Uncoupling of mRNA synthesis and degradation impairs adaptation to host temperature in Cryptococcus neoformans

Summary: The pathogenic fungus Cryptococcus neoformans must overcome multiple stressors to cause disease in its human host. In this study, we report that C.neoformans rapidly and transiently repressed ribosomal protein (RP) transcripts during a transition from 30°C to host temperature. This repression was accompanied by accelerated mRNA degradation mediated by the major deadenylase, Ccr4, and influenced by the dissociable RNA polymerase II subunit, Rpb4. Destabilization and deadenylation of RP transcripts were impaired in an rpb4Δ mutant, suggesting that Rpb4 may be involved in host temperature-induced Ccr4-mediated decay. Accelerated decay of ER stress transcripts 1h following a shift to host temperature was also impaired in the rpb4Δ mutant. In response to host temperature, Rpb4 moved from the nucleus to the cytoplasm, supporting a role for Rpb4 in coupling transcription and degradation. The PKH signalling pathway was implicated as a regulator of accelerated degradation of the RP transcripts, but not of the ER stress transcripts, revealing a further level of specificity. When transcription and degradation were uncoupled by deletion of Rpb4, growth at host temperature was impaired and virulence was attenuated. These data suggest that mRNA synthesis and decay are coupled in C.neoformans via Rpb4, and this tight coordination promotes host-temperature adaptation and pathogenicity.