Ribosome Biogenesis in Plants: from Functional 45S Ribosomal DNA Organization to Ribosome Assembly Factors.

The transcription of 18S, 5.8S and 18S rRNA genes (45S rDNA), co-transcriptional processing of pre-rRNA and assembly of mature rRNA with ribosomal proteins are the linchpins of ribosome biogenesis. In yeast and in animal cells, hundreds of pre-rRNA processing factors have been identified and their involvement in ribosome assembly determined. These studies, together with structural analyses, have yielded comprehensive models of the pre-40S and pre-60S ribosome subunits, as well as of the largest co-transcriptionally assembled pre-ribosome particle: the 90S/SSU-processome. Here we present our current knowledge of the functional organization of rDNA, pre-rRNA transcription, rRNA processing activities and ribosome assembly factors in plants, focusing on data from Arabidopsis thaliana. Based on yeast and mammalian cell studies, we describe the ribonucleoprotein complexes and RNA-associated activities and discuss how they might specifically affect production of 40S and 60S subunits. Furthermore, we review recent findings concerning pre-rRNA processing pathways and a novel mechanism involved in a ribosome stress response in plants.