| Popis: |
In eukaryotes, hundreds of ribosomal RNA (rRNA) genes are clustered at chromosomal loci called nucleolus organizer regions (NORs).Arabidopsis thalianahas two NORs, one on chromosome 2 (NOR2) and the other on chromosome 4 (NOR4). Each NOR consists of ∼ 400 rRNA gene copies. We recently showed that rRNA gene subtypes that map toNOR2are silenced during development, whereas those that map toNOR4are active. In several DNA methylation mutants of Arabidopsis, we show disruption of theNOR2gene silencing to varying degrees. Significantly, the highest disruption ofNOR2gene silencing correlates with a maximum loss of cytosine methylation in the CHH context followed by the CG context, independent of RNA-directed DNA methylation (RdDM). Next, we show in Col-0 thatNOR2genes are relatively hypermethylated andNOR4genes are hypomethylated using multiple methylation analysis of genomic DNA carried out with different types of methylation-sensitive restriction enzymes. We demonstrate similar differential methylation status betweenNOR2andNOR4genes in an introgression line named ColSf-NOR4, which carriesNOR2from Col-0 andNOR4from ecotype Sf-2. Lastly, using Tn5 transposon-mediated transposition into native chromatin, we show thatNOR2gene chromatin is in more condensed state thanNOR4gene chromatin. |
