## 4 Conclusions and Limitations  
This study presents a comprehensive analysis of the PKS gene content of the de novo sequenced genome of _B. rubella_ and twenty-two publicly available genomes of mainly lichen-forming fungi. Our results reveal that a BGC including PKS23 is likely involved in biosynthesis of atranorin in _B. rubella_. Similar to previous studies (e.g., [6; 23; 24; 29]), we observed a large diversity of PKS genes in lichen-forming fungi as well as _B. rubella_, much larger than expected based on their recorded secondary metabolite profiles. This highlights the potential of lichen-forming fungi to produce a much higher number of substances than previously assumed, as mentioned by [PERSON] et al. [6] focusing on foliose lichens. Our in silico approach provides first insights into the possible roles of PKS genes in crustose _B. rubella_; however, we are aware that this comes with limitations. Only detailed studies of individual BGCs combining gene expression analyses with analytical chemistry and metabolomics will allow thorough testing of the hypotheses proposed here. The prospects for this are promising as an increasing number of studies succeeded in the heterologous expression of lichen-forming fungal genes, (e.g., [29; 76; 86; 102; 103]). Subsequent in vivo studies of metabolite profiles in lichen-forming fungi supplemented by high-resolution MS/MS spectra [104] or metabolic profiling based on stable isotope analysis [105] will contribute to our knowledge on how secondary metabolites in lichen-forming fungi are produced and what roles they play. Combined with the growing number of available lichen-forming fungal genomes, we will be able to refine our understanding and formulate novel hypotheses about the biosynthetic potential of lichens.  
Conceptualization, J.V.G., A.B., S.W. and P.R.; methodology, software and formal analysis, J.V.G. and P.R.; investigation, J.V.G. and A.B.; resources and funding acquisition, S.W. and A.B.; data curation, J.V.G. and P.R.; writing--original draft preparation, J.V.G.; writing--review and editing, J.V.G., A.B., S.W. and P.R.; visualization, J.V.G.; supervision, A.B., S.W. and P.R. All authors have read and agreed to the published version of the manuscript.  
[PERSON] was supported by a BAYHOST fellowship from the Bayerische Staatsministerium fur Bildung und Kultus, Wissenschaft und Kunst and an LMU travel grant (April 2021). Laboratory work and genome sequencing were funded by the LMU Munich start-up funds of S.W. and by the Staatliche Naturwissenschaftliche Sammlungen Bayerns, grant SNSB innovativ to A.B.  
The data supporting the findings of this study are available open access in figshare at [[http://doi.org/10.6084/m9.figshare.19487837](http://doi.org/10.6084/m9.figshare.19487837)]([http://doi.org/10.6084/m9.figshare.19487837](http://doi.org/10.6084/m9.figshare.19487837)). These include gff3 files and protein sequences from twenty-two re-annotated genomes downloaded from the NCBI. In addition, the alignment used for the PKS tree calculation is deposited. The de novo sequenced genome of _Bacidia rubella_ is available under the NCBI BioProject accession number PRJNA821848 and on the Sequence Read Archive (SRA).  
We thank [PERSON] (LMU Munich) for his valuable help in the figure preparation and [PERSON] (LMU Munich) for improving the English text. [PERSON] and [PERSON] (both LMU Munich) helped with the lab work. We thank the government of the administrative district of Upper Bavaria for the sampling permit.  
The authors declare no conflict of interest.