Sebacinales form ectendomycorrhizas with Cavendishia nobilis, a member of the Andean clade of Ericaceae, in the mountain rain forest of southern Ecuador

Abstract

Summary• Cavendishia nobilis var . capitata is an endemic member of the Ericaceae growing as a hemiepiphyte in the tropical mountain rain forest of southern Ecuador.• Mycorrhizas were collected from 20 individuals along an altitudinal gradient between 1850 and 2300 m. Transmission electron microscopy was used to study the symbiotic association in detail, and phylogenetic analyses based on nuclear rDNA coding for the ribosomal large subunit (nucLSU) were carried out to identify the associated mycorrhizal fungi.• Microscopic and ultrastructural investigations showed the formation of a hyphal sheath, intercellular penetration of fine hyphae and colonization of the cortical cells by swollen hyphae of the same fungus. These structures were formed by hymenomycetes and ascomycetes. Molecular phylogenetic analysis detected seven groups of mycorrhizal fungi belonging to the Sebacinales. This is the first study to obtain evidence of ectendomycorrhizas in the Vaccinioideae. The ascomycetous nucLSU sequences belonged to members of the Leotiomycetes.• The ectendomycorrhiza of C. nobilis with Sebacinales is discussed as a specific, hitherto undescribed mycorrhizal subcategory of ectomycorrhizas. We propose the term 'cavendishioid mycorrhiza'. This subcategory is most likely specific for the Andean clade of Ericaceae.

The root endophytic fungus Piriformospora indica requires host cell death for proliferation during mutualistic symbiosis with barley

“…In orchid mycorrhizae, however, the fungus invades vital cortical root cells of the host to form intracellular hyphal coils. The strains tested in the present study also are closely related to members of the Sebacinales that form cavendishioid mycorrhizas (14) with certain hemiepiphytic ericads (Fig. 1).…”

Enigmatic Sebacinales

“…In following studies, more and more extended samplings of root-derived sebacinalean sequences became available. The originally indicated dichotomy of two intra-sebacinalean clades ("Group A" versus "Group B") became gradually more evident (Urban et al 2003;Setaro et al 2006a;Selosse et al 2007;Weiß 2007;Selosse et al 2009, Weiß 2010Weiß et al 2011).…”

“…Orchid mycorrhizal research has been summarized by Dearnaley (2007), by Smith and Read (2008) in their famous "Mycorrhizal symbiosis", covering all other aspects of mycorrhizae, and by Kottke and Suárez Chacón (2009) A breakthrough in experimental research was the successful isolation and axenic culture of mycobionts, including Sebacina vermifera, of terrestrial Australian orchids by Warcup and Talbot (1967). Molecular techniques had a stimulating impact on ORM research, and the design of a selective primer for Sebacinales' internal transcribed spacer, namely ITS3Seb, by Berbee (Setaro et al 2006a) was another remarkable step forward for studies of these fungi. The ITS primers and sequences for improved characterization of basidiomycetous ORMs were reviewed by Taylor and McCormick (2007).…”

“…g Sebacina-Gaultheria poeppigii ERM, arrowheads point to continuous parenthesomes, star marks hyphal septal wall, bar 0.2 μm, Selosse et al (2007). h Sebacina-Cavendishia nobilis CVM, cc cortical cell, cw cell wall, hs hyphal sheath, ih intracellular hyphae, V vacuoles, bar 5 μm, Setaro et al (2006a). i SebacinaPsammisia guianensis CVM, ih intracellular mycobiont hyphae, hs hyphal sheath, bar 10 μm, Setaro et al (2006b).…”

“…In a subalpine peat bog and in adjacent dolomitic rock formations of the Bavarian Alps, Garnica et al (2012) recorded sebacinalean ERMs on Andromeda polifolia, Calluna vulgaris, Rhododendron hirsutum, Vaccinium myrtillus, V. oxycoccum, and V. uliginosum. Setaro et al (2006a) studied the ectendomycorrhizal Sebacinales of the Andean Cavendishia nobilis, an endemic, hemiepiphytic species of the Ericaceae in mountain rain forests of southern Ecuador (Fig. 3h).…”