Decoupled evolution of antimicrobial repertoires in lichen-forming fungi
Lichens are stable multipartite symbioses in which a fungal mycobiont associates with one or more photosynthetic partners while hosting complex microbiomes. Secreted antimicrobial proteins (AMPs) have recently emerged as important mediators of fungal interactions with surrounding microbial communities, yet their evolutionary distribution and diversity in lichen-forming fungi remain largely…
Lichens, a symbiotic association between a fungal mycobiont and photosynthetic partners, harbor complex microbiomes and secrete antimicrobial proteins (AMPs) that regulate interactions with surrounding microbial communities. However, the evolution and diversity of these AMP repertoires in lichen-forming fungi have not been thoroughly examined.
In a recent study, researchers investigated AMP repertoires across 80 phylogenetically diverse lichen-forming fungi, encompassing three distinct photobiont association types: chlorolichens, cyanolichens, and tripartite lichens. To their surprise, they found that average repertoire size remained consistent among these diverse lichen types, with an average of 363 AMPs per species.
Despite this quantitative similarity, repertoire size varied significantly among individual species, and 23 AMP families showed enrichment or depletion based on the photobiont association. This apparent conservation, however, concealed substantial compositional turnover, as certain AMP families coexisted in at least 90% of species alongside numerous lineage-specific groups.
These findings were further supported by population sequencing of 11 Umbilicaria phaea populations along two elevational gradients, which revealed recurrent presence-absence variation of AMPs within a single lichen species. Additionally, the study observed that biosynthetic gene clusters (BGCs) and carbohydrate-active enzymes (CAZymes), known to produce antimicrobials, were significantly less abundant in cyanolichens compared to chlorolichens.
These results suggest that lichen-forming fungi maintain a consistent baseline capacity for AMP production while concurrently undergoing turnover in their AMP compositions and differentiation through additional chemical and enzymatic systems. This dual pattern of conservation and turnover in AMP repertoires likely enables lichen-forming fungi to adapt to their ecological niches and lifestyle-associated requirements.
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