Lichens are known for their importance in evolution and ecology but our knowledge of molecular mechanisms regulating symbiont interactions in lichen symbiosis is very lim-ited. Recent studies have shown that Umbilicaria muhlenbergii has a relative fast growth rate and is amenable to molecular genetic studies for efficiently generating transformants and targeted gene disruption mutants. It is the only known dimorphic lichen-forming fungus, and pseudohyphal growth is associated with symbiotic interactions with algal cells of Trebouxia jamesii, its photobiont. Pharmacological stud-ies and functional characterization of the Gα subunit UmGpa2 of the trimeric G-proteins have shown the involvement of the cAMP-PKA (cyclic AMP-protein kinase A) pathway in regulating yeast-to-pseudohypha transition and fungal–algal interactions. The importance of cAMP-PKA signaling in lichen symbiosis proved for the first time in U. muhlenbergii argues for further characterization of this and other well-conserved signal transduction pathways that are known to crosstalk and co-regulate fungal–plant interactions in plant pathogens. The Umbilicaria muhlenbergii genome contains key components of mitogen-activated protein (MAP) kinase pathways that may regulate fungal–algal interactions during lichen symbiosis. Although there are still challenges, U. muhlenbergii has the potential to be used as a model to study early stages of symbiotic interactions and sig-nal transduction pathways involved in the rec-ognition of compatible symbiont cells and development of highly differentiated masses of fungal–algal cells. Keywords: Lichen symbiosis · Signal transduction pathways · Fungal–algal interactions · Trebouxia jamesii · Early re-lichenization stages.