Gigascience. 2020 Jun 1;9(6). doi: 10.1093/gigascience/giaa070.
Polyploidy is centrally important in the evolution and domestication of plants because it leads to major genomic changes, such as altered patterns of gene expression, which are thought to underlie the emergence of new traits. Despite the common occurrence of these globally altered patterns of gene expression in polyploids, the mechanisms involved are not well understood.
Using a precisely defined framework of highly conserved syntenic genes on hexaploid wheat chromosome 3DL and its progenitor 3 L chromosome arm of diploid Aegilops tauschii, we show that 70% of these gene pairs exhibited proportionately reduced gene expression, in which expression in the hexaploid context of the 3DL genes was ∼40% of the levels observed in diploid Ae tauschii. Several genes showed elevated expression during the later stages of grain development in wheat compared with Ae tauschii. Gene sequence and methylation differences probably accounted for only a few cases of differences in gene expression. In contrast, chromosome-wide patterns of reduced chromatin accessibility of genes in the hexaploid chromosome arm compared with its diploid progenitor were correlated with both reduced gene expression and the imposition of new patterns of gene expression.
Our pilot-scale analyses show that chromatin compaction may orchestrate reduced gene expression levels in the hexaploid chromosome arm of wheat compared to its diploid progenitor chromosome arm.
多倍体在植物的进化和驯化中起着至关重要的作用，因为它导致了主要的基因组变化，例如基因表达模式的改变，这些改变被认为是新性状出现的基础。尽管这些全球改变的基因表达模式在多倍体中经常发生，但涉及的机制尚不清楚。
利用六倍体小麦第 3DL 染色体及其二倍体祖先 Ae tauschii 的 3L 染色体臂上高度保守的同源基因的精确定义框架，我们表明，这些基因对中有 70%表现出比例性降低的基因表达，其中 3DL 基因在六倍体背景下的表达水平约为在 Ae tauschii 中观察到的水平的 40%。与 Ae tauschii 相比，小麦中几个基因在籽粒发育的后期阶段表现出更高的表达。基因序列和甲基化差异可能只解释了少数基因表达差异的情况。相比之下，与二倍体祖先相比，六倍体染色体臂上基因的染色质可及性降低的染色体-wide 模式与基因表达降低和新的基因表达模式的施加相关。
我们的初步分析表明，与二倍体祖先染色体臂相比，染色质紧缩可能协调了小麦六倍体染色体臂中基因表达水平的降低。
