Conclusions
This is the first study reporting differential gene expression of lichen
photomorphs based on compound thalli. Our differential gene expression
analyses illustrate the effects of temperature stress on all partners
involved in the lichen symbiosis and show a distinct photomorph-mediated
fungal gene expression pattern in P. britannica influencing
mycobiont-photobiont contact and management of photobiont growth. This
suggests an interplay and plasticity of fungal, cyanobacterial and algal
gene expression in lichen symbioses that was previously undocumented.
Moreover, our results show that the symbiosis partners possess different
temperature optima. Each organism in the lichen symbiosis, be it the
fungus, the alga, or the cyanobacterium, reacted to thermal stress –
and each organism did so in a distinct manner. The fungi and
cyanobacteria were heat stressed at 15 °C already, whereas the green
algae were heat stressed only at 25 °C. Our study offers novel insights
into how symbiotic partners in P. britannica photomorphs manage
their interactions and responses to environmental factors such as
temperature through differential gene expression. We hope that our
results contribute to a better understanding of how different
photosynthetic partners can influence the ecology of lichens.