Argon-ion beam induced mutants of the ectomycorrhizal agaricomycete Tricholoma matsutake defective in β-1,4-endoglucanase activity promote the seedling growth of Pinus densiflora in vitro

Tricholoma matsutake is an ectomycorrhizal agaricomycete that produces the prized matsutake mushroom in conifer forests. Here, we isolated mutants generated by the argon-ion beam irradiation of T. matsutake NBRC 33136, designated as Ar 5002 and Ar 5012, which are defective in β-1,4-endoglucanase activity, that promoted the above- and below-ground growth of the symbiotic partner Pinus densiflora in vitro, compared with the control. Pine seedlings associated with Ar 5002, compared with NBRC 33136, had significantly higher above-ground dry mass and significantly greater plant growth, while those associated with Ar 5012 had significantly higher above- and below-ground dry mass. There were no significant differences between the numbers of mycorrhizal root-tips synthesized by the wild-type and mutants, indicating that β-1,4-endoglucanase did not influence the mycorrhization of T. matsutake. In seedlings inoculated with Ar 5002- and Ar 5012, the Hartig nets resembled those of seedlings inoculated with NBRC 33136. The data suggest that T. matsutake lacking β-1,4-endoglucanase activity confer beneficial effects on the growth of P. densiflora. Further studies are necessary to determine whether the symbiotic relationship could be strengthened by such a mutated fungal trait.