A Duplicated NUCLEOLIN Gene with Antagonistic Activity Is Required for Chromatin Organization of Silent 45S rDNA in Arabidopsis      . Issue 3 (25th March 2014)

• Record Type: Journal Article
• Authors: Durut, Nathalie; Abou-Ellail, Mohamed; Pontvianne, Frédéric; Das, Sadhan; Kojima, Hisae; Ukai, Seiko; de Bures, Anne; Comella, Pascale; Nidelet, Sabine; Rialle, Stéphanie; Merret, Remy; Echeverria, Manuel; Bouvet, Philippe; Nakamura, Kenzo; Sáez-Vásquez, Julio
• Is Part Of: The Plant Cell. Volume 26:Issue 3(2014)
• Page Start: 1330
• Page End: 1344
• Publication Date: 2014-03-25
• DOI: 10.1105/tpc.114.123893
• Languages: English
• ISSNs: 1040-4651

Abstract

Abstract : The nucleolus, the most prominent nuclear structure, is involved in ribosome biogenesis and nuclear and nucleolar chromatin organization. Nucleolins are among the most abundant nucleolar proteins. In contrast with mammals, plants encode two nucleolins. Characterization of Arabidopsis thaliana nuc2 mutants shows the importance of these proteins in chromatin silencing and ribosomal DNA organization. Abstract: In plants as well as in animals, hundreds to thousands of 45S rRNA gene copies localize in Nucleolus Organizer Regions (NORs), and the activation or repression of specific sets of rDNA depends on epigenetic mechanisms. Previously, we reported that the Arabidopsis thaliana nucleolin protein NUC1, an abundant and evolutionarily conserved nucleolar protein in eukaryotic organisms, is required for maintaining DNA methylation levels and for controlling the expression of specific rDNA variants in Arabidopsis . Interestingly, in contrast with animal or yeast cells, plants contain a second nucleolin gene. Here, we report that Arabidopsis NUC1 and NUC2 nucleolin genes are both required for plant growth and survival and that NUC2 disruption represses flowering. However, these genes seem to be functionally antagonistic. In contrast with NUC1, disruption of NUC2 induces CG hypermethylation of rDNA and NOR association with the nucleolus. Moreover, NUC2 loss of function triggers major changes in rDNA spatial organization, expression, and transgenerational stability. Our analyses indicate that silencing of specific rRNA genes is mostly determined by the active or repressed state of the NORs and that nucleolin proteins play a key role in the developmental control of this process.