Transposable Element Diversification and the Evolution of Peltigerales Lichen Symbionts

Lichens are composite organisms formed through the symbiotic association between fungi, algae and/or bacteria. Multiple independent origins of the lichenized lifestyle have been reported in both fungal and algal lineages, but the molecular mechanisms and evolution underpinning these symbiotic relationships remain largely unknown. In this study, we performed long-read metagenomic sequencing on 11 Peltigerales lichen species to characterize the genomic content of lichen symbionts via metagenome assembled genomes (MAGs). Peltigerales genomes generated in this work represent the largest Lecanoromycetes genome sequenced to date, driven by high transposable element content. Transposable elements (TEs) are known to drive genome evolution in other symbioses, but have been underexplored in lichen symbionts due technological limitations. Transcriptomics revealed that many genes associated with adaptations to the lichenized lifestyle are associated with TEs suggesting that they may play a key role in the evolution of lichenization.