Molecular organization, epigenetic status and transcriptional activity of the 18S-5.8S-26S rDNA locus of Quercus robur

Vičić Bočkor, Vedrana (2015) Molecular organization, epigenetic status and transcriptional activity of the 18S-5.8S-26S rDNA locus of Quercus robur. Doctoral thesis, Faculty of Science > Department of Biology.

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Abstract

The position of rDNA loci in the nucleus, rDNA chromatin organization and the presence of characteristic epigenetic marks are indicators of transcriptional activity of rRNA genes. Results of the research within this doctoral disertation suggest that of the two rDNA loci present in the genome of Q. robur, only NOR-1 is transcriptionaly active in normal physiological conditions, since it exhibits different levels of decondensation, associates with the nucleolus, stains with silver and is hypomethylated. On the contrary, NOR-2 is always condensed, does not associate with the nucleolus or stain with silver. In addition, NOR-2 is hipermethylated and enriched in H3K9me1 heterochromatic mark, indicating its transcriptional silence. The treatment of oak cells with epigenetic inhibitor 5-aza-2'-dC results in a decrease of methylation of NOR-2 locus and its repositioning closer to the nucleolus, however, rDNA chromatin stays highly condensed. In plants, small interfering RNA (siRNA) molecules derived from intergenic spacer (IGS) transcription play an important role in transcriptional regulation of rRNA genes. This research revealed the presence of two spacer lenght variants in the genome of Q. robur, a 2 kb and a 4 kb length variant. The 4 kb variant posseses the gene and the spacer promoter. Transcription from the spacer promoter probably generates siRNA molecules involved in silencing of rRNA genes within the NOR-2 locus and a fraction of genes within the NOR-1 locus. Indeed, Northern blotting revealed the existence of 24 nt siRNA in total RNA pool in oak root-tip cells.

Item Type: Thesis (Doctoral thesis)
Keywords: rDNA chromatin, NOR, histone modifications, DNA methylation, intergenic spacer, siRNA
Supervisor: Zoldoš, Vlatka
Date: 2015
Number of Pages: 111
Subjects: NATURAL SCIENCES > Biology
Divisions: Faculty of Science > Department of Biology
Depositing User: Silvana Šehić
Date Deposited: 06 Jul 2015 09:55
Last Modified: 06 Jul 2015 09:55
URI: http://digre.pmf.unizg.hr/id/eprint/4092

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