，巴塞尔。
Recent studies have shown that allopolyploidy accelerates genome evolution in wheat in two ways: ( 1) allopolyploidization triggers rapid genome changes ( revolutionary changes) through the instantaneous generation of a variety of cardinal genetic and epigenetic alterations, and ( 2) the allopolyploid condition facilitates sporadic genomic changes during the life of the species ( evolutionary changes) that are not attainable at the diploid level. The revolutionary changes comprise ( 1) non-random elimination of coding and non-coding DNA sequences, ( 2) epigenetic changes such as DNA methylation of coding and non-coding DNA leading, among others, to gene silencing, ( 3) activation of genes and retroelements which in turn alters the expression of adjacent genes. These highly reproducible changes occur in the F-1 hybrids or in the first generation( s) of the nascent allopolyploids and were similar to those that occurred twice in nature: first in the formation of allotetraploid wheat (similar to 0.5 million years ago) and second in the formation of hexaploid wheat ( similar to 10,000 years ago). Elimination of non-coding sequences from one of the two homoeologous pairs in tetraploids and from two homoeologous pairs in hexaploids, augments the differentiation of homoeologous chromosomes at the polyploid level, thus providing the physical basis for the diploid-like meiotic behavior of allopolyploid wheat. Regulation of gene expression may lead to improved inter-genomic interactions. Gene inactivation brings about rapid diploidization while activation of genes through demethylation or through transcriptional activation of retroelements altering the expression of adjacent genes, leads to novel expression patterns. The evolutionary changes comprise ( 1) horizontal intergenomic transfer of chromosome segments between the constituent genomes, ( 2) production of recombinant genomes through hybridization and introgression between different allopolyploid species or, more seldom, between allopolyploids and diploids, and ( 3) mutations. These phenomena, emphasizing the plasticity of the genome with regards to both structure and function, might improve the adaptability of the newly formed allopolyploids and facilitate their rapid and successful establishment in nature. Copyright (C) 2005 S. Karger AG, Basel.