Nucleolar localization of Aspergillus fumigatus CgrA is temperature-dependent

Pathogenic fungi must adapt to multiple adverse environmental conditions during the transition from the environment to a mammalian host, one of which is temperature. The ability of Aspergillus fumigatus to grow optimally under conditions of thermal stress requires the nucleolar protein CgrA. In this study, we have determined how temperature affects the intracellular localization of CgrA in A. fumigatus using a green fluorescent protein (GFP)-tagging approach. At 22 °C, CgrA was almost exclusively in the nucleolus, with a ratio of nucleolar to cytoplasmic fluorescence of 10:1. At 37 °C, the ratio of nucleolar to cytoplasmic fluorescence was reduced fivefold, and increased correspondingly in the cytoplasm. This effect was not seen with the nucleolar protein NopA in wild-type A. fumigatus. However, in a ΔcgrA mutant NopA was delocalized from the nucleolus at 37 °C but not at 22 °C. These results provide evidence for a temperature-dependent mechanism of intracellular localization for CgrA, and suggest that CgrA facilitates nucleolar compartmentalization of NopA at higher temperature.