Abstract
How yeast cells respond to cell wall stress is relatively well understood; however, how filamentous fungi cope with cell wall damage is largely unexplored. Here we report the first transcriptome analysis of Aspergillus niger exposed to the antifungal compounds caspofungin, an inhibitor of beta-1,3-glucan synthesis, and fenpropimorph, which inhibits ergosterol synthesis. The presence of sublethal drug concentrations allowed A. niger to adapt to the stress conditions and to continue growth by the establishment of new polarity axes and formation of new germ tubes. By comparing the expression profile between caspofungin-exposed and nonexposed A. niger germlings, we identified a total of 172 responsive genes out of 14,509 open reading frames present on the Affymetrix microarray chips. Among 165 up-regulated genes, mainly genes predicted to function in (i) cell wall assembly and remodeling, (ii) cytoskeletal organization, (iii) signaling, and (iv) oxidative stress response were affected. Fenpropimorph modulated expression of 43 genes, of which 41 showed enhanced expression. Here, genes predicted to function in (i) membrane reconstruction, (ii) lipid signaling, (iii) cell wall remodeling, and (iv) oxidative stress response were identified. Northern analyses of selected genes were used to confirm the microarray analyses. The results further show that expression of the agsA gene encoding an alpha-1,3-glucan synthase is up-regulated by both compounds. Using two PagsA-GFP reporter strains of A. niger and subjecting them to 16 different antifungal compounds, including caspofungin and fenpropimorph, we could show that agsA is specifically activated by compounds interfering directly or indirectly with cell wall biosynthesis.
Highlights
How yeast cells respond to cell wall stress is relatively well understood; how filamentous fungi cope with cell wall damage is largely unexplored
Screening for Morphology-affecting Compounds—To select suitable compounds that affect the morphology of A. niger, we have screened various substances proposed to interfere with fungal cell wall synthesis, ergosterol synthesis, sphingolipid synthesis, and cAMP-dependent protein kinase signaling (8-Br-cAMP and caffeine)
We have shown previously that the agsA gene coding for ␣-1,3-glucan synthase (An04g09890) is strongly induced in response to compounds that interfere with cell wall or cell membrane integrity of A. niger such as calcofluor white, SDS, caspofungin, and AFP [21, 25], suggesting that ␣-1,3-glucan synthesis might be generally involved in securing cell surface integrity
Summary
How yeast cells respond to cell wall stress is relatively well understood; how filamentous fungi cope with cell wall damage is largely unexplored. Among 165 up-regulated genes, mainly genes predicted to function in (i) cell wall assembly and remodeling, (ii) cytoskeletal organization, (iii) signaling, and (iv) oxidative stress response were affected. Genes predicted to function in (i) membrane reconstruction, (ii) lipid signaling, (iii) cell wall remodeling, and (iv) oxidative stress response were identified. Using two PagsA-GFP reporter strains of A. niger and subjecting them to 16 different antifungal compounds, including caspofungin and fenpropimorph, we could show that agsA is activated by compounds interfering directly or indirectly with cell wall biosynthesis. To prevent cell lysis and to ensure cell survival, fungi have developed mechanisms to sense cell surface stress and to respond to these stresses via a remodeling of the cell wall The composition of fungal cell walls and the mechanisms involved in ensuring cell surface integrity have been studied most intensively in the model yeast Saccharomyces cerevisiae. Information about cell wall biology in filamentous fungi and the mechanisms important for maintain-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
