# Living in each other’s pockets: insights into the life cycle of Tremella caloplacae s. l

## TL;DR

This study explores the life cycle of fungi living in lichens, revealing how different phases of the fungi's life are associated with specific parts of the lichen.

## Contribution

The study provides new insights into the dimorphic life cycle of Tremella species inhabiting lichens and their lichen-specific associations.

## Key findings

- The filamentous phase of Tremella parietinae is found only in the hymenium of Xanthoria parietina.
- The yeast phase of T. parietinae is found in other parts of the lichen thallus.
- Tremella caloplacae is detected in multiple lichen genera but forms basidiomata only in Variospora.

## Abstract

Complex life-cycles are common among fungi. Dimorphism in basidiomycetes involves alternation between a unicellular yeast phase and a filamentous phase, frequently forming basidiomata. Here we have studied the dimorphic life cycle of the lichen-inhabiting basidiomycetes in the Tremella
caloplacae species complex, with particular focus on the newly distinguished Tremella
parietinae. Using FISH-CLSM, PCR and Sanger sequencing, we have investigated the presence and distribution of the different life-cycle phases of T.
parietinae within the lichen Xanthoria
parietina, and also conducted an exploratory investigation into the presence of a Tremella yeast phase in other lichens of the Teloschistaceae. We could show that the filamentous phase of T.
parietinae is restricted to the hymenium of X.
parietina, whereas the yeast phase also grows elsewhere in the thallus. Tremella
caloplacae s. str. is detected by PCR in Calogaya, Flavoplaca and Gyalolechia lichens, whereas its basidiomata are restricted to Variospora lichens. These findings suggests different lichen-specificity of T.
caloplacae in the different phases of its life-cycle.