Working on this project:
Ribosome biogenesis is a very ancient process that involves many snoRNAs and proteins catalysing rRNA maturation and modification, but species-specific variations and adaptation of this central cellular process have evolved. In project B9, the plant-specific regulation of ribosome biogenesis is investigated. In the 2nd period, we identified plant-specific ribosome assembly factors and snoRNAs and determined their impact on rRNA maturation and modification. Among other observations, we found that 5.8S rRNA maturation occurs in a plant-specific manner. The 5.8S maturation in plants is initiated in the nucleolus, while the last steps take place in cytoplasm. We identified factors are essential for the maturation of the plant-specific 5’-5.8S pre-rRNA precursor. One factor annotated as IRP9 is involved in this processing step and is essential for plant growth. In addition, we discovered snoRNAs specific for plants that target 5.8S. This provides strong evidence that the final maturation of the 5.8S rRNA is an important event for quality control of ribosome biogenesis. Thus, our discoveries of the last funding period now funnel into three research aims: (1) Characterization of the RNA elements and RNA-protein interactions required for final maturation of the 5.8S rRNA. Since it is plant specific it marks a clear distinction from the common picture of ribosome biogenesis established on yeast. (2) Dissection of the impact of 5.8S rRNA modifications on its maturation and on ribosome quality control or fidelity, as we observed at least two not yet characterized modifications of this rRNA as well as several uncharacterized snoRNAs targeting this rRNA element. (3) Definition of the function of 5.8S rRNA processing for ribosome quality control, as the last steps occur in the cytoplasm which might involve specific factors as described for the 25S rRNA in yeast. Our study will resolve the impact of the 5.8S centred ribosome maturation processes to define general and plant specific events during ribosome biogenesis.