异源多倍体（2n = 4x = 32，BBDD）和（2n = 6x = 48，AABBDD）及其亲本物种中35S rDNA的结构与甲基化显示出核仁显性的证据。

Structure and Methylation of 35S rDNA in Allopolyploids (2 = 4 = 32, BBDD) and (2 = 6 = 48, AABBDD) and Their Parental Species Show Evidence of Nucleolar Dominance.

作者信息

Mlinarec Jelena, Boštjančić Ljudevit Luka, Malenica Nenad, Jurković Adela, Boland Todd, Yakovlev Sonja Siljak, Besendorfer Višnja

机构信息

Oikon ltd.-Institute of Applied Ecology, Zagreb, Croatia.

LOEWE Centre for Translational Biodiversity Genomics (LOEWE-TBG), Senckenberg Biodiversity and Climate Research Centre, Senckenberg Gesellschaft für Naturforschung, Frankfurt, Germany.

出版信息

Front Plant Sci. 2022 Jul 6;13:908218. doi: 10.3389/fpls.2022.908218. eCollection 2022.

Transcriptional silencing of 35S rDNA loci inherited from one parental species is occurring relatively frequently in allopolyploids. However, molecular mechanisms by which it is selected for transcriptional silencing remain unclear. We applied NGS, silver staining and bisulfite sequencing to study the structure, expression and methylation landscape of 35S rDNA in two allopolyploids of common origin, allotetraploid (2 = 4 = 32, genome composition BBDD) and allohexaploid (2 = 6 = 48, AABBDD), and their genome donors, (2 = 16, AA), (2 = 16, BB) and (2 = 16, DD). The size of the recovered 35S rDNA units varied from 10,489 bp in to 12,084 bp in . showed an organization typical of most ribosomal 35S rDNA composed of NTS, ETS, rRNA genes, TTS and TIS with structural features of plant IGS sequences and all functional elements needed for rRNA gene activity. The NTS was more variable than the ETS and consisted of SRs which are highly variable among . Five to six CpG-rich islands were found within the ETS. CpG island located adjacent to the transcription initiation site (TIS) was highly variable regarding the sequence size and methylation level and exhibited in most of the species lower levels of methylation than CpG islands located adjacent to the 18S rRNA gene. Our results uncover hypomethylation of - and -derived 35S rDNA units in allopolyploids and . Hypomethylation of -derived 35S rDNA was more prominent in than in . We showed that underwent coupled -derived 35S rDNA array expansion and -derived 35S rDNA copy number decrease that was accompanied by lower methylation level of -derived 35S rDNA units in comparison to -derived 35S rDNA units. These observations suggest that in nucleolar dominance is directed toward -derived chromosomes. This work broadens our current knowledge of the 35S rDNA organization in and provides evidence of the progenitor-specific 35S rDNA methylation in nucleolar dominance.

在异源多倍体中，从一个亲本物种遗传而来的35S核糖体DNA（rDNA）位点的转录沉默相对频繁地发生。然而，其被选择用于转录沉默的分子机制仍不清楚。我们应用二代测序（NGS）、银染和亚硫酸氢盐测序来研究两个具有共同起源的异源多倍体——异源四倍体（2n = 4x = 32，基因组组成为BBDD）和异源六倍体（2n = 6x = 48，AABBDD）及其基因组供体——二倍体A（2n = 2x = 16，AA）、二倍体B（2n = 2x = 16，BB）和二倍体D（2n = 2x = 16，DD）中35S rDNA的结构、表达和甲基化图谱。回收的35S rDNA单元大小在二倍体A中为10,489 bp，在二倍体D中为12,084 bp。二倍体A显示出大多数核糖体35S rDNA典型的组织形式，由非转录间隔区（NTS）、外部转录间隔区（ETS）、核糖体RNA（rRNA）基因、转录终止区（TTS）和转录起始区（TIS）组成，具有植物间隔区序列（IGS）的结构特征以及rRNA基因活性所需的所有功能元件。NTS比ETS更具变异性，由在不同物种间高度可变的简单重复序列（SRs）组成。在ETS内发现了五到六个富含CpG的岛。位于转录起始位点（TIS）附近的CpG岛在序列大小和甲基化水平方面高度可变，并且在大多数物种中，其甲基化水平低于位于18S rRNA基因附近的CpG岛。我们的结果揭示了异源多倍体中源自二倍体A和二倍体B的35S rDNA单元的低甲基化。源自二倍体B的35S rDNA的低甲基化在异源六倍体中比在异源四倍体中更显著。我们表明异源六倍体经历了源自二倍体B的35S rDNA阵列扩增和源自二倍体A的35S rDNA拷贝数减少，与源自二倍体A的35S rDNA单元相比，源自二倍体B的35S rDNA单元甲基化水平更低。这些观察结果表明，在异源六倍体中，核仁显性指向源自二倍体A的染色体。这项工作拓宽了我们目前对异源多倍体中35S rDNA组织的认识，并为核仁显性中祖源特异性35S rDNA甲基化提供了证据。