Project description:The rapid transport of ribosomal proteins (RPs) into the nucleus and their efficient assembly into rRNA are prerequisites for ribosome biogenesis. Proteins that act as dedicated chaperones for RPs to maintain their stability and facilitate their assembly have not been identified in filamentous fungi. PlCYP5 is a nuclear cyclophilin in the nematophagous fungus Purpureocillium lilacinum, and up-regulated expression in response to abiotic stress and nematode egg-parasitism. Here, we found that PlCYP5 interacted with the unassembled small ribosomal subunit protein, PlRPS15, of the uS19 family. PlRPS15 contained a eukaryote-specific N-terminal extension that mediated the interaction. The phenotypes of the PlCYP5 loss-of-function mutant were similar to those of the PlRPS15 knockdown mutant (e.g., growth and ribosome biogenesis defects). PlCYP5 maintained the solubility of PlRPS15 independent of its catalytic peptide-prolyl isomerase function and supported the integration of PlRPS15 into pre-ribosomes. PlCYP5 homologs in Arabidopsis thaliana, Homo sapiens, Schizosaccharomyces pombe, Sclerotinia sclerotiorum, Botytis cinerea, and Metarhizium anisopliae were identified. Notably, the interaction of their homologs corresponding to the PlCYP5-PlRPS15 pattern existed in three filamentous fungi, while lacked in other species. In summary, our data disclosed a special RP dedicated chaperone system in filamentous fungi, in which cyclophilin was enlisted to perform the chaperone funtion.
