Biology subjects

Mayrhofer, H.

Publications and source records attributed to Mayrhofer, H..

3 recordsLinked to original sources

bioRxiv2023

Evidence for a core set of microbial lichen symbionts from a global survey of metagenomes

Lichens are the archetypal symbiosis and the one for which the term was coined. Although application of shotgun sequencing techniques has shown that many lichen symbioses can harbour more symbionts than the canonically recognized fungus and photobiont, no global census of lichen organismal composition has been undertaken. Here, we analyze the genome content of 437 lichen metagenomes from six continents, and show that four bacterial lineages occur in the majority of lichen symbioses, at a frequency on par with algal photobionts. A single bacterial genus, Lichenihabitans, occurs in nearly one-third of all lichens sampled. Genome annotations from the most common lichen bacterial symbionts suggest they are aerobic anoxygenic photoheterotrophs and produce essential vitamins, but do not fix nitrogen. We also detected secondary basidiomycete symbionts in about two-thirds of analyzed metagenomes. Our survey suggests a core set of four to seven microbial symbionts are involved in forming and maintaining lichen symbioses.

microbiology↗

bioRxiv2023

Introgressive descent and hypersexuality drive the evolution of sexual parasitism and morphological reduction in a fungal species complex.

Taxonomists consider species as discrete units of biological organization, which are subject to a continuous process of evolutionary change and are connected through their shared ancestry. However, the continuous nature of evolutionary change is difficult to reconcile with the discrete outcome of speciation, especially where species boundaries are permeable. A good example of this inconsistency is the lichen genus Pyrenodesmia, which shows a high morphologic and genetic diversity that that defies systematization by taxonomic or phylogenetic methods. Here we show that hybridization explains the presence of discordant morphs and that European species are interconnected through cross-mating in a single reproductive network, a syngameon, despite which species remain largely distinct and distinguishable. Whole genome data reflect the important role played by genome defense mechanisms in the genomic stabilization of fungal hybrids. The recurrence of Repeat Induced Point mutations (RIP) shapes genomes with islands of suppressed recombination and loss of gene content, which in turn generates a feedback loop reinforcing the lack of reproductive isolation through the loss of heterokaryon incompatibility and a tendency towards morphological reduction.

evolutionary biology↗

bioRxiv2021

Large differences in carbohydrate degradation and transport potential in the genomes of lichen fungal symbionts

Lichen symbioses are generally thought to be stabilized by the transfer of fixed carbon compounds from a photosynthesizing unicellular symbiont to a fungus. In other fungal symbioses, carbohydrate subsidies correlate with genomic reductions in the number of genes for plant cell wall-degrading enzymes (PCWDEs), but whether this is the case with lichen fungal symbionts (LFSs) is unknown. We predicted genes encoding carbohydrate-active enzymes (CAZymes) and sugar transporters in 17 existing and 29 newly sequenced genomes from across the class Lecanoromycetes, the largest extant clade of LFSs. Despite possessing lower mean numbers of PCWDE genes compared to non-symbiont Ascomycota, all LFS genomes possessed a robust suite of predicted PCWDEs. The largest CAZyme gene numbers, on par with model species such as Penicillium, were retained in genomes from the subclass Ostropomycetidae, which are found in crust lichens with highly specific ecologies. The lowest numbers were in the subclass Lecanoromycetidae, which are symbionts of many generalist macrolichens. Our results suggest that association with phototroph symbionts does not in itself result in functional loss of PCWDEs and that PCWDE losses may have been driven by adaptive processes within the evolution of specific LFS lineages. The inferred capability of some LFSs to access a wide range of carbohydrates suggests that some lichen symbioses may augment fixed CO2 with carbon from external sources. SignificanceLichen symbioses are considered self-contained autotrophic systems in which the total carbon economy is the sum of phototroph-fixed CO2, supplied to a fungus as sugars. In other fungal-plant symbioses, such as mycorrhizae, plant-derived sugar subsidies are associated with loss of plant cell wall-degrading enzymes (PCWDEs). We compared PCWDE inventories in 46 genomes from the largest group of lichen fungal symbionts (LFSs) with non-symbionts from across Ascomycota. We found that despite lower overall gene numbers, all LFSs retain PCWDEs, and some possess gene numbers and functional diversity on par with non-symbionts. Our results suggest that association with a phototroph does not necessarily result in PCWDE loss, and some lichens may obtain carbon from sources other than CO2 fixation.

genomics↗