Ericoid mycorrhizal root fungi and their multicopper oxidases from a temperate forest shrub

Abstract

Ericoid mycorrhizal fungi (ERM) may specialize in capturing nutrients from their host's litter as a strategy for regulating nutrient cycles in terrestrial ecosystems. In spite of their potential significance, we know little about the structure of ERM fungal communities and the genetic basis of their saprotrophic traits (e.g., genes encoding extracellular enzymes). Rhododendron maximum is a model ERM understory shrub that influences the nutrient cycles of montane hardwood forests in the southern Appalachians (North Carolina, USA). We sampled ERM roots of R. maximum from organic and mineral soil horizons and identified root fungi by amplifying and sequencing internal transcribed spacer (ITS) ribosomal DNA (rDNA) collected from cultures and clones. We observed 71 fungal taxa on ERM roots, including known symbionts Rhizoscyphus ericae and Oidiodendron maius, putative symbionts from the Helotiales, Chaetothyriales, and Sebacinales, ectomycorrhizal symbionts, and saprotrophs. Supporting the idea that ERM fungi are adept saprotrophs, richness of root-fungi was greater in organic than in mineral soil horizons. To study the genetic diversity of oxidative enzymes that contribute to decomposition, we amplified and sequenced a portion of genes encoding multicopper oxidases (MCOs) from ERM ascomycetes. Most fungi possessed multiple copies of MCO sequences with strong similarities to known ferroxidases and laccases. Our findings indicate that R. maximum associates with a taxonomically and ecologically diverse fungal community. The study of MCO gene diversity and expression may be useful for understanding how ERM root fungi regulate the cycling of nutrients between the host plant and the soil environment.

Assembly processes of trophic guilds in the root mycobiome of temperate forests

“…Similarly, the trophic composition of RAMs along a successional gradient of willows and birches was also relatively stable with a strong enrichment of mycorrhizas (>56% read abundance) compared with saprotrophs and endophytes (together 17%); however, ericoid fungal taxa were enriched in later successional stages (Kolaříková et al., ). Ericoid fungi occur frequently on nonericoid plants, such as conifers, as well as other tree species (Chambers, Curlevski, & Cairney, ; Dučić, Berthold, Langenfeld‐Heyser, Beese, & Polle, ; Jankowiak, Bilański, Paluch, & Kołodziej, ; Leopold, ; Maghnia et al., ; Reininger & Schlegel, ; Toju, Sato, et al., ; Toju, Yamamoto, et al., ), facilitate seedling growth on stressed soils (Yamaji et al., ) and enhance the host N supply from recalcitrant organic sources in nutrient‐poor environments (Wei, Chen, Zhang, & Pan, ; Wurzburger, Higgins, & Hendrick, ). We found a higher fraction of endophytes in Pinaceae than Fagaceae roots.…”

Enigmatic Sebacinales

“…Neotropical and temperate Vaccinioideae of North America share their Sebacinales communities, thus indicating that hosts and mycobionts co-migrated (Setaro and Kron 2011). The high number of 71 fungal taxa, including Sebacina vermifera-like ones, was observed on roots of the model understorey shrub, Rhododendron maximum, from montane hardwood forests in the southern Appalachians, North Carolina (Wurzburger et al 2011). However, except for R. ericae and Oidiodendron maius, these diverse fungi could not be verified as ERM mycobionts.…”

Mycorrhizal types differ in ecophysiology and alter plant nutrition and soil processes

“…Wood and litter saprotrophs belonging to Basidiomycota display the greatest decomposition activities, but genes responsible for efficient cellulolysis have been partly lost in mycorrhizal fungi to maintain the stability of symbiosis. While the ancestors of Glomeromycota and contemporary AM fungi lack a strong degradation machinery (Tisserant et al, 2013;Chen et al, 2018a), certain ascomycete and basidiomycete EcM and ErM symbionts are capable of producing Fenton radicals and polyphenol oxidases to release N from organic polymers (Wurzburger, Higgins & Hendrick, 2012;Lindahl & Tunlid, 2015;Adamczyk et al, 2016). Although most EcM fungi have secondarily lost Mn-peroxidase genes, certain species of Cortinarius and Hebeloma possess and express these powerful oxidases to mobilise lignin-bound N (Bödeker et al, 2014;Kohler et al, 2015).…”