Transformation of the ectomycorrhizal agaricomycete Tricholoma matsutake byγ-ray irradiation

Conversion from mutualism to parasitism: a mutant of the ectomycorrhizal agaricomycete Tricholoma matsutake that induces stunting, wilting and root degeneration in seedlings of its symbiotic partner Pinus densiflora in vitro

Hitoshi Murata (a), Shota Nakano (a), Takashi Yamanaka (b), Tomoko Shimokawa (c), Tomoko Abe (d), Hiroyuki Ichida (d), Yoriko Hayashi (d), Ko Tahara (e), Akira Ohta (f)

(a) Department of Mushroom Science and Forest Microbiology, FFPRI, Tsukuba, Ibaraki, Japan.

(b) Principal Research Director, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Department of Forest Resource Chemistry, FFPRI, Tsukuba, Ibaraki, Japan.

(d) RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama, Japan.

(e) Department of Forest Molecular Genetics and Biotechnology, FFPRI, Tsukuba, Ibaraki, Japan.

(f) Lake Biwa Environmental Research Institute, Otsu, Shiga, Japan.

Botany, 97(8):463–474, Canadian Science Publishing, July 2019 DOI：10.1139/cjb-2019-0060( External link )

The ectomycorrhizal agaricomycete Tricholoma matsutake is symbiotically associated with Pinaceae plants, such as Pinus densiflora; it grows on the roots of such plants using their photosynthetic products. While wood-decaying fungi, such as Lentinula edodes and Flamulina veltipes, can be cultivated using sawdust-based spawn substrates, the ectomycorrhizal agaricomycete Tricholoma matsutake can barely degrade plant biomass and, to date, has never been successfully cultivated using spawn substrates. Therefore, we undertook an approach involving the transformation of the ectomycorrhizal agaricomycete Tricholoma matsutake by radiation mutagenesis of cultured mycelia to create a strain that is compatible with spawn cultivation.

In the present study, we irradiated cultured mycelia of the ectomycorrhizal agaricomycete Tricholoma matsutake with γ-rays at the Institute of Crop Science, the National Agriculture and Food Research Organization, and successfully obtained a mutant strain with degrading enzymatic activities, namely, the G1 strain. With substantially higher amylase and cellulase activities compared to that of the natural strain, this mutant strain grew well on spawn substrates (Figure). In addition, we found that the G1 strain inhibited the growth of Pinus densiflora seedlings, with which the ectomycorrhizal agaricomycete Tricholoma matsutake usually enjoys a symbiotic relationship (Figure). In the future, we will analyze the genetic characteristics of this mutant strain and continue endeavoring to obtain new mutants.

Figure. Characteristics of the natural strain of the ectomycorrhizal agaricomycete Tricholoma matsutake (NBRC 33136) and its mutant G1. (Left) Fungal floras and degrading enzymatic activities. (Upper right) Effect on Pinus densiflora seedlings. (Lower right) Mushroom beds using rolled barley substrates.