Abstract
Despite vast differences between organisms, some characteristics of their genomes are conserved, such as the nucleolus organizing region (NOR). The NOR is constituted of multiple, highly repetitive rDNA genes, encoding the catalytic ribosomal core RNAs which are transcribed from 45S rDNA units. Their precise sequence information and organization remain uncharacterized. Here, using a combination of long- and short-read sequencing technologies we assemble contigs of the Arabidopsis NOR2 rDNA domain. We identify several expressed rRNA gene variants which are integrated into translating ribosomes in a tissue-specific manner. These findings support the concept of tissue specific ribosome subpopulations that differ in their rRNA composition and provide insights into the higher order organization of NOR2.
Highlights
Despite vast differences between organisms, some characteristics of their genomes are conserved, such as the nucleolus organizing region (NOR)
To successfully sequence and build NOR2, we relied on a bacterial artificial chromosomes (BACs)-based approach[13] (Fig. 1a)
BACs, initially generated to obtain the Arabidopsis physical map[14], containing rDNA repeats were ordered from the Arabidopsis Biological Resource Center (ABRC) stock center[15]
Summary
Despite vast differences between organisms, some characteristics of their genomes are conserved, such as the nucleolus organizing region (NOR). The NOR is constituted of multiple, highly repetitive rDNA genes, encoding the catalytic ribosomal core RNAs which are transcribed from 45S rDNA units Their precise sequence information and organization remain uncharacterized. Several studies have shown that the rDNA repeats are not completely identical, with variability within the intergenic regions and, to some extent, in the coding sequences[5,6,7] It remains unknown whether these variations (VARs) are present in the translating ribosome and have a functional impact. We identified several sequence VARs in the rRNA genes and established that the corresponding rRNAs are expressed and integrated into mature and translating ribosomes in a tissue-specific manner These findings uncover a complex transcriptional regulation of rDNA genes and support the concept of tissue-specific ribosome subpopulations[12] that differ in their rRNA composition
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