Chloroplast ribogenesis: from transcripts to functional ribosomes. The entire biogenesis pathway is schematically illustrated from rRNA transcripts to the assembly of functional chloroplast 70S ribosomes. Some factors involved in ribogenesis are exemplified. The initial processing of the primary polycistronic rRNA transcript is mediated by exo- and endoribonucleases as well as numerous RNA-binding proteins that facilitate further rRNA maturation steps. Methyltransferases and other writers install epitranscriptomic marks into rRNA species to support the processing, assembly and function of ribosomes. DEAD-box RNA-helicases, which generally contain two RecA-like domains, are often important under abiotic stress conditions to unwind dysfunctional RNA structures (red duplexes) that are thermodynamically trapped especially in the cold. This process typically requires energy in the form of GTP or ATP hydrolysis or even heat. RNA chaperones enable the correct folding of functional rRNAs (black duplexes) without requiring further energy input. Subsequently, RPs are delivered, which partially assemble into the immature ribosomal 30S and 50S subunits presumably due to their own RNA chaperone activity. This process is supported by GTPases, which can serve as placeholders and facilitate the incorporation of additional proteins into the ribosomal subunits. Finally, both subunits come together to form translational competent 70S ribosomes. Note that the coordinated sequence of rRNA maturation and ribosome assembly events does not strictly follow the order shown in the simplified figure, that temporal aspects have not been considered and that the contribution of the 4.5S and 5S rRNAs has been excluded.