Lichen morphogenesis

The yellow lichen Xanthoria parietina is a shared body: a fungus builds around algae that use light to make food. The algae are arranged beneath an outer fungal layer, where they can still receive light. How do these separate organisms coordinate their growth into that orderly structure?[1] [3]

The fungus and algae of Xanthoria parietina build a layered body, or thallus, that neither makes alone. How do partner-produced cues place the cells and change fungal growth so that these layers develop?

The 2025 Xanthoria study used growing margins, older centers and reproductive structures as spatial proxies for developmental states. Candidate transporters for carbon-containing polyols and ammonium, a nitrogen source, and proteins released outside cells suggest processes at the partner interface. Many transcripts that increase in the lichen still have no assigned function. August 2026 nanoCT imaging and elemental measurements add local contact geometry and wall chemistry to that molecular inventory.[1] [3] [4]

Scientists have clues about the genes active in a lichen, but have not established which messages tell the partners where and how to grow. They must distinguish a signal that builds the body from a change that merely occurs after the partners are already together.[1] [2]

A region’s transcript abundance mixes cell types and developmental histories; it cannot by itself assign a morphogenetic instruction. The missing account must connect a partner-produced cue to a specific cellular response and then to layer formation. Spatial measurements preserve context, while cell dissociation can remove it; neither observation alone demonstrates that a candidate is necessary or sufficient.[1] [2] [4]

The layered body creates an arrangement neither partner makes alone. Explaining its construction would show how cells belonging to different organisms coordinate something resembling a common anatomy.[1]

A fungus builds an outer layer around algae, so one anatomy assigns different positions to cells from separate organisms. Fungi also make complex structures such as mushrooms without forming a lichen. Comparing these bodies asks whether fungal growth processes can be reused to organize a partnership, or whether coordination between partners needs distinct instructions. The answer would connect symbiosis to the broader biology of how complex fungal forms develop. Similar gene-expression patterns suggest shared developmental processes, but they do not establish which instructions coordinate the lichen’s cells.[1] [2]