The nucleolar protein NOL12 is required for 5' end processing of large ribosomal subunit rRNA precursors in Arabidopsis

Background NOL12 5'-3' exoribonucleases, conserved among eukaryotes, play important roles in pre-rRNA processing, ribosome assembly and export. The best described yeast counterpart, Rrp17, is required for maturation of 5.8S and 25S rRNAs, whereas human hNOL12 is crucial for the separation of the large (LSU) and small (SSU) ribosome subunit rRNA precursors. Results Here we show that plant AtNOL12 is also involved in rRNA biogenesis, particularly in the processing of the LSU rRNA precursor, 27S pre-rRNA. Importantly, the absence of AtNOL12 alters the expression of many ribosomal protein and ribosome biogenesis genes, which may further exacerbate rRNA biogenesis defects, or, alternatively, may be the effect of the disturbed ribosome assembly caused by delayed pre-rRNA processing. Also, exposure of nol12 mutants to stress factors, including heat, salt and pathogen Pseudomonas syringae, enhances the observed molecular phenotypes, linking pre-rRNA processing to stress response pathways. AtNOL12-dependent aberrant rRNA processing may affect ribosome function, as indicated by improved mutant resistance to ribosome-targeting antibiotics. Conclusion The pre-rRNA processing pathway, although extensively studied, is still poorly described in plants. Our work reveals the involvement of AtNOL12 in the 5' end maturation of rRNA precursors, which is related to stress response in Arabidopsis. This contributes to a better characterization of plant ribosome biogenesis.