Why Sequence Xanthoria parietina?

The lichen-forming fungus Xanthoria parietina would be the first lichen fungus 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. Lichens grow in soil-less habitats such as on rocks or tree bark, or on poorly developed soils. Although these habitats occur in all terrestrial biomes, they are particularly abundant at high latitudes in the Subarctic, Arctic, and Antarctic, where lichens are of great ecological importance and where global warming and climate change pose a special threat.

There are approximately 13,500 species of lichen-forming fungi, each producing a distinct lichen association (i.e., a “lichen species”). Lichen-forming fungi represent a major component of the fungal kingdom, and it is essential that they are included among a group of organisms selected to represent global biodiversity. There is now intense interest in the phylogenetic position of lichen fungi, and there is evidence that many non-lichenized ascomycetes, including economically important genera such as Aspergillus and Penicillium, are derived from lichenized ancestors. Knowledge of the genome structure and sequence would greatly promote understanding of ascomycete evolution, including the evolution of genes responsible for secondary product synthesis and sexuality. It will also reveal genome specialization relating to the lichenized habit. These features are consistent with the DOE mission to discover and characterize basic principles and relationships underlying the organization, function and evolution of living systems.

Xanthoria parietina has been chosen as a model organism to represent lichen-forming fungi because it has a wide distribution, has a typical thallus morphology, is amenable to axenic cultivation, and is one of the most commonly studied lichen fungi. The data will be of interest to the more general worldwide fungal, climate change, and cell biology communities. Genome analysis is anticipated to provide insights into the genetic basis of biological phenomena such as mutualistic symbiosis, adaptation to harsh environments, secondary metabolism, and control of growth rate.

CSP project participants: Paul S. Dyer (proposer), Peter D. Crittenden, and David B. Archer (Univ. of Nottingham).