Mechanisms and impact of ribosomal RNA methylation in plants
Résumé
Ribose methylation (2'-O-Me) is the most common modification of ribosomal RNAs (rRNA)
in various life forms and are pivotal for ribosome assembly and translation. These 2-O-Me modifications
are guided by small nucleolar C/D-box RNAs (C/D snoRNA) and are deposited by the
methyltransferase FIBRILLARIN (FIB). Our work, performed in the plant model Arabidopsis
thaliana, highlights that rRNA 2-O-Me is a dynamic process. To understand the impact of
such modulation of rRNA 2-O-Me on translation, we examined Arabidopsis plants lacking the
major nucleolar protein Nucleolin 1 (NUC1). Depletion of NUC1 (nuc1 ) resulted in decreased
rRNA 2-O-Me levels(1) and, hence, in ribosome hypomethylation. Our findings suggest that
reduced rRNA 2-O-Me in nuc1 may be triggered by defects in the assembly of the C/D snoRNP
complex. Ribosome hypomethylation leads to an accumulation of polysomes detectable in their
polysome profiles and a stalling of ribosomes at the start codon shown in 5’Pseq analysis. We
are now trying to elucidate if this stalling could be either inferred to the formation of the 80S
complex or to difficulties in interacting with translation initiation factors. All in all, our results
underscore the crucial role of rRNA methylation and the heterogeneity of ribosomes in their
assembly and translation processes.
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