Résumé
In plant cells, a large pool of iron (Fe) is contained in the nucleolus, together with that in chloroplasts and mitochondria. A central determinant for intracellular distribution of Fe is nicotianamine (NA) generated by nicotianamine synthase (NAS). Here, we characterized Arabidopsis thaliana plants with disrupted NAS genes to modify accumulation of nucleolar iron and understand its role in nucleolar functions and more specifically in rRNA gene expression. We found that nas124 triple mutant plants, which contain lower quantities of the iron ligand NA, also contain less iron in the nucleolus. This is concurrent with the expression of normally silenced rRNA genes from Nucleolar Organizer Regions 2 (NOR2). Notably, in nas234 triple mutant plants, which also contain lower quantities of NA, nucleolar iron and rDNA expression are not affected. In contrast, in both nas124 and nas234, specific RNA modifications are differentially regulated in a genotype dependent manner. Taken together the data point out the impact of specific NAS activities in RNA gene expression. We discuss the interplay between NA and nucleolar iron with rDNA functional organization and RNA methylation.