Nm in translation A.thaliana Supplement

Across all kingdoms of life, the ribose methylation (2' O Me) is the most abundant modification of ribosomal RNAs (rRNA), which are the lynchpins of ribosome assembly and function. Biosynthesis of these 2' O Me residues at specific rRNA sites is guided by small nucleolar C/D box RNAs (C/D snoRNA) and performed by the methyltransferase FIBRILLARIN (FIB). Here, we show that 2' O Me of rRNA is dynamically regulated during development of Arabidopsis thaliana (Col 0) plants. To study 2' O Me regulation and its impact on translation, we characterised Arabidopsis plants depleted in the major nucleolar protein NUCLEOLIN 1 (NUC1). The absence of NUC1 induces low rRNA 2' O Me levels and, consequently, hypomethylation of ribosomes. We show that rRNA 2' O Me hypomethylation is likely to be related to the assembly defect, but not to the global expression of the C/D snoRNP com-plexes, whereas ribosome hypomethylation causes an accumulation of polysomes and subsequently affects loading and translation initiation at the start codon. These results highlight the importance of rRNA modifications and propose that ribosome heterogeneity plays the major role in the orchestration of ribosome assembly and translation.