A conserved C2H2 zinc finger protein, Rel1, links ribosome biogenesis to sexual development and environmental stress response in a ubiquitous human fungal pathogen

Sexual development is a fundamental process that promotes infection and the emergence of highly virulent and drug-resistant isolates in the human fungal pathogen Cryptococcus neoformans. While the genetic factors involved in sexual life cycle have been extensively investigated in this pathogenic fungus, the critical regulator(s) beyond transcriptional machinery remains poorly understood. Rei1, a conserved C2H2-type zinc finger protein, functions as a 60S ribosome biogenesis factor and plays a crucial role in maintaining cellular growth at low temperature in yeast. In this study, we identified a yeast Rei1-like protein, Rel1, based on its encoding gene that was dynamically up-regulated during unisexual reproduction in C. neoformans. Similar to Rei1's role in yeast, disruption of REL1 gene results in significant growth retardation under low temperature conditions. Consistent with its upregulation during sexual development, REL1 deletion compromised the entire sexual cycle, including yeast-hyphae morphogenesis, basidial differentiation, meiosis and sporulation. RNA-Seq analysis revealed that Rei1 is required for the transcriptional activation of key sexual reproduction gene sets involved in mating response, morphogenesis and meiosis, suggesting a potential link between ribosome biogenesis and sexual development in C. neoformans. Furthermore, REL1 disruption increased susceptibility to the antifungal drug 5'-flucytosine (5'-FC) but enhanced resistance to fluconazole, indicating its differential role in antifungal drugs resistance mechanisms. Collectively, this study provides critical insights into how C. neoformans utilize a conserved ribosome biogenesis factor to coordinate cold resistance, sexual development, and antifungal susceptibility, highlighting both conserved and divergent functions of this C2H2 zinc-finger protein compared to its ortholog in budding yeast. Overall design: RNA-seg profiling of wild type Cryptococcus neoformans strain XL280 and its knockout derivative (rel1 mutant) at 24 hours of mating induction on V8 medium.