Oral Paper

         Comparative Genomics/Transcriptomics

lichen PKS genes

Presenting Author
Julia Gerasimova
Description
Fungi synthesize an extensive array of chemically and functionally diverse natural products, termed secondary metabolites, with roles in defence, self-protection and development. Based on their properties and the core enzymes and precursors involved in their biosynthesis, four major groups of fungal secondary metabolites are distinguished: polyketides, non-ribosomal peptides (NRPS), terpenoids, and tryptophan derivatives. The most common lichen secondary metabolites polyketides—are synthesized by polyketide synthases, particularly by Type I PKS (TI-PKS). We conducted a comparative genomic analysis of the TI-PKS gene content of 23 lichen-forming fungal genomes from Ascomycota, including the de novo sequenced genome of the crustose lichen Bacidia rubella. Our comparative analysis included 1) an identification of a putative atranorin cluster in Bacidia rubella, 2) an overview of TI-PKS gene diversity in lichen-forming fungi, and 3) a reconstruction of the most comprehensive Type I PKS phylogeny of lichen-forming fungi to date, including 624 sequences. We revealed a high number of biosynthetic gene clusters and examined their domain composition in the context of previously characterized genes, confirming that PKS genes outnumber known secondary substances in lichens. Similar to previous studies, 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. Particularly, our results reveal that a biosynthetic gene cluster, including PKS23, is likely involved in the biosynthesis of atranorin in Bacidia rubella. Although many PKSs remain without functional assignments, our findings highlight those genes from lichen-forming fungi represent an untapped source of novel polyketide compounds.