Identification of genes involved in the symbiotic interactions in the lichen Xanthoria parietina

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Lichens are composed of at least two different organisms, an alga (photobiont) and a fungus (mycobiont). These form an often highly differentiated structure, the lichen thallus. Even if this interaction between the partaking symbionts is not exclusive, many mycobionts are rather selective in their photobiont choice, like, for example, the foliose lichen Xanthoria parietina. Both partners can be isolated into axenic cultures and cultivated separately in the laboratory. The first steps of the relichenisation can be induced by co-culturing these isolates. This offers the opportunity to study the molecular mechanisms underlying the establishment of lichen symbiosis. The symbionts exchange signals leading to close metabolic coupling (e.g. release of sugar alcohols by the alga and subsequent uptake and metabolism by the mycobiont) and finally responses to light, leading to an optimal arrangement of the algae in a lichen thallus to perform photosynthesis. Genes involved in the very early symbiotic interaction of the symbionts will be identified in order to gain first insight in the genetic basis of signal exchange in lichen symbiosis.