Filamentous fungi form hyphal networks, that grow by regular branching and fusion. In contrast to most other multicellular organisms, fungi do not have cell compartments or leaky ones, so that nuclei generally can move through the mycelium. Therefore, the units in the fungal colony that cooperate to form the fungal colony are the nuclei, and not the cells. Filamentous fungi can also fuse with other individuals, potentially leading to the formation of chimeras between genetically different colonies. Fusion can provide benefits to both fusing partners, but also carries risks since genetic parasites can be transmitted. Under conditions of free fusion, experimental evolution of Neurospora crassa resulted in selection of cheater variants (Bastiaans et al., 2016, https://doi.org/10.1038/ncomms11435). Those cheaters had increased individual competitiveness relative to the ancestor, but had decreased total spore production both in monoculture and in mixed culture with the competitor.
The primary aim is to understand the balance between the benefits and risks of fusion between fungal colonies. In particular, the evolutionary benefit of allorecognition will be established. The next steps in this research are i) to understand the mechanism of cheating and ii) the reason that cheaters normally are not selected. We are particular interested in the role of allorecognition, the ability to distinguish self from non-self. Allorecognition puts limits to fusion and the most widely accepted hypothesis is that allorecognition has evolved to protect selection of cheating variants. However, this hypothesis has not been verified experimentally yet.
We use experimental evolution, genome sequencing and experimental verification of identified mutants. A large part of the work involves culturing cheating variants together with wild types under various conditions and measure or observe the fate of both types. Neurospora crassa forms many asexual spores in a matter of days that can be conveniently used as inoculum and as a fitness measure. In order to understand the mechanism of cheating we try to figure out where, when and under which circumstances the cheater is benefiting. To study the co-evolution between allorecognition and cheating we follow the fate of cheaters under varying degrees of allorecognition, and also vice versa the effect of the presence of cheating on allorecognition diversity.
We are open to applications for thesis projects! We have different thesis topics available, including projects with Fungal Culturing, Fitness Assays and/or Experimental Evolution.
- Thesis projects
- Are you interested? Please contact Eric.Bastiaans@wur.nl.