Sequencing and analysis of Arabidopsis thaliana NOR2 reveal its distinct organization and tissue-specific expression of rRNA ribosomal variants

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 remained uncharacterized. We used a combination of long- and short-read sequencing technologies to assemble contigs of the Arabidopsis NOR2 rDNA domain providing a first map. We identified 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 the higher order organization of NOR2.