Photobiont association and genetic diversity of the optionally lichenized fungus Schizoxylon albescens

Abstract

The fungus Schizoxylon albescens occurs both as lichen and as saprobe. Lichenized colonies grow on the bark of Populus tremula; saprotrophic morphs grow on dead Populus branches. We wanted to (1) test whether lichenized and saprotrophic S. albescens are genetically distinct, (2) investigate photobiont association and diversity, (3) investigate the interactions between fungi and algae that occur during co-cultivation and (4) test whether Schizoxylon shows algal selectivity during lichenization. Fungal and algal genetic diversity were investigated for three markers. Algae from lichenized thalli were isolated in axenic cultures, and isolate sequence diversity was compared with algae amplified directly from thallus fragments. Co-culture experiments of fungi and algae were performed to study the morphological interaction patterns. Two distinct phylogenetic units are revealed in S. albescens, which are interpreted as phenotypically cryptic species. The algae are related to Coccomyxa and Pseudococcomyxa, and form two distinct sister clades separating samples isolated in cultures from those amplified directly from thallus fragments, indicating that more easily cultured strains of algae are not necessarily major components of the lichens. Schizoxylon albescens interacts with isolated algal strains, similar to fungal-Coccomyxa symbioses in nature. As the system is maintained without difficulty in culture, it can potentially be an easily controlled lichen symbiosis study system under laboratory conditions.

Cryptodiscus muriformis and Schizoxylon gilenstamii, two new species of Stictidaceae (Ascomycota)

“…This is supported by the combination of morphological characters that Sherwood (1977a) stated as diagnostic for the genus: cartilaginous apothecia, with a margin lacking periphysoids, long cylindrical asci with a thickened apex opened by a broad pore, and long filiform multiseptate ascospores disarticulating into part-spores. All Schizoxylon species are saprotrophs, except for S. albescens that can live either as a saprotroph or as loosely lichenized with algal clumps associated with its fruiting bodies (Wedin et al 2006;Muggia et al 2011). No algae were observed associated with S. gilenstamii.…”

The complexity of symbiotic interactions influences the ecological amplitude of the host: A case study inStereocaulon(lichenized Ascomycota)

“…However, as the rbcL marker generally shows lower resolution than the ITS rDNA, we did not further analyse it here. Although previously overlooked, the co‐occurrence of several phycobionts in individual lichen thalli (i.e., algal plurality) is a relative common phenomenon (Bačkor et al., ; Moya, Molins, Martinez‐Alberola, Muggia, & Barreno, ; Muggia, Baloch, Stabentheiner, Grube, & Wedin, ; Muggia et al., ; Onuț‐Brännström et al., ; Park et al., ; Voytsekhovich & Beck, ). We also obtained evidence for algal plurality in several Stereocaulon samples, which strengthens the potential of this lichen genus as a suitable model for high‐throughput sequencing studies.…”

Molecular analyses uncover the phylogenetic placement of the lichenized hyphomycetous genusCheiromycina

“…failed and the fungi grown in cultures were identified as Sordariomycetes. It is well known that lecanoralean lichen mycobionts grow rather slowly in axenic cultures, whereas Ostropalean fungi, which include also several nonlichenized and optionally lichenized taxa (Wedin et al 2004, 2006), seem to be easier to culture (Muggia et al 2011, 2016). This anecdotal observation further supports the likely different phylogenetic placement for the two fungi.…”