Rho2 regulates granulocyte-triggered stress adaptation and cell wall remodeling in Aspergillus fumigatus.

The airborne opportunistic fungal pathogen Aspergillus fumigatus poses a deadly threat to immunocompromised patients. Neutrophil granulocytes play a key role in the defense against invasive infections caused by this pathogen. The mechanisms by which Aspergillus defends itself against attacks by the immune system are only partially understood. Here we show that human granulocytes activate the cell wall integrity (CWI) pathway of A. fumigatus and that key components of the CWI such as the cell wall stress sensor MidA and the Rho GTPases Rho2 and Rho4 are important for the survival of Aspergillus hyphae under granulocyte attacks. A more detailed investigation of the role of Rho2 revealed that a mutant lacking rho2 is less virulent in a Galleria mellonella infection model. Overexpression of Rho2 increases the resistance of A. fumigatus hyphae to killing by granulocytes. While a mutant lacking Rho2 has a normal cell wall composition, overexpression or constitutive activation of Rho2 leads to an altered cell wall composition and impairs growths of the pathogen. The fungicidal effect of constitutive activation of Rho2 signaling, which correlates with the formation of cell wall chitin bulges, depends on the CWI MAP kinase MpkA. However, Rho2 itself does not appear to be a direct activator of the CWI MAP kinase module. Our results support a model where Rho2 in A. fumigatus actively counteracts granulocyte attacks by upregulating cell wall biosynthesis, thereby strengthening the cell wall and aiding the fungus in surviving the stress condition.