Lichenised fungi living in deserts and high-altitude regions face a challenge from intense UV light, which is known to cause DNA damage. Recently, we have shown that the family Teloschistaceae (Ascomycota) underwent an adaptive radiation ∼100 Mya, experiencing an increase in diversification rates associated with a switch from bark to rock and from shady to sun-exposed habitats. Our hypothesis is that the adaptation to sunny habitats is likely to have been enabled by a contemporaneous key novel phenotypic innovation: the production of anthraquinones, secondary metabolites known to protect against UV light.
Whereas UV-absorbing anthraquinones are almost unique to the Teloschistaceae clade, with only a few scattered exceptions, UV protection in other fungal clades is mainly achieved using melanin, which is synthesised from phenols using the enzyme tyrosinase. Paradoxically, although anthraquinones protect from UV radiation they are themselves cytotoxic antifungal compounds. A key question is, therefore, why has the Teloschistales opted for anthraquinone-based UV protection given that anthraquinones are potentially toxic to the producing organism? We intend to use this unique system as a model to understand the evolution of functional secondary metabolites in a phylogenomic context, which would allow to search for co-evolved traits such as loss or gain of function of tyrosinase genes, and co-adaptation to UV light though improved DNA repair mechanisms. We also intend to determine the antifungal mode of action of Teloschistales anthraquinones and use this to observe how natural immunity to these compounds is acquired in the fungi that produce them.