Scientists identify biosynthetic genes involved in the production of usnic acid in lichens

Scientists from the Faculty of Pharmacy at the Complutense University of Madrid have headed an international study that has successfully detected a sequence of biosynthetic genes that play a key role in the synthesis of usnic acid in lichen—a kind of compound that exhibits antioxidant, antiviral, antibacterial, anticancer, and neuroprotective activity.

But not all lichens—that is, composite organisms emerging from the symbiosis of fungi and cyanobacteria or green algae—are able to create this compound. And the new study, published in the Genome Biology and Evolution journal, has demonstrated why certain biosynthetic genes are lost in non-producing species.

Identifying the genes involved in the biosynthesis of these compounds is essential for future studies that require their isolation and mass production; similarly, the genomic approach adopted in this study has helped us identify new biosynthetic genes (PKS) of as yet unknown compounds that may be of pharmacological interest.”

David Pizarro, Study First Author and Researcher, Department of Pharmacology, Pharmacognosy and Botany, Universidad Complutense de Madrid

To perform this research work, the team sequenced the genomes of 40 lichen species that both synthesize and do not synthesize usnic acid.

The genomes were assembled, annotated and compared using bioinformatics tools and computational biology, and we also analyzed the diversity of lichen compounds using chromatography.”

David Pizarro, Study First Author and Researcher, Department of Pharmacology, Pharmacognosy and Botany, Universidad Complutense de Madrid

New family with unknown function

Furthermore, the new study identified and explained a new family of biosynthetic genes (PKS) with an unfamiliar function that may be specific to lichens.

We identified numerous clusters of biosynthetic genes of unknown function, some of which are homologous to other genes involved in the biosynthesis of antibiotics and toxins, thus opening a novel avenue of research into new molecules in the pharmaceutical industry.”

Pradeep Divakar, Researcher, Department of Pharmacology, Pharmacognosy and Botany, Universidad Complutense de Madrid

Lichens hold a great ecological significance. They have been extensively used as bio-indicators of various factors, including air pollution, due to their high sensitivity to changes in the environment, and they also form the basis of the food chain in dedicated ecosystems. Lichens are also a significant nesting for birds because of the antifungal and antibacterial activity of their secondary compounds.

Another important function of lichens relates to soil formation, since they can prevent soil erosion and help maintain moisture, facilitating the establishment of vascular plants, “concluded Pizarro.

Source:
Journal reference:

Pizarro, D., et al. (2020) Genome-Wide Analysis of Biosynthetic Gene Cluster Reveals Correlated Gene Loss with Absence of Usnic Acid in Lichen-Forming Fungi. Genome Biology and Evolution. doi.org/10.1093/gbe/evaa189.

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