NOR Sequence Assembly for Arabidopsis thaliana Col-0

Arabidopsis thaliana has two ribosomal RNA gene loci, nucleolus organizer regions NOR2 and NOR4. Using PacBio SMRT sequencing and ultra-long ONT sequencing, we assembled 5.5 and 3.9 Mbp sequences for NOR2 and NOR4 in the reference strain, Col-0. We defined the SNPs within 45S rRNA gene copies within the NORs using high-depth Illumina whole genome sequencing. We then used ONT sequencing of nucleolar enriched DNA and RNA sequencing to show that most, but not all, NOR4 genes are active whereas most, but not all, NOR2 genes are epigenetically silenced.