Why do we need model organisms in experimental lichenology?

Honegger, R.
Institute of Plant Biology, University of Zürich, Zürich, Switzerland

Suitable model systems are essential for studies on fungal interactions with photoautotrophic partners. This will be illustrated with brief summaries of (multiauthored) published data on gene regulation during the infection process of the rice pathogen Magnaporthe grisea and during ectomycorrhization of eucalypt roots by Pisolithus tinctoria. For studies on gene expression and on functions of gene products during the establishment and maintenance of lichen symbiosis we urgently need one or few model organisms. Despite many promising results lichenologists have not yet succeeded in finding a model system which can be handled and maintained in every laboratory with adequate infrastructure. As unsuccessful experiments are usually not published, newcomers experience the same failures as many of their colleagues before. This discussion session aims at 1) compiling published and unpublished data on lichen-forming fungi and their photoautotrophic partners which have so far been used, successfully or not, in different types of experiments under sterile conditions, the focus being on re-lichenization, production of secondary metabolites, or mating; 2) discussing important parameters such as reproducibility, synchronization and standardization of experiments; 3) stimulating the search for model organisms and discussing which groups of lichen-forming fungi might contain promising candidates; 4) summarizing data on culturing methods, maintenance and deposition of isolates and on their genetic stability over time.


Secondary chemistry, molecular studies and ecophysiology of crustose lichens: culture of selected mycobionts of the genera Haematomma and Rhizocarpon

Stocker-Wörgötter, E. (1), Feuerer, T. (2) & Elix, J. A. (3)
(1) Institute of Plant Physiology, University of Salzburg, Austria; (2) Biozentrum Klein Flottbek, University of Hamburg, Germany; (3) Department of Chemistry, Australian National University, Canberra, Australia

The investigated Rhizocarpon lecanorinum Anders is a pioneer growing on sun exposed siliceous boulders in relatively low altitutes. Its distribution ranges from the northern temperate and boreal regions to Patagonia, South Africa and South Australia. Taxonomically it belongs to the complex ‘Rhizocarpon geographicum’ group and is sometimes difficult to distinghuish from some subspecies of Rhizocarpon geographicum.
The mycobiont was grown from spores and thallus fragments. For the spore derived cultures a novel nutrient medium was introduced. Under stress conditions, a defined combination of low temperature treatment, desiccation and exposure to UV-light, the typical depsidones and also the pulvinic acid derivatives (rhizocarpic acid) were biosynthesised. Together with a broad molecular investigation, the results will help to clarify the species boundaries within this group.
Further experiments were performed with selected species of the genus Haematomma, e.g. H. persoonii (Fée) Massal., H. fenzlianum Massal. and H. flourescens Kalb & Staiger collected in the subtropical and tropical regions of North and South America. Both spore and fragment cultures gave a yield of 10-30 mg (dry weight) after an incubation period of six months. The typical medullary metobolites in the cultures, sphaerophorin, isophaeric acid, etc were documented by TLC and HPLC analyses. The appearance of flourescent compounds (rhizocarpic acid, lichexanthone) during mycelia development was studied by fluorescence microscopy.