Abstract

Self-eating is important for mycelium growth.

When studying fungal mycelium growth and development it is customary to think in terms of nutrient uptake, growth in biomass, and especially when studying growth I heterogeneous environments, nutrient translocation. Newly taken up nutrients are not the only sources of nutrients to the advancing front of a mycelium. Old biomass can be recycled into new biomass. Autophagy, or self-eating, is a general process for recycling biomass to nutrients within an eukaryotic cell.

One of the key proteins in macroautophagy Atg8p is necessary for the formation of autophagosomes. In order to evaluate if internal recycling of nutrients is important for F. graminearum we used homologous recombination and an Agrobacterium-mediated transformation technique to make Fg?Atg8-deletion strains.

The Fg?Atg8-deletion mutants have less extensive aerial mycelium but otherwise they grow as fast and dense and with similar colour as the wild type on standard media. In an infection assay on heads of wheat the Fg?Atg8-deletion mutants had a considerable reduced virulence in comparison with the wild type. A closer investigation of the aerial mycelium showed that it becomes filled with lipid droplets indicating starvation of some mineral nutrient and surplus of carbon/energy. The Fg?Atg8-deletion mutants have almost no ability to extend over inert plastic surfaces although the wild type does it to a great extent. Thus, virulence as well as formation of aerial hyphae and growth over inert surfaces is dependent on internal recycling of nutrients. These results highlight the importance of nutrient recycling within a mycelium for mycelium growth and development.