Root endophyte symbiosis in vitro between the ectomycorrhizal basidiomycete Tricholoma matsutake and the arbuscular mycorrhizal plant Prunus speciosa

Abstract

We previously reported that Tricholoma matsutake and Tricholoma fulvocastaneum, ectomycorrhizal basidiomycetes that associate with Pinaceae and Fagaceae, respectively, in the Northern Hemisphere, could interact in vitro as a root endophyte of somatic plants of Cedrela odorata (Meliaceae), which naturally harbors arbuscular mycorrhizal fungi in South America, to form a characteristic rhizospheric colony or "shiro". We questioned whether this phenomenon could have occurred because of plant-microbe interactions between geographically separated species that never encounter one another in nature. In the present study, we document that these fungi formed root endophyte interactions and shiro within 140 days of inoculation with somatic plants of Prunus speciosa (=Cerasus speciosa, Rosaceae), a wild cherry tree that naturally harbors arbuscular mycorrhizal fungi in Japan. Compared with C. odorata, infected P. speciosa plants had less mycelial sheath surrounding the exodermis, and the older the roots, especially main roots, the more hyphae penetrated. In addition, a large number of juvenile roots were not associated with hyphae. We concluded that such root endophyte interactions were not events isolated to the interactions between exotic plants and microbes but could occur generally in vitro. Our pure culture system with a somatic plant allowed these fungi to express symbiosis-related phenotypes that varied with the plant host; these traits are innately programmed but suppressed in nature and could be useful in genetic analyses of plant-fungal symbiosis.

Innate traits of Pinaceae-specific ectomycorrhizal symbiont Suillus luteus that differentially associates with arbuscular mycorrhizal broad-leaved trees in vitro

“…It produces edible mushrooms with pores at the sites of the basidia (Dahlberg and Finlay 1999;Hibbett and Thorn 2001;Smith and Read 2008). We previously reported the in vitro axenic synthesis of root endophytic symbioses between Tricholoma matsutake (S. Ito & S. Imai) Singer and a somatic plant, Cedrela odorata, in the mahogany family (Meliaceae) from the Southern Hemisphere, or T. matsutake and a somatic plant, Prunus speciosa (Rosaceae), the wild flowering cherry tree from Japan (Murata et al 2013(Murata et al , 2014. Tricholoma fulvocastaneum Hongo also behaved in the same way as T. matsutake with these arbuscular mycorrhizal plants (Murata et al 2013(Murata et al , 2014.…”

“…Tricholoma matsutake and T. fulvocastaneum are ectomycorrhizal fungi in the Agaricales (Agaricomycetes) that specifically associate with the Pinaceae and the Fagaceae, respectively, and produce gilled edible mushrooms (Hosford et al 1997;Hibbett and Thorn 2001). Both C. odorata and P. speciosa have a root exodermis, unlike Pinaceae plants that do not, and naturally harbor arbuscular mycorrhizal fungi (Peterson et al 2004;Smith and Read 2008;Urgiles et al 2009); however, these plants and the gill fungi successfully established symbioses, thereby promoting each other's growth (Murata et al 2013(Murata et al , 2014.…”

“…We previously reported the in vitro axenic synthesis of root endophytic symbioses between Tricholoma matsutake (S. Ito & S. Imai) Singer and a somatic plant, Cedrela odorata, in the mahogany family (Meliaceae) from the Southern Hemisphere, or T. matsutake and a somatic plant, Prunus speciosa (Rosaceae), the wild flowering cherry tree from Japan (Murata et al 2013(Murata et al , 2014. Tricholoma fulvocastaneum Hongo also behaved in the same way as T. matsutake with these arbuscular mycorrhizal plants (Murata et al 2013(Murata et al , 2014. Tricholoma matsutake and T. fulvocastaneum are ectomycorrhizal fungi in the Agaricales (Agaricomycetes) that specifically associate with the Pinaceae and the Fagaceae, respectively, and produce gilled edible mushrooms (Hosford et al 1997;Hibbett and Thorn 2001).…”

“…Mycelia were grown at 25 C on modified MelinNorkrans (MMN) agar plates containing 1.5% V8 juice (Murata et al 1999). Maruyama et al (1989) and Murata et al (2013Murata et al ( , 2014 described the somatic plants of C. odorata Co-3LfSE and of P. speciosa PS-YS05. Briefly, C. odorata Co-3LfSE was regenerated through somatic embryogenesis initiated from explants originating from leaves excised from 20-y-old micropropagated plants (Maruyama et al 1989;Maruyama 2009 Lloyd and McCown, 1980) containing 2% sucrose, 5 mm benzyl adenine, and 0.8% agar, pH 5.8, at 25 C under a regimen of 16 h of 30 mmol m À2 s À1 light with an 8-h dark period for 4 wk.…”

Ectomycorrhizas in vitro between Tricholoma matsutake, a basidiomycete that associates with Pinaceae, and Betula platyphylla var. japonica, an early-successional birch species, in cool-temperate forests

“…The small amounts of sugars were added to sustain the initial growth of both cultured partners, although the fungus acted as a root endophyte, and not as an ectomycorrhizal symbiont (Murata et al 2013. When sterilized properly, the granite-based soil substrate performed well for co-culturing T. matsutake and plants without any contamination over a prolonged incubation period (Kobayashi et al 2007;Murata et al 2013Murata et al , 2014Yamada et al 2006Yamada et al , 2010Yamada et al , 2014. Thus far, this is the only in vitro system to reproduce naturally occurring T. matsutake ectomycorrhizas, i.e., roots containing both Hartig nets and thin but distinct fungal sheaths, which are tightly covered by the dense aerial hyphae shiros (Kobayashi et al 2007;Masui 1927;Yamada et al 2006Yamada et al , 2010Yamada et al , 2014.…”