Autophagy promotes survival in aging submerged cultures of the filamentous fungus Aspergillus niger

Abstract

Autophagy is a well-conserved catabolic process constitutively active in eukaryotes that is involved in maintaining cellular homeostasis by the targeting of cytoplasmic content and organelles to vacuoles. Autophagy is strongly induced by the limitation of nutrients including carbon, nitrogen, and oxygen and is clearly associated with cell death. It has been demonstrated that the accumulation of empty hyphal compartments and cryptic growth in carbon-starved submerged cultures of the filamentous fungus Aspergillus niger is accompanied by a joint transcriptional induction of autophagy genes. This study examines the role of autophagy by deleting the atg1, atg8, and atg17 orthologs in A. niger and phenotypically analyzing the deletion mutants in surface and submerged cultures. The results indicate that atg1 and atg8 are essential for efficient autophagy, whereas deletion of atg17 has little to no effect on autophagy in A. niger. Depending on the kind of oxidative stress confronted with, autophagy deficiency renders A. niger either more resistant (menadione) or more sensitive (H2O2) to oxidative stress. Fluorescence microscopy showed that mitochondrial turnover upon carbon depletion in submerged cultures is severely blocked in autophagy-impaired A. niger mutants. Furthermore, automated image analysis demonstrated that autophagy promotes survival in maintained carbon-starved cultures of A. niger. Taken together, the results suggest that besides its function in nutrient recycling, autophagy plays important roles in physiological adaptation by organelle turnover and protection against cell death upon carbon depletion in submerged cultures.

Autophagy contributes to regulation of nuclear dynamics during vegetative growth and hyphal fusion inFusarium oxysporum

“…29,37 In line with this idea, Foatg8D mutants exhibited reduced aerial hyphae and conidiation, as reported in other filamentous fungi. 5,910,14,28,29 In fungal pathogens, successful infection might depend on the recycling of macromolecules to support cellular activity under nutrient-limiting conditions in the host. We found that virulence of Foatg8D mutants on both tomato plants and G. melonella larvae was significantly attenuated.…”

“…5,9,10,14,28,29 We therefore determined vegetative growth and conidiation on solid and in liquid media, both in rich and minimal medium. Under highnutrient conditions, colonies of the Foatg8D mutants showed slightly reduced radial growth ( Fig.…”

“…For fluorescence video microscopy analysis, 20-ml droplets containing a mixture of 2.5 £ 10 6 spores/mL were inoculated on glass slides provided with a cavity of 15 to 18 mm diameter (depth 0.6 to 0.8 mm) (Marienfeld, 13 200 00) filled with 150 mL fusion medium containing 1% agarose, covered with a coverslip, and incubated at 28 C for up to 10 h. Images were taken every 5 min using the microscope mentioned above and time-lapse picture series were converted to QuickTime movies.…”

Transcriptional Regulation and Responses in Filamentous Fungi Exposed to Lignocellulose

“…The transition from nutrient-rich growth conditions to lignocellulose involves a carbon starvation response in A. niger [42]. The carbon starvation response involves the induction of ER-autophagy genes and CAZyme-encoding genes (many of which are predicted to be involved in cell autolysis) [47,146]. Wheat straw also up-regulated the transcript levels of ER-autophagy genes in T. reesei [121].…”

Chitinase but N-acetyl-β-D-glucosaminidase production correlates to the biomass decline in Penicillium and Aspergillus species

“…The phenomenon contributes to the survival of filamentous fungi under harsh environmental conditions like carbon shortage [3] as its main function is to supply developmental processes with energy sources [4,5].…”