Borowska-Zuchowska Natalia, Kwasniewski Miroslaw, Hasterok Robert
Department of Plant Anatomy and Cytology, Faculty of Biology and Environmental Protection, University of Silesia in Katowice Katowice, Poland.
Department of Genetics, Faculty of Biology and Environmental Protection, University of Silesia in Katowice Katowice, Poland.
Front Plant Sci. 2016 Oct 14;7:1499. doi: 10.3389/fpls.2016.01499. eCollection 2016.
Nucleolar dominance is an epigenetic phenomenon associated with nuclear 35S rRNA genes and consists in selective suppression of gene loci inherited from one of the progenitors in the allopolyploid. Our understanding of the exact mechanisms that determine this process is still fragmentary, especially in case of the grass species. This study aimed to shed some light on the molecular basis of this genome-specific inactivation of 35S rDNA loci in an allotetraploid (2 = 30), which arose from the interspecific hybridization between two diploid ancestors that were very similar to modern (2 = 10) and (2 = 20). Using fluorescence hybridization with 25S rDNA and chromosome-specific BAC clones as probes we revealed that the nucleolar dominance is present not only in meristematic root-tip cells but also in differentiated cell fraction of . Additionally, the intergenic spacers (IGSs) from both of the putative ancestors and the allotetraploid were sequenced and analyzed. The presumptive transcription initiation sites, spacer promoters and repeated elements were identified within the IGSs. Two different length variants, 2.3 and 3.5 kb, of IGSs were identified in and , respectively, however only the IGS that had originated from -like ancestor was present in the allotetraploid. The amplification pattern of IGSs suggests that some genetic changes occurred in inactive like rDNA loci during the evolution of the allotetraploid. We hypothesize that their preferential silencing is an effect of structural changes in the sequence rather than just the result of the sole inactivation at the epigenetic level.
核仁显性是一种与核35S rRNA基因相关的表观遗传现象，表现为在异源多倍体中对来自一个亲本的基因座进行选择性抑制。我们对决定这一过程的确切机制的理解仍然不完整，尤其是在禾本科植物中。本研究旨在揭示一个异源四倍体（2n = 30）中35S rDNA基因座这种基因组特异性失活的分子基础，该异源四倍体由两个与现代二倍体（2n = 10）和（2n = 20）非常相似的二倍体祖先种间杂交产生。使用以25S rDNA和染色体特异性BAC克隆为探针的荧光原位杂交技术，我们发现核仁显性不仅存在于根尖分生组织细胞中，也存在于的分化细胞部分。此外，对两个假定祖先种和异源四倍体的基因间隔区（IGSs）进行了测序和分析。在IGSs中鉴定出了推定的转录起始位点、间隔区启动子和重复元件。在和中分别鉴定出了两种不同长度变体的IGSs，即2.3 kb和3.5 kb，然而在异源四倍体中仅存在源自类似祖先的IGS。IGSs的扩增模式表明，在异源四倍体的进化过程中，无活性的类似rDNA基因座发生了一些遗传变化。我们推测，它们的优先沉默是序列结构变化而非仅仅是表观遗传水平上单独失活的结果。
