Novel Root-Fungus Symbiosis in Ericaceae: Sheathed Ericoid Mycorrhiza Formed by a Hitherto Undescribed Basidiomycete with Affinities to Trechisporales

Abstract

Ericaceae (the heath family) are widely distributed calcifuges inhabiting soils with inherently poor nutrient status. Ericaceae overcome nutrient limitation through symbiosis with ericoid mycorrhizal (ErM) fungi that mobilize nutrients complexed in recalcitrant organic matter. At present, recognized ErM fungi include a narrow taxonomic range within the Ascomycota, and the Sebacinales, basal Hymenomycetes with unclamped hyphae and imperforate parenthesomes. Here we describe a novel type of basidiomycetous ErM symbiosis, termed ‘sheathed ericoid mycorrhiza’, discovered in two habitats in mid-Norway as a co-dominant mycorrhizal symbiosis in Vaccinium spp. The basidiomycete forming sheathed ErM possesses clamped hyphae with perforate parenthesomes, produces 1- to 3-layer sheaths around terminal parts of hair roots and colonizes their rhizodermis intracellularly forming hyphal coils typical for ErM symbiosis. Two basidiomycetous isolates were obtained from sheathed ErM and molecular and phylogenetic tools were used to determine their identity; they were also examined for the ability to form sheathed ErM and lignocellulolytic potential. Surprisingly, ITS rDNA of both conspecific isolates failed to amplify with the most commonly used primer pairs, including ITS1 and ITS1F + ITS4. Phylogenetic analysis of nuclear LSU, SSU and 5.8S rDNA indicates that the basidiomycete occupies a long branch residing in the proximity of Trechisporales and Hymenochaetales, but lacks a clear sequence relationship (>90% similarity) to fungi currently placed in these orders. The basidiomycete formed the characteristic sheathed ErM symbiosis and enhanced growth of Vaccinium spp. in vitro, and degraded a recalcitrant aromatic substrate that was left unaltered by common ErM ascomycetes. Our findings provide coherent evidence that this hitherto undescribed basidiomycete forms a morphologically distinct ErM symbiosis that may occur at significant levels under natural conditions, yet remain undetected when subject to amplification by ‘universal’ primers. The lignocellulolytic assay suggests the basidiomycete may confer host adaptations distinct from those provisioned by the so far investigated ascomycetous ErM fungi.

Communities of Cultivable Root Mycobionts of the Seagrass Posidonia oceanica in the Northwest Mediterranean Sea Are Dominated by a Hitherto Undescribed Pleosporalean Dark Septate Endophyte

“…2e; cf. [37]). The microscopic screening of the hand sections showed that most of the colonies emerging from root segments actually developed from intracellular melanized microsclerotia occurring in the P. oceanica root hypodermis (Fig.…”

“…SSU (18S) ribosomal DNA (rDNA) was amplified using the NS1 + NS24 primer pair [34], ITS1-5.8S-ITS2 rDNA using the ITS1F + ITS4 primer pair [34,35] and LSU (28S) rDNA using the LR0R + LR5 primer pair [36]. For PCR parameters and gel electrophoresis, see [37]. PCR products were purified and sequenced by Macrogen Europe Laboratory (Macrogen Inc., The Netherlands/South Korea) using the NS1, NS4, NS5 and NS24, ITS1F, and LR0R primers.…”

Rare phytomyxid infection on the alien seagrass Halophila stipulacea in the southeast Aegean Sea

“…Scanning electron microscopy (SEM) of semi-thin hand sections was performed using a FEI Quanta 200 scanning electron microscope in the ESEM mode at low temperatures (−6°C to −3°C). The protocol for transmission electron microscopy (TEM) was the same as in Vohník et al (2012), the Spurr Resin-embedded and uranyl acetate and lead citrate-contrasted samples were observed using a JEOL 1011 microscope equipped with a digital TEM camera (Veleta, Olympus). Photographs were modified for clarity as needed and assembled into Figures using Paint.net ver.…”

Experimental evidence of ericoid mycorrhizal potential within Serendipitaceae (Sebacinales)

“…We are only aware of one report on isolation of a serendipitoid mycobiont from Ericaceae hair roots, but this isolate (Sebacinales sp. JPK 89; GenBank JQ926170) soon lost its viability, preventing its use in re-synthesis experiments (Vohník et al 2012a). Sebacinales sp.…”