An Ssd1 Homolog Impacts Trehalose and Chitin Biosynthesis and Contributes to Virulence in Aspergillus fumigatus

Abstract

Regulation of fungal cell wall biosynthesis is critical to maintain cell wall integrity in dynamic fungal infection microenvironments. Genes involved in this response that impact fungal fitness and host immune responses remain to be fully defined. In this study, we observed that a yeast ssd1 homolog, ssdA, in the filamentous fungus Aspergillus fumigatus is involved in trehalose and cell wall homeostasis. An ssdA null mutant strain exhibited an increase in trehalose levels and a reduction in fungal colony growth rate. In contrast, overexpression of ssdA perturbed trehalose biosynthesis and reduced germination of conidia. The ssdA null mutant strain was more resistant to cell wall-perturbing agents, while overexpression of ssdA increased sensitivity. Overexpression of ssdA significantly increased chitin levels, and both loss and overexpression of ssdA altered subcellular localization of the class V chitin synthase CsmA. Strikingly, overexpression of ssdA abolished adherence to abiotic surfaces and severely attenuated the virulence of A. fumigatus in a murine model of invasive pulmonary aspergillosis. Despite the severe in vitro fitness defects observed upon loss of ssdA, neither surface adherence nor murine survival was impacted. In conclusion, A. fumigatus SsdA plays a critical role in cell wall homeostasis impacting A. fumigatus-host interactions. IMPORTANCE The incidence of life-threatening infections caused by the filamentous fungus Aspergillus fumigatus is increasing along with an increase in the number of fungal strains resistant to contemporary antifungal therapies. The fungal cell wall and the associated carbohydrates required for its synthesis and maintenance are attractive drug targets given that many genes encoding proteins involved in cell wall biosynthesis and integrity are absent in humans. Importantly, genes and associated cell wall biosynthesis and homeostasis regulatory pathways remain to be fully defined in A. fumigatus. In this report, we identify SsdA as an important component of trehalose and fungal cell wall biosynthesis in A. fumigatus that consequently impacts the host immune response and fungal virulence in animal models of infection.

Reducing Aspergillus fumigatus Virulence through Targeted Dysregulation of the Conidiation Pathway

“…Doxycycline treatment had no effect on the wild-type hyphal trehalose. As an inverse relationship between trehalose synthesis and virulence has been reported in A. fumigatus (32,33), this increase in hyphal trehalose synthesis may also contribute to brlA-mediated attenuation of virulence.…”

“…5B and C). Overexpression of brlA also resulted in altered regulation of the genes governing the biosynthesis of galactosaminogalactan (GAG) and trehalose, two other carbohydrates known to play a role in A. fumigatus virulence (32)(33)(34)(35). Genes involved in the biosynthesis of GAG were downregulated in response to high-level brlA overexpression, whereas those involved in trehalose biosynthesis were upregulated ( Fig.…”

The STRIPAK signaling complex regulates dephosphorylation of GUL1, an RNA-binding protein that shuttles on endosomes

“…Our analysis has now revealed an RNA-binding domain, a nuclear localization signal, and a nuclear export signal-among others-in the primary sequence of GUL1. These domains have led us to the conclusion that S. macrospora GUL1 is an RNAbinding protein, as was previously shown by functional analysis in other filamentous fungi and yeasts [27,33,[57][58][59]. In the human pathogenic yeast Candida albicans, Ssd1, the GUL1 homolog, was described as an mRNA-binding protein acting as a translational repressor [59], and the GUL1 homologs in Magnaporthe oryzae and Aspergillus fumigatus were described as cell wall biogenesis proteins [57,58].…”

The Inhibitory Effect of Validamycin A onAspergillus flavus

“…However, further trehalase activity assay using high-performance liquid chromatography (HPLC) is also necessary to confirm the effect of validamycin A against trehalase enzymes in A. flavus . As the trehalose pathway is crucial in the early stages of conidial germination [ 18 , 19 , 47 , 59 ], we further investigated the effect of validamycin A on conidial germination of A. flavus . Expectedly, validamycin A significantly delayed conidial germination of A. flavus ( Figure 4(b) ).…”

“…Sterile distilled water was then utilized to wash twice, and 100% ethanol was used to destain for 10 min. Supernatants were then measured at 600 nm using a spectrophotometer (Lambda 1050+ UV/Vis/NIR, PerkinElmer, USA) [ 47 ].…”