The lichen-forming fungus Xanthoria parietina represents one of the first lichen-forming fungi to be sequenced. A lichen is an association between a fungus (usually an ascomycete) and either a microalga or a cyanobacterium, or both. Lichens are widely regarded as the classic example of a mutualistic symbiosis and form a major component of biodiversity within the fungal kingdom.
Xanthoria parietina was chosen as a model organism to represent lichen-forming fungi because it has a wide distribution (being found in temperate and circumpolar regions worldwide), has a characteristic stratified thallus morphology, is amenable to axenic cultivation, and is one of the most commonly studied lichenized fungi. It can occur on a variety of substrates including rock, tree bark and man-made strata. Genome analysis is anticipated to provide insights into the genetic basis of biological phenomena such as mutualistic symbiosis, adaptation to harsh environments, secondary metabolism, fungal sexuality, and control of growth rate in the lichenized habit.
To enable genome studies, ascospore progeny from an
individual thallus of X. parietina (from
the Peak District, UK) were collected and grown in axenic culture
to allow extraction of DNA purely of the fungal mycobiont.
Sequencing and auto-annotation of the genomic DNA is now being
performed at the DOE Joint Genome Institute.