A systems biology approach to dissect the function of the antifungal protein AnAFP for Aspergillus niger
Metabolism, Biochemistry and Genetics of Microorganisms
Final Report Abstract
Antimicrobial peptides are currently viewed as promising alternatives to conventional antibiotics to fight human and plant pathogens. They are produced by all life forms where they often serve as defense molecules against nutrient competitors. This study focused on the antimicrobial peptide AnAFP from the filamentous ascomycete Aspergillus niger to unravel whether it might exert an additional intracellular function that goes beyond host defense. We proposed that AnAFP could function as a cannibal toxin in axenic cultures of A. niger to promote controlled cell death and asexual development during nutrient limiting conditions. This assumption was based on our previous work that uncovered that the transcriptional expression profile of anafp correlates with the expression of genes predicted to function during autophagy, nutrient recycling, and asexual development. To test this hypothesis, we harnessed different methodological tools from systems and synthetic biology (RNAseq, gene coexpression networks, gene switches), microscopy (fluorescent protein tagging, light microscopy, in vivo imaging through confocal laser scanning microscopy), fermentation technology (controlled submerged cultivation), and protein chemistry (protein purification and detection methods including HPLC, FPLC, and mass spectrometry). This allowed us to study the temporal and spatial dynamics of anafp expression within the mycelium of A. niger during carbon limitation and how this expression profile is linked to the life cycle of this fungal species. We were able to uncover that (i) anafp gene expression is embedded in a network of 1349 genes, many of which are predicted to function in the transport and breakdown of carbohydrates, proteins, lipids, and nucleobases, as well as in asexual development, (ii) premature anafp transcription reduces growth of A. niger, (iii) anafp translation depends on regulatory sequences within its mRNA, (iv) AnAFP localizes to the cell surface of individual hyphal compartments and aerial hyphae, and (v) increased AnAFP levels provoke premature induction of autophagy but not apoptosis, which coincides with a noticeable reduction in hyphal diameters of individual hyphae. Based on these and further data we conclude that AnAFP plays an important role for the survival of A. niger when it faces carbon limitation. We propose that the peptide promotes vegetative growth and asexual development of selected hyphal compartments through autophagic recycling of neighboring hyphal compartments. We thus predict that AnAFP could indeed be considered as a fungal cannibal toxin that is part of an intracellular nutrient mobilization and recycling program that selectively sacrifice some hyphal compartments to ensure the survival of the whole colony during phases of carbon starvation.
Publications
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High-quality co-expression networks for accurate gene function predictions in the fungal cell factory Aspergillus niger and beyond. openRxiv.
Schäpe, Paul; Starke, Stephan; Schuetze, Tabea; Basenko, Evelina; Jung, Sascha; Cairns, Timothy & Meyer, Vera
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Unraveling the Role of the Antifungal Peptide AnAFP in Aspergillus niger through a Systems Biology Perspective. Doktorarbeit TU Berlin
Stephan Starke
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The antifungal peptide AnAFP from Aspergillus niger promotes nutrient mobilization through autophagic recycling during asexual development. Frontiers in Microbiology, 15.
Starke, Stephan; Velleman, Laura; Dobbert, Birgit; Seibert, Luis; Witte, Jordi; Jung, Sascha & Meyer, Vera
