Unravelling the genomic complexity of Peltigera cyanolichens: Insights into a complex cross-kingdom community

Many fungi engage in diverse symbiotic relationships, ranging from pathogenic and commensal to mutualistic interactions. Lichens exemplify a highly successful mutualistic system, typically formed between a fungus (mycobiont) and one or more photosynthetic organisms (photobionts), including green algae and/or cyanobacteria. In addition to this core partnership, lichens host a variety of associated fungal and bacterial communities.

The genus Peltigera is widespread across multiple continents and serves as a representative of cyanolichens due to its symbiotic relationship with the cyanobacterial photobiont Nostoc. Despite more than two centuries of lichen research, many aspects of lichen biology remain unresolved. However, recent advances in genomics are beginning to fill these gaps, providing new insights into their complex biology. This includes the discovery of a carbohydrate-active- enzyme from the glycoside hydrolase 8 (GH8) family, likely acquired through horizontal gene transfer, as a candidate for facilitating lichen symbiosis in Trebouxiophyceae [1].

To contribute to this growing knowledge, we present over 30 metagenome assemblies from Peltigera lichens collected across Germany, the Netherlands, Switzerland, and Lithuania. These assemblies, which capture both photobiont and mycobiont genomes, were produced using state-of-the-art long-read sequencing. Our analyses include interspecies comparisons among Peltigera mycobionts and investigations of structural variations between symbiotic Nostoc and its free-living counterparts. Additionally, we analyze the metagenome assembled genomes (MAGs) of the Peltigera microbiome to identify core microbial members across species and sampling locations. To gain insights into the spatial organization of these core microbes within the lichen thallus, we aim to integrate our omics data with microscopy. For this, we established the LichenMetaImage Use Case, a collaborative effort among CRC 1535 MibiNet and the NFDIs NFDI4Microbiota, DataPLANT, and NFDI4BIOIMAGE.

This study offers an in-depth analysis of the complex genomic structure of Peltigera lichens, comparing their primary components (myco- and photobiont) and examining the core members of the microbiome within the lichen community, contributing valuable insights to the growing field of lichen research.

References: 1. Puginier et al. (2024): Phylogenomics reveals the evolutionary origins of lichenization in chlorophyte algae. Nat Commun 15, 445.