The <i>Aspergillus fumigatus pkcA</i>^G579R Mutant Is Defective in the Activation of the Cell Wall Integrity Pathway but Is Dispensable for Virulence in a Neutropenic Mouse Infection Model

<div><p><i>Aspergillus fumigatus</i> is an opportunistic human pathogen, which causes the life-threatening disease, invasive pulmonary aspergillosis. In fungi, cell wall homeostasis is controlled by the conserved <u>C</u>ell <u>W</u>all <u>I</u>ntegrity (CWI) pathway. In <i>A</i>. <i>fumigatus</i> this signaling cascade is partially characterized, but the mechanisms by which it is activated are not fully elucidated. In this study we investigated the role of protein kinase C (PkcA) in this signaling cascade. Our results suggest that <i>pkcA</i> is an essential gene and is activated in response to cell wall stress. Subsequently, we constructed and analyzed a non-essential <i>A</i>. <i>fumigatus pkcA</i>^G579R mutant, carrying a Gly579Arg substitution in the PkcA C1B regulatory domain. The <i>pkcA</i>^G579R mutation has a reduced activation of the downstream <u>M</u>itogen-<u>A</u>ctivated <u>P</u>rotein <u>K</u>inase, MpkA, resulting in the altered expression of genes encoding cell wall-related proteins, markers of endoplasmic reticulum stress and the unfolded protein response. Furthermore, PkcA^G579R is involved in the formation of proper conidial architecture and protection to oxidative damage. The <i>pkcA</i>^G579R mutant elicits increased production of TNF-α and phagocytosis but it has no impact on virulence in a murine model of invasive pulmonary aspergillosis. These results highlight the importance of PkcA to the CWI pathway but also indicated that additional regulatory circuits may be involved in the biosynthesis and/or reinforcement of the <i>A</i>. <i>fumigatus</i> cell wall during infection.</p></div