Impaired Ribosome Biogenesis Disrupts the Integration between Morphogenesis and Nuclear Duplication during the Germination ofAspergillus fumigatus

Abstract

ABSTRACTAspergillus fumigatusis an important opportunistic fungal pathogen that is responsible for high mortality rates in the immunosuppressed population. CgrA, theA. fumigatusortholog of aSaccharomyces cerevisiaenucleolar protein involved in ribosome biogenesis, contributes to the virulence of this fungus by supporting rapid growth at 37°C. To determine how CgrA affects ribosome biogenesis inA. fumigatus, polysome profile and ribosomal subunit analyses were performed on both wild-typeA. fumigatusand a ΔcgrAmutant. The loss of CgrA was associated with a reduction in the level of 80S monosomes as well as an imbalance in the 60S:40S subunit ratio and the appearance of half-mer ribosomes. The gene expression profile in the ΔcgrAmutant revealed increased abundance of a subset of translational machinery mRNAs relative to the wild type, suggesting a potential compensatory response to CgrA deficiency. Although ΔcgrAconidia germinated normally at 22°C, they swelled excessively when incubated at 37°C and accumulated abnormally high numbers of nuclei. This hypernucleated phenotype could be replicated pharmacologically by germinating wild-type conidia under conditions of reductive stress. These findings indicate that the germination process is particularly vulnerable to global disruption of protein synthesis and suggest that CgrA is involved in both ribosome biogenesis and polarized cell growth inA. fumigatus.