Use of Fungal Model Systems to Address Evolutionary Questions
Many ascomycetes, like the well known species Neurospora crassa1 have a coenocytical organization. They are ideally suited as model organisms in molecular biology or evolutionary studies2 due to their short life cycles, easy propagation, and the existence of many molecular tools for genetic engineering and the like. Genome sequences are not only available from A. niger or N. crassa, but from an ever increasing number of species thus enabling large scale evolutionary work. In my laboratory we use these and other fungi to address different evolutionary questions:
(1) Horizontal Gene Transfer of Secondary Metabolite Gene Cluster
There is an open question to what extend secondary metabolite gene cluster evolution is driven or at least influenced by horizontal gene transfer. The use of appropriate marker genes provides a simple experimental screen to follow gene transfer, e.g. from Aspergillus niger to Neurospora crassa. Within the project extend, frequency and size limitations of transfered genomic fragments will be investigated. Filamentous fungi are ideally suited for this approach due to their ability to form hyphal fusions, even if these are instable or led to hyphal death. All necessary molecular genetic components are easily available or established in the laboratory. We do have fluorescent markers to monitor hyphal fusion (see Fig. 1).
(2) Evolution Forces Which Drive Secondary Metabolite Production in Fungi
My lab is analyzing the relevance of fungal secondary metabolites in competition experiments with insect larvae. Here we use the model organism Aspergillus nidulans. Figure 2 shows an experimental setup, where we analyze the effect of fungal growth priority on egg laying activity. We also use fungal strains with specific mutations in single secondary metabolite genes or gene clusters for competition experiments to monitor larval survival. In addition to continuing efforts to determine larval survival in competition with different mutant strains, we would be interested to test survival of different fungal strains when competing with insects. To this end mixtures of wild type and a variety of mutant strains would be exposed to insects. Surviving spores would be collected, tested for wild type to mutant ratios and again exposed to insect larvae. After repeated cycles the fitness of different genotypes under competing conditions will be determined. In addition we are expecting RNA-seq data from competing conditions soon, which will help to identify further targets for experimental set-ups.
1 – Roche CM et al. (2014) Neurospora crassa: Looking back and looking forward at a model microbe. American Journal of Botany 101:2022-2035
2 - Billiard S et al. (2012) Sex, outcrossing and mating types: unsolved questions in fungi and beyond. Journal of Evolutionary Biology 25 (2012) 1020–1038
3 - Kempken F, Rohlfs M (2010) Fungal secondary metabolite biosynthesis - a chemical defense strategy against antagonistic animals? Fungal Ecol 3:107-114