Ectomycorrhization of Tricholoma matsutake with Quercus aquifolioides affects the endophytic microbial community of host plant

Effects of four bolete species on ectomycorrhizae formation and development in Pinus thunbergii and Quercus acutissima

BACKGROUND

Bolete cultivation is economically and ecologically valuable. Ectomycorrhizae are advantageous for plant development and productivity. This study investigated how boletes affect the formation of Pinus thunbergii and Quercus acutissima ectomycorrhizae using greenhouse-based mycorrhizal experiments, inoculating P. thunbergii and Q. acutissima with four species of boletes (Suillus bovinus, Suillus luteus, Suillus grevillei, and Retiboletus sinensis).

RESULTS

Three months after inoculation, morphological and molecular analyses identified S. bovinus, S. luteus, S. grevillei and R. sinensis ectomycorrhizae formation on the roots of both tree species. The mycorrhizal infection rate ranged from 40 to 55%. The host plant species determined the mycorrhiza morphology, which was independent of the bolete species. Differences in plant growth, photosynthesis, and endogenous hormone secretion primarily correlated with the host plant species. Infection with all four bolete species significantly promoted the host plants' growth and photosynthesis rates; indole-3-acetic acid, zeatin, and gibberellic acid secretion increased, and the abscisic acid level significantly decreased. Indole-3-acetic acid was also detected in the fermentation broths of all bolete species.

CONCLUSIONS

Inoculation with bolete and subsequent mycorrhizae formation significantly altered the morphology and hormone content in the host seedlings, indicating growth promotion. These findings have practical implications for culturing pine and oak tree species.

Comparative Mitogenomic Analysis Reveals Dynamics of Intron Within and Between Tricholoma Species and Phylogeny of Basidiomycota

The genus of Tricholoma is a group of important ectomycorrhizal fungi. The overlapping of morphological characteristics often leads to the confusion of Tricholoma species classification. In this study, the mitogenomes of five Tricholoma species were sequenced based on the next-generation sequencing technology, including T. matsutake SCYJ1, T. bakamatsutake, T. terreum, T. flavovirens, and T. saponaceum. These five mitogenomes were all composed of circular DNA molecules, with sizes ranging from 49,480 to 103,090 bp. Intergenic sequences were considered to be the main factor contributing to size variations of Tricholoma mitogenomes. Comparative mitogenomic analysis showed that the introns of the Agaricales mitogenome experienced frequent loss/gain events. In addition, potential gene transfer was detected between the mitochondrial and nuclear genomes of the five species of Tricholoma. Evolutionary analysis showed that the rps3 gene of the Tricholoma species was under positive selection or relaxed selection in the evolutionary process. In addition, large-scale gene rearrangements were detected between some Tricholoma species. Phylogenetic analysis using the Bayesian inference and maximum likelihood methods based on a combined mitochondrial gene set yielded identical and well-supported tree topologies. This study promoted the understanding of the genetics, evolution, and phylogeny of the Tricholoma genus and related species.

Bioactive properties of streptomyces may affect the dominance of Tricholoma matsutake in shiro

Tricholoma matsutake is known to be the dominant fungal species in matsutake fruitbody neighboring (shiro) soil. To understand the mechanisms behind matsutake dominance, we studied the bacterial communities in matsutake dominant shiro soil and non-shiro soil, isolated the strains of Streptomyces from matsutake mycorrhizal root tips both from shiro soil and from the Pinus densiflora seedlings cultivated in shiro soil. Further, we investigated three Streptomyces spp. for their ability to inhibit fungal growth and Pinus densiflora seedling root elongation as well as two strains for their antifungal and antioxidative properties.

Our results showed that Actinobacteria was the most abundant phylum in shiro soil. However, the differences in the Actinobacterial community composition (phylum or order level) between shiro and non-shiro soils were not significant, as indicated by PERMANOVA analyses. A genus belonging to Actinobacteria, Streptomyces, was present on the matsutake mycorrhizas, although in minority. The two antifungal assays revealed that the broths of three Streptomyces spp. had either inhibitory, neutral or promoting effects on the growth of different forest soil fungi as well as on the root elongation of the seedlings. The extracts of two strains, including one isolated from the P. densiflora seedlings, inhibited the growth of either pathogenic or ectomycorrhizal fungi. The effect depended on the medium used to cultivate the strains, but not the solvent used for the extraction. Two Streptomyces spp. showed antioxidant activity in one out of three assays used, in a ferric reducing antioxidant power assay. The observed properties seem to have several functions in matsutake shiro soil and they may contribute to the protection of the shiro area for T. matsutake dominance.